Structures of 2:1 molar adducts from dimethyl acetylenedicarboxylate with thiazoles and related heterocycles

Abstract

Thiazoles and related heterocycles with dimethyl acetylenedicarboxylate combine directly to give 1:2 molar adducts [e.g. (12)], and also two types of isomeric products which can be formed from the initial adducts by a [1,5] sigmatropic hydrogen shift [e.g. (4)] or by molecular rearrangement [e.g. (11)]; the structures were established by ¹³C n.m.r. spectroscopy and for the pyridothiazoles (11) and (12) also confirmed by X-ray crystallography.