Enantioselective Protonation Catalyzed by a Chiral Bicyclic Guanidine Derivative

Abstract

Simple is beautiful: The guanidine derivative 1 catalyzes a tandem conjugate addition–enantioselective protonation reaction of phthalimidoacrylates with thiols (see scheme) and itaconimides with phosphine oxides. Optically pure analogues of cysteine and cystine were obtained in this way. In highly enantioselective deuteration reactions, a small but significant kinetic isotope effect was observed. R=aryl, benzhydryl; R1–R4=H, Me, Cl, F.