LIPASE-CATALYZED IRREVERSIBLE TRANSESTERIFICATIONS USING ENOL ESTERS AS ACYLATING REAGENTS - PREPARATIVE ENANTIOSELECTIVE AND REGIOSELECTIVE SYNTHESES OF ALCOHOLS, GLYCEROL DERIVATIVES, SUGARS, AND ORGANOMETALLICS
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Isopropenyl and vinyl esters have been found to be useful for lipase-catalyzed stereoselective acylation of a number of hydroxy compounds including glycerol and serinol derivatives, ferrocenylethanol, sugars, and other alcohols. The reactions are faster, more selective, and easier to optimize than other transesterifications using alkyl esters as acylating reagents. The alcohol freed from the transesterification rapidly tautomerizes to volatile acetaldehyde or acetone, making the process irreversible and simpler for product isolation. The process is particularly useful for synthesis of certain chiral compounds, such as ferrocenyl ethyl esters and acyl sugars, which are difficult to prepare in aqueous solution. Compared to hydrolysis, transesterifications are about 102-104 times slower with normal alkyl esters as acylating reagents and about 10 times slower with the enol esters as acylating reagents. In some cases, transesterifications are less selective than hydrolyses. 1988, American Chemical Society. All rights reserved.