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Special Issue "Heterocycles"

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A special issue of Molecules (ISSN 1420-3049). This special issue belongs to the section "Organic Synthesis".

Deadline for manuscript submissions: closed (15 December 2011)

Special Issue Editors

Editor-in-Chief
Dr. Derek J. McPhee

Senior Director, Technology Strategy, Amyris, Inc., 5885 Hollis St, Suite 100, Emeryville, CA 94608, USA
Fax: +1 510 225 2645
Interests: organic synthesis; medicinal chemistry; biotechnology
Publisher
Dr. Shu-Kun Lin (Website)

MDPI AG, St. Alban-Anlage 66, CH-4052 Basel, Switzerland
Interests: Gibbs paradox; entropy; symmetry; similarity; diversity; information theory; thermodynamics; process irreversibility or spontaneity; stability; nature of the chemical processes; molecular recognition; open access journals

Published Papers (36 papers)

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Research

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Open AccessArticle Synthesis, Antibacterial and Antifungal Activity of Some New Pyrazoline and Pyrazole Derivatives
Molecules 2013, 18(3), 2683-2711; doi:10.3390/molecules18032683
Received: 31 October 2012 / Revised: 7 January 2013 / Accepted: 9 January 2013 / Published: 28 February 2013
Cited by 18 | PDF Full-text (759 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
A series of 2-pyrazolines 59 have been synthesized from α,β-unsaturated ketones 24. New 2-pyrazoline derivatives 1315 bearing benzenesulfonamide moieties were then synthesized by condensing the appropriate chalcones 24 with 4-hydrazinyl benzenesulfonamide hydrochloride. [...] Read more.
A series of 2-pyrazolines 59 have been synthesized from α,β-unsaturated ketones 24. New 2-pyrazoline derivatives 1315 bearing benzenesulfonamide moieties were then synthesized by condensing the appropriate chalcones 24 with 4-hydrazinyl benzenesulfonamide hydrochloride. Ethyl [1,2,4] triazolo[3,4-c][1,2,4]triazino[5,6-b]-5H-indole-5-ethanoate (26) and 1-(5H-[1,2,4]triazino[5,6-b] indol-3-yl)-3-methyl-1H-pyrazol-5(4H)-one (32) were synthesized from 3-hydrazinyl-5H-[1,2,4]triazino[5,6-b]indole (24). On the other hand ethyl[1,2,4]triazolo[3,4-c][1,2,4]triazino[5,6-b]-5,10-dihydroquinoxaline- 5-ethanoate (27) and 1-(5,10-dihydro-[1,2,4]triazino[5,6-b]quinoxalin-3-yl)-3-methyl-1H-pyrazol-5(4H)-one (33) were synthesized from 3-hydrazinyl-5,10-dihydro-[1,2,4]triazino[5,6-b]quinoxaline (25) by reaction with diethyl malonate or ethyl acetoacetate, respectively. Condensation of 6,6-dimethyl-4-oxo-4,5,6,7-tetrahydro-1H-indole-2-carbaldehyde (1') with compound 24 or 25 afforded the corresponding Schiff's bases 36 and 37, respectively. Reaction of the Schiff's base 37 with benzoyl hydrazine or acetic anhydride afforded benzohydrazide derivative 39 and the cyclized compound 40, respectively. Furthermore, the pyrazole derivatives 4244 were synthesized by cyclization of hydrazine derivative 25 with the prepared chalcones 24. All the newly synthesized compounds have been characterized on the basis of IR and 1H-NMR spectral data as well as physical data. Antimicrobial activity against the organisms E. coli ATCC8739 and P. aeruginosa ATCC 9027 as examples of Gram-negative bacteria, S. aureus ATCC 6583P as an example of Gram-positive bacteria and C. albicans ATCC 2091 as an example of a yeast-like fungus have been studied using the Nutrient Agar (NA) and Sabouraud Dextrose Agar (SDA) diffusion methods. The best performance was found for the compounds 16, 17, 19 and 20. Full article
(This article belongs to the Special Issue Heterocycles)
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Open AccessArticle Ultrasound-Promoted One-Pot, Three-Component Synthesis of Spiro[indoline-3,1'-pyrazolo[1,2-b]phthalazine] Derivatives
Molecules 2012, 17(7), 8674-8686; doi:10.3390/molecules17078674
Received: 8 June 2012 / Revised: 28 June 2012 / Accepted: 13 July 2012 / Published: 23 July 2012
Cited by 10 | PDF Full-text (252 KB)
Abstract
A series of 3'-aminospiro[indoline-3,1'-pyrazolo[1,2-b]phthalazine]-2,5',10'-trione derivatives have been synthesized by a one-pot three-component reaction of isatin, malononitrile or ethyl cyanoacetate and phthalhydrazide catalyzed by piperidine under ultrasound irradiation. For comparison the reactions were carried out under both conventional and ultrasonic conditions. [...] Read more.
A series of 3'-aminospiro[indoline-3,1'-pyrazolo[1,2-b]phthalazine]-2,5',10'-trione derivatives have been synthesized by a one-pot three-component reaction of isatin, malononitrile or ethyl cyanoacetate and phthalhydrazide catalyzed by piperidine under ultrasound irradiation. For comparison the reactions were carried out under both conventional and ultrasonic conditions. In general, improvement in rates and yields were observed when the reactions were carried out under sonication compared with classical conditions. Full article
(This article belongs to the Special Issue Heterocycles)
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Open AccessArticle Ring-Expansion Reaction of Oximes with Aluminum Reductants
Molecules 2012, 17(6), 7348-7355; doi:10.3390/molecules17067348
Received: 5 April 2012 / Revised: 4 June 2012 / Accepted: 7 June 2012 / Published: 14 June 2012
Cited by 11 | PDF Full-text (198 KB)
Abstract
The ring-expansion reactions of heterocyclic ketoximes and carbocyclic ketoximes with several reductants such as AlHCl2, AlH3 (alane), LiAlH4, LiAlH(OtBu)3, and (MeOCH2CH2O)2AlH2Na (Red-Al) were examined. Among [...] Read more.
The ring-expansion reactions of heterocyclic ketoximes and carbocyclic ketoximes with several reductants such as AlHCl2, AlH3 (alane), LiAlH4, LiAlH(OtBu)3, and (MeOCH2CH2O)2AlH2Na (Red-Al) were examined. Among reductants, AlHCl2 (LiAlH4:AlCl3 = 1:3) in cyclopentyl methyl ether (CPME) has been found to be a suitable reagent for the reaction, and the rearranged cyclic secondary amines were obtained in good to excellent yields. Full article
(This article belongs to the Special Issue Heterocycles)
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Open AccessArticle 5-(5-Aryl-1,3,4-oxadiazole-2-carbonyl)furan-3-carboxylate and New Cyclic C-Glycoside Analogues from Carbohydrate Precursors with MAO-B, Antimicrobial and Antifungal Activities
Molecules 2012, 17(6), 7010-7027; doi:10.3390/molecules17067010
Received: 1 April 2012 / Revised: 27 April 2012 / Accepted: 9 May 2012 / Published: 7 June 2012
Cited by 2 | PDF Full-text (633 KB)
Abstract
Cyclization of acyclic C-glycoside derivatives 1a,b to 2a,b as the major isomers, and 4a,b as the minor isomers were carried out. The isopropylidene derivatives 3a,b were prepared, as well as the hydrazide derivative 6, which was condensed with a variety [...] Read more.
Cyclization of acyclic C-glycoside derivatives 1a,b to 2a,b as the major isomers, and 4a,b as the minor isomers were carried out. The isopropylidene derivatives 3a,b were prepared, as well as the hydrazide derivative 6, which was condensed with a variety of aldehydes to give hydrazones 7a–e which were also prepared from the compounds 12a–e. Acetylation of 7a,d gave the corresponding acetyl derivatives 8a,d, respectively. In addition, the dicarbonyl compound 9 was prepared in the hydrate form, which reacted with a number of aroylhydrazines to give the corresponding bisaroyl-hydrazones 10a–d, which were cyclized into 1,3,4-oxadiazoles 11a–d. Furthermore, two of the prepared compounds were examined to show the ability to activate MAO-B. In addition a number of prepared compounds showed antibacterial and antiviral activities. Full article
(This article belongs to the Special Issue Heterocycles)
Open AccessArticle Scope and Limitations of a Novel Synthesis of 3-Arylazonicotinates
Molecules 2012, 17(5), 5924-5934; doi:10.3390/molecules17055924
Received: 27 January 2012 / Revised: 13 May 2012 / Accepted: 15 May 2012 / Published: 18 May 2012
Cited by 3 | PDF Full-text (214 KB) | Supplementary Files
Abstract The reaction of 3-oxo-3-phenyl-2-phenylhydrazonal with functionally substituted and heteroaromatic substituted acetonitrile to yield arylazonicotinic acid derivatives and 5-arylsubstituted pyridines was established. In some cases the produced nicotinates could not be isolated as they underwent thermally induced 6π-electrocyclization yielding polynuclear pyridine derivatives. Full article
(This article belongs to the Special Issue Heterocycles)
Open AccessArticle Synthesis and Antimicrobial Evaluation of Some Pyrazole Derivatives
Molecules 2012, 17(5), 4962-4971; doi:10.3390/molecules17054962
Received: 20 February 2012 / Revised: 23 March 2012 / Accepted: 18 April 2012 / Published: 30 April 2012
Cited by 14 | PDF Full-text (325 KB)
Abstract
Reaction of a series of (E)-3-phenyl-4-(p-substituted phenyl)-3-buten-2-ones with p-sulfamylphenyl hydrazine in glacial acetic acid gave the corresponding hydrazones, subsequent treatment of which with 30% HCl afforded pyrazole-1-sulphonamides. On the other hand, refluxing of chalcones with either thiosemicarbazide or [...] Read more.
Reaction of a series of (E)-3-phenyl-4-(p-substituted phenyl)-3-buten-2-ones with p-sulfamylphenyl hydrazine in glacial acetic acid gave the corresponding hydrazones, subsequent treatment of which with 30% HCl afforded pyrazole-1-sulphonamides. On the other hand, refluxing of chalcones with either thiosemicarbazide or isonicotinic acid hydrazide in ethanol containing a few drops of acetic acid gave pyrazoline-1-thiocarboxamides and isonicotinoyl pyrazolines, respectively. The structures of the synthesized compounds were determined on the basis of their elemental analyses and spectroscopic data. The antimicrobial activity of the newly isolated heterocyclic compounds was evaluated against Gram-positive, Gram-negative bacteria and fungi. Most of the compounds showed a moderate degree of potent antimicrobial activity. Full article
(This article belongs to the Special Issue Heterocycles)
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Open AccessArticle A New Class of Heterocycles: 1,4,3,5-Oxathiadiazepane 4,4-dioxides
Molecules 2012, 17(2), 1890-1899; doi:10.3390/molecules17021890
Received: 19 January 2012 / Revised: 6 February 2012 / Accepted: 8 February 2012 / Published: 14 February 2012
PDF Full-text (192 KB)
Abstract
This work reports the synthesis of novel 1,4,3,5-oxathiadiazepanes 4,4-dioxides from the reaction of N’-benzyl-N-(2-hydroxyethyl)-sarcosine or proline sulfamide with aromatic aldehydes under acid catalysis. To prepare the starting materials N-Boc-sulfamide derivatives of sarcosine or proline were alkylated with benzyl [...] Read more.
This work reports the synthesis of novel 1,4,3,5-oxathiadiazepanes 4,4-dioxides from the reaction of N’-benzyl-N-(2-hydroxyethyl)-sarcosine or proline sulfamide with aromatic aldehydes under acid catalysis. To prepare the starting materials N-Boc-sulfamide derivatives of sarcosine or proline were alkylated with benzyl alcohol under Mitsunobu reaction conditions, the Boc group was removed chemoselectively by acidolysis, and the resulting product reduced to the corresponding alcohol in good yields. Full article
(This article belongs to the Special Issue Heterocycles)
Open AccessArticle Synthesis of Novel IP Agonists via N-Aminoethyl Cyclic Amines Prepared by Decarboxylative Ring-Opening Reactions
Molecules 2012, 17(2), 1233-1246; doi:10.3390/molecules17021233
Received: 7 December 2011 / Revised: 20 January 2012 / Accepted: 21 January 2012 / Published: 31 January 2012
PDF Full-text (445 KB)
Abstract
An efficient synthesis of a highly potent and selective IP (PGI2 receptor) agonist that is not structurally analogous to PGI2 is described. This synthesis is accomplished through the following key steps: Nucleophilic ring-opening of 3-(4-chlorophenyl)-oxazolidin-2-one prepared by a one-pot procedure [...] Read more.
An efficient synthesis of a highly potent and selective IP (PGI2 receptor) agonist that is not structurally analogous to PGI2 is described. This synthesis is accomplished through the following key steps: Nucleophilic ring-opening of 3-(4-chlorophenyl)-oxazolidin-2-one prepared by a one-pot procedure with 4-piperidinol and selective O-alkylation of 1-(2-(4-chlorophenylamino)ethyl)piperidin-4-ol. The obtained compound is a potent and selective IP agonist displaying a long duration of action. Full article
(This article belongs to the Special Issue Heterocycles)
Open AccessArticle Studies on 3-Oxoalkanenitriles: Novel Rearrangement Reactions Observed in Studies of the Chemistry of 3-Heteroaroyl-3-Oxoalkanenitriles as Novel Routes to 2-Dialkylaminopyridines
Molecules 2012, 17(1), 897-909; doi:10.3390/molecules17010897
Received: 1 December 2011 / Revised: 16 January 2012 / Accepted: 16 January 2012 / Published: 18 January 2012
Cited by 6 | PDF Full-text (442 KB) | Supplementary Files
Abstract
3-Aroyl and 3-heteroaroyl substituted 3-oxoalkanenitriles were synthesized by the reactions of activated aromatic and hetero-aromatic substances with cyanoacetic acid in the presence of acetic anhydride. As part of studies focusing on the preparation of cyanoacetyl-1-N-methylbenzimidazole, we observed that reaction of [...] Read more.
3-Aroyl and 3-heteroaroyl substituted 3-oxoalkanenitriles were synthesized by the reactions of activated aromatic and hetero-aromatic substances with cyanoacetic acid in the presence of acetic anhydride. As part of studies focusing on the preparation of cyanoacetyl-1-N-methylbenzimidazole, we observed that reaction of N-methyl-benzimidazole with the cyanoanhydride formed by condensation of cyanoacetic acid with acetic anhydride, leads to the formation of 2-(1,3-diacetyl-2,3-dihydro-1H-benzo[d]-imidazol-2-yl)acetonitrile (5), whose structure was confirmed by X-ray crystallographic analysis. 3-Oxoalkanenitriles 3a,b were observed to undergo condensation reactions with dimethylformamide dimethyl acetal (DMFDMA) to afford the corresponding enamino-nitriles, which react with malononitrile to give 2-dialkylaminopyridines through a pathway involving a new, unexpected rearrangement process. Reactions of 3-oxoalkanenitriles with ethyl acetoacetate were found to afford 2-oxopyran-3-carbonitriles, also occurring via this unexpected rearrangement process. Mechanisms to account for both rearrangement reactions are suggested. In addition, reactions of 3-oxoalkanenitriles with acetylacetone in acetic acid in the presence of ammonium acetate result in the formation of pyridine-3-carbonitriles. Finally, upon heating in the presence of zeolite 3-oxoalkanenitriles 3b,c self-trimerized to produce the corresponding aniline derivatives 23b,c. Full article
(This article belongs to the Special Issue Heterocycles)
Open AccessArticle Synthesis, Reactions and Antimicrobial Activities of 8-Ethoxycoumarin Derivatives
Molecules 2012, 17(1), 971-988; doi:10.3390/molecules17010971
Received: 14 November 2011 / Revised: 1 January 2012 / Accepted: 4 January 2012 / Published: 18 January 2012
Cited by 7 | PDF Full-text (809 KB)
Abstract
Condensation of 3-acetyl-8-ethoxycoumarin (3) with thiosemicarbazide gave ethylidenehydrazinecarbothioamide 5, which was transformed into the thiazolidin-4-one derivatives 6,7. Interaction of 3 with DMF/POCl3 gave b-chloroacroline derivative 8. Treatment of 3 with malononitrile gave benzo[ [...] Read more.
Condensation of 3-acetyl-8-ethoxycoumarin (3) with thiosemicarbazide gave ethylidenehydrazinecarbothioamide 5, which was transformed into the thiazolidin-4-one derivatives 6,7. Interaction of 3 with DMF/POCl3 gave b-chloroacroline derivative 8. Treatment of 3 with malononitrile gave benzo[c]chromone and 2-aminobenzonitrile derivatives 9 and 10, respectively with respect to the reaction conditions. Condensation of 3-(2-bromoacetyl)-8-ethoxycoumarin (4) with o-phenylenediamine gave 3-(quioxaline-2-yl)-8-ethoxycoumarin hydrobromide (11), while 4 reacted with 2-aminopyridine to give chromenopyridopyrimidine derivative 12. Condensation of 4 with potassium thio-cyanate/methanol gave an unexpected derivative, 2H-chromeno-3-carboxy(methyl-carbonimidic)thioanhydride 16, which upon treatment with (NH2)2·H2O gave 3-ethoxy-2-hydroxybenzaldehyde azine 19. Interaction of 4 with thiourea derivatives gave thiazole derivatives 20a–c. The structures of the newly synthesized compounds were confirmed by their spectra data. The newly synthesized compounds were also screened for their antimicrobial activity. Full article
(This article belongs to the Special Issue Heterocycles)
Open AccessArticle Quantum Mechanics Calculations, Basicity and Crystal Structure: The Route to Transition Metal Complexes of Azahelicenes
Molecules 2012, 17(1), 463-479; doi:10.3390/molecules17010463
Received: 13 December 2011 / Revised: 22 December 2011 / Accepted: 23 December 2011 / Published: 5 January 2012
Cited by 6 | PDF Full-text (684 KB) | Supplementary Files
Abstract
Quantum mechanics density functional calculations provided gas-phase electron distributions and proton affinities for several mono- and diaza[5]helicenes; computational results, together with experimental data concerning crystal structures and propensity to methylation of the nitrogen atom(s), provide a basis for designing azahelicene complexes with [...] Read more.
Quantum mechanics density functional calculations provided gas-phase electron distributions and proton affinities for several mono- and diaza[5]helicenes; computational results, together with experimental data concerning crystal structures and propensity to methylation of the nitrogen atom(s), provide a basis for designing azahelicene complexes with transition metal ions. Full article
(This article belongs to the Special Issue Heterocycles)
Open AccessArticle Synthesis and Biological Activity of Some 3-(4-(Substituted)-piperazin-1-yl)cinnolines
Molecules 2012, 17(1), 227-239; doi:10.3390/molecules17010227
Received: 15 November 2011 / Revised: 21 December 2011 / Accepted: 22 December 2011 / Published: 28 December 2011
Cited by 5 | PDF Full-text (259 KB)
Abstract
A new series of 6-substituted-4-methyl-3-(4-arylpiperazin-1-yl)cinnolines 810 were synthesized as potential antifungal agents via intramolecular cyclization of the respective 1-(2-arylhydrazono)-1-(4-arylpiperazin-1-yl)propan-2-ones 57, mediated by polyphosphoric acid (PPA). The amidrazones themselves were synthesized via direct interaction of the appropriate hydrazonoyl [...] Read more.
A new series of 6-substituted-4-methyl-3-(4-arylpiperazin-1-yl)cinnolines 810 were synthesized as potential antifungal agents via intramolecular cyclization of the respective 1-(2-arylhydrazono)-1-(4-arylpiperazin-1-yl)propan-2-ones 57, mediated by polyphosphoric acid (PPA). The amidrazones themselves were synthesized via direct interaction of the appropriate hydrazonoyl chlorides 4ad with the corresponding N-substituted piperazine in the presence of triethylamine. The structures of the new prepared compounds were confirmed by elemental analyses, 1H-NMR, 13C-NMR, and ESI-HRMS spectral data. The antitumor, antibacterial, and antifungal activity of the newly synthesized compounds was evaluated. Full article
(This article belongs to the Special Issue Heterocycles)
Open AccessArticle Synthesis and Antibacterial Activities of Novel 2,5-Diphenylindolo[2,3-e] Pyrazolo[1',5':3",4"]pyrimido[2",1"-c] [1,2,4]triazines
Molecules 2011, 16(12), 10387-10408; doi:10.3390/molecules161210387
Received: 3 October 2011 / Revised: 2 November 2011 / Accepted: 16 November 2011 / Published: 15 December 2011
Cited by 5 | PDF Full-text (390 KB)
Abstract
The formation of (E)-3-{2-(2,5-diphenylpyrazolo[1,5-c]pyrimidin-7-yl)hydrazono}indolin-2-ones 3 has been achieved by condensation of equimolar amounts of 7-hydrazino-2,5-diphenylpyrazolo[1,5-c]pyrimidine (1) and isatin (or isatin derivatives) 2 at room temperature. The (E)-products could be isomerized into corresponding [...] Read more.
The formation of (E)-3-{2-(2,5-diphenylpyrazolo[1,5-c]pyrimidin-7-yl)hydrazono}indolin-2-ones 3 has been achieved by condensation of equimolar amounts of 7-hydrazino-2,5-diphenylpyrazolo[1,5-c]pyrimidine (1) and isatin (or isatin derivatives) 2 at room temperature. The (E)-products could be isomerized into corresponding the (Z)-3 isomers. Reactions of the latter fused heterocyclic hydrazones towards different electro-philic reagents yielded the corresponding 3-substituted derivatives 47. Dehydrative cyclisation of the hydrazones 3 using phosphorus oxychloride afforded the 2,5-diphenyl- indolo[2,3-e]pyrazolo[1',5':3",4"]pyrimido[2",1"-c][1,2,4] triazines 13. The polyfused heterocyclic ring system 13 underwent electrophilic substitution reactions at position 4 rather than at position 3. The 3-bromo isomer of 17 was prepared by a sequence of reactions starting from 2,5-diphenylpyrazolo[1,5-c]pyrimidine-7(6H)-thione (11). The orientation of the electrophilic attack was supported by spectroscopic and chemical evidence. Some of the synthesized compounds were found to possess slight to moderate activity against the microorganisms Bacillus subtilis, Micrococcus luteus, Staphylococcus aureus, Escherichia coli and Pseudomonas aeruginosa. Full article
(This article belongs to the Special Issue Heterocycles)
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Open AccessArticle One-Pot Synthesis of Novel 2,3-Dihydro-1H-indazoles
Molecules 2011, 16(11), 9553-9561; doi:10.3390/molecules16119553
Received: 8 October 2011 / Revised: 8 November 2011 / Accepted: 10 November 2011 / Published: 16 November 2011
Cited by 4 | PDF Full-text (237 KB) | Supplementary Files
Abstract
A copper(I)-mediated one-pot synthesis of 2,3-dihydro-1H-indazole heterocycles has been developed. This synthetic route provides the desired indazoles in moderate to good yields (55%–72%) which are substantially better than those achievable with an alternative two-step reaction sequence. The reaction is tolerant [...] Read more.
A copper(I)-mediated one-pot synthesis of 2,3-dihydro-1H-indazole heterocycles has been developed. This synthetic route provides the desired indazoles in moderate to good yields (55%–72%) which are substantially better than those achievable with an alternative two-step reaction sequence. The reaction is tolerant of functionality on the aromatic ring. Full article
(This article belongs to the Special Issue Heterocycles)
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Open AccessArticle Synthesis of [(4-Chloro-5H-1,2,3-dithiazol-5-ylidene)amino]azines
Molecules 2011, 16(11), 8992-9002; doi:10.3390/molecules16118992
Received: 26 September 2011 / Revised: 21 October 2011 / Accepted: 21 October 2011 / Published: 25 October 2011
Cited by 9 | PDF Full-text (238 KB)
Abstract
The reactions of 2-, 3- and 4-aminopyridines with 4,5-dichloro-1,2,3-dithiazol-ium chloride (Appel salt) 4 to give N-(4-chloro-5H-1,2,3-dithiazol-5-ylidene)pyridin-X-amines 1a (X = 2), 1g (X = 3) and 1k (X = 4) were optimized with respect to base, temperature and reaction [...] Read more.
The reactions of 2-, 3- and 4-aminopyridines with 4,5-dichloro-1,2,3-dithiazol-ium chloride (Appel salt) 4 to give N-(4-chloro-5H-1,2,3-dithiazol-5-ylidene)pyridin-X-amines 1a (X = 2), 1g (X = 3) and 1k (X = 4) were optimized with respect to base, temperature and reaction time. Based on these conditions a total of thirteen [(dithiazol-ylidene)amino]azines 1a-m were prepared and fully characterized. Full article
(This article belongs to the Special Issue Heterocycles)
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Open AccessArticle Facile Synthesis of Functionalized Spiropyrrolizidine Oxindoles via a Three-Component Tandem Cycloaddition Reaction
Molecules 2011, 16(10), 8745-8757; doi:10.3390/molecules16108745
Received: 26 August 2011 / Revised: 30 September 2011 / Accepted: 3 October 2011 / Published: 19 October 2011
Cited by 14 | PDF Full-text (323 KB) | Supplementary Files
Abstract
An efficient synthesis of functionalized spiropyrrolizidine oxindoles via a three-component tandem cycloaddition has been achieved. This strategy can provide direct and rapid access to spiropyrrolizidine oxindoles in high yields (up to 99%) with excellent diastereoselectivities (up to 99:1 dr). The features of [...] Read more.
An efficient synthesis of functionalized spiropyrrolizidine oxindoles via a three-component tandem cycloaddition has been achieved. This strategy can provide direct and rapid access to spiropyrrolizidine oxindoles in high yields (up to 99%) with excellent diastereoselectivities (up to 99:1 dr). The features of this procedure are the following: mild reaction conditions, high yields, high diastereoselectivities, one-pot procedure and operational simplicity. Full article
(This article belongs to the Special Issue Heterocycles)
Open AccessArticle Synthesis, Acidity Constants and Tautomeric Structure of the Diazonium Coupling Products of 2-(Benzylsulfanyl)-7H-purin-6-one in Its Ground and Excited States
Molecules 2011, 16(10), 8788-8802; doi:10.3390/molecules16108788
Received: 22 September 2011 / Revised: 7 October 2011 / Accepted: 12 October 2011 / Published: 19 October 2011
Cited by 5 | PDF Full-text (276 KB)
Abstract
A series of new 8-arylhydrazono-2-(benzylsulfanyl)-7H-purin-6-ones 6 were synthesized, their electronic absorption spectra in different organic solvents of varying polarities were investigated and their acid dissociation constants in both the ground and excited states were determined spectrophotometrically. The tautomeric structures of [...] Read more.
A series of new 8-arylhydrazono-2-(benzylsulfanyl)-7H-purin-6-ones 6 were synthesized, their electronic absorption spectra in different organic solvents of varying polarities were investigated and their acid dissociation constants in both the ground and excited states were determined spectrophotometrically. The tautomeric structures of such products were elucidated by spectral analyses and correlation of their acid dissociation constants with the Hammett equation. The results indicated that the studied compounds 6 exist predominantly in the hydrazone tautomeric form 6A in both the ground and excited states. Full article
(This article belongs to the Special Issue Heterocycles)
Open AccessArticle Synthesis and in Vitro Antimicrobial Activity of Some Pyrazolyl-1-carboxamide Derivatives
Molecules 2011, 16(9), 7736-7745; doi:10.3390/molecules16097736
Received: 13 August 2011 / Revised: 25 August 2011 / Accepted: 31 August 2011 / Published: 9 September 2011
Cited by 11 | PDF Full-text (430 KB)
Abstract
A series of 3,5-disubstituted pyrazole-1-carboxamides were obtained by treatment of chalcones with semicarbazide hydrochloride in dioxane containing sodium acetate/acetic acid as a buffer solution. N-acetyl derivatives of pyrazole-1-carboxamides were isolated in good yields either by treatment of the carboxamide derivatives with acetic [...] Read more.
A series of 3,5-disubstituted pyrazole-1-carboxamides were obtained by treatment of chalcones with semicarbazide hydrochloride in dioxane containing sodium acetate/acetic acid as a buffer solution. N-acetyl derivatives of pyrazole-1-carboxamides were isolated in good yields either by treatment of the carboxamide derivatives with acetic anhydride or refluxing chalcones with semicarbazide in ethanol containing few drops of acetic acid to give the corresponding hydrazones. Subsequent treatment of hydrazones with acetic anhydride gave the desired N-acetyl pyrazole-1-carboxamides derivatives. When chalcones were refluxed with dioxane containing few drops of acetic acid, 4,5-dihydropyrazole-1-carboxamides were isolated, which were subsequently oxidized using 5% sodium hypochlorite in dioxane to afford pyrazole-1-carboxamides. The structures of isolated compounds were confirmed by elemental analyses and spectral methods. The isolated compounds were tested for their antimicrobial activities. Full article
(This article belongs to the Special Issue Heterocycles)
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Open AccessArticle Synthesis and Electrophilic Substitutions of Novel Pyrazolo[1,5-c]-1,2,4-triazolo[4,3-a]pyrimidines
Molecules 2011, 16(8), 7081-7096; doi:10.3390/molecules16087081
Received: 30 June 2011 / Revised: 1 August 2011 / Accepted: 4 August 2011 / Published: 18 August 2011
Cited by 4 | PDF Full-text (454 KB)
Abstract
5-Aryl-7-hydrazino-2-phenylpyrazolo[1,5-c]pyrimidines 1 were used as precursors for the preparation of a new series of 5-aryl-8-phenylpyrazolo[1,5-c]-1,2,4- triazolo[4,3-a]pyrimidines 2. The reactions of 2 with certain electrophilic reagents gave the respective 6-substituted derivatives 3-5 rather than [...] Read more.
5-Aryl-7-hydrazino-2-phenylpyrazolo[1,5-c]pyrimidines 1 were used as precursors for the preparation of a new series of 5-aryl-8-phenylpyrazolo[1,5-c]-1,2,4- triazolo[4,3-a]pyrimidines 2. The reactions of 2 with certain electrophilic reagents gave the respective 6-substituted derivatives 3-5 rather than the 7-isomeric products. Formylation of the key compounds 1 with ethyl formate yielded the formyl derivatives 6. Furthermore, boiling of compounds 1 with acetic acid afforded 7-acetylhydrazino-5-aryl-2-phenylpyrazolo[1,5-c]pyrimidines 7. Bromination of 7 yielded the dibromo- derivatives 8, while their iodination and nitration gave the monosubstituted derivatives 9 and 10, respectively. Also, treatment of 1 with boiling acetic anhydride yielded the triacetyl derivatives 11. The structure of synthesized products was confirmed by elemental analyses, IR, 1H NMR and MS spectra. Full article
(This article belongs to the Special Issue Heterocycles)
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Open AccessArticle Synthesis and Contractile Activity of Substituted 1,2,3,4-Tetrahydroisoquinolines
Molecules 2011, 16(8), 7019-7042; doi:10.3390/molecules16087019
Received: 22 July 2011 / Revised: 10 August 2011 / Accepted: 11 August 2011 / Published: 16 August 2011
Cited by 8 | PDF Full-text (510 KB)
Abstract
A series of different 1-monosubstituted and 1,1-disubstituted 1,2,3,4-tetrahydro-isoquinolines was synthesized in high yields from different ketoamides. We have developed a convenient method for the synthesis of disubstituted derivatives by interaction of ketoamides with organomagnesium compounds, followed by cyclization in the presence of [...] Read more.
A series of different 1-monosubstituted and 1,1-disubstituted 1,2,3,4-tetrahydro-isoquinolines was synthesized in high yields from different ketoamides. We have developed a convenient method for the synthesis of disubstituted derivatives by interaction of ketoamides with organomagnesium compounds, followed by cyclization in the presence of catalytic amounts of p-toluenesulfonic acid (PTSA). A number of substituents at the C-1 in the isoquinoline skeleton were introduced varying either carboxylic acid or organomagnesium compound. Some of the obtained 1,1-dialkyl-1,2,3,4-tetrahydro-isoquinolines possess contractile activity against guinea pig’s gastric smooth muscle preparations. Full article
(This article belongs to the Special Issue Heterocycles)
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Open AccessArticle Synthesis and Antimicrobial Activity of Some New Pyrazoles, Fused Pyrazolo[3,4-d]-pyrimidine and 1,2-Dihydroimidazo-[2,1-c][1,2,4]triazin-6-one Derivatives
Molecules 2011, 16(8), 6549-6560; doi:10.3390/molecules16086549
Received: 6 July 2011 / Revised: 25 July 2011 / Accepted: 28 July 2011 / Published: 4 August 2011
Cited by 26 | PDF Full-text (480 KB)
Abstract
A novel series of 7,7-diphenyl-1,2-dihydroimidazo[2,1-c][1,2,4]triazin-6(7H)-one 6a–h, were easily prepared via reactions of novel 2-hydrazinyl-4,4-diphenyl-1H-imidazol-5(4H)-one (2) with hydrazonoyl halides 3a–h. In addition, we also examined the reaction of compound 2 with [...] Read more.
A novel series of 7,7-diphenyl-1,2-dihydroimidazo[2,1-c][1,2,4]triazin-6(7H)-one 6a–h, were easily prepared via reactions of novel 2-hydrazinyl-4,4-diphenyl-1H-imidazol-5(4H)-one (2) with hydrazonoyl halides 3a–h. In addition, we also examined the reaction of compound 2 with commercially available active methylene compounds to afford new pyrazoles containing an imidazolone moiety, expected to be biologically active. The structures of the synthesized compounds were assigned on the basis of elemental analysis, IR, 1H-NMR and mass spectral data. The antifungal and antibacterial activities of the newly synthesized compounds were evaluated. Full article
(This article belongs to the Special Issue Heterocycles)
Open AccessArticle 1,1’-(3-Methyl-4-phenylthieno[2,3-b]thiophene-2,5-diyl)diethanone as a Building Block in Heterocyclic Synthesis. Novel Synthesis of Some Pyrazole and Pyrimidine Derivatives
Molecules 2011, 16(8), 6502-6511; doi:10.3390/molecules16086502
Received: 20 June 2011 / Revised: 25 July 2011 / Accepted: 29 July 2011 / Published: 3 August 2011
Cited by 16 | PDF Full-text (430 KB)
Abstract
A series of new bis(heterocycles) featuring thieno[2,3-b]thiophene rings was synthesized in a combinatorial manner. Intramolecular cyclization of enaminone derivatives with appropriate N-nucleophiles afforded the target compounds. All compounds were characterized by 1H-, 13C-NMR, GCMS, IR, and UV-Vis [...] Read more.
A series of new bis(heterocycles) featuring thieno[2,3-b]thiophene rings was synthesized in a combinatorial manner. Intramolecular cyclization of enaminone derivatives with appropriate N-nucleophiles afforded the target compounds. All compounds were characterized by 1H-, 13C-NMR, GCMS, IR, and UV-Vis spectrometry. These compounds represent a new class of sulfur- and nitrogen-containing heterocycles that should also be of interest as new materials. Full article
(This article belongs to the Special Issue Heterocycles)
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Open AccessArticle Expeditious Entry to Novel 2-Methylene-2,3-dihydrofuro[3,2-c] chromen-2-ones from 6-Chloro-4-hydroxychromen-2-one and Propargylic Alcohols
Molecules 2011, 16(8), 6470-6480; doi:10.3390/molecules16086470
Received: 14 July 2011 / Revised: 27 July 2011 / Accepted: 28 July 2011 / Published: 2 August 2011
Cited by 5 | PDF Full-text (366 KB)
Abstract A catalytic system consisting of the ruthenium(II) complex [Ru(η3-2-C3H4Me)(CO)(dppf)][SbF6] (dppf = 1,1’-bis(diphenylphosphino)ferrocene) and trifluoroacetic acid has been used to promote the coupling of secondary propargylic alcohols with 6-chloro-4-hydroxychromen-2-one. The reactions afforded unusual 2-methylene-2,3-dihydrofuro[3,2-c]chromen-2-ones in good yields. Full article
(This article belongs to the Special Issue Heterocycles)
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Open AccessArticle Synthesis and E/Z Configuration Determination of Novel Derivatives of 3-Aryl-2-(benzothiazol-2'-ylthio) Acrylonitrile, 3-(Benzothiazol-2'-ylthio)-4-(furan-2''-yl)-3-buten-2-one and 2-(1-(Furan-2''-yl)-3'-oxobut-1''-en-2-ylthio)-3-phenylquinazolin-4(3H)-one
Molecules 2011, 16(7), 6129-6147; doi:10.3390/molecules16076129
Received: 21 June 2011 / Revised: 11 July 2011 / Accepted: 14 July 2011 / Published: 20 July 2011
Cited by 6 | PDF Full-text (870 KB)
Abstract
Knoevenagel condensation of 2-(benzothiazol-2-ylthio) acetonitrile (2) with either furan-2-carbaldehyde or thiophene-2-carbaldehydes leads to E-isomers 4a–b exclusively, while the condensation of the compound 2 with benzaldehyde or para-substituted benzaldehydes with an electron-donating group afforded E/Z mixtures 4c–e with preferentially [...] Read more.
Knoevenagel condensation of 2-(benzothiazol-2-ylthio) acetonitrile (2) with either furan-2-carbaldehyde or thiophene-2-carbaldehydes leads to E-isomers 4a–b exclusively, while the condensation of the compound 2 with benzaldehyde or para-substituted benzaldehydes with an electron-donating group afforded E/Z mixtures 4c–e with preferentially formation of the E-isomer. Condensation of furan-2-carbaldehyde (3a) with either 1-(benzothiazol-2'-ylthio) propan-2-one (5) or 2-(2'-oxo propylthio)-3-phenyl-quinazolin-4(3H)-one (9) leads exclusively to the Z-isomers of 6 and 10, respectively. The structures of the newly synthesized compounds were elucidated by elemental analyses, 1H-NMR and 13C-NMR spectra, COSY, HSQC, HMBC, NOE, MS and X-ray crystallographic investigations. Full article
(This article belongs to the Special Issue Heterocycles)
Open AccessCommunication Acid-catalyzed Epimerization of Kobophenol A to Carasinol B
Molecules 2008, 13(4), 938-942; doi:10.3390/molecules13040938
Received: 13 March 2008 / Revised: 4 April 2008 / Accepted: 4 April 2008 / Published: 19 April 2008
Cited by 4 | PDF Full-text (177 KB) | HTML Full-text | XML Full-text
Abstract The conversion from kobophenol A into carasinol B, two main chemicalconstituents of Caragana sinica, was confirmed by in vitro acid-catalyzed epimerization.The result provides important information about the biotransformation of kobophenol A inplants and its metabolism in rats. Full article
(This article belongs to the Special Issue Heterocycles)
Open AccessArticle Palladate Salts from Chiral Pyridinium Ionic Liquids: Synthesis and Crystal Structures
Molecules 2007, 12(8), 1940-1949; doi:10.3390/12081940
Received: 23 May 2007 / Revised: 19 July 2007 / Accepted: 19 July 2007 / Published: 20 August 2007
Cited by 8 | PDF Full-text (154 KB) | HTML Full-text | XML Full-text
Abstract This paper reports the preparation, characterization and the crystal X-ray structures of metal-containing ionic liquid complexes based on chiral pyridinium cations and tetrachloropalladate (II) [PdCl4]2-. Full article
(This article belongs to the Special Issue Heterocycles)
Open AccessArticle o-Quinonoid Heterocycles: Synthesis and Crystal Structure of 2,3-Dicyano-5,7-bismethylthieno[3,4-b]pyrazine
Molecules 2007, 12(8), 1623-1631; doi:10.3390/12081623
Received: 1 June 2007 / Revised: 20 July 2007 / Accepted: 20 July 2007 / Published: 30 July 2007
Cited by 2 | PDF Full-text (203 KB) | HTML Full-text | XML Full-text
Abstract
2,3-Dicyano-5,7-bismethylthieno[3,4-b]pyrazine (5), has been obtained as a minor product from reactions of S-nucleophiles with 5,6-di(1-bromoethyl)pyrazine-2,3- dicarbonitrile (3), or from a condensation of 4-hydroxy-2,5-dimethyl-2,3-dihydrothiophen- 3-one (4) with diaminomaleonitrile. The molecular structure of compound 5 has been confirmed by X-ray diffraction. A partial [...] Read more.
2,3-Dicyano-5,7-bismethylthieno[3,4-b]pyrazine (5), has been obtained as a minor product from reactions of S-nucleophiles with 5,6-di(1-bromoethyl)pyrazine-2,3- dicarbonitrile (3), or from a condensation of 4-hydroxy-2,5-dimethyl-2,3-dihydrothiophen- 3-one (4) with diaminomaleonitrile. The molecular structure of compound 5 has been confirmed by X-ray diffraction. A partial separation of charge causes a donor-acceptor type arrangement of the planar molecules in uniform parallel stacks with an interplanar spacing of 3.334(2) Å at 100 K. Full article
(This article belongs to the Special Issue Heterocycles)
Open AccessArticle New “Green” Approaches to the Synthesis of Pyrazole Derivatives
Molecules 2007, 12(7), 1482-1495; doi:10.3390/12071482
Received: 31 May 2007 / Revised: 16 July 2007 / Accepted: 16 July 2007 / Published: 19 July 2007
Cited by 28 | PDF Full-text (199 KB) | HTML Full-text | XML Full-text
Abstract
A novel approach to the synthesis of pyrazole derivatives from tosylhydrazones of α,β-unsaturated carbonyl compounds possessing a β-hydrogen is proposed, exploiting microwave (MW) activation coupled with solvent free reaction conditions. The cycloaddition was studied on three ketones (trans-4-phenyl-3-buten-2-one, β-ionone and trans-chalcone). The [...] Read more.
A novel approach to the synthesis of pyrazole derivatives from tosylhydrazones of α,β-unsaturated carbonyl compounds possessing a β-hydrogen is proposed, exploiting microwave (MW) activation coupled with solvent free reaction conditions. The cycloaddition was studied on three ketones (trans-4-phenyl-3-buten-2-one, β-ionone and trans-chalcone). The corresponding 3,5-disubstitued-1H-pyrazoles were obtained in high yields and after short reaction times. In order to simplify and point out the green chemistry features of the method, a further improvement was achieved under the same catalytic conditions with a “one pot” synthesis of these heterocyclic compounds, starting directly from their carbonyl precursors via tosylhydrazones generated in situ. For an exhaustive study, the dielectric properties of the solid reaction mixtures were also measured, in order to obtain input data for the numerical simulation of their heating behaviour in the single mode MW cavity which was used for experimental work. In order to supply a valid methodology and tool for measuring the environmental impact, a comparative study between the synthetic route proposed and the classical synthetic route has been carried out. Full article
(This article belongs to the Special Issue Heterocycles)
Open AccessArticle Synthesis and Characterization of 5,10,15,20-Tetra[3-(3-trifluoromethyl)phenoxy] Porphyrin
Molecules 2007, 12(7), 1389-1398; doi:10.3390/12071389
Received: 30 May 2007 / Revised: 8 July 2007 / Accepted: 9 July 2007 / Published: 11 July 2007
Cited by 5 | PDF Full-text (80 KB)
Abstract
The newly synthesized 5,10,15,20-tetra[3-(3-trifluoromethyl)phenoxy]porphyrin, TTFMPP, has been characterized using mass spectroscopy, 1H-, 13C- and 19F-NMR, MALDI-TOF mass spectrometry, UV-Vis and fluorescence spectrophotometry, andcyclic voltammetry. The NMR confirmed the structure of the compound and the massspectrum was in agreement with [...] Read more.
The newly synthesized 5,10,15,20-tetra[3-(3-trifluoromethyl)phenoxy]porphyrin, TTFMPP, has been characterized using mass spectroscopy, 1H-, 13C- and 19F-NMR, MALDI-TOF mass spectrometry, UV-Vis and fluorescence spectrophotometry, andcyclic voltammetry. The NMR confirmed the structure of the compound and the massspectrum was in agreement with the proposed molecular formula. The UV-Vis absorptionspectrum of TTFMPP shows characteristic spectral patterns similar to those of tetraphenylporphryin, with a Soret band at 419 nm and four Q bands at 515, 550, 590, and 648 nm.Protonation of the porphyrin with TFA resulted in the expected red shift of the Soret band.Excitation at 419 nm gave an emission at 650 nm. The quantum yield of the porphyrin wasdetermined to be 0.08. Cyclic voltammetry was used to determine the oxidation andreduction potentials of the new porphyrin. Two quasi-reversible one-electron reductions at–1.00 and –1.32 V and a quasi-reversible oxidation at 1.20 V versus the silver/silverchloride reference electrode with tetrabutylammonium tetrafluoroborate as the supportingelectrolyte in methylene chloride were observed. Full article
(This article belongs to the Special Issue Heterocycles)
Open AccessArticle Facile Synthesis of Optically Active Imidazole Derivatives
Molecules 2007, 12(5), 1183-1190; doi:10.3390/12051183
Received: 11 May 2007 / Revised: 22 May 2007 / Accepted: 23 May 2007 / Published: 30 May 2007
Cited by 20 | PDF Full-text (72 KB) | HTML Full-text | XML Full-text
Abstract
Five optically active imidazole derivatives have been synthesized via a facile 4-step reaction sequence starting from commercially available and inexpensive N-Cbz amino acids. While microwave assisted condensation was unsuccessful, the condensation of the corresponding α-bromoketones with formamidine acetate in liquid ammonia [...] Read more.
Five optically active imidazole derivatives have been synthesized via a facile 4-step reaction sequence starting from commercially available and inexpensive N-Cbz amino acids. While microwave assisted condensation was unsuccessful, the condensation of the corresponding α-bromoketones with formamidine acetate in liquid ammonia was revealed to be a useful method for the synthesis of such imidazole derivatives. The derivatives thus prepared are structurally-related to histamine. Full article
(This article belongs to the Special Issue Heterocycles)
Open AccessArticle Investigation on the Binding of Polycyclic AromaticHydrocarbons with Soil Organic Matter: A Theoretical Approach
Molecules 2007, 12(4), 703-715; doi:10.3390/12040703
Received: 26 February 2007 / Revised: 22 March 2007 / Accepted: 23 March 2007 / Published: 5 April 2007
Cited by 7 | PDF Full-text (477 KB) | HTML Full-text | XML Full-text
Abstract
Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous contaminants of the terrestrial environment that have been designated as Environmental Protection Agency (EPA) Priority Pollutants. In this study, molecular modeling was used to examine the physical and chemical characteristics of soil organic matter (SOM), fulvic [...] Read more.
Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous contaminants of the terrestrial environment that have been designated as Environmental Protection Agency (EPA) Priority Pollutants. In this study, molecular modeling was used to examine the physical and chemical characteristics of soil organic matter (SOM), fulvic acid (FA) and humic acid (HA), as well as their binding interactions with PAHs. The molecular structures of 18 PAHs were built by using the SYBYL 7.0 program and then fully optimized by a semiempirical (AM1) method. A molecular docking program, AutoDock 3.05, was used to calculate the binding interactions between the PAHs, and three molecular structure models including FA (Buffle’s model), HA (Stevenson’s model) and SOM (Schulten and Schnitzer’s model). The π-π interactions and H-bonding interactions were found to play an important role in the intermolecular bonding of the SOM/PAHs complexes. In addition, significant correlations between two chemical properties, boiling point (bp) and octanol/water partition coefficient (Log Kow) and final docking energies were observed. The preliminary docking results provided knowledge of the important binding modes to FA, HA and SOM, and thereby to predict the sorption behavior of PAHs and other pollutants. Full article
(This article belongs to the Special Issue Heterocycles)
Open AccessArticle Synthesis of 5-Acetoxymethyl- and 5-Hydroxymethyl-2-vinyl-furan
Molecules 2007, 12(3), 634-640; doi:10.3390/12030634
Received: 8 March 2007 / Revised: 23 March 2007 / Accepted: 23 March 2007 / Published: 26 March 2007
Cited by 7 | PDF Full-text (60 KB) | HTML Full-text | XML Full-text
Abstract
5-Acetoxymethyl- and 5-hydroxymethyl-2-vinylfuran were synthesized by two routes. The first route starts from 2-methylfuran and the second from furfuryl acetate. The latter route, involving successive Vilsmeier-Haack and Wittig reactions, is suitable for producing 5-acetoxymethyl-2-vinylfuran and 5-hydroxymethyl-2 vinylfuran in 68% and 60%yields, respectively. [...] Read more.
5-Acetoxymethyl- and 5-hydroxymethyl-2-vinylfuran were synthesized by two routes. The first route starts from 2-methylfuran and the second from furfuryl acetate. The latter route, involving successive Vilsmeier-Haack and Wittig reactions, is suitable for producing 5-acetoxymethyl-2-vinylfuran and 5-hydroxymethyl-2 vinylfuran in 68% and 60%yields, respectively. Full article
(This article belongs to the Special Issue Heterocycles)
Open AccessArticle New Diterpenoid Alkaloids from the Roots of Delphinium tiantaishanense
Molecules 2007, 12(3), 353-360; doi:10.3390/12030353
Received: 11 January 2007 / Revised: 14 February 2007 / Accepted: 18 February 2007 / Published: 8 March 2007
Cited by 5 | PDF Full-text (95 KB) | HTML Full-text | XML Full-text
Abstract Four new diterpenoid alkaloids: tiantaishansine (1), tiantaishannine (2), tiantaishanmine (3), and tiantaishandine (4) have been isolated from the roots of Delphinium tiantaishan. Their structures were elucidated by chemical evidence andspectral analyses, including ESI-MS, HR-EI-MS, 1D- and 2D-NMR. Full article
(This article belongs to the Special Issue Heterocycles)
Open AccessArticle Heteropolyacids as Green and Reusable Catalysts for the Synthesis of 3,1,5-Benzoxadiazepines
Molecules 2007, 12(2), 255-262; doi:10.3390/12020255
Received: 8 January 2007 / Revised: 10 February 2007 / Accepted: 12 February 2007 / Published: 26 February 2007
Cited by 27 | PDF Full-text (73 KB) | HTML Full-text | XML Full-text
Abstract Synthesis of 3,1,5-benzoxadiazepines from the condensation of o-phenylenediamine (o-PDA) and acyl chlorides in the presence of a catalytic amount of various heteropolyacids (HPAs) is reported. Full article
(This article belongs to the Special Issue Heterocycles)

Review

Jump to: Research

Open AccessReview Benzoxetes and Benzothietes ¾ Heterocyclic Analogues of Benzocyclobutene
Molecules 2012, 17(2), 1548-1570; doi:10.3390/molecules17021548
Received: 7 December 2011 / Revised: 13 January 2012 / Accepted: 17 January 2012 / Published: 7 February 2012
Cited by 7 | PDF Full-text (902 KB)
Abstract
Benzo-condensed four-ring heterocycles, such as benzoxetes 1 and benzothietes 3 represent multi-purpose starting compounds for the preparation of various higher heterocyclic ring systems. The thermal or photochemical valence isomerizations between the benzenoid forms 1,3 and the higher reactive o-quinoid [...] Read more.
Benzo-condensed four-ring heterocycles, such as benzoxetes 1 and benzothietes 3 represent multi-purpose starting compounds for the preparation of various higher heterocyclic ring systems. The thermal or photochemical valence isomerizations between the benzenoid forms 1,3 and the higher reactive o-quinoid structures 2,4 provide the basis for the synthetic applications. On the other hand, this valence isomerization impedes in particular the generation and storage of 1 because the thermal equilibrium 1 2 is completely on the side of 2. Thus, the number of erroneous or questionable benzoxete structures published to date is surprisingly high. On the contrary, the thermal equilibrium 3 4 is on the side of the benzothietes 3, which makes them easily accessible, especially by different flash vacuum pyrolysis techniques. The present article gives a survey of the preparations of 1 and 2, and tries to stimulate their use in synthetic projects. Naphtho-condensed and higher condensed compounds and compounds with an exocyclic C=O or S=O double bond (lactones, thiolactones, sulfoxides and sulfones) are not covered in this article. Full article
(This article belongs to the Special Issue Heterocycles)
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Open AccessReview Isoselenocyanates: A Powerful Tool for the Synthesis of Selenium-Containing Heterocycles
Molecules 2007, 12(3), 504-535; doi:10.3390/12030504
Received: 5 March 2007 / Revised: 15 March 2007 / Accepted: 15 March 2007 / Published: 17 March 2007
Cited by 58 | PDF Full-text (259 KB) | HTML Full-text | XML Full-text
Abstract
Selenium-containingheterocyclic compounds have been well recognized, not only because of their remarkable reactivities and chemical properties, but also because of their diverse pharmaceutical applications. In this context, isoselenocyanates have been emerged as a powerful tool for the synthesis of selenium-containing heterocycles, since [...] Read more.
Selenium-containingheterocyclic compounds have been well recognized, not only because of their remarkable reactivities and chemical properties, but also because of their diverse pharmaceutical applications. In this context, isoselenocyanates have been emerged as a powerful tool for the synthesis of selenium-containing heterocycles, since they are easy to prepare and store and are safe to handle. In this review the recent advances in the development of synthesis methods forselenium-containing heterocycles from isoselenocyanates are presented and discussed. Full article
(This article belongs to the Special Issue Heterocycles)

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