Enantioselective acylation using a second-generation P-aryl-2-phosphabicyclo[3.3.0]octane catalyst

The synthesis of P-aryl-2-phosphabicyleo[3.3.0]octane-HBF4 salts 3a and 3c is described. Incorporation of the P-3,5-di-tert-butyl-4-methoxyphenyl group in 3c allows use of a less expensive aryl bromide starting material. Deprotonation of the air-stable salts in situ with triethylamine releases the corresponding phosphines 1a and 1c for use in the kinetic resolution of representative secondary alcohols. The method is convenient for small-scale experiments and affords enantioselectivities s close to the values obtained using the free phosphines 1a and 1b, in cases where s is ca. 40 or lower.