Direct regioselective C-H borylation of [5]helicene

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%).