Synthesis of thieno[2,3-b]indole-2,3-diones and their ring expansions induced by diazomethane

Indole-2-thione 3 reacted quickly with oxalyl chloride to yield thieno[2,3-b]indole-2,3-dione 4 together with the isomer thiazolo[3,2-a]indole-2,3-dione 5. These thieno[2,3-b]indole-2,3diones underwent ring expansions when treated with diazomethane and e.g. thieno[2,3-b]indole-2,3-dione 4 gave the thiopyrano derivative 16, after two insertions.

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