A method for the kinetic resolution of 3-(aryloxy)-1,2-propanediols rac-1a-n without additional protection-deprotection steps using a lipase-catalyzed sequential transesterification with lipase amnno PS has been developed. In the first step of this one-pot procedure the racemic 1,2-diols are acylated regioselectively at the primary hydroxy group without enantioselection. The subsequent acylation at the secondary hydroxy group of the formed primary monoacetate is responsible for high enantioselection. The enantioselectivity of this transformation depends significantly on the substitution pattern of the aryl ring and the organic solvent used. 3-(Aryloxy)-1,2-propanediols with substituents in the para-position show a much higher enantioselectivity than the corresponding derivatives with ortho-substituents. Among other substrates, the pharmaceuticals Mephenesin, Guaifenesin, and Chlorphenesin have been resolved. The replacement of the aryloxy by alkyl substituent causes a dramatic decrease of enantioselectivity.
Synthesis of optically active 2-hydroxy monoesters via-kinetic resolution and asymmetric cyclization catalyzed by heterometallic chiral (salen) Co complex
作者:Wenji Li、Santosh Singh Thakur、Shu-Wei Chen、Chang-Kyo Shin、Rahul B. Kawthekar、Geon-Joong Kim
DOI:10.1016/j.tetlet.2006.03.042
日期:2006.5
The binuclear chiral (salen) Co complexes bearing Lewis acids of Al and Ga catalyze regio- and enantioselective ring opening of terminal epoxides with carboxylic acids. The ring opened product of epichlorohydrin with carboxylic acids followed by cyclization step in the presence of catalyst and base represent straightforward, efficient methods for the synthesis of enatiomerically enriched (>99% ee)