Asymmetric aldol reactions: a novel model for switching between chelation- and non-chelation-controlled aldol reactions
摘要:
A new camphor-based N-propionyloxazolidinethione provides remarkable levels of asymmetric induction for both chelation-and non-chelation-controlled aldol processes. While the aldol condensation of the derived di-n-butylboryl enolate with various aldehydes affords the 'Evans'' syn aldol with excellent diastereoselectivity, the chlorotitanium enolate gives the ''non-Evans' syn aldol expected from chelation control. Most noteworthy is the observation that the sense of facial selectivity from the chlorotitanium enolate of propionyloxazolidinethione is opposite to that obtained from propionyloxazolidinone. This important finding illustrates the importance of increased chelating potential of the enolate ligand, ring thiocarbonyl, in maximizing the aldol pi-facial discrimination. Final nondestructive chiral auxiliary removal via hydroperoxide-assisted hydrolysis and subsequent esterification provides enantiomerically pure methoxy-carbonyl aldols.
Cu-catalyzed asymmetric Henry reaction promoted by chiral camphor Schiff bases
作者:Tangqian Jiao、Jingxuan Tu、Gaoqiang Li、Feng Xu
DOI:10.1016/j.molcata.2016.02.004
日期:2016.5
Abstract Five novel chiral camphor Schiffbases have been synthesized and utilized as ligands in asymmetric Henry reaction between nitromethane and aldehydes. The diastereoisomeric Schiffbases 5a and 5a' were separated successfully and gave completely different absolute configurations in the reaction. The reactions were carried out with CuCl-Schiff base 5a complex under mild condition with good yields
Enantioselective Addition of Dialkylzinc to Aromatic Aldimines Mediated by Camphor-Derived Chiral β-Amino Alcohols
作者:Wei-Ming Huang、Biing-Jiun Uang
DOI:10.1002/asia.201403240
日期:2015.4
The enantioselective addition of diethylzinc or dimethylzinc to N‐(diphenylphosphinoyl)imines mediated by 1 or 2 could be achieved in high yields (70–97 %) and enantioselectivities (85–98 % ee). The catalytic loading of 1 or 2 a could be reduced to 10 mol % for methylation or ethylation of imines in high yields and enantioselectivities (79–96 %) when the reaction was conducted in the presence of 1
The present invention relates to a method of enantioselective addition to imines, including: reacting R
2
CH═NY with R
3
ZnR
4
in the presence of a compound represented by the following formula (I),
in which Y, R
1
, R
2
, R
3
and R
4
are defined the same as the specification. Accordingly, the present invention can prepare secondary amines in high yields and enantiomeric excess by the above-mentioned method.
Fe(III) catalyzed enantioselective hydrophosphonylation of aldehydes promoted by chiral camphor Schiff bases
作者:Feng Xu、Yanpeng Liu、Jingxuan Tu、Chao Lei、Gaoqiang Li
DOI:10.1016/j.tetasy.2015.07.004
日期:2015.9
Five novel chiral camphor Schiffbases were designed. Schiff base L3 showed high efficiency in Fe(III)-catalyzed asymmetric hydrophosphonylations of aldehydes, giving the corresponding products in high yields (up to 91%) along with moderate to good enantioselectivities (up to 82%).