The Chemistry of Pyrimidinethiols. II. The Preparation and Reactions of Some 2-Arenecarbonylmethylthiopyrimidines

Abstract

A number of 2-arenecarbonylmethylthiopyrimidin-4(1H)-ones has been synthesized. Those having H, Me or Pr as a 6-substituent undergo ready sulfur extrusion on heating in diphenyl ether to give 2- ( arenecarbonylmethylene )-2,3-dihydropyrimidin-4(1H)-ones, but those that have a 6-amino substituent or a 5-methyl substituent did not undergo this reaction under these conditions. Some other arenecarbonylmethylthiopyrimidines also did not undergo sulfur extrusion under these conditions.

The methylenepyrimidinones formed from 6-methyl-(and 6-propyl-) pyrimidines show two ¹H n.m.r. signals for both the pyrimidine H 5 and for the methylene H which collapse to single signals on raising the temperature to about 100°C. The methyl signal similarly appears as a double signal which collapses to one on heating. We interpret this as being due to the existence of two thermally isomerized cis and trans forms of the methylenepyrimidinones. However, for the 4-phenylbenzoyl and the 2-naphthoyl compounds this multiplicity of signals was not seen. The same effect was observed for the 3-methoxyphenyl and 2,5- dimethoxyphenyl derivatives.

Cyclization of the arenecarbonylmethylthiopyrimidinones in sulfuric acid at ambient temperature yields 5H-thiazolo[3,2-a]pyrimidin-5-ones.