Synthesis of novel 5H, 11H‐pyrido[2′,3′:2,3]thiopyrano[4,3‐b]‐indoles by fischer‐indole cyclization

The synthesis of the title compounds 5H, 11H‐pyrido2′,3′:2,3]thiopyrano4,3‐b]indoles was accomplished by the Fischer indole cyclization of some 2,3‐dihydrothiopyrano2,3‐b]pyridin‐4(4H)‐one phenylhydrazones and 7‐methyl‐2,3‐dihydrothiopyrano2,3‐b]pyridin‐4(4H)‐one phenylhydrazones. The synthesis of the new 2,3‐dihydrothiopyrano2,3‐b]pyridin‐4(4H)‐one, which was used as one of the starting compounds, is also described.