Resolution of (4RS,5RS)-4,5-diphenylimidazolidine-2-thione using pentafluorophenyl active esters

(4RS,5RS)-4,5-Diphenylimidazolidine-2-thione is resolved efficiently by treatment with NaHMDS and an enantiomerically pure pentafluorophenyl active ester. The levels of diastereocontrol were excellent (up to 90% de).