INTRAMOLECULAR CYCLOADDITION VERSUS 1,4-HYDROGEN SHIFT IN INDOLIUM-N-METHYLIDES
2,3-Dimethyl-3-(but-3-enyl)-indolium-N-methylide undergoes facile stereospecific intramolecular cycloaddition to yield a novel tetracyclic indoline ring system.The analogous -(pent-4-enyl) and -(hex-5-enyl) systems fail to undergo cycloaddition but yield the corresponding N-methyl-2-methylene derivatives in moderate yield.
Fishwick, Colin W. G.,Jones, Andrew D.,Mitchell, Michael B.