Base-catalysed prototropic isomerisations. Part II. The isomerisation of N-prop-2-ynyl heterocycles into N-substituted allenes and acetylenes

Abstract

Various heterocycles (I) substituted by a prop-2-ynyl group at the ring nitrogen have been synthesised and isomerised on a potassium amide catalyst. In view of the results with NN-dialkyl prop-2-ynylamines the following equilibria were expected: [graphic omitted] where R = pyrrol-1-yl, pyrazol-1-yl, imidazol-1-yl, indol-1-yl, and carbazol-9-yl.

The starting material (I) disappeared rapidly and the formation of allene (II) was observed in each case. N-Prop-1-ynyl isomers (III) were only detected in two cases as minor components.