A novel homochiral magnesium bisamide has been readily prepared and, following careful optimisation, this species has been shown to react efficiently with a series of prochiral 4-substituted cyclohexanones in the presence of TMSCl to give the corresponding silyl enol ethers in enantiomeric ratios of up to 95:5. Additionally, the same chiral base system has been shown to be highly effective in the desymmetrisation of cis-2,6-disubstituted cyclohexanones, providing excellent levels of both conversion and enantioselection (up to >99.5:0.5 er). Furthermore, the magnesium bisamide has also been shown to mediate a kinetic resolution process with the corresponding trans-disubstituted substrates, allowing access to enantioenriched enol ethers and ketones. (C) 2002 Elsevier Science Ltd. All rights reserved.
Enantioselective Deprotonation of 2,6-Disubstituted Cyclohexanones with a Homochiral Magnesium Amide Base and the Observation of a Novel Kinetic Resolution Process
Enantioselective deprotonation reactions using polymer-supported chiral magnesium amide bases
作者:Kenneth W. Henderson、William J. Kerr、Jennifer H. Moir
DOI:10.1039/b104417f
日期:——
Novel and readily accessible polymer-supported chiral magnesium amide reagents have been prepared and shown to be effective in the asymmetricdeprotonation of a series of prochiral cyclohexanones, affording good to excellent levels of both conversion and enantiomeric ratio (up to 93:7); the Merrifield-based chiral amine species has been shown to be readily recyclable.