Chemo- and Stereoselective Crotylation of Aldehydes and Cyclic Aldimines with Allylic gem-Diboronate Ester.

We report a highly chemo- and stereoselective crotylation of aldehydes and cyclic aldimines with allylic-gem-diboronate ester as a new type of organoboron reagent. The allylic-gem-diboronate ester undergoes the crotylation with aldehydes and cyclic aldimines in excellent stereoselectivity, forming anti-5,6-disubstituted oxaborinin-2-ols or (E)-δ-boryl-anti-homoallylic amines in high efficiency. The reaction shows a wide range of substrate scope and excellent functional group tolerance. The synthetic applications of the obtained products, including stereospecific C-C, C-O, and C-Cl bond formation, are also demonstrated.