Chemoselective conversion of biologically sourced polyols into chiral synthons

Abstract

Crude oil currently provides much of the world's energy, but it is also the source of many feedstock chemicals. Methodology for the conversion of biomass into useful chemicals has often focused on either complete deoxygenation or the production of high-volume platform chemicals. Here, we describe the chemoselective partial reduction of silyl-protected C6O6-derived polyols to produce a diverse set of oxygen-functionalized chiral synthons. The combination of B(C6F5)3 and a tertiary silane efficiently generates a reactive equivalent of an electrophilic silylium ion (R3Si(+)) and a hydride (H(-)) reducing agent. The mechanism of oxygen loss does not involve a dehydrative elimination and thus avoids ablation of stereochemistry. Neighbouring group participation and the formation of cyclic intermediates is key to achieving selectivity in these reactions and, where both primary and secondary C-O bonds are present, the mechanism allows further control. The method provides--in one or two synthetic steps--highly improved syntheses of many C6On synthons as well as several previously undescribed products.