Cyclization of N-formyl- and N-thioformyl-sarcosine-N-methylthioamide into methylaminothiazolium and anhydro-mercaptoimidazolium hydroxide derivatives

Abstract

N-Formylsarcosine-N-methylthioamide is transformed into 1,3-dimethyl-4-mercaptoimidazolium ion on treatment with trifluoroacetic acid in acetonitrile, while the thioformyl analogue produces 3-methyl-5-methylaminothiazolium ion under the same conditions. The latter ion rearranges irreversibly to the former in aqueous acid or, in base, to its deprotonated derivative, anhydro-1,3-dimethyl-4-mercaptoimidazolium hydroxide. Aqueous base deformylates N-formylsarcosine-N-methylthioamide, while aqueous or non-aqueous bases convert the thioformyl analogue into anhydro-1,3-dimethyl-4-mercaptoimidazolium hydroxide. N-Formyl- and N-thioformyl-sarcosine-N-methylthioamide yield 3-methyl-5-acylmethylaminothiazolium salts when treated with acetyl chloride or trifluoroacetic anhydride. The trifluoracetylaminothiazolium salt is readily deacylated. Mechanisms are elucidated by means of deuterium exchange experiments. The reaction of 5-methylthiothiazolium salts with amines has been rationalized.