Palladium-catalyzed synthesis and isolation of functionalized allylboronic acids: Selective, direct allylboration of ketones

Abstract

Allyl boronates are very important reagents in advanced organic synthesis for the allylation of carbonyl compounds[1] and in cross-coupling[2] reactions. A practically unrivalled property of allylboronates is their highly regio- and stereoselective addition to carbonyl compounds to afford homoallylic alcohols.[1a-d, 3] This high selectivity is mainly based on two factors: 1) Allylboronates are configurationally stable, and unlike many allyl metal compounds[4] (such as allyl- Grignard reagents, allyl lithium compounds or allylboranes) do not undergo metallotropic rearrangement and E/Z isomerization at ambient conditions. 2) The six-membered ring transition state (TS) of the allylboration of carbonyl compounds is highly conformationally constrained, which leads to a strong differentiation in the stereoselection process.[3a, 5] Method development for broadening the number of accessible functionalized allyl boronates is one of the most important challenges in organoboron chemistry. © 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.