One-Pot Three-Component Highly Selective Synthesis of Homoallylboronates by Using Metal-Free Catalysis
作者:Ismail Ibrahem、Palle Breistein、Armando Córdova
DOI:10.1002/chem.201103572
日期:2012.4.23
Metal‐free selectivity: The first metal‐free one‐pot three‐component highly chemo‐ and regioselective catalytic synthesis of homoallylboranes using simple N‐heterocyclic carbenes (NHC) and amines is presented. The catalytic reaction between B2(pin)2, α,β‐unsaturated aldehydes and 2‐(triphenylphosphoranylidene)acetate esters proceeds through a catalytic metal‐free β‐boration/Wittig cascade sequence
Structure and Reactivity of a Preactivated sp<sup>2</sup>–sp<sup>3</sup> Diboron Reagent: Catalytic Regioselective Boration of α,β-Unsaturated Conjugated Compounds
作者:Ming Gao、Steven B. Thorpe、Christian Kleeberg、Carla Slebodnick、Todd B. Marder、Webster L. Santos
DOI:10.1021/jo2003488
日期:2011.5.20
A novel sp(2)-sp(3) diboron reagent has been developed for the copper-catalyzed beta-boration of alpha,beta-unsaturated conjugated compounds. The reaction proceeds under mild conditions with various substrates, i.e., alpha,beta-unsaturated esters, ketones, nitriles, ynones, amides, and aldehydes, in the absence of additives such as phosphine and sodium tert-butoxide to provide beta-borylhomoenolates in good to excellent yields. The presence of an sp(3)-hybridized boron center, un-ambigously 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 beta-boration catalytic cycle.