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Journal ArticleDOI

Diels–Alder trapping of in situ generated dienes from 3,4-dihydro-2H-pyran with p-quinone catalysed by p-toluenesulfonic acid

TL;DR: This comprehensive study portrays that p-toluenesulfonic acid is a more efficient catalyst for the reaction between p-quinones and 3,4-dihydro-2H-pyran, than the Lewis acids.
Abstract: This comprehensive study portrays that p-toluenesulfonic acid is a more efficient catalyst for the reaction between p-quinones and 3,4-dihydro-2H-pyran, than the Lewis acids. The products were accomplished by the Diels–Alder cycloaddition reaction and their mechanistic pathways have been formulated. The impact of C2 and C2,5 substituents of the p-quinones on the cycloaddition reaction has been explored. Remarkably, it is the first report to explore this kind of in situ generated diene for the Diels–Alder cycloaddition reaction.
Citations
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Journal ArticleDOI
TL;DR: In this paper, an efficient enantioselective construction of tetrahydronaphthalene-1,4-diones as well as dihydronaphthalene 1,4diols by a chiral phosphoric acid catalyzed quinone Diels-Alder reaction with dienecarbamates is reported.
Abstract: An efficient enantioselective construction of tetrahydronaphthalene-1,4-diones as well as dihydronaphthalene-1,4-diols by a chiral phosphoric acid catalyzed quinone Diels-Alder reaction with dienecarbamates is reported. The nature of the protecting group on the diene is key to the success of achieving high enantioselectivity. The divergent "redox" selectivity is controlled by using an adequate amount of quinones. Reversible redox switching without erosion of enantioselectivity was possible from individual redox isomers.

24 citations

Journal ArticleDOI
TL;DR: Pro-aromatic and volatile 1-methyl-1,4-cyclohexadiene (MeCHD) was used for the first time as a valid H-atom source in an innovative method to reduce ortho or para quinones to obtain the corresponding catechols and hydroquinones in good to excellent yields.
Abstract: Pro-aromatic and volatile 1-methyl-1,4-cyclohexadiene (MeCHD) was used for the first time as a valid H-atom source in an innovative method to reduce ortho or para quinones to obtain the corresponding catechols and hydroquinones in good to excellent yields. Notably, the excess of MeCHD and the toluene formed as the oxidation product can be easily removed by evaporation. In some cases, trifluoroacetic acid as a catalyst was added to obtain the desired products. The reaction proceeds in air and under mild conditions, without metal catalysts and sulfur derivatives, resulting in an excellent and competitive method to reduce quinones. The mechanism is attributed to a radical reaction triggered by a hydrogen atom transfer from MeCHD to quinones, or, in the presence of trifluoroacetic acid, to a hydride transfer process.

13 citations

Journal ArticleDOI
TL;DR: In this article, a tricyclique de structure voisine de celle des precurseurs des podocarpanes, par cycloaddition du vinylcyclohexene avec l'acide benzoquinone-1,4 carboxylique, is presented.
Abstract: On prepare un compose tricyclique de structure voisine de celle des precurseurs des podocarpanes, par cycloaddition du vinylcyclohexene avec l'acide benzoquinone-1,4 carboxylique. On etudie la structure cristalline du compose et on explique par une etude theorique la stereochimie de la reaction

6 citations

References
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Journal ArticleDOI
TL;DR: In this paper, the absorption spectra of pyrylium salts were determined in the region 220-400 mμ for alkyl and phenyl-substituted pyryls.

45 citations

Journal ArticleDOI
TL;DR: In this article, the authors discuss the analoge Umwandlung von Pyridin-Derivaten in Pyrylium-Salz ubertragen.
Abstract: Es wird uber ein Verfahren berichtet, das erlaubt, Pyridin in einer Mehrstufenreaktion in ein Pyrylium-Salz uberzufuhren. Die Methode ist zur praparativen Gewinnung des nichtsubstituierten Pyryliumperchlorats geeignet, konnte jedoch bisher noch nicht auf die analoge Umwandlung von Pyridin-Derivaten ubertragen werden.

44 citations

Journal ArticleDOI
TL;DR: Chiral racemic vinylcyclohexenes 1a−m, bearing allylic and nonallylic oxygenated substituents on the cyclohexene ring, were submitted to Diels−Alder reactions with enantiomerically pure (SS)-(2-p-tolylsulfinyl)-1,4-naphthoquinone.
Abstract: Chiral racemic vinylcyclohexenes 1a−m, bearing allylic and nonallylic oxygenated substituents on the cyclohexene ring, were submitted to Diels−Alder reactions with enantiomerically pure (SS)-(2-p-tolylsulfinyl)-1,4-naphthoquinone. The tandem cycloaddition/pyrolytic sulfoxide elimination led to the formation of enantiomerically enriched angularly tetracyclic quinones (+)-8a and (+)-12, arising from the kinetic resolution of the racemic diene. Dienes 1a−c, bearing an alkoxy substituent at the allylic position C-3, and 1d−g, with C-3 alkoxy and C-5 methyl groups, gave exclusively quinones (+)-8a−g, resulting from the anti approach to the dienophile. A similar anti selectivity occurred in cycloadditions of dienes 1i,j, with the alkoxy group situated at the allylic position C-6. Nonallylic 4-substituted vinylcyclohexenes 1k−m evolved to ca. 75:25 mixtures of (+)-anti-8k−m and (+)-syn-12k−m derivatives. In all cases, (SS)-(2-p-tolylsulfinyl)-1,4-naphthoquinone reacted from the less hindered face of the more rea...

40 citations

Journal ArticleDOI
TL;DR: Indigocarpan and mucronulatol were isolated from chloroform extracts of Indigofera aspalathoides and their structures were established by spectroscopic methods, including single-crystal X-ray analysis.

38 citations

Journal ArticleDOI
TL;DR: Biological studies revealed products modulating immune responses in sesquiterpene quinones and hydroquinones isolated from the sponge Smenospongia sp, which revealed different behaviours on normal cells.

30 citations