Brønsted‐Acid‐Mediated Divergent Reactions of Betti Bases with Indoles: An Approach to Chromeno[2,3‐<i>b</i>]indoles through Intramolecular Dehydrogenative C2‐Alkoxylation of Indole

Abstract

Divergent reactions of various 1‐(aminoalkyl)naphthols and 2‐(aminoalkyl)phenols (commonly known as Betti bases) with indoles under Brønsted acid catalysis is reported. With the reaction strategies, one can efficiently synthesize important indole derivatives such as 3‐(α,α‐diarylmethyl)indoles and chromeno[2,3‐ b ]indoles. Furthermore, we disclose here a new C–C bond‐cleavage reaction, in which naphthol and phenol behave as leaving groups to produce diarylmethanes. Inexpensive reagents such as p ‐toluenesulfonic acid monohydrate and molecular iodine are used to catalyze the reactions. No metal catalyst is required. The starting material of the reactions, Betti bases, are easily prepared from a three‐component reaction of naphthol/phenol, aldehydes, and secondary amines. The mechanisms for the reactions are established through some control experiments. Quinone methide is the key intermediate for all the reactions reported herein.