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A recently developed (4+3) cycloaddition between dienes and furfuryl alcohols, as precursors of oxyallyl-type cations, has been used as a key step in the racemic syntheses of two natural products: frondosin B and liphagal. This wo...
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A recently developed (4+3) cycloaddition between dienes and furfuryl alcohols, as precursors of oxyallyl-type cations, has been used as a key step in the racemic syntheses of two natural products: frondosin B and liphagal. This work demonstrates the synthetic potential of this cycloaddition reaction, and offers a short synthetic route to an interesting family of natural products. A full account of these synthetic studies is presented, further illustrating the mechanism, scope, and limitations of this straightforward synthetic method for seven-membered rings.
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A one-pot, three-cornponent approach to a new family of 4,5-functionalized triazolyl-nucleosides is described. The method relies on the one-pot azide-alkyne 1,3-cycloaddition/electrophilic addition tandem reaction, which affords g...
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A one-pot, three-cornponent approach to a new family of 4,5-functionalized triazolyl-nucleosides is described. The method relies on the one-pot azide-alkyne 1,3-cycloaddition/electrophilic addition tandem reaction, which affords good yields of the corresponding 4,5-disubstituted nucleosides.
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The utility of 2-isoxazolines (Δ~2-isoxazolines, 4,5-dihydroisoxazoles) in the preparation of natural products and other compounds of medicinal and materials interest is growing because the 2-isoxazoline serves both as a desirabl...
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The utility of 2-isoxazolines (Δ~2-isoxazolines, 4,5-dihydroisoxazoles) in the preparation of natural products and other compounds of medicinal and materials interest is growing because the 2-isoxazoline serves both as a desirable functional group and a versatile synthetic intermediate. Nitrile oxide cycloaddition (NOC) to alkenes is the most common method for the preparation of 2-isoxazolines, and the intramolecular version of this reaction provides a powerful entry into complex polycyclic systems. This review is the first to compile studies on the intramolecular nitrile oxide cycloaddition (INOC) reaction, with an emphasis on studies from 2000 to 2009. Trends in stereo- and regioselectivity are discussed from observations made in the formation of a wide variety of polycyclic 2-isoxazoline compounds.
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The substituent effect on the diastereoselectivity in Sulfa-Staudinger cycloadditions has been investigated. The diastereoselectivity is controlled by the competition between the direct conrotatory ring closure of the thiazabutadi...
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The substituent effect on the diastereoselectivity in Sulfa-Staudinger cycloadditions has been investigated. The diastereoselectivity is controlled by the competition between the direct conrotatory ring closure of the thiazabutadiene-type zwitterionic intermediates, generated from sulfonyl chlorides and imines, and the isomerization of their iminium moiety. The direct ring closure generates cis-beta-sultams, while the isomerization and subsequent ring closure deliver trans-beta-sultams. The C-electron-withdrawing substituents of imines reduce the bond order of imines and their iminium moiety, favoring the isomerization of the 'thiazabutadiene-type intermediates, resulting in the increase of trans-selectivity. Otherwise, the cis-selectivity is predominant for imines with electron-donating N- and C-substituents. The trans-beta-sultams are afforded favorably, or even exclusively in some cases, as the effect of the electron-withdrawing substituents of sulfonyl chlorides, because the substituents decelerate the direct ring closure obviously. The N- and C-substituent effects of imines are opposite to those in the Staudinger ketene imine cycloadditions, while the substituent effect of sulfonyl chlorides is accordant to the ketene-substituent effect in the Staudinger cycloadditions. The solvent and temperature do not affect the diastereoselectivity obviously. The current results provide useful information on controlling the diastereoselectivity in the synthesis of trans-beta-sultams via sulfa-Staudinger cycloaddition. (C) 2015 Elsevier Ltd. All rights reserved.
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The reactions of kinetically stabilized 9-anthryldiphosphene 1b with 2,3-dimethyl-1,3-dimethyl-1,3-butadiene and electron defficient oleflins 3 were found to afford the corresponding [4 + 2] cycloadducts 2 and 4, respectively. The...
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The reactions of kinetically stabilized 9-anthryldiphosphene 1b with 2,3-dimethyl-1,3-dimethyl-1,3-butadiene and electron defficient oleflins 3 were found to afford the corresponding [4 + 2] cycloadducts 2 and 4, respectively. The transformation of A into alkylaryldiphosphene derivatives 4 via the Diels-Alder reactions should be noteworthy as a unique example of the transformation of a diphosphene into other diphosphenes with keeping the highly reactive diphosphene unit. Both the spectral features and the results of X-ray crystallographic analyses of 4 support their P=P double-band character. Furthermore, unique E-Z isomerization fumaronitrile (3c) was found to occur in the reaction with a diphosphene such as Bbt P=P Bbt.
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A collection of 1,4-disubstituted 1,2,3-triazoles was achieved by decarboxylative [3 + 2] cycloaddition of organic azides and cinnamic acids. Metal-free condition, high regioselectivity and easy accessibility of starting materials...
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A collection of 1,4-disubstituted 1,2,3-triazoles was achieved by decarboxylative [3 + 2] cycloaddition of organic azides and cinnamic acids. Metal-free condition, high regioselectivity and easy accessibility of starting materials are the salient attributes of this protocol. (c) 2021 Elsevier Ltd. All rights reserved.
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The use of microwave irradiation in organic chemistry and, in particular in 1,3-dipolar cycloaddition has recently gained much attention and great progress has been accomplished in this area in the last years. In general, the mode...
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The use of microwave irradiation in organic chemistry and, in particular in 1,3-dipolar cycloaddition has recently gained much attention and great progress has been accomplished in this area in the last years. In general, the modern synthetic chemistry is benefited by microwave irradiation that provides an environmentally benign approach, reduced reaction times and a few formation of byproducts, increasing the yield. This review aims to collect recent developments on the synthesis of isoxazolidine compounds by microwave-assisted 1,3-dipolar cycloaddition, considering the absence of a recent review about this specific reaction method. Owing to the large extent of available literature, we have decided to restrict our review to the developments in the last six years, making a selection of the literature from 2010 to 2016. The discussion of several examples to construct isoxazolidines by irradiation of microwave will allow to focus on the advances in the development of microwave-assisted 1,3dipolar cycloadditions, obtaining a broader vision of the real effects of this reaction methodology on yields, regio-and stereoselectivity of the reaction.
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By selective reaction of the chlorimine function in the adducts 2 from 3,5-dichloro-2H-1,4-oxazin-2-ones and double bond systems, a series of 6-substituted 2-oxa-5-azabicyclo[2.2.2]oct-5-en-3-ones 3 could be generated. Lactone cle...
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By selective reaction of the chlorimine function in the adducts 2 from 3,5-dichloro-2H-1,4-oxazin-2-ones and double bond systems, a series of 6-substituted 2-oxa-5-azabicyclo[2.2.2]oct-5-en-3-ones 3 could be generated. Lactone cleavage of the latter with alcohols or amines yielded variously substituted 4,5-dihydro-5-hydroxy-2-pyridinecarboxylic acid derivatives which were dehydrated to afford the corresponding pyridine systems. Some 6-amino substituted 2-pyridinecarboxamides could be obtained in a one step procedure by reacting 2 with Me(3)Al/amine. Copyright (C) 1996 Elsevier Science Ltd [References: 24]
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Inter- and intramolecular cycloaddition reactions of ethenetricarboxylates with styrenes and.-halostyrenes have been investigated. The reactions of ethenetricarboxylates with styrenes or.-bromostyrenes in the presence of SnCl4 or ...
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Inter- and intramolecular cycloaddition reactions of ethenetricarboxylates with styrenes and.-halostyrenes have been investigated. The reactions of ethenetricarboxylates with styrenes or.-bromostyrenes in the presence of SnCl4 or SnBr4 stereoselectively gave 2,4-cissubstituted cyclobutanes. The intramolecular cycloaddition reactions of a series of styrene-functionalized ethenetricarboxylate amides, including in situ generated derivatives, showed high diversity of reaction modes depending on the structures and substituents of the substrates. The regioselectivity and stereoselectivity of the reactions as well as reaction mechanisms were discussed based on the DFT calculations.
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Imidazo[1,5-a]pyridines react in one of two ways with methyl- and phenyl triazolinediones and diethyl azodicarboxylate to give either Michael type addition products at C-3 or C-1, or novel 1,2,4-triazolines. The nature of the prod...
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Imidazo[1,5-a]pyridines react in one of two ways with methyl- and phenyl triazolinediones and diethyl azodicarboxylate to give either Michael type addition products at C-3 or C-1, or novel 1,2,4-triazolines. The nature of the product depends upon the dienophile and the substitution pattern of the imidazo[1,5-a]pyridine. [References: 17]
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