Reaction of metallated tert-butyl(phenyl)phosphane oxide with electrophiles as a route to functionalized tertiary phosphane oxides: Alkylation reactions

P-Chiral tertiary phosphane oxides have been prepared from each of the seco ndary phosphane oxides racemic 1, (S-p)-(-)-4 and (R-p)-(+)-tert-butylpheny lphosphane oxide (5) by lithiation with LDA or nBuLi, or sodiation with sod ium hydride, in THF, and then by treatment with a series of primary alkyl h alides. Doubly P-chiral ditertiary bis(phosphane oxides) are also obtained from these metallated secondary phosphane oxides by treatment with electrop hiles based on straight-chain, tartrate-derived, and bishalomethylarene dih alides. In general, the bis-phosphane oxides are obtained in good yields. H owever, when the alpha,omega-dihalide bears an embedded heteroatom (O or Si ), yields are diminished. The enantiomeric purity of each of the products w as assessed through admixture with (R-p)- and (S-p)-tert-butyl(phenyl)phosp hanylthioic acids and measurement of the tert-butyl resonances in the H-1-N MR spectra. In all cases, the act of metallation of the enantiomerically pu re secondary phosphane oxide followed by its alkylation is not accompanied by detectable racemization. This method for preparing P-chiral tertiary pho sphane oxides is therefore more straightforward than those described previo usly.