Methyleneketenes and methylenecarbenes. XIII. Cycloaddition of ketenes and of a 1-pyrroline 1-oxide to isopropylideneketene

Abstract

Isopropylideneketene (3-methylbuta-1,2-dien-1-one), Me₂C=C=C=O, reacts with ketene and substituted ketenes to give oxetanones or cyclobutane-1,3-diones formed by [2+2] cycloadditions involving the central C=C bond of the methyleneketene. By contrast Me₂C=C=C=O reacts with 5,5- dimethylpyrroline 1-oxide to give a spirooxazolidinone (13) and an oxetanone (17), both of which appear to be formed by initial cycloaddition of the pyrroline 1-oxide to the terminal C=C bond of the methyleneketene and formation of an intermediate bicyclic ketene (15). The structure of the oxetanone (17) has been confirmed and its stereochemistry established by X-ray crystallography.