Bis(Mu-Oxo)-Dititanium(Iv)-Chiral Binaphthyldisulfonate Complexes For Highly Enantioselective Intramolecular Hydroalkoxylation Of Nonactivated Alkenes

A series of chiral 1,1'-binaphthyl-2,2'-disulfonic acids was designed, synthesized, and applied in a highly enantioselective Ti-catalyzed intramolecular hydroalkoxylation of nonactivated alkenes. The catalyst is probably a complex between two chiral binaphthyldisulfonate ligands and a bis(mu-oxo)-dititanium(IV) core structure. The sulfonamide groups of the ligands and water are necessary for the catalysis, as they may stabilize the catalytically active complex through hydrogen bonding. Various 2-methylcoumarans were obtained in up to greater than 99% yields and up to 97% enantiomeric excess under mild conditions.