Cyclization of Nitrospirobenzopyrans to Bridged Benzoxazepino[3,2-a]indoles

摘要

Condensation of 1-substituted 1,2,3,9a-tetrahydro-9H-imidazo[1,2-a]indol-2-ones with 5-nitrosalicylaldehyde afforded 1'-[(N-monosubstituted carbamoyl)methyl]indoline nitrospirobenzopyrans.Treatment of the latter with strong base led to the formation of a mixture of cis/trans-5a,13-methano-1,3-benzoxazepino[3,2-a]indoles.Results of semiempirical calculations gave evidence that such a transformation of nitrospirobenzopyrans to bicyclic indole derivatives could proceed via a single transition state,where the negatively charged carbon atom attacks the vinylic double bond of the spiropyran system.