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

A BF 3 ⋅Et 2 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 BF 3 ⋅Et 2 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.