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)2] as the catalyst is reported. Activation and borylation of N–H
bonds by [Ni­(IMes)2] 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 in situ back to an
N–H group by the oxidative addition product of [Ni­(IMes)2] and in situ-generated HBpin. The catalytic
reactions are operationally simple, allowing borylation of a variety
of substituted indoles with B2pin2 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.