Stereoselective Synthesis of All Possible Phosferrox Ligand Diastereoisomers Displaying Three Elements of Chirality: Stereochemical Optimization for Asymmetric Catalysis

All four possible diastereoisomers of phosphinofer- rocenyloxazoline (Phosferrox type) ligands containing three elements of chirality were synthesized as single enantiomers. The S-c configured oxazoline moiety (R = Me, i-Pr) was used to control the generation of planar chirality by lithiation, with the alternative diastereoisomer formed by use of a deuterium blocking group. In each case subsequent addition of PhPCl2 followed by o-TolMgBr resulted in a single P-stereogenic diastereoisomer (S-c,S-p,S-phos and S-c,S-p,R-phos,R- respectively). The alternative diastereoisomers were formed selectively by addition of o-TolPCl(2) followed by PhMgBr ((S-c,S-p,R-phos and S-c,S-p,S-phos,S- respectively). Preliminary application of these four ligand diastereoisomers, together with (S-c,S-p) and (S-c,R-p) Phosferrox PPh2, to palladium catalyzed allylic alkylation of trans-1,3-diphenylallyl acetate revealed a stepwise increase/decrease in ee, with the configuration of the matched/matched diastereoisomer as S-c,S-p,S-phos (97% ee).