Novel MOP-type H8-binaphthyl monodentate phosphite ligands and their applications in transition metal-catalyzed asymmetric 1,4-conjugate additions and hydroformylations

Abstract

A new series of monodentate phosphites based on the rigid, axially chiral monoesterified H8-BINOL, which are easy to prepare from the readily accessible phosphorylating reagents (Sa)- or (Ra)-1,1′-binaphthyl-2,2′-diylchlorophosphite and (Sa)- or (Ra)-1,1′-H8-binaphthyl-2,2′-diylchlorophosphite, have been synthesized. All ligands were purified on a silica gel column under a nitrogen atmosphere with moderate yields, and were white solids and air-stable at room temperature. These ligands afforded good to excellent enantioselectivities in the Cu-catalyzed 1,4-conjugate addition of 2-cyclohexenone with nucleophiles Et2Zn (96% ee) and with Ph2Zn (65% ee), 2-cyclopentenone with Et2Zn (95% ee), 2-cycloheptenone with Et2Zn (76% ee), and 5,6-dihydro-2H-pyran-2-one with Et2Zn (90% ee). In the Rh-catalyzed asymmetric hydroformylation of styrene, these ligands showed a chemoselectivity of >99% in aldehydes, and a satisfactory branched over linear ratio (96/4). Moreover, the sense of the enantiodiscrimination of the products was mainly determined by the configuration of the BINOL-based or H8-BINOL-based phosphocycle.