A novel straightforward synthesis of 2-imino-4-thiazolmes has been performed by reaction of cy-bromoketimines with potassium thiocyanate in acetonitrile. Comrary to other syntheses of these heterocycles, no side reactions were observed. The sbuctuml assignment of these relatively rare 2-imino-2,3-dihy&thiaxoles was executed by spectroscopic means, by the synthesis of model compounds by an alternative route and by X-ray crystallographic analysis of an N-ace@ derivative, excluding any other isomer+ possibility.
The Hantxsch thiaxole synthesis using the condensation of a-haloketones with thiourea was established 'a century ago.' The problem of isomerism of the heterocycles emerged soon when it was observed that the free base of the salt formed upon methylation of 2-amino4methyhhiaxole (obtamed from chloroacetone and thiourea)' was isomeric with the free base resulting from the condensation of chl oroa&one with N-methylthiourea.* It was shown and later generally accepted that the former methylation product was 2-imino-3,4dimethyl-4-thiaxoline 2 and the latter 4-methyl-2-(metbylamii)thiaxooo)thiazole 1.
The condensation of ar-haloketones with N-monosubstituted thiomeas in the usual organic solvents has been studied extensively and led to 2-(N-substituted amino)thiiles.'~' However, the same condensation