Evaluation of Effect of Microwave Irradiation on Syntheses and Reactions of Some New 3-Acyl-methylchromones

Lacova, Margita; El-Shaaer, Hafez M.; Loos, Dusan; Matulova, Maria; Chovancova, Jarmila; Furdik, Mikulas

doi:10.3390/30300120

Open AccessArticle

Evaluation of Effect of Microwave Irradiation on Syntheses and Reactions of Some New 3-Acyl-methylchromones

¹

Department of Organic Chemistry, Faculty of Natural Sciences, Comenius University, Mlynska dolina CH-2, SK-842 15 Bratislava, Slovak Republic

²

Department of Chemistry, Faculty of Education, Ain Shams University, Roxy, Cairo, Egypt

³

Institute of Chemistry Slovak Academic Sciences, 842 38 Bratislava, Slovak Republic

^*

Author to whom correspondence should be addressed.

Molecules 1998, 3(3), 120-131; https://doi.org/10.3390/30300120

Submission received: 16 January 1998 / Accepted: 17 February 1998 / Published: 10 March 1998

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Abstract

:

The 3-Acyl-2-R-methylchromones (R = H, ArO, C₆H₄(CO)₂N) were prepared in good yields by different methods from 2-hydroxyaroylacetone derivatives. Some subsequent reactions of these compounds with hydroxylamine and 3-formylchromones are described. The effect of microwave irradation on some condensation reactions was studied.

Keywords:

Microwave irradiation; aldol reaction; 4-oxo-4H-[1]-benzopyran derivatives; rearrengement of chromones; 3-formylchromones

Introduction

This paper is a continuation of our previous works [1,2,3,4] where we reported synthesis, theoretical, spectral and biological studies of chromone derivatives. The present work describes the study and the preparation of some new 3-acylchromones and their reactions by classic or microwave methods.

The 3-Acyl-2-R-methylchromones with their several functional groups are useful building-blocks in organic synthesis. The chromones are possible precursors in forming new nitrogen heterocycles after nucleophilic opening of the γ-pyrone ring [5,6].

Methyl groups at position 2 and at a carbonyl group of the studied compounds can be active in aldol type reactions. Electron-deficit centres at carbonyl groups and carbon at position 2 of the γ-pyrone ring are very effective in reactions with nucleophilic reagents. The synthesized compounds 2, 5, 8 - 11 are useful for further transformations.

Results and Discussions

The composition of the prepared compounds 2-11 were proved by elemental analysis and their structures were determined by NMR and IR spectra.

The main goal of this study was the preparation of new 3-acyl-2-R-methylchromones and the comparison of the reaction results obtained by the classical method with microwave irradiation. Structural formulas of prepared compounds are depicted in schemes 1 - 3.

To prepare compounds 2, two known methods can be used. One of them is the Kostanecki-Robinson acetylation of 2-hydroxyacetophenone derivatives with acetic anhydride and sodium acetate [7,8,9]. This cyclocondensation reaction is known so far only as a classic modification by heating the reacting mixture. The use of a rearrangement of 2-acyloxy-1-acetoarones by treating with metallic sodium is another, more general method for the preparation of 3-acyl-2-methylchromones. The rearranged intermediates - 2-hydroxyaroylacetones 1, were formed. Compounds 1 rendered 3-acyl-2-methylchromones or 2-methylchromones by acid-catalyzed cyclization.

Scheme 1.

Scheme 2.

Scheme 3.

Table 1. Physical data of the prepared compounds.

**Table 1.** Physical data of the prepared compounds.
Comp	Formula	M.P., °C	Calc. / Found				ν_(C=O)^c	ν_(C=O)^c	ν_(C=N)^c	ν_(OH)^c
Yield, %	M.W.	Solvent	%C	%H	%N	%Cl	pyrone	acetyl
2a	C₁₂H₁₀O₃	86-87	71.28	4.98			1637	1687
72	202.21	P.Ether^b	71.56	5.07
2b	C₁₂H₁₂O³	116-118	72.21	5.59			1639	1691
85	216.24	Cyclohex^a	72.45	5.64
2c	C₁₂H₉ClO₃	129-131	60.90	3.83		14.98	1639	1691
82	236.65	Cyclohex^a	60.77	3.84		14.98
2d	C₁₂H₉BrO₃	124-125	51.27	3.23		28.42	1640	1692
82	281.11	Cyclohex^a	51.31	3.17		28.63
2e	C₁₂H₈Cl₂O₃	132-134	53.17	2.97		26.15	1643	1680
98	271.10	Cyclohex^a	53.40	3.01		26.18
2f	C₁₃H₁₁ClO₃	152-153	62.29	4.42		14.14	1637	1687
91	250.68	Cyclohex^a	62.56	4.45		14.29
2g	C₁₄H₁₄O₃	112-114	73.03	6.13			1636	1677
84	230.26	Cyclohex^a	73.31	6.14
2h	C₁₆H₁₂O₃	154-156	76.18	4.79			1637	1685
91	252.27	Cyclohex^a	76.22	4.81
2i	C₁₆H₁₂O₃	136-138	76.18	4.79			1648	1699
95	252.27	Cyclohex^a	76.24	4.79
5a	C₁₇H₁₂O₃	113.5-115	77.21	4.54
73	264.2	Cyclohex^a	77.38	4.41
5b	C₁₈H₁₄O₃	90-93	77.64	5.03
26	278.22	Cyclohex^a	77.52	5.11
5c	C₁₇H₁₁BrO₃	141-143	59.48	3.21
74	343.2	Cyclohex^a	59.73	3.29
5d	C₂₁H₁₆O₃	210-212	80.20	4.45
72	314.2	Dioxane	80.09	4.32
7a	C₁₉H₁₆Cl₂O₅	119-121	57.74	4.08		17.94
21	395.24	Cyclohex^a	57.32	4.02		17.77
7b	C₁₉H₁₅Cl₃O₅	94-95	53.11	3.52		24.75
18	429.68	Cyclohex^a	53.50	3.45		24.50
7c	C₁₉H₁₆Cl₂O₅	104-105	57.74	4.08		17.94
25	395.24	Cyclohex^a	52.85	4.19		17.75
7f	C₂₄H₁₇NO₈	112-114	64.43	3.83		3.13
18	447.40	Toluene	64.28	3.72		3.15
8a	C₁₉H₁₄Cl₂O₄	150-151	60.80	3.74		18.80
	377.22	Ethanole	59.96	3.69		18.82
8b	C₁₉H₁₃Cl₃O₄	187-189	55.44	3.18		25.84
	411.67	Ethanole	55.25	3.18		25.95
8c	C₁₉H₁₄Cl₂O₄	145-148	60.50	3.74		18.89
	377.20	Ethanole	60.44	3.52		18.01
8d	C₂₀H₁₆Cl₂O₄	127-129	61.40	4.12		18.12
	391.25	Ethanole	61.28	4.05		18.25
8e	C₂₀H₁₇ClO₄	153-156	67.33	4.80		9.94
	356.81	Ethanole	67.45	4.92		10.23
8f	C₂₁H₁₅NO₅	241-244
9a	C₁₃H₁₂ClNO₃	114-115	58.77	4.55	5.27	13.34		1683	1612	3100
57	265.70	Cyclohex^a	58.46	4.55	5.06	13.58				(br)
9b	C₁₄H₁₅NO₃	119-121	68.56	6.16	5.71			1680	1613	3100
62	245.28	Cyclohex^a	68.55	6.19	5.52					(br)
9c	C₁₇H₁₃NO₃	73-75	73.12	4.66	5.02
48	279.2	Cyclohex^a	73.17	4.82	4.88
9d	C₁₈H₁₅NO₃	90-92	73.72	5.12	4.78
50	293.2	Cyclohex^a	73.72	5.21	4.79
9e	C₁₇H₁₂BrNO₃	121-123	56.98	3.35	3.91
52	358.2		57.12	3.38	3.94
10a	C₁₃H₁₂ClNO₃	150-151	58.77	4.55	5.27	13.34		1681	1620	3120
20	265.70	Benzene	58.35	4.60	5.02	13.61
10b	C₁₄H₁₅NO₃	142-144	68.56	6.16	5.71			1675	1620	3127
28	245.28	Benzene	68.61	6.16	5.74
10c	C₁₄H₁₅NO₃	212-214	73.12	4.66	5.02
33	279.2	Toluene	73.15	4.70	5.06
10d	C₁₈H₁₅NO₃	182-187	73.72	5.12	4.78
35	293.2	Toluene	73.64	5.20	4.72
10e	C₁₇H₁₂BrNO₃	221-223	56.98	3.35	3.91
24	358.2	Toluene	57.04	3.34	3.86
11a	C₁₂H₂₂O₅	174-175	73.74	3.94
	358.35	Ethanol	73.64	3.70
11b	C₂₃H₁₆O₅	289-291	74.19	4.33
	372.38	Ethanol	73.99	4.23
11c	C₂₂H₁₃ClO₅	270-273	67.27	3.34		9.03
	392.80	Ethanol	67.17	3.10		8.93
11d	C₂₃H₁₅ClO₅	264-266	67.91	3.72		8.71
	406.85	Ethanol	67.70	3.52		8.50
11e	C₂₄H₁₈O₅	224-226	74.60	4.70
	386.40	Ethanol	74.40	4.65
11f	C₂₂H₁₂Cl₂O₅	300-301	61.85	2.83		16.60
	427.20	DM-Et^c	61.59	2.73		16.73
11g	C₂₂H₁₃Cl₂O₅	265-267	67.27	3.34		9.03
	392.8	Ethanol	67.10	3.20		9.09

^a solvent is cyclohexane, ^b 40-60, ^c in cm^-1, ^csolvent DMSO-ethanol

In our study we prepared 3-acetyl-2-methylchromone derivatives 2 in high yield (72-98%) using 2-(hydroxyaroyl) acetone derivatives 1 with freshly prepared sodium acetate and acetic anhydride under classic reaction conditions by refluxing for 2 hours. Using microwave irradiation the preparation times of products 2 from the same components were shortened to only 3 - 8 minutes.

The structure of compounds 2 ( R=H) was confirmed by IR, ¹H-NMR, and ¹³C-NMR spectra. IR-spectra (in nujol) showed acetyl carbonyl stretching frequencies as a strong band at 1699-1677 cm^-1 and γ- pyrone at 1648-1636 cm^-1. In the ¹H-NMR spectra the CH₃ acetyl signals occurred at δ 2.70 - 2.62 ppm, while the signals of CH₂CH₃ occurred at δ 2.66 - 2.52 ppm . Other proton signals and the ¹³C-NMR spectra are listed in Table 2 and Table 3.

3-Benzoyl-2-methylchromone derivatives 5 were prepared by treatment of 2-hydroxybenzoyl-acetophenones with acetic anhydride and sodium acetate at 110^o C for 3 hours. On the other hand compounds 5 were produced after 3 - 6 minutes in a yield of 80% by focused microwave irradiation.

Scheme 4.

3-Benzoyl-2-methylchromone derivatives 5 were prepared by treatment of 2-hydroxybenzoyl-acetcophenones with acetic anhydride and sodium acetate at 110^o C for 3 hours. On the other hand compounds 5 were produced after 3 - 6 minutes in a yield of 80% by focused microwave irradiation.

The preparation of compounds 7 and 8 paved a new route to synthesis of the title compounds. Reaction of compounds 1 with acid chlorides and potassium carbonate in acetone under reflux for 3 hours yielded 3-acetyl-2-aryloxymethylchromone derivatives 3 in about 47% yields. Intermediates 7 could be isolated from a cold waterhydrogen carbonate solution after gentle acidification with CH₃COOH in about 27-30% yields. The cyclocondensation of intermediates 7 with compounds 8 is very easy to affect by heating in toluene. Furthermore, by heating the starting compounds under reflux in dry toluene for 3 hrs, only cyclic products 8 were isolated (80% yields). In the microwave oven the condensation reaction of components 1 with acylchlorides, potassium carbonate and acetone took only 2 minutes to achieve 85 % yield of compounds 8. No intermediates 7 were isolated.

Compounds 2 contain two active CH₃ groups which can react by aldol reaction. The aldol condensation product 11 was obtained by the reaction of 2 with 3-formyl chromones in an acetyl anhydride medium by both classic and microwave irradiation methods. In both cases, the reaction occured only at the methyl group position 2 of the γ-pyrone ring. Again, the classic method required heating at about 120−130 ^oC for 2−3 hrs. The microwave irradiation shortened the reaction time to 40 sec to 2 min.

Scheme 5.

It is known that the reaction of 3-acetyl-2,6-dimethylchromone with hydroxylamine in acetic acid gave monoxime and dioxime [10]. Reaction of 3-acetyl-2-methylchromone with hydroxylamine hydrochloride and sodium acetate in ethanol gave 4-acetyl-5-(2-hydroxyphenyl)-3-methylisoxazole [11]. However in the present study we found that 3-acetyl-2-methylchromones reacted with hydroxylamine hydrochloride in pyridine at boiling point and resulted in a mixture of two different products. They were separated by fractional crystallisation from cyclohexane (Scheme 4).

The first product gave a deep red colour with alcoholic ferric chloride, and was soluble in aqueous sodium hydroxide, confirming the presence of a phenolic hydroxyl group. Their IR spectra showed a broad band centered at 3100 cm^-1 for the OH group and a band at 1683 - 1680 cm^-1 for the C=O acetyl group. These products were thus identified as isoxazole derivatives 9a - 9e. Additionally, the structure of these isoxazoles was confirmed by ¹HNMR spectra (Table 2).

The second product gave no colouration with alcoholic ferric chloride and their IR spectra (Table 1), indicated the absence of a pyrone CO group of the 3-acetyl-2-methylchromones. The observed IR bands at 1681 - 1675 cm^-1 showed the presence of a CO acetyl group and 3127 - 3120 cm^-1 of an OH group. The second products were identifited as oxime derivatives 10 of compounds 2. their structure was confirmed by ¹H NMR spectra (Table 2).

Isoxazoles turned out to be the preferred compounds with 50 - 70 % yields. Yields of oximes 10 were less, about 20 - 30 %.

Experimental Section

General

Infrared spectra were recorded on a Specord IR 75 spectrometer (Zeiss, Jena), in 400 - 4000 cm^-1 region in nujol. ¹H-NMR spectra (δ, ppm) for compounds 3a, 3b and 4a, 4b were measured with Tesla BS 487 A (80 MHz). ¹H-NMR (300 MHz) and ¹³C-NMR (75 MHz) spectra for compounds 2a - 2i were measured with a FT NMR spectrometer Bruker AM 300 at 300^o K in solution of CDCl₃ with TMS as internal standard. ¹³C NMR was obtained with a 40^o flip angle and relaxation delays, CCOSY using a chemical-shift-selective filter as well as a semiselective INEPT optimalized for the value of long range coupling constant ⁿJ_CH = 6 Hz, used for assignment of 1D H signals. The melting points were determined with a Kofler apparatus.

All microwave assisted reactions were carried out in a Lavis-1000 multi Quant microwave oven. The apparatus has been adapted for laboratory application with an external reflux condenser.

3-Acetyl-2-methylchromone derivatives 2a - 2i

Method A (classic)

A mixture of 2-hydroxyaroylacetones 1a - 1i (1g), acetic anhydride (8 ml) and freshly prepared sodium acetate (1g) was refluxed for 6hrs and allowed to cool down. The mixture was diluted with cold water (50 ml) and stirred at room temperature for 30 min. The solid products, which separated, were filtered, washed with water and recrystallized from an appropriate solvent to give 2a - 2i (Table 1).

Method B ( microwave irradiation)

The same mixture as used in the procedure A was irradiated in microwave oven at 270 W for 8 minutes. The isolation procedure is the same as above. The compounds are given in Table 1.

4-Acetyl-5-(2-hydroxyaryl)-3-methylisoxazoles 9a - 9e and 4-(3-acetyl-2, 7-dimethylchromone)-oximes 10a - 10e

A mixture of 2 (0.0022 mol) in pyridine (3 ml) and hydroxylamine hydrochloride (0.15 g, 0.0022 mol) in water (1 ml) was refluxed for 4 hr. The cooled mixture was poured onto crushed ice and acidified with acetic acid, and the solid separated from the liquid was filtered and recrystallized from cyclohexane to give 9a - 9e. The unsoluble product in cyclohexane was recrystallized from benzene to give 10a - 10e.

2-Aryloxymethyl-3-acetylchromone derivatives 8a - 8e and intermediates 7a - 7c

Method A

To a mixture of 2-hydroxyaroylacetones 1 (1g), K₂CO₃ (0.5g) in dry acetone (20 ml), after 2 hrs stirring at reflux, the aryloxyacetyl chlorides were added. The reaction mixture was stirred and heated under reflux for 2 h and left overnight at room temperature. The mixture was poured onto crushed ice (50g) and the solid product was separated. The product was diluted with 5 % cold NaHCO₃. The insoluble fraction (compounds 8a - 8e) was separated and recrystallized from ethanol. The compounds 7 dissolved in aq. NaHCO₃ were separated after acetic acid acidification and recrystallized from cyclohexane.

Method B

The mixture of the same components for preparation of the salt of compounds 1 and dry toluene (20 ml) were stirred at reflux for 2 hrs. After cooling the aryloxyacetyl chloride was slowly added (dropwise). The stirring continued at room temperature for 1 hr and then for an additonal 2 hrs at reflux. Toluene was removed by water vacuum distillation, thereafter the mixture was dried and then dissolved in a 1 % aq. solution of NaHCO_3. The solid part was isolated and recrystallized from ethanol. The yield of compound 8 was 87%. No products 7 were isolated from the NaHCO₃ solution.

Method C

The mixture of the same reaction components as above (Method B) was stirred and irradiated viz. microwave at 270 W for 3 minutes (the preparation of the salt) and then, after addition of components 6, the stirring continued for an additional 6 minutes.

Condensation products 11 of 2 with 3-formylchromones 6

Method A ( classic)

A mixture of compounds 2 (0.01mol), 3-formylchromones (0.01 mol), acetic anhydride (5 ml) and freshly fused potassium acetate (0.5g) was heated at 120 - 130^o C for 2h. The cooled mixture was diluted with cooled water and the solid was separated and recrystallized from acetic acid.

Method B

A mixture of the same composition as in method A was irradiated in microwave oven for 40 sec to 2 min. The isolation of the compounds proceeded along the same lines as described in Method A.

Acknowledgement

Financial support for this research by the Slovak Grant Agency (grant No. 1/2178/95) is gratefully acknowledged.

References

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Sample Availability: Available from the MDPI.

Table 2. ¹H-NMR spectra of the prepared compounds.

**Table 2.** ¹H-NMR spectra of the prepared compounds.
Compound	¹H-NMR spectrum^a (solvent CDCl₃ or DMSO^x) δ (ppm)
2a	8.14(1H, dd, ³J=8.4 and 1.6, H-5), 7.64(1H, ddd, ³J=7.1, 8.2 and 1.6, H-7), 7.39(1H, dd, ⁴J=8.2 and 1.1, H-8), 7.37(1H, ddd, J=8.4, 7.1 and 1.1, H-6), 2.63(3H, s, CH₃ acetyl), and 2.52(3H, s, C₂-CH₃).
2b	7.99(1H, d, ⁴J=2.3, H-5), 7.50(1H, dd, ⁴J=8.7 and ⁴J=2.3, H-7), 7.34(1H, d, ³J=8.7, H-8), 2.67(3H, s, CH₃ acetyl), 2.55(3H, s, C₂-CH₃), and 2.45(3H, s, C₆-CH₃).
2c	8.14(1H, d, ⁴J=2.6, H-5), 7.60(1H, dd, ³J=8.8 and ⁴J=2.6, H-7), 7.38(1H, d, ³J=8.8, H-8), 2.64(3H, s, CH₃ acetyl), and 2.54(3H, s, C₂-CH₃).
2d	8.30(1H, d, ⁴J=2.4, H-5), 7.76(1H, dd, ³J=8.8 and ⁴J=2.4, H-7), 7.33(1H, d, ³J=8.8, H-8), 2.64(3H, s, CH₃ acetyl), and 2.53(3H, s, C₂-CH₃).
2e	8.04(1H, d, ⁴J=2.2, H-5), 7.70(1H, d, ⁴J=2.2, H-7), 2.62(3H, s, CH₃ acetyl), and 2.60(3H, s, C₂-CH₃).
2f	8.12(1H, s, H-5), 7.33(1H, s, H-8), 2.65(3H, s, CH₃ acetyl), 2.52(3H, s, C₂-CH₃), and 2.49(3H, s, C₇-CH₃).
2g	7.89(1H, s, H-5), 7.18(1H, s, H-8), 2.66(3H, s, CH₃ acetyl), 2.52(3H, s, C₂-CH₃), 2.42(3H, s, C₇-CH₃), and 2.35(3H, s, C₆-CH₃).
2h	9.97(1H, d, ³J=8.6, H-9), 8.06(1H, d, ³J=8.9, H-7), 7.85(1H, d, ³J=9.5, H-12), 7.68(1H, dd, ³J=8.6 and 6.9, H-10), 7.61(1H, dd, ³J=6.9 and 9.5, H-11), 7.45(1H, d, ³J=8.9, H-8), 2.70(3H, s, CH₃ acetyl), and 2.52(3H, s, C₂-CH₃).
2i^b	8.45(1H, d, ³J=7.5, H-9), 8.12(1H, d, ³J=8.7, H-5), 7.92(1H, d, ³J=6.8, H-12), 7.76(1H, d, ³J=8.7, H-6), 7.72(1H, d, ³J=7.5, H-10), 7.67(1H, d, ³J=6.8, H-11), 2.70(3H, s, CH₃ acetyl), and 2.66(3H, s, C₂-CH₃).
3c	8,23-7.07(8H, m, arH); 2.52(3H, s)
4b	15.57(1H, s, 1OH); 11.87(1H, s, 2OH); 7.98-6.70(9H, m)
4c	15.48(1H, s, 1OH); 12.01(1H, s, 2OH); 8.02-7.44(9H, m)
5a	7.40-7.96(9H, m); 2.37(3H)
5b^x	7.95-7.85(3H, m); 7.53-7.40(5H, s); 2.44(3H, s); 2.36(3H, s)
5d	8.56-7.43(11H, m); 2.20(3H, s)
7a	7.92(1H, s, OH); 7.45-6.76(7H, m); 4.71(2H, s, CH₂-O-); 2.44(3H, CH₃-); 2.39(3H, CH₃)
7b	7.98(1H, s, OH); 7.48-7.26(5H, m); 6.99(1H, s); 7.74(2H, s, CH₂-O); 2.44(3H, s); 2.40(3H, s)
7c	10.55(1H, s, OH); 8.44(1H, d, ³J 8.2 Hz); 6.99(1H, s); 7.64-6.60(7H, m); 4.66(2H, s, CH₂O); 2.40(3H, s); 2.39(3H, s)
8a	7.97(1H, s, H-5); 7.49-6.95(5H, Ar-H); 5.40(2H, s, CH₂O); 2.60(3H, s); 2.47(3H, s)
8b insoluble
8c	8.19(1H, s, H-5); 7.74-6.63(5H, m); 5.26(2H, s); 2.57(3H, s); 2.20(3H, s)
8d	7.95(1H, s); 7.48-7.15(5H, m); 5.99-5.90(1H, q, CH-O); 2.50(3H, s); 2.46(3H, s); 1.6(3H, d ³J=6.8Hz)
8e	7.99(1H, s, H-5); 7.59-6.60(5H, m); 5.29(2H, s, CH₂-O); 2.56(3H, s); 2.46(3H, s); 2.21(3H, s)
8f	8.03(1H, s, H-5); 7.87-7.46(6H, m); 5.19(2H, s, CH₂-N); 2.62(3H, s); 2.49(3H, s)
9a	11.58(1H, s, OH), 7.38(1H, s, H-6), 6.96(1H, s, H-3), 2.44(3H, s, CH₃), 2.41(3H, s, CH₃), and 2.32(3H, s, CH₃).
9b	11.63(1H, s, OH), 7.19(1H, s, H-6), 6.86(1H, s, H-3), 2.32(3H, s, CH₃), 2.30(3H, s, CH₃), 2.28(3H, s, CH₃), and 2.24(3H, s, CH₃).
9c	11.95(14, s, OH); 7.65-6.55(9H, m); 2.33(3H, s)
9d	11.77(1H, s OH); 7.68-7.30(8H, m); 2.34(3H, s); 2.01(3H, s)
9e	11.81(1H, s OH); 7.62-6.9(8H, m); 2.33(3H, s)
10a	7.43(1H, s, H-5), 6.98(1H, s, H-8), 2.54(3H, s, CH₃ acetyl), and 2.41(6H, brs, C2-CH₃ and C₇-CH₃).
10b	7.18(1H, s, H-5), 6.85(1H, s, H-8), 2.50(3H, s, CH₃ acetyl), 2.32(3H, s, C₂-CH₃), 2.27(3H, s, C₇-CH₃), and 2.22(3H, s, C₆-CH₃).
10c^x	10.10(1H, s, OH); 7.72-6.60(9H, m); 2.26(3H,s)
10d^x	9.87(1H, s, OH); 7.62-6.60(8H, m); 2.25(3H, s); 2.20(3H, s)
10c^x	10.49(1H, s, OH); 7.68-6.53(8H, m); 2.25(3H, s)
11a	8.25(1H, s, H-2); 7.18-7.50(5H, m); 2.70(3H, s)
11b	8.25(1H, s, H-2); 8.50-8.10(2H, m); 7.78-7.39(7H, m); 2.69(3H, s); 2.65(3H, s)
11c	8.22(1H, s, H-2); 8.10-7.78(2H, m); 7.66-7.45(6H, m); 2.68(3H, s); 2.46(3H, s)
11d	8.23(1H, s, H-2); 8.32-8.03(2H, m); 7.80-7.42(7H, m); 2.68(3H, s);
11e	8.22(1H, s, H-2); 8.25-7.96(2H, m); 7.81-7.39(6H, m); 2.38(3H, s); 2.30(3H, s); 2.24(3H, s)
11f	8.24(1H, s, H-2); 8.32-7.40(7H, m); 2.69(3H, s); 2.39(3H, s); 2.34(3H, s)

^a J in Hz, ^b J_10,11 not resolved

Table 3. ¹³C-NMR spectra of the compound 2a - 2i.

**Table 3.** ¹³C-NMR spectra of the compound **2a - 2i.**
Comp.	C-2	C-3	C-4	C-4a	C-5	C-6	C-7	C-8	C-8a	CO acetyl	CH₃ acetyl	CH₃
2a	168.5	123.6^a	175.7	123.8^a	125.5	125.8	133.9	117.6	155.2	200.3	32.1	19.7
2b	168.3	123.3^a	175.9	123.4^a	125.1	135.5	135.2	117.4	153.5	200.5	32.1	20.9 19.7
2c	168.8	123.6	174.7	124.7	125.3	131.5	134.2	119.5	153.6	200.0	32.2	19.8
2d	168.7	123.6	174.4	125.0	128.5	118.9	136.9	119.6	154.0	199.8	32.0	19.7
2e	168.9	124.0^a	174.0	125.6	124.0	131.2	134.0	123.6^a	149.7	199.3	32.0	19.7
2f	168.6	123.4	174.6	122.7	125.5	132.2	143.3	119.5	153.5	200.1	32.1	20.8 19.8
2g	168.0	123.3	175.7	121.4	125.3	134.7	144.4	117.7	153.7	200.7	32.1	20.3 19.7 19.2
2h^b	164.7	126.4	177.8	117.0	130.2	130.6	135.8	117.0	156.6	201.1	32.0	19.0
2i^c	167.4	124.6	175.7	123.5	120.5	125.6	135.9	120.1	152.7	200.5	32.2	19.7

^a The assignment can be interchanged.^b values C-9 126.8, C-10 129.4, C-11 126.7, C-12 128.3.^c values C-9 122.0, C-10 127.3, C-11 129.4, C-12 128.1.

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Lacova, M.; El-Shaaer, H.M.; Loos, D.; Matulova, M.; Chovancova, J.; Furdik, M. Evaluation of Effect of Microwave Irradiation on Syntheses and Reactions of Some New 3-Acyl-methylchromones. Molecules 1998, 3, 120-131. https://doi.org/10.3390/30300120

AMA Style

Lacova M, El-Shaaer HM, Loos D, Matulova M, Chovancova J, Furdik M. Evaluation of Effect of Microwave Irradiation on Syntheses and Reactions of Some New 3-Acyl-methylchromones. Molecules. 1998; 3(3):120-131. https://doi.org/10.3390/30300120

Chicago/Turabian Style

Lacova, Margita, Hafez M. El-Shaaer, Dusan Loos, Maria Matulova, Jarmila Chovancova, and Mikulas Furdik. 1998. "Evaluation of Effect of Microwave Irradiation on Syntheses and Reactions of Some New 3-Acyl-methylchromones" Molecules 3, no. 3: 120-131. https://doi.org/10.3390/30300120

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Evaluation of Effect of Microwave Irradiation on Syntheses and Reactions of Some New 3-Acyl-methylchromones

Abstract

Introduction

Results and Discussions

Experimental Section

General

3-Acetyl-2-methylchromone derivatives 2a - 2i

Method A (classic)

Method B ( microwave irradiation)

4-Acetyl-5-(2-hydroxyaryl)-3-methylisoxazoles 9a - 9e and 4-(3-acetyl-2, 7-dimethylchromone)-oximes 10a - 10e

2-Aryloxymethyl-3-acetylchromone derivatives 8a - 8e and intermediates 7a - 7c

Method A

Method B

Method C

Condensation products 11 of 2 with 3-formylchromones 6

Method A ( classic)

Method B

Acknowledgement

References

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