Vicinal Stereocenter Construction via α-Boryl Carbanions from Borylated Cyclopropanes

We report generation and stereocontrolled electrophilic trapping of α-boryl carbanions via the selective anionic ring-opening of stereodefined iodomethyl cyclopropylboronic esters. The strategy relies on a lithium-iodine exchange to generate borata alkene intermediates, affording vicinal tri- and tetrasubstituted boronic esters with excellent levels of diastereoselectivity after electrophilic trapping. The stereocontrol arises from conformational preferences of the boron alkylidene, driven by its unique electronic structure. This work expands the synthetic utility of α-boryl carbanions and demonstrates their potential in the stereocontrolled construction of sp³-rich organoboron frameworks.