RING CONTRACTION OF 5-OXO-4-PHENYL-5,6-DIHYDRO-4H-1,3,4-THIADIAZINE WITH SODIUM METHOXIDE

The reaction of 5-oxo-4-phenyl-5,6-dihydro-4H-1,3,4-thiadiazine (1a) with sodium methoxide in methanol at 35-degrees-C was found to give 2-anilino-4-oxo-1,3-thiazoline (2a) in a quantitative yield via cleavage of the nitrogen-nitrogen bond. The mechanisms of formation of 2 were discussed by a few kinetic studies using 4-p-substituted phenyl-5-oxo-5,6-dihydro-4H-1,3,4-thiadiazine (1b, c), and related reaction of 5-oxo-4-phenyl-4,5-dihydro-4H-1,3,4-thiadiazole (3), 5-oxo-2,4-diphenyl-5,6-dihydro-4H-1,3,4-thiadiazine (4) and 5-oxo-2,4-diphenyl-4,5-dihydro-4H-1,3,4-thiadiazole (5).