Synthesis Of Chiral Phosphite Ligands And Their Applications In Asymmetric Catalytic Reactions

Chiral phosphite ligands are attractive for asymmetric catalysis due to their ease of preparation, stability to oxidation of air and modulatory feature of the structure. They show superior catalytic efficiency to chiral phosphine ligands in many asymmetric catalytic reactions, such as asymmetric hydroformylation of olefins. We have prepared six new phosphite ligands derived from L-4-hydroxy-proline and chiral BINOL. The ligand-rhodium complexes were used as the catalysts in the asymmetric hydroformylation of olefins. The influence of the ligand-to-metal ratio, reaction temperature and the pressure of syn-gas on the catalytic activity, regioselectivity and enantioselectivity were also studied. Good catalytic activity and regioselectivity were observed with several phosphite ligands-rhodium complexes, but the enantioselectivities obtained so far were rather low. Based on the rational examination of the relationship of the spatial structure, distribution of the functional groups of catalysts with the catalytic activity, regioselectivity and enantioselectivity, a general rule was suggested for the development of better chiral phosphite ligands. The less effective chiral pockets around the rhodium center may result in the low enantioselectivity obtained with several chiral phosphite ligands. We are developing more effective chiral phosphite ligands along this way. We also studied the application of the complexes of the chiral phosphite ligands with copper salt in the asymmetric conjugate addition of diethylzinc to enones.In addition, the iodine-catalyzed reaction of imine with diethyl phosphite was studied and theα-amino phosphonates were obtained in good yields. The one pot synthesis ofα-amino phosphonates from aldehydes, anilines and phosphates was achieved using iodine as the catalyst. Facile experiment procedure, mild reaction conditions, good yields of products and the low price of iodine make this new method attractive for the synthesis of manyα-amino phosphonates.