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Abstracts of Congress of Heterocyclic Chemistry | Regular issue | Vol 14, No. 10, 1980, pp.1547-1566
Published online, 1st January, 1970
DOI: 10.3987/R-1980-10-1547
Heterocycles from 1,2- and 1,4-Cycloadditions to Ketenimines

Alessandro Dondoni*

*Dipartimento di Chimica, Laboratorio di Chimica Organica, Università degli Studi di Ferrara, Via Fossato di Mortara 17-19, I-44100 Ferrara, Italy

Abstract

Cycloadditions of thiobenzophenone to ketenimines illustrate the possibility of multiple modes of reaction across various centres of the cumulene depending on the substituents at nitrogen and carbon as well. 1,2-Cycloaddition across the C=C bond of the cumulene to give iminothietanes, as well as two types of 1,4-cycloaddition, one involving the C=N bond of the cumulene and the N-aryl group to give benzothiazines, the other involving the C=C bond of the cumulene and the C-vinyl to give iminothiacyclohexenes, have been observed. The variable siteselectivity in ketenimine-thioketone cycloadditions appears to be determined by a balance between steric and electronic effects, the latter being interpreted in terms of frontier MO’s of the cumulene. Cycloadditions of electron-poor heteroenes (tosylisocyanate, N-dicyanomethylene-p-chloroaniline, sulfur dioxide) offer other examples of variable siteselectivity which produce four- and six-membered heterocycles. On the other hand, vinylketene although more reactive than vinylketenimine, appears to undergo exclusively 1,2-cycloaddition across the C=C bond of the cumulene to give four-membered adducts. The possibility of stereochemical variables in ketenimine cycloadditions increases the value of these heterocumulenes as intermediates for the synthesis of heterocycles.