Diastereoselective Homocoupling of Benzylic C(sp)-H Bonds Enabled by Halogen Transfer.

A transition-metal- and harsh-oxidant-free strategy for diastereoselective homocoupling of benzylic α-boryl carbanions has been developed. Central to this methodology is the ability of the halogen transfer reagent to seamlessly integrate halogenation and substitution within a compatible process. Additionally, this methodology is also applicable to the homocoupling of diarylmethanes and alkylheteroarenes. Substrates bearing oxidatively sensitive functional groups were well-tolerated. Preliminary studies suggest that the hydrogen bond between two boryl groups contributes to the high diastereoselectivities.