Chiral N-heterocyclic carbenes as asymmetric acylation catalysts

Chiral N-heterocyclic carbenes are generated from C2-symmetric 1,3-bis(1-arylethyl)imidazolium salts and potassium tert-butoxide. These C2-symmetric imidazolidenyl carbenes catalyze enantioselective acylation of racemic secondary alcohols. The asymmetric acylation of 1-(1-naphthyl)ethanol was achieved in up to 68% ee of the acylated product, using (R,R)-1,3-bis[(1-naphthyl)ethyl]imidazolium tetrafluoroborate as a precursor of the chiral N-heterocyclic carbene and vinyl propionate as the acyl donor.