Recent progress on the lipase-catalyzed asymmetric syntheses

The lipase-catalyzed transesterification of alcohols with acyl donors in organic media has gained increased attention as a powerful method for the preparation of optically enriched compounds under very mild conditions, in which the vinyl esters 2 have been most frequently employed as the acyl donors; however, they are not always satisfactory. We applied the ethoxyvinyl esters 6 to the lipase-catalyzed transesterification reactions for the first time and discovered their advantages, viz., (i) the efficient reactivity and enantiotopic selectivity similar to or higher than those of 2 and (ii) the ready availability of the esters 6 having a suitably functionalized acyl moiety from the corresponding carboxylic acids and their applicability to the enzymatic reactions. These findings have opened a new possibility of the lipase-catalyzed reactions. In this review, several examples are introduced along with some related recent progress on the lipase -catalyzed asymmetric syntheses. The topics include (i) the enantio selective desymmetrization of prochiral 2,2-disubstituted 1,3-propanediols using 1-ethoxyvinyl 2-furoate 6b, (ii) the lipase-catalyzed domino reactions using suitably functionalized acyl donors 6e-i for the direct preparation of optically enriched cyclic compounds having multi stereogenic carbon centers, (iii) the dynamic kinetic resolution (DKR) of racemic secondary alcohols by the combined use of lipases and the ruthenium complexes 36a-g, and (iv) the DKR of racemic allylic alcohols (44, 45) by the combination of lipases and the vanadium compound 43. Application of these reactions to the asymmetric total synthesis of natural products is also described.