Studies on mesoionic compounds. V. Synthesis and cycloaddition reaction of anhydro-5-hydroxy-1,3-oxathiolium hydroxide system.

Synthesis and 1, 3-dipolar cycloaddition of the mesoionic ring system, anhydro-5-hydroxy-1, 3-oxathiolium hydroxide, were studied. Acylthioglycolic acids (IIa, b) afforded the mesoionic products (IIIa, b) in the reaction with trifluoroacetic anhydride. In the case of α-substituted thioglycolic acids (IId, e), the mesoionic intermediates which couldn't be isolated were trapped with dimethyl acetylenedicarboxylate in situ.