Dual Functionalization of α-Monoboryl Carbanions through Deoxygenative Enolization with Carboxylic Acids.

A dual functionalization of 1,1-diborylalkanes through deoxygenative enolization with carboxylic acids was developed. 1,1-Diborylalkanes were activated by MeLi to generate α-monoboryl carbanions. In situ IR spectroscopy indicated an interaction between carboxylic acid and 1,1-diborylalkane before addition of the activation reagent. Release of the active α-monoboryl carbanion from the masked form was necessary for its reaction with carboxylate to afford enolate species. Electrophilic trapping of enolate species with various electrophiles achieved dual functionalization of 1,1-diborylalkanes to afford a variety of α-mono, di-, and tri-substituted ketones.