Ring-ring interconversions. Part 3. On the effect of the substituents on the thiazole moiety in the ring-opening/ring-closing reactions of nitrosoimidazo[2,1-b][1,3]thiazoles with hydrochloric acid

The reaction of 6-(4-chlorophenyl)-5-nitrosoimidazo[2,1 -b] [1,3]thiazole 1 b, 6-(4-chlorophenyl)-2-methyl-5-nitrosoimidazo[2,1-b][1,3]thiazole 1c, 6-( 4-chlorophenyl)-2,3-dimethyl-5-nitrosoimidazo- [2,1-b][1,3]thiazole 1d and 2-(4-chlorophenyl)-3-nitrosobenzo[d]imidazo[2,1 -b][1,3]thiazole 1e with hy drochloric acid has been carried out in order to investigate the effect of substituents on the thiazole ring in a recently reported ring-ring intercon version reaction. In every case the corresponding [1,4]-thiazino[3,4-c][1,2 ,4]oxadiazol-3-ones 2b-e have been obtained. In particular, the benzoderiva tive 1e furnished the 4-(4-chlorophenyl)-4-hydroxy-4H-benzo[5,6], [1,4]thia zino[3,4-c][1,2,4]oxadiazol-1-one 2e, containing a new tricyclic system wit h a quasi-planar geometry whose pharmacological potentialities appear promi sing.