AbstractLewis acid mediated reaction of acyclic vinyl allenes and imines gives tetrahydropyridines with complete diastereoselectivity.

The Lewis acid mediated reaction of acyclic vinyl allenes and imines, yielding tetrahydropyridines has been carried out. Only one cycloadduct was observed in each case, and thus, the reaction progressed in all cases with total regio-, face- and endo/exo selectivities. The cycloadducts were transformed into polysubstituted pyridines, including bipyridines, by catalytic transfer hydrogenation using cyclohexene as hydrogen donor in good yield. The reaction was extended to the aromatization of the bicyclic cycloadducts prepared in previous works from the reaction of semicyclic vinyl allenes and imines, yielding tetrahydropyridines.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

The Lewis acid catalyzed hetero-Diels-Alder reaction between acyclic vinyl allenes and aldehydes as heterodienophiles was studied. This reaction allows for the preparation of pyrane derivatives in good yields, high facial and regioselectivity and moderate endo/exo ratio. When benzaldehyde was used as the heterodienophile, rearranged products were obtained depending on the reaction conditions. DFT calculations were used to study the rearrangement, concluding that it is a highly selective ionic process, driven by the stability of the rearranged products.

A simple method for conversion of ketones to their corresponding dimethyl acetals using montmorillonite K 10 and p-toluenesulfonic acid as acidic cocatalysts under very mild reaction conditions is described.

The hetero Diels-Alder reaction of vinyl allenes and aldehydes in the presence of a Lewis acid has been studied both experimentally and theoretically. Differently substituted vinyl allenes and aldehydes were used to obtain information on the structural requirements of the reaction. Theoretical calculations using the density functional theory indicate that the reaction proceeds through a highly asynchronous polar transition state.

The intramolecular hetero-Diels-Alder reaction of vinyl-allenes and imines has been carried out. Depending on the substituents on the allene and the length of the tether linking diene and heterodienophile, the reaction proceeds thermally or with Lewis acid activation. The transformation of one of the adducts into a 9-substituted octahydroacridine is reported.

The reaction of vinyl allenes with imines under Lewis acid catalysis has been explored. Vinyl allenes in which the allenic portion of the molecule is tri- or tetrasubstituted gave octahydroquinoline derivatives as single isomers together with a minor compound formed by an ene reaction of the imine with the allene. Compounds in which the allene is 1,3-disubstituted do not react under the conditions assayed.

Compounds containing a vinyl allene moiety linked to an aldehyde by a tether have been synthesised and shown to undergo the intramolecular hetero Diels–Alder reaction. Only one compound with stereochemistry consistent with an exo approach of the dienophile to the dienic portion of the vinyl allene was obtained in each case. Depending on the length of the tether and on the substitution pattern on the allene the reactions were spontaneous at room temperature or required heating or the presence of a Lewis acid to proceed.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

The Lewis acid-mediated, hetero Diels–Alder reaction of a vinyl-allene system with aldehydes as heterodienophiles has been carried out. In the cases studied, only two cycloadducts have been obtained, which correspond to the endo (major compound) and exo (minor compound) approach of the aldehyde through the less hindered face of the dienic system.