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Keywords = hetero-Diels–Alder reaction with inverse electron demand

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13 pages, 1424 KB  
Article
Synthesis and Trapping of the Elusive Ortho-Iminoquinone Methide Derived from α-Tocopheramine and Comparison to the Case of α-Tocopherol
by Anjan Patel and Thomas Rosenau
Molecules 2025, 30(15), 3257; https://doi.org/10.3390/molecules30153257 - 4 Aug 2025
Viewed by 382
Abstract
Tocopheramines are a class of antioxidants which are distinguished from tocopherols (vitamin E) by the presence of an amino group instead of the phenolic hydroxyl group. α-Tocopheramine is intensively studied for biomedical applications but also as a stabilizer for synthetic and natural polymers, [...] Read more.
Tocopheramines are a class of antioxidants which are distinguished from tocopherols (vitamin E) by the presence of an amino group instead of the phenolic hydroxyl group. α-Tocopheramine is intensively studied for biomedical applications but also as a stabilizer for synthetic and natural polymers, in particular for cellulose solutions and spinning dopes for cellulosic fibers. This study addresses a fundamental difference in the oxidation chemistry of α-tocopheramine and its tocopherol counterpart: while the formation of the ortho-quinone methide (o-QM) involving C-5a is one of the most fundamental reactions of α-tocopherol, the corresponding ortho-iminoquinone methide (o-IQM) derived from α-tocopheramine has been elusive so far. Synthesis of the transient intermediate succeeded initially via 5a-hydroxy-α-tocopheramine, and its occurrence was confirmed by dimerization to the corresponding spiro-dimer and by trapping with ethyl vinyl ether. Eventually, suitable oxidation conditions were found which allowed for the generation of the o-IQM directly from α-tocopheramine. The underlying oxidation chemistry of α-tocopherol and α-tocopheramine is concisely discussed. Full article
(This article belongs to the Special Issue 10th Anniversary of Green Chemistry Section)
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10 pages, 788 KB  
Communication
Convenient Synthesis of Functionalized Unsymmetrical Vinyl Disulfides and Their Inverse Electron-Demand Hetero-Diels-Alder Reaction
by Bartosz Jędrzejewski, Mateusz Musiejuk, Justyna Doroszuk and Dariusz Witt
Materials 2021, 14(6), 1342; https://doi.org/10.3390/ma14061342 - 10 Mar 2021
Cited by 2 | Viewed by 2377
Abstract
The simple, convenient, and efficient methods for the preparation of unsymmetrical vinyl disulfides with additional functional groups under mild conditions with moderate to high yields were designed. The developed methods include the reaction of S-vinyl phosphorodithioate with thiotosylates or S-vinyl thiotosylate [...] Read more.
The simple, convenient, and efficient methods for the preparation of unsymmetrical vinyl disulfides with additional functional groups under mild conditions with moderate to high yields were designed. The developed methods include the reaction of S-vinyl phosphorodithioate with thiotosylates or S-vinyl thiotosylate with thiols. The designed methods allow for the synthesis of unsymmetrical vinyl disulfides with additional functionalities such as hydroxy, carboxy, protected amino, or ester groups. Vinyl disulfides reacted with the generated transient o-iminothioquinones in an inverse electron-demand [4+2] cycloaddition to produce benzo[b][1,4]thiazine derivatives. Full article
(This article belongs to the Special Issue Collection of Scientific Papers by Polish Scientists in the Field of Materials Research)
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14 pages, 1792 KB  
Article
Biogenesis of Triterpene Dimers from Orthoquinones Related to Quinonemethides: Theoretical Study on the Reaction Mechanism
by Mariana Quesadas-Rojas, Gonzalo J. Mena-Rejón, David Cáceres-Castillo, Gabriel Cuevas and Ramiro F. Quijano-Quiñones
Molecules 2016, 21(11), 1551; https://doi.org/10.3390/molecules21111551 - 17 Nov 2016
Cited by 6 | Viewed by 5393
Abstract
The biogenetic origin of triterpene dimers from the Celastraceae family has been proposed as assisted hetero-Diels-Alder reaction (HDA). In this work, computational calculation of HDA between natural quinonemethides (tingenone and isopristimerol) and hypothetical orthoquinones has been performed at the M06-2X/6-31G(d) level of theory. [...] Read more.
The biogenetic origin of triterpene dimers from the Celastraceae family has been proposed as assisted hetero-Diels-Alder reaction (HDA). In this work, computational calculation of HDA between natural quinonemethides (tingenone and isopristimerol) and hypothetical orthoquinones has been performed at the M06-2X/6-31G(d) level of theory. We have located all the HDA transition states supporting the biogenetic route via HDA cycloadditions. We found that all reactions take place through a concerted inverse electron demand and asynchronous mechanism. The enzymatic assistance for dimer formation was analyzed in terms of the calculated transition state energy barrier. Full article
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24 pages, 232 KB  
Review
Reactivity and Synthetic Applications of 4,5-Dicyanopyridazine: An Overview
by Renzo Alfini, Marco Cecchi and Donatella Giomi
Molecules 2010, 15(3), 1722-1745; https://doi.org/10.3390/molecules15031722 - 12 Mar 2010
Cited by 13 | Viewed by 12069
Abstract
Despite the poor reputation of electron-deficient pyridazines in intermolecular Hetero Diels-Alder (HDA) reactions, 4,5-dicyanopyridazine (DCP) showed a surprising reactivity as a heterocyclic azadiene in inverse electron-demand HDA processes with different dienophiles. The use of alkenes, alkynes and enamines as 2p electron counterparts afforded [...] Read more.
Despite the poor reputation of electron-deficient pyridazines in intermolecular Hetero Diels-Alder (HDA) reactions, 4,5-dicyanopyridazine (DCP) showed a surprising reactivity as a heterocyclic azadiene in inverse electron-demand HDA processes with different dienophiles. The use of alkenes, alkynes and enamines as 2p electron counterparts afforded dicyanocyclohexa-1,3-dienes and substituted phthalonitriles, respectively, while the use of suitable bis-dienophiles provides a general strategy for the one-pot synthesis of polycyclic carbo- and hetero-cage systemsthrough pericyclic three-step homodomino processes. HDA reactions with heterocyclic dienophiles allowed direct benzoannelation: in particular, pyrrole and indole derivatives were converted to dicyano-indoles and -carbazoles. In addition an unprecedented reactivity of DCP as a very reactive heterocyclic electrophile at the C-4 carbon was also evidenced: by changing the experimental conditions, cyanopyrrolyl- and cyanoindolyl-pyridazines were obtained through reactions of pyrrole and indole systems as carbon nucleophiles in formal SNAr2 processes where a CN group of DCP acts as leaving group. Thus, careful control of the reaction conditions allows exploitation of both pathways for the synthesis of different classes of heterocyclic derivatives. Full article
(This article belongs to the Special Issue Advances in Heterocyclic Chemistry)
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