Stereoselective 1,2-Metalate Rearrangement of α-Chloroalkylboronic Esters with gem -Diborylalkanes

Abstract

Highly diastereoselective 1,2-metalate rearrangements of α-haloalkylboronic esters that simultaneously construct contiguous stereogenic centers remain limited. Herein, we report a highly diastereoselective and stereospecific 1,2-metalate rearrangement of enantioenriched α-haloalkylboronic esters using gem-diborylalkanes as pronucleophiles. Controlled in situ generation of α-borylcarbanions, achieved by tuning the boron activator, enables efficient boron-ate complex formation and subsequent Lewis acid-promoted 1,2-metalate rearrangement to furnish vicinal diboronic esters in high yields with excellent diastereoselectivity. Mechanistic studies, including in situ11B NMR spectroscopy and density functional theory calculations, support the formation of a boron-ate intermediate and suggest that activator-dependent carbanion generation and minimization of alkyl–alkyl steric repulsion contribute to the high diastereoselectivity. The synthetic versatility of the products is demonstrated through diverse derivatizations and the concise synthesis of enantioenriched 1,2-dicyclohexylethane-1,2-diol.