Synthesis, X‐ray crystal structure determination and antiinflammatory activity of the regioisomers: 5‐phenyl‐6‐(4‐pyridyl)‐2,3‐dihydroimidazo[2,1‐ b ]thiazole and 6‐phenyl‐5‐(4‐pyridyl)‐2,3‐dihydroimidazo[2,1‐ b ]thiazole. A structural reassignment

A regiospecific synthesis of 6‐phenyl‐5‐(4‐pyridyl)‐2,3‐dihydroimidazo[2,1‐ b ]thiazole ( 2 ) was accomplished by treatment of 6‐phenyl‐2,3‐dihydroimidazo[2,1‐ b ]thiazole ( 10 ) with the reactive complex of pyridine and ethyl chloroformate followed by oxidation with chromium(VI) oxide. Reaction of 4‐phenyl‐5‐(4‐pyridyl)imidazole‐2‐thione ( 12 ) with 1,2‐dibromoethane in the presence of base also gave 2 together with its regioisomer 3 . The structures of 2 and 3 were confirmed by X‐ray crystallography. Evaluation, on oral administration, in a one hour arachidonic acid‐induced mouse ear inflammation assay, showed the inhibition of edema by 2 (48%) and 3 (34%) to be less than that of the 6‐(4‐fluorophenyl) analog 1 (SK&/F 86002) (69%), a known antiinflammatory agent.