Synthesis of optically active vicinal fluorohydrins by lipase-catalyzed deracemization

Three microbial lipases have been used to deracemize trans-2-fluorocycloalkanols 2 both by hydrolysis of the corresponding acetates 3 or chloroacetates 4 and by esterification of the fluorohydrins 2 using vinyl acetate and vinyl chloroacetate, respectively. Pseudomonas cepacia lipase was the most selective for the six- and the seven-membered-ring compounds, while the lipase from Candida rugosa was most useful for the eight-membered-ring compounds. Both lipases transform the (R)-enantiomers preferentially. In contrast the lipase from Candida antarctica hydrolyzed the esters of trans-2-fluorocyclohexanol 2a and esterified the fluorohydrin itself with very low enantiopreference for the (R)-isomers. The seven- and the eight-membered ring esters and the corresponding fluorohydrins were also transformed with low, but reverse, enantioselectivity.