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

Abstract

Abstract 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. 11 B 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.