Lithium Amide Assisted Asymmetric Mannich-Type Reactions of Menthyl Acetate with PMP-Aldimines
摘要:
A lithium enolate of menthyl acetate added to PMP-imines, in the presence of an equimolar amount of lithium diisopropylamide, affords the Mannich-type addition products in high stereoselectivity.
Novel metal-free, readily available chiral catalytic systems for the enantioselective reduction of keto imines are reported. Different β-imino esters were reduced by trichlorosilane in the presence of 10 mol% of a chiral Lewis base easily obtained in one step only from prolinol, in high yields and in up to 85% enantioselectivity; imines bearing an inexpensive and removable chiral auxiliary, were reduced with complete control of the absolute stereochemistry. The methodology was successfully extended to the stereoselective synthesis of α-amino esters.
Solid Supported Chiral <i>N</i>
-Picolylimidazolidinones: Recyclable Catalysts for the Enantioselective, Metal- and Hydrogen-Free Reduction of Imines in Batch and in Flow Mode
organocatalysts for the catalytic reduction of imines with trichlorosilane has been developed. Polystyrene proved to be a more effective support than silica in terms of both chemical and stereochemical efficiency. Even with a loading as low as 1 mol% the best performing supported catalyst showed a remarkable activity and stereocontrol ability, promoting the reduction with stereoselectivities reaching 98% ee and
Asymmetric transfer hydrogenations of β-N-substituted enamino esters with ammonia borane
作者:Weiwei Zhao、Xiangqing Feng、Jing Yang、Haifeng Du
DOI:10.1016/j.tetlet.2019.03.060
日期:2019.4
β-enamino esters is one of the most efficientapproaches for their synthesis. Ammonia borane with low molecular weight, high hydrogen capacity, and good stability, is an ideal hydrogen source for the transfer hydrogenation. However, only a few successful examples have been reported for the asymmetric reduction with ammonia borane. In this work, an asymmetric metal-free transfer hydrogenation of β-N-substituted
A new class of chiral Lewis bases for the enantioselective HSiCl3‐mediated reduction of imines was developed. Through extensive catalyst structure optimization, an extremely active species was identified that was able to promote the reduction of a large variety of functionalized substrates in high yields with enantioselectivities typically above 90 % with catalyst loadings as low as 0.1–1 mol %. The
Cinchona-Derived Picolinamides: Effective Organocatalysts for Stereoselective Imine Hydrosilylation
作者:Pedro C. Barrulas、Andrea Genoni、Maurizio Benaglia、Anthony J. Burke
DOI:10.1002/ejoc.201403180
日期:2014.11
Picolinamide–cinchona organocatalysts for the successful enantioselective reduction of ketomines were developed. For the first time, a new type of chiral Lewis base, a cationic species, is reported to efficiently organocatalyze the addition of trichlorosilane to imines. Excellent yields with good to high enantioselectivities (up to 91 %) were obtained in the reduction of differently substituted substrates