Asymmetric Acylations of Alcohols
A highly efficient dynamic kinetic resolution (DKR) of secondary alcohols at room temperature was developed. In situ racemization of substrates using a Ru catalyst and lipase-catalyzed acylation provides enantiopure products in high yields in very short reaction times. The use of isopropenyl acetate as the acyl donor makes the purification of the products very easy.
B. Martin-Matute, M. Edin, Krisztian Bogar, J.-E. Baeckvall, Angew. Chem. Int. Ed., 2004, 43, 6535-6539.
Dynamic kinetic resolution (DKR) of various aromatic chlorohydrins using Pseudomonas cepacia lipase (PS-C “Amano” II) and a ruthenium catalyst afforded chlorohydrin acetates in high yields and high enantiomeric excesses. These optically pure chlorohydrin acetates can be transformed to a wide range of important chiral compounds.
A. Träff, K. Bogár, M. Warner, J.-E. Bäckvall, Org. Lett., 2008, 10, 4807-4810.
A practical procedure has been developed for the dynamic kinetic resolution of 1,2-diarylethanols using a highly enantioselective lipase from Pseudomonas stutzeri as the resolution catalyst and a ruthenium complex as the racemization catalyst. Various 1,2-diarylethanols have been efficiently resolved to provide their acetyl derivatives with good yields and high enantiomeric excesses.
M.-J. Kim, Y. K. Choi, S. Kim, D. Kim, K. Han, S.-B. Ko, J. Park, Org. Lett., 2008, 10, 1295-1298.
Lipase-catalyzed acylation of racemic alcohols with a highly fluorinated acyl donor allows their kinetic resolution and a subsequent, efficient partition of both the tagged and untagged enantiomer between a fluorous and an organic phase. The method has been successfully applied to the resolution of secondary alcohols of low molecular weight. The fluorous label can be recovered quantitatively.
B. Hungerhoff, H. Sonnenschein, F. Theil, J. Org. Chem, 2002, 67, 1781-1785.
The combination of a vanadium-oxo compound with a lipase enables the regio- and enantioconvergent transformation of racemic allyl alcohols into optically active allyl esters. In this dynamic kinetic resolution, the vanadium compounds catalyzes both the racemization and the transposition of the hydroxyl group, while the lipase effects the chemo- and enantioselective esterification.
S. Akai, R. Hanada, N. Fujiwara, Y. Kita, M. Egi, Org. Lett., 2010, 12, 4900-4903.