title: Structure and reactivity of a preactivated sp2-sp3 diboron reagent: catalytic regioselective boration of α,β-unsaturated conjugated compounds.
abstract: A novel sp(2)-sp(3) diboron reagent has been developed for the copper-catalyzed β-boration of α,β-unsaturated conjugated compounds. The reaction proceeds under mild conditions with various substrates, i.e., α,β-unsaturated esters, ketones, nitriles, ynones, amides, and aldehydes, in the absence of additives such as phosphine and sodium tert-butoxide to provide β-borylhomoenolates in good to excellent yields. The presence of an sp(3)-hybridized boron center, unambigously confirmed by X-ray crystallography, sufficiently activates the unsymmetrical pinacolato diisopropanolaminato diboron (PDIPA diboron, 2) to transfer the sp(2)-hybridized boron moiety chemoselectively. These observations suggest that the activation of one of the boron atoms is an essential step in the Cu-catalyzed β-boration catalytic cycle.
authors.affiliation: Department of Chemistry, Virginia Tech, Blacksburg, Virginia 24061, United States.
authors.forename: Ming
authors.initials: M
authors.lastname: Gao
authors.forename: Steven B
authors.initials: SB
authors.lastname: Thorpe
authors.forename: Christian
authors.initials: C
authors.lastname: Kleeberg
authors.forename: Carla
authors.initials: C
authors.lastname: Slebodnick
authors.forename: Todd B
authors.initials: TB
authors.lastname: Marder
authors.forename: Webster L
authors.initials: WL
authors.lastname: Santos