Ni-Catalyzed Traceless, Directed C3-Selective C-H Borylation of Indoles.

A highly efficient and general protocol for traceless, directed C3-selective C-H borylation of indoles with [Ni(IMes)] as the catalyst is reported. Activation and borylation of N-H bonds by [Ni(IMes)] is essential to install a Bpin moiety at the N-position as a traceless directing group, which enables the C3-selective borylation of C-H bonds. The N-Bpin group which is formed is easily converted back to an N-H group by the oxidative addition product of [Ni(IMes)] and -generated HBpin. The catalytic reactions are operationally simple, allowing borylation of a variety of substituted indoles with Bpin in excellent yields and with high selectivity. The C-H borylation can be followed by Suzuki-Miyaura cross-coupling of the C-borylated indoles in an overall two-step, one-pot process providing an efficient method for synthesizing C3-functionalized heteroarenes.