Asymmetric hydrogenation of α-keto acid derivatives by rhodium-}amidophosphine-phosphinite{ catalysts
摘要:
The enantioselective hydrogenation of several alpha-keto esters (3a-f, 5a-j), alpha-keto amides (7a-e) and isatine derivatives (9a-d) with a set of four representative neutral homogeneous rhodium-amidophosphine-phosphinite catalysts has been investigated. Trifluoroacetato-Rh-AMPP catalytic precursors promoted the rapid, efficient synthesis of aliphatic oc-hydroxy esters 4a-f in moderate to high enantioselectivities (66-95% ee), in contrast to most aromatic alpha-hydroxy esters 6a-j (8-81% ee). Best enantioselectivities for alpha-hydroxy amides 8a-e (85-95% ee) and dioxindoles 10a-d (80-94% ee) were obtained with chloro-Rh-AMPP precursors. It is proposed that, contrary to alpha-keto amides, alpha-keto esters do not chelate onto the rhodium center and that, in such circumstances, the asymmetric induction is mainly controlled by the steric hindrance around the C=O function. (C) 1997 Elsevier Science Ltd.
Asymmetric Aerobic Oxidation of α-Hydroxy Acid Derivatives Catalyzed by Reusable, Polystyrene-Supported Chiral N-Salicylidene Oxidovanadium tert-Leucinates
作者:Santosh B. Salunke、N.Seshu Babu、Chien-Tien Chen
DOI:10.1002/adsc.201100062
日期:2011.5
The direct immobilization of two different C‐5‐propargyl ether‐modified, chiral N‐salicylidene vanadyl(V) tert‐leucinates onto 4‐azidomethyl‐substituted polystyrene by clickchemistry was examined. Among the eight different solvents investigated, the resulting polystyrene‐supported catalysts promote the asymmetric, aerobic oxidation of α‐hydroxy (thio)esters and amides with enantioselectivities of
Biocatalytic reduction of α-keto amides to (R)-α-hydroxy amides using Candida parapsilosis ATCC 7330
作者:Selvaraj Stella、Anju Chadha
DOI:10.1016/j.cattod.2012.03.081
日期:2012.12
Biocatalytic reduction of primary and secondary alpha-keto amides was accomplished using whole cells of Candida parapsilosis ATCC 7330. The primary (R)-alpha-hydroxy amides were obtained in good enantiomeric excess (up to 94%) and conversion (88-99%) as compared to the secondary (R)-alpha-hydroxy amides. (C) 2012 Elsevier B.V. All rights reserved.
Asymmetric Aerobic Oxidation of α-Hydroxy Acid Derivatives by <i>C</i><sub>4</sub>-Symmetric, Vanadate-Centered, Tetrakisvanadyl(V) Clusters Derived from <i>N</i>-Salicylidene-α-aminocarboxylates
作者:Chien-Tien Chen、Sampada Bettigeri、Shiue-Shien Weng、Vijay D. Pawar、Ya-Hui Lin、Cheng-Yuan Liu、Way-Zen Lee
DOI:10.1021/jo070575f
日期:2007.10.1
A series of chiral vanadyl(V) methoxides bearing 3-t-butyl-5-substituted N-salicylene-L-valinate and L-t-leucinate as chiral auxiliaries has been prepared. In all cases except the 3,5-di-t-butyl analogue, they exist as monomers both in solution and in the single crystal state. In the case of the 3,5-di-t-butyl analogue, the architectural nature of the vanadyl(V) complex highly depends on the base used during the complex formation event. A pentanuclear C-4-symmetric complex was formed when potassium salts were employed instead of the corresponding sodium salts. A central vanadate(V) unit serves to grip four identical chiral monomeric vanadyl(V) units together, by which a potassium ion sits on top of the four flanking units through carbonyl coordinations and serves to hold the whole cluster by cooperation with the central vanadate(V) unit. In comparison with the corresponding monomeric vanadyl(V) methoxide complex, the cluster complex was utilized to facilitate the asymmetric aerobic oxidations of various racemic alpha-hydroxyesters, -amides, and -thioesters with excellent selectivity factors (k(rel) 40 to >500).