Brønsted acid-catalysed regiodivergent phosphorylation of 2-indolylmethanols to synthesize benzylic site or C3-phosphorylated indole derivatives

Abstract

A Brønsted acid catalysed regiodivergent phosphorylation of 2-indolylmethanols with diarylphosphine oxides has been established, which provides a brand-new strategy for accessing highly functionalized phosphorus-containing indoles with structural diversity. Under the catalysis of HOTs·H₂O, 2-indolylmethanols undergo regioselective benzylic phosphorylation at room temperature to afford benzylic site phosphorylated indoles in good to high yields (29 examples, up to 98% yield), while C3-phosphorylated indoles are obtained in the presence of HOTf under heating conditions (16 examples, up to 83% yield). Preliminary mechanistic studies suggest that C3-phosphorylated indoles are possibly obtained partially from direct C3-phosphorylation and dominantly from a tandem benzylic phosphorylation/[1,3]-P migration/isomerization sequence from 2-indolylmethanols. Furthermore, the acidity of the Brønsted acid and the reaction temperature play a vital role in the [1,3]-P migration of benzylic phosphorylated indoles to form C3-phosphorylated indoles. This protocol serves as a good example for regioselective benzylic functionalization of 2-indolylmethanols.