Indole-2,3-quinodimethanes: A New Strategy for the Synthesis of Tetracyclic Systems of Indole Alkaloids

Article abstract of DOI:10.1021/ja00352a037

The imine 7, derived from N-<(4-methoxyphenyl)sulfonyl>-2-methylindole-3-carboxaldehyde (6) and 4-pentenylamine, on treatment with a range of chloroformates gave cis-octahydropyridocarbazoles 8, in yields ranging from 43 to 92percent.Similarly the series of imines 18-24 derived from 6 and the corresponding amine gave, on treatmnt with the mixed carbonyc anhydride from ethyl chloroformate and 4-pentenoic acid 25, the tetracyclic amides 26-31.The equivalent series of transformations with a 4a-ethyl group present leads directly to cis-fused tetracyclic precursors 40-42 and 45.The structure and relative stereochemistry of the tetracyclic carbamate 43 is confirmed by single-crystal X-ray crystallography.Some general examples of indole-2,3-quinodimethane cyclizations that give fused pentacyclic and spirocyclic compounds 49, 50, and 51 directly are described.