A New Route to Protected Acyloins and Their Enzymatic Resolution with Lipases

A series of 16 different 3‐acyloxy methyl ketones, the acyloin acetates and butyrates (±)‐ 5 , was synthesised by a straightforward new method through alkylation of tert ‐butyl 2‐acyloxyacetoacetates 3 , followed by chemoselective dealkoxycarbonylation of the tert ‐butyloxycarbonyl group in the presence of other ester groups. Subsequent hydrolysis of (±)‐ 5 can be achieved with base to give racemic acyloins 6 , or with lipase catalysis to afford the corresponding non‐racemic acyloins ( S )‐ 6 . The remaining ( R )‐acyloin esters 5 can be racemised and resubjected to the procedure, or hydrolysed chemically. The kinetic resolution with two of the six tested enzymes, CAL‐B and BCL (PS) lipase, proceeded selectively [enantiomeric ratio ( E ) values between 50 and > 200] and most of the acyloins ( S )‐ 6 were obtained in very high enantiomeric excesses (up to > 99%  ee ). (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)