An asymmetric intramolecular Cannizzaro reaction of aryl and alkyl glyoxals with alcohols has been realized with an unprecedented high level of enantioselectivity, on the basis of a newly developed congested TOX ligand and a gradual liberation protocol of active glyoxals from glyoxal monohydrates. Preliminary results suggested a mechanism of enantioselective addition of alcohols to glyoxals contributing
Enantio- and chemoselective Brønsted-acid/Mg(<sup>n</sup>Bu)<sub>2</sub> catalysed reduction of α-keto esters with catecholborane
作者:Dieter Enders、Bianca A. Stöckel、Andreas Rembiak
DOI:10.1039/c4cc00427b
日期:——
The first enantio- and chemoselective Bronsted-acid catalysed reduction of alpha-keto esters with catecholborane has been developed. The alpha-hydroxy esters were obtained under mild reaction conditions in virtually quantitative yields and excellent enantioselectivities. With slight modifications both enantiomers can be obtained without any loss of selectivity.
Synthesis of chiral α-aryl-α-hydroxyacetic acids: Substituent effects in pig liver acetone powder (PLAP) induced enantioselective hydrolysis
作者:Deevi Basavaiah、Peddinti Rama Krishna
DOI:10.1016/0040-4020(94)01105-9
日期:1995.2
Pig liveracetonepowder (PLAP) catalyzed hydrolysis of alkyl α-acetoxy-α-arylacetates produces alkyl (S)-α-aryl-α-hydroxyacetates in 23–80% enantiomeric purities. Enantioselectivity is dependent on the ester group of O-acetylmandelates. Substitution on the aromatic ring results in inferior selectivities. Only acetate group is hydrolyzed by PLAP while the ester functionality is found to be completely
Steric and electronic effects in the enantioselective hydrogenation of activated ketones on platinum: Directing effect of ester group
作者:S DIEZI、S REIMANN、N BONALUMI、T MALLAT、A BAIKER
DOI:10.1016/j.jcat.2006.02.001
日期:2006.4.25
of the steric bulkiness of the α -ketoester. None of the mechanistic models developed for ketonehydrogenation on Pt are conform to the observations. Only additional steric effects in the modifiers and replacement of toluene by acetic acid as a reaction medium enhanced the sensitivity of the catalyst system to steric effects in the substrates (ee=0–94%ee=0–94%). An important mechanistic consequence
Chiral cobalt-catalyzed enantioselective aerobic oxidation of α-hydroxy esters
作者:Santosh Kumar Alamsetti、Govindasamy Sekar
DOI:10.1039/c0cc01917h
日期:——
A chiral cobalt-catalyzed enantioselective aerobic oxidative kinetic resolution of (±)-α-hydroxy esters, using molecular oxygen as a sole oxidant, is reported and a maximum of selectivity factor (s) 31.9 was achieved with >99% enantiomeric excess for unreacted α-hydroxy esters.