Optically Active Phosphines. Facile Preparation of the Optically Active n-Propylmethylbenzyl- and Methylphenylbenzylphosphine Oxides as Precursors to the Corresponding Tertiary Phosphines

Article abstract of DOI:10.1021/ja00352a035

The optically active phosphine oxides MePhP(O)CH2Ph (6) and n-PrMeP(O)CH2Ph (9) are readily prepared by a new route from the easily available, essentially optically pure, O-isopropyl S-alkyl methylphosphonothioates 4 and 7.Two successive Grignard reactions give 6 in 52-55percent and 9 in 18-24percent overall chemical yields.Reductions of 6 and 9 with PhSiH3 afford the corresponding optically active phosphines MePhCH2Ph (1) and n-PrMePCH2Ph (2) of optical purities (45-70percent and 53-57percent, respectively) which are quite suitable for studies of the stereochemistries of reactions occurring at phosphorus.The relative ease of the procedure and the fact that both enantiomers are equally readily available especially recommend this route for the preperation of 1.Moreover, no other experimentally detailed, published method for the preparation of an optically active trialkylphosphine such as 2 in reasonably high optical purity is available.The route to phosphine 1 depends on the use of potentially tridentate ligand (SCH2CH2OCH2CH2OCH2CH3) on phosphorus which activates 4 toward reaction with PhMgBr and also allows CH3CH2OCH2CH2OCH2CH2 to be selectively displaced.Quite surprisingly, this displacement occurs with inversion of configuration at phosphorus by contrast to the retentive stereochemistry normally observed on reaction of O-alkyl S-alkyl methylphosphonothioates with Grignards.Evidence is also presented for the potential generality of this method for the preparation of optically active dialkylphenyl- and trialkylphosphines.