Boron(III)-Catalyzed C2-Selective C-H Borylation of Heteroarenes

Abstract

A BF₃ ⋅Et₂ O-catalyzed C2-selective C-H borylation of indoles with bis(pinacolato)diboron was developed to afford indole-2-boronic acid pinacol esters. A variety of functional groups were tolerated, and other heteroarenes like pyrrole and benzo[b]thiophene were also suitable substrates. An electrophilic substitution mechanism was proposed based on the preliminary mechanistic studies. This novel transformation utilizes simple and cheap BF₃ ⋅Et₂ O as catalyst and exhibits unusual C2 regioselectivity, providing a significant non-transition-metal-catalyzed C-H borylation and an efficient method towards the synthesis of C2-functionalized heteroarenes.

Keywords: boron; heteroarenes; homogeneous catalysis; reaction mechanisms; synthetic methods.