Boron-Copper 1,3-Rearrangement: the New Concept Behind the Boryl Migration from C(sp2 ) in Alkenyl Boranes to C(sp3 ).

Abstract

Regioselective borylcupration of borylated skipped (Z)-dienes generates diborylated alkylcopper species that are involved in an intramolecular stereospecific B/Cu 1,3-rearrangement by migration of Bpin moiety from C(sp2 ) to C(sp3 ). DFT mechanistic studies showed that boryl migration occurs through the formation of 4-membered boracycle intermediate with a moderate free-energy barrier. Moreover, the use of KOMe forms stable Lewis base adducts with Bpin moieties that blocks the reaction. Subsequently to the 1,3-boron shift, the in situ electrophilic trapping allows selective C-H, C-C and C-X bonds, followed by intramolecular cross coupling giving access to cyclic functionalized alkylidenecyclohexanes or alkylidenecyclobutanes.