Routes to pyrrolo[2,1-b]thiazoles. Rotational isomerism of pyrrolo[2,1-b]thiazole-5-carbaldehydes

Abstract

Four 3,6-disubstituted pyrrolo[2,1-b]thiazoles (one containing a 3-aryl group) were prepared from 2,4-disubstituted thiazoles by the known method, and this work clarified some confusion in the literature. A new route, involving substitution into the thiazole 2-methyl group followed by intramolecular cyclisation and dehydration, gave the 3-methyl-6-phenyl- and 3,6-dimethylpyrrolothiazole in higher yield.Spectrometric examination of the derived 5-carbaldehydes established the proportions of the O,N-syn and -anti rotational isomers present and (in two cases) the barrier to rotation of the aldehyde group.