Selective Nucleophilic Substitution Using Pyrazolate Anions:Easy Approach to Modular Chiral Ligands with Complexing Pyrazole Moieties

摘要

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.