Nonenzymatic kinetic resolution of racemic 2,2,2-trifluoro-1-aryl ethanol via enantioselective acylation
作者:Qing Xu、Hui Zhou、Xiaohong Geng、Peiran Chen
DOI:10.1016/j.tet.2009.01.058
日期:2009.3
Kineticresolution of a series of 2,2,2-trifluoro-1-aryl ethanol with (R)-benzotetramisole as the catalyst has been investigated. The result showed that when the aryl group in the substrate was a phenyl (or a phenyl substituted by an electron-donating group) or a naphthyl (an extended phenyl) group, the system could give an s value higher than 20. Preparative KR examples demonstrated the applicability
observed in the reduction of hinderedketones such as isopropyl ketone, while the stereoselectivity was inverted in the reduction of ketones with electron-withdrawing atoms such as chlorine. The mechanism for the inversion in stereochemistry was investigated by enzymatic studies. Several enzymes with different stereoselectivities were isolated; one of them catalyzed the reduction of methyl ketones, and another
Enantioselectivities in asymmetric reduction of ketones were controlled by atmospheric carbon dioxide concentrations: the reaction in high carbon dioxide concentrations under illumination of fluorescent light afforded the corresponding l-alcohol while that in low carbon dioxide concentrations in the presence of glucose under dark conditions gave the antipode, d-alcohol.
The reduction of trifluoromethyl ketones containing a sulfur functionality by the crude alcohol dehydrogenase from Geotrichum proceeded successfully, and the corresponding optically active alcohols were synthesized with high yields and excellent enantioselectivities.