A facile approach to the synthesis of 3,4-dihydro-2 H -benzo[4,5]imidazo[2,1-b][1,3,4]thiadiazines

An efficient approach to the synthesis of novel 2,3-diaryl-3,4-dihydro-2H-benzo[4,5]imidazo[2,1-b][1,3,4]thiadiazines via a base-catalyzed intramolecular cyclization of 2-arylmethylthio-N-arylidene-1H-benzo[d]imidazol-1-amines has been developed. The use of alkali is critical for the annulation of the thiadiazine ring. In the absence of strong bases, the starting compounds undergo deamination with elimination of benzonitrile and formation of 2-arylmethylthiobenzimidazoles.