The vilsmeier-haack reaction on methyl homologues of N-benzyltetrahydrocarbazole (synthetic studies on indoles 52')

To examine the steric effect in the Vilsmeier-Haack reaction of N-benzyl-1,2,3,4-tetrahydrocarbazole (1), the reactions were carried out on three methyl homologues of 1. It was found that 1-methyl- or 4,4-dimethyl group has a large effect on reactivity due to their steric bulkiness. This result shows the importance of an initial attack at the 4a-position for the formation of these products.