Chemo- and Enantioselective Brønsted Acid-Catalyzed Reduction of α-Imino Esters with Catecholborane
作者:Dieter Enders、Andreas Rembiak、Bianca Anne Stöckel
DOI:10.1002/adsc.201300352
日期:2013.7.8
The chemo‐ and enantioselectivereduction of α‐imino esters with catecholborane has been developed employing 10 mol% of an enantiopure BINOL‐based phosphoric acid as organocatalyst. Various differently substituted aromatic α‐amino acid derivatives can be achieved in almost quantitative yields and very good to excellent enantioselectivities of up to 96% ee under mild reaction conditions.
Dynamic kinetic resolution of α-chloro esters in asymmetric nucleophilic substitution using diacetone-D-glucose as a chiral auxiliary
作者:Hyun Jung Kim、Eun-kyoung Shin、Ji-yeon Chang、Yongtae Kim、Yong Sun Park
DOI:10.1016/j.tetlet.2005.04.003
日期:2005.6
Diacetone-D-glucose mediated dynamickineticresolution of α-chloro-α-aryl esters in nucleophilicsubstitution reactions has been investigated. Reactions of various amine nucleophiles in the presence of TBAI and DIEA can provide the substitution products 2–10 up to 97% yield and 97:3 dr. This simple procedure with easy removal of the chiral auxiliary provides a practical protocol for asymmetricsyntheses of α-amino
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
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