1, 3-Thlazolioin-4-Ones. Synthesis and X-Ray Structure Clarification of the Structure of the Products Derived from the Condensation of Thioureas and Acetylene Dicarboxylc Acid or its Esters

Abstract

The reaction of thioureus or N-Substituted Thioureas with dimethyl acetylene dicarboxylate is an extremely simple reaction which proceeds rapidly and quantitatively. The resultant heterocyclic products have been the subject of numerous publication, ^2–8 the variety of which demonstrates the truly international interest in the field. Various structures have ben proposed and received support: the 5-membered ring systems 1, 3-thiazolidines (3)^2–4 and 2-thiohydantoius (e.g.12)⁵ and the 6-membered 1,3-thiazines (5)^6–8. The most convincing chemical and spectroscopic evidence has been reported by loan and ifa ⁶ in support of the 1,3-thiazine system. This work has since been challenged by ourselves ⁹ and others⁴. Indeed the recent work by Cameron et al ⁴, who have carried out an X-Ray structure analysis on Product (1)(Derived from the reaction of N-thiocarbomaoyl-piperidine and dimethyl actylane dicarboxylate), fully justifies our reservation.