Chemistry of Nitrosoimines. XVI. A New Method for Facile Preparation of AzamonomethinecyaninesviaNitrosoimines

The reaction of 3-substituted 2-nitrosoimino-2,3-dihydrobenzothiazoles (1) with Grignard-type reagents of 3-substituted 2-imino-2,3-dihydrobenzothiazoles (2) gave azamonomethinecyanines (3) in high yields (71–96%). This is a new type of reaction for the preparation of 3. Hydrolysis of 3 afforded ring-opened disulfides, bis[o-{N-methyl-N-(3-methyl-2,3-dihydrobenzothiazol-2-ylidenecarbamoyl)amino}-phenyl] disulfides, in high yields (78–85%). Formation of by-products is explained by the presence of transnitrosation between 1 and 2 and ring-opening equilibrium of Grignard-type reagent of 2-imino-3-phenyl-2,3-dihydrobenzothiazole.