Rh(III)-Catalyzed Annulation of 2-Biphenylboronic Acid with Diverse Activated Alkenes.

Abstract

Rhodium(III)-catalyzed annulation of 2-biphenylboronic acids with three classes of activated alkenes has been realized, leading to the synthesis of fused or bridged cyclic skeletons via transmetalation-initiated C-H activation. In the annulative coupling of 2-biphenylboronic acid with a CF3-substituted enone, the bulky cyclopentadienyl ligand (CptBu) in the catalyst proved effective to promote the reductive elimination process prior to protonolysis, affording the [4 + 2] annulated products instead of the simple 1,4-addition product. Seven-membered rings were obtained when disubstituted cyclopropenones were employed. Bridged cycles were isolated from the coupling of 2-biphenylboronic acid with benzoquinones as a result of 2-fold Michael additions. The substrate scopes were found to be broad with up to 99% yield under air-tolerant conditions.