Enantioselective Synthesis of Chiral Organophosphorous Compounds by Cationic Rhodium(I)/Modified-BINAP-catalyzed 2 + 2 + 2 Cycloadditions

摘要

Cationic rhodium(I)/modified-BINAP [2,2'-bis(diphenyl-phosphino)-1,1'-binaphthyl] complex-catalyzed enantioselective [2 + 2 + 2] cycloadditions have been demonstrated as a powerful tool for the synthesis of chiral aromatic compounds. Recently, we have reported the highly enantioselective synthesis of axially chiral biarylphosphine oxides through the cationic rhodium(I)/H8-BINAP complex-catalyzed [2 + 2 + 2] cycloaddition between 1,6-diynes and alkynylphosphine oxides bearing a 2-alkoxynaphthyl group at an alkyne terminus. On the other hand, not only axially chiral biarylphosphorus compounds but also P-stereogenic phosphorus compounds have been employed as effective ligands for a wide variety of transition-metal-catalyzed asymmetric reactions. Very recently, Imamoto and co-workers have demonstrated that P-stereogenic phosphine ligands bearing alkynyl groups induced excellent enantioselectivity in various transition-metal-catalyzed asymmetric reactions. We anticipated that if selective mono [2 + 2 + 2] cycloaddition of 1,6-diynes with symmetrical dialkynylphosphine oxides (phosphorus-linked electron-deficient 1,4-diynes) proceeds by using the cationic rhodium(I)/modified-BINAP complex as a catalyst, P-stereogenic alkynylphosphine oxides would be generated through enantioselective desymmetrization.