Enzymatic Synthesis of Enantiopure Precursors of Chiral Bidentate and Tridentate Phosphorus Catalysts

The Candida antarctica lipase (CAL-B)catalyzed acetylation of racemic 2-hydroxy-methylphenyl(methyl)phenylphosphine oxide, performed in diethyl ether, led to kinetic resolution with an unusually high enantioselectivity (E = 3000). The CAL-B-mediated desymmetrization of prochiral bis(2-hydroxymethylphenyl) methylphosphine oxide gave, via its enantioselective monoacetylation, the corresponding monoacetate in 80% yield and with ee > 98%. The latter transformation allowed us to efficiently transform the prochiral substrate into the enantiomerically pure product in one single step. In both cases the stereogenic or prostereogenic phosphorus atom and the reacting hydroxy oxygen are distant from each other by four bonds. The absolute configurations of all the products were determined by a chemical correlation and X-ray analysis. The products will be used as enantiopure substrates in the preparation of a variety of chiral organophosphorus ligands/catalysts for asymmetric synthesis.