Enantioselective Protonation: Hydrophosphinylation of 1,1‐Vinyl Azaheterocycle N ‐Oxides Catalyzed by Chiral Bis(guanidino)iminophosphorane Organosuperbase

Enantioselective protonation by hydrophosphinylation of diarylphosphine oxides with 2‐vinyl azaheterocycle N ‐oxide derivatives was demonstrated using chiral bis(guanidino)iminophosphorane as the higher‐order organosuperbase catalyst. It was confirmed by several control experiments that a chiral weak conjugate acid of the chiral bis(guanidino)iminophosphorane, instead of achiral diarylphosphine oxides, directly functioned as the proton source to afford the corresponding product in a highly enantioselective manner in most cases. Enantioselective protonation by a weak conjugate acid generated from the higher‐order organosuperbase would broaden the scope of enantioselective reaction systems because of utilization of a range of less acidic pronucleophiles. This method is highlighted by the valuable synthesis of a series of chiral P,N‐ligands for chiral metal complexes through the reduction of phosphine oxide and N ‐oxide units of the corresponding product without loss of enantiomeric purity.