Iridium-Catalyzed Intermolecular Asymmetric Hydroheteroarylation of Bicycloalkenes

Catalytic hydroarylation of alkenes is a desirable process
because
it can occur under neutral conditions with regioselectivity complementary
to that of acid-catalyzed reactions and stereoselectivity derived
from the catalyst. We report an intermolecular asymmetric addition
of the C–H bonds of indoles, thiophenes, pyrroles, and furans
to bicycloalkenes in high yield with high enantiomeric excess. These
heteroarene alkylations occur ortho to the heteroatom. This selectivity
is observed even with unprotected indoles, which typically undergo
alkylation at the C3 position. Initial mechanistic studies revealed
that oxidative addition of a heteroarene C–H bond to a neutral
IrI species occurs within minutes at room temperature and
occurs in the catalytic cycle prior to the turnover-limiting step.
Products from syn addition of the C–H bond across the olefin
were observed.