Strain-Release Induced 1,2-Metallate Rearrangement of Geminal Diborons: Multicomponent 1,5-Difunctionalization via Ring-Opening Coupling.

1,2-metallate rearrangement of geminal diboryl alkanes typically requires an α-leaving group and results in monofunctionalization at the proximal carbon. We present a strategy to engage non-terminal geminal diborons in 1,2-boronate shift via ring-opening of strained vinyl cyclopropyl diborons (VCPDBs). This multicomponent reaction enabled proximal and remote 1,5-difunctionalization yielding densely functionalized homoallylic diboryl alkanes featuring allylic halide or branched 1,5-diene motifs which are components of bioactive natural products. The VCPDB reaction displayed polarity inversion relative to majority of the previous VCP ring-opening reactions. The protocol showed broad substrate scope, providing alkenyl products with high E-stereoselectivity, and their downstream synthetic utility was also demonstrated. Employing a chiral ligand in the allylation preserved the reaction efficiency while indicating enantioenrichment in the ring-opening coupling. 11B NMR studies indicated the involvement of "ate-complex" and the role of trans-orientation of vinyl and boronate groups to facilitate ring opening. To the best of our knowledge, this work represents the first examples of strain-release induced 1,2-metallate rearrangement on geminal diborons and Ir catalyzed multicomponent allylation of organoborons beyond 1,2 or 1,3-addition.