P-chirogenic phosphines. MOP/diPAMP hybrids, their oxide crystal structures, reduction studies and alternative syntheses

Abstract

The novel P-chirogenic anisylphenylMOP derivatives ( R, R) and ( R, S)-2-(anisylphenylphosphino)-2′-methoxy-1,1′-binaphthyl ( 10a and b) have been synthesized and their corresponding oxides characterised by X-ray crystallography. The results of a parallel screening regimen with various reducing agents highlight the sensitivity of the tertiary phosphine oxides to epimerisation and, interestingly, reveal that the P O, O–CH 3 and P–C 6H 5 bonds can all be cleaved selectively depending on the reducing agents employed. An alternative synthesis was provided by direct coupling of the secondary phosphine with ( R)-methoxytriflate 4, which led to the isolation of the optically pure P-chirogenic phosphines via their borane adducts. A brief study of the coordination chemistry of 10a with different rhodium precursors, relevant to the catalytic asymmetric addition of boronic acids to aldehydes is also reported.