Brønsted‐Acid‐Mediated Divergent Reactions of Betti Bases with Indoles: An Approach to Chromeno[2, 3‐b]indoles through Intramolecular Dehydrogenative C2‐Alkoxylation of Indole. Issue 20 (19th June 2016) - Deb, Mohit L.
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. Abstract : Parents of three siblings: Three different kinds of indole derivatives, namely, 3‐(α, α‐diarylmethyl)indoles, chromeno[2, 3‐ b ]indoles, and bis(indolyl)methanes, can be synthesized from the reaction of indole with Betti bases. o ‐Quinone methide is the key intermediate in the reactions. A metal‐free dearylation is also reported here for the first time.