Chiral N-oxides as catalysts or ligands in enantioselective reactions

New enantioselective reactions catalyzed by chiral N-oxides or chiral N-oxide-metal complexes are discussed. Enantioselective allylations of aldehydes with allyltrichlorosilanes, aldol reactions with trichlorosilyl enol ethers, and epoxide-opening reactions with tetrachlorosilane were accomplished by using chiral bipyridine N,N'-dioxide derivatives as catalysts. In these reactions, hexacoordinate silicate intermediates played pivotal roles in the enantioselection. Furthermore, the N-oxides were efficient chiral ligands for the enantio selective conjugate addition of thiols catalyzed by cadmium complexes and Michael addition of beta-keto esters catalyzed by scandium complexes.