Direct regioselective C–H borylation of [5]helicene

Abstract

Ir-catalyzed borylation of [5]helicene was studied for the first time. The obtained results indicate that borylation proceeded preferentially at the 2- and 3-positions. By using an appropriate catalytic system, 3-borylated [5]helicene can be formed as the major product in a high yield and regioselectivity (up to 89%, 8 : 1 ratio of isomers). The monoborylated [5]helicenes were further utilized in a Suzuki–Miyaura cross-coupling reaction to produce 2- or 3-arylated helicenes in very good isolated yields (80–94%).