Enantioselective introduction of fluoride into organic compounds: First asymmetric ring opening of epoxides by hydrofluorinating reagents

The first enantioselective epoxide ring opening with hydrofluorinating agents mediated by chiral non-racemic Lewis acids is reported. The reaction of cyclohexene oxide (1) with KHF2/18-crown-6 is trans-diastereoselective and proceeds with 55% ee to form (R,R)-(−)-2-fluorocyclohexanol (2) in the presence of Jacobsen’s (S,S)-(+)-(salen)chromium chloride complex A. From racemic epoxides such as styrene oxide (9) or phenyl glycidether (13), mainly or exclusively the products with fluorine in primary position are formed with 90 or 62% ee, respectively. In all cases minor amounts of corresponding chlorohydrins are formed.