S<sub>N</sub>2 Ring Opening of β-Lactones: An Alternative to Catalytic Asymmetric Conjugate Additions
作者:Scott G. Nelson、Zhonghui Wan、Magdalena A. Stan
DOI:10.1021/jo025519n
日期:2002.7.1
Merging catalyticasymmetricacylhalide-aldehydecyclocondensation (AAC) reactions with ensuing Grignard-mediated ring opening of the derived enantiomerically enriched beta-lactones is presented as a generally useful asymmetric synthesis of beta-disubstituted carboxylic acids. Enantiomerically enriched beta-lactones are subject to efficient S(N)2 ring opening with a variety of copper-modified alkyl
<i>C</i><sub>2</sub>-Symmetric Cu(II) Complexes as Chiral Lewis Acids. Catalytic, Enantioselective Cycloadditions of Silyl Ketenes
作者:David A. Evans、Jacob M. Janey
DOI:10.1021/ol016096z
日期:2001.6.1
[reaction: see text] C(2)-Symmetric bis(oxazoline)-Cu(II) complexes (4a-g) catalyze the enantioselective [2 + 2] cycloaddition between (silyl)ketenes and chelating carbonyl substrates. A range of substituted beta-lactones can be produced in excellent yields and selectivities. It was also found that (trimethylsilyl)ketene (1) may also undergo a highly selective hetero Diels-Alder reaction with beta
Predicting the R/S absolute configuration in asymmetric bifunctional catalysis (ABC)
作者:Yun-Ming Lin、Zhongtao Li、Julie Boucau
DOI:10.1016/j.tetlet.2007.05.131
日期:2007.7
A predictive model for assigning the R/S absolute configuration in chiral Lewis base-dependent asymmetric bifunctional catalysis (ABC) has been developed. Chiral Lewis base (LB*)-dependent ABC abolishes the chiral Lewis acid (LA*) component as the stereochemical determining factor in asymmetric catalysis. By correlating the constant LB* chirality to the facial preference for the LA*-bound carbonyl group for nucleophile delivery, the R/S absolute configuration of the products can be predicted a priori. (c) 2007 Elsevier Ltd. All rights reserved.
Cinchona Alkaloid-Lewis Acid Catalyst Systems for Enantioselective Ketene−Aldehyde Cycloadditions
作者:Cheng Zhu、Xiaoqiang Shen、Scott G. Nelson
DOI:10.1021/ja0492900
日期:2004.5.1
Asymmetric cinchona alkaloid-catalyzed acid chloride-aldehyde cyclocondensation (AAC) reactions afford enantioenriched 4-substituted and 3,4-disubstituted beta-lactones with near perfect absolute and relative stereocontrol. These reactions are characterized by the operational simplicity derived from using commercially available or easily obtained (one-step) reaction catalysts and in situ ketene generation from acid chlorides. The range of aldehyde substrates that serve as effective AAC substrates include sterically hindered aldehydes such as cyclohexanecarboxaldehyde and pivaldehyde.
Catalytic Asymmetric Acyl Halide−Aldehyde Cyclocondensations. A Strategy for Enantioselective Catalyzed Cross Aldol Reactions