THE SYNTHESIS OF SEVERAL IMIDAZO[4,5-D]ISOTHIAZOLES - DERIVATIVES OF A NEW RING-SYSTEM

Several derivatives of the new imidazo[4,5-d]isothiazole ring system have been synthesized from the appropriately substituted isothiazolediamines. The reaction of 3-methyl-4,5-diaminoisothiazole (4a) with diethoxy-methyl acetate gave a low yield of 3-methylimidazo[4,5-d]isothiazole (5a). However, the analogous reaction of 4,5-diaminoisothiazole (4b) with diethoxymethyl acetate failed to yield the parent imidazo[4,5-d]isothiazole ring system. The diamines 4a and 4b were readily cyclized with thiocarbonyldiimidazole to give the unstable thiones 6a and 6b, which were alkylated in situ to afford good yields of the corresponding 5-methylthioimidazo[4,5-d]isothiazoles 7a and 7b, respectively. Neither of these compounds could be reduced to the corresponding 5-unsubstituted derivatives via treatment with Raney nickel. To the best of our knowledge, this is the first report of the imidazo[4,5-d]isothiazole ring system.