New Potentially Chelating Chiral Magnesium Amide Bases for Use in Enantioselective Deprotonation Reactions
作者:William Kerr、Michael Middleditch、Allan Watson
DOI:10.1055/s-0030-1259282
日期:2011.1
to prepare novel chiral magnesium bisamide reagents. These amide bases were subsequently applied within asymmetric deprotonation reactions to probe the potential for chelation-assisted selectivity enhancement. Good levels of selectivity could be achieved (up to 87:13 e.r. (R:S)) across a range of prochiral cyclohexanone substrates when employing a thiophene-derived magnesium bisamide complex.
合成了一系列手性仲胺,结合了 5 或 6 元杂环,并用于制备新型手性镁双酰胺试剂。随后将这些酰胺碱应用于不对称去质子化反应中,以探索螯合辅助选择性增强的潜力。当使用噻吩衍生的镁双酰胺复合物时,可以在一系列前手性环己酮底物上实现良好的选择性(高达 87:13 er (R:S))。
Stereoselective reactions. 28. Effects of the alkyl group at the amide nitrogen of chiral bidentate lithium amides on enantioselective deprotonation reaction
作者:Kazumasa Aoki、Kiyoshi Tomioka、Hiroshi Noguchi、Kenji Koga
DOI:10.1016/s0040-4020(97)00901-0
日期:1997.10
chiral bidentate lithium amides () having an alkyl- or a fluoroalkyl substituent at the amide nitrogen was examined. having a 2,2,2-trifluoroethyl group at the amide nitrogen was found to be an excellent chiral base for the present deprotonation reaction. Structures of in solution and solid state are discussed.
The first desymmetrization of 4-substituted cyclohexanones by organocatalytic asymmetric deprotonation at low catalyst loading is reported. The combination of N,O-bis(trimethylsilyl)acetamide (BSA) and chiralquaternaryammoniumaryloxide salts has been used as an efficientorganocatalyticsystem to provide silyl enolates in high yields and with modest ee.
Enantioselective deprotonation reactions using a novel homochiral magnesium amide base
作者:Kenneth W. Henderson、William J. Kerr、Jennifer H. Moir
DOI:10.1039/b000425l
日期:——
A novel homochiral magnesium bisamide base system has been
prepared and reacted with a series of prochiral ketones in the presence of
TMSCl to give efficient formation of the corresponding enol ethers in
enantiomeric ratios of up to 95∶5.
Stereoselective Reactions. XXXIV.<SUP>1)</SUP> Enantioselective Deprotonation of Prochiral 4-Substituted Cyclohexanones Using Chiral Bidentate Lithium Amides Having a Bulky Group Instead of a Phenyl Group on the Chiral Carbon
作者:Masaharu TORIYAMA、Keizo SUGASAWA、Shigeyasu MOTOHASHI、Norio TOKUTAKE、Kenji KOGA
DOI:10.1248/cpb.49.468
日期:——
Using chiral bidentate lithium amides having a bulky group instead of a phenyl group on the chiral carbon, enantioselective deprotonation of prochiral 4-substituted cyclohexanones in the presence of excess trimethylsilyl chloride was examined in THF in the absence and in the presence of HMPA. It is shown that enantioselectivity of the reactions decreases as the substituent on the chiral carbon of the chiral lithium amides and the substituent at the 4-position of cyclohexanones become reasonably bulky. An eight-membered cyclic transition state model is proposed for this deprotonation reaction.