Synthesis of 5-Substituted 4,5,6,7-Tetrahydroindoles from Cyclohexanones

Lee, C. K.; Lee, I. S. H.; Noland, W. E. Heterocycles 2007, 71, 419

5-Substituted 4,5,6,7-tetrahydroind oles were prepared from 4-substituted cyclohexanones in three steps: conversion to an enol silyl ether, introduction of a formylmethyl group at 2-C, and the Paal-Knorr pyrrole synthesis by reacting the 1,4-dicarbonyl compounds with ammonia. The substituents are H, methyl, ethyl, tert-butyl, methoxy, and phenyl.