Selective nucleophilic substitution using pyrazolate anions: Easy approach to modular chiral ligands with complexing pyrazole moieties

A simple method for the stereoselective synthesis of 3,5-disubstituted pyrazolyl alcohols from readily available chiral epoxides is reported. The key step of the synthesis is the ring-opening reaction, which occurs by a regio- and enantioselective nucleophilic substitution with pyrazolate anions. An analogous reaction of the pyrazolate anions gave nonracemic (pyrazolyl)oxazolines. Thus obtained modular pyrazole chiral ligands were tested in the Pd-catalyzed Tsuji-Trost and Cu-catalyzed asymmetric cyclopropanation reactions and the enantioselectivities up to 52% ee and 64% ee were attained in both model reactions, correspondingly.