Synthesis and characterization of some new mesoionic 1,3-thiazolium-5-thiolates via cyclodehydration and in situ 1,3-dipolar cycloaddition/cycloreversion

The title compounds were synthesized from C-aryl-N-methylglycines by N-aroylation followed by a cyclodehydration to form the corresponding 1,3-oxazolium-5-olates. These were not isolated but converted to the title compounds by an in situ 1,3-dipolar cycloaddition/cycloreversion sequence using carbon disulphide. We have studied the cyclodehydration step using acetic anhydride, trifluoroacetic anhydride and 1,3-dicyclohexyl-carbodiimide (DCC) at temperatures not exceding 60degreesC. Trifluroacetic anhydride proved to be the best reagent, giving a better yield and more easily purified products, although yields were also acceptable with the other two reagents.