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 secondary phosphane oxides racemic 1, (S(p))-(-)-4 and (Rp)-(+)-tert-butylphenylphosphane oxide (5) by lithiation with LDA or nBuLi, or sodiation with sodium hydride, in THF, and then by treatment with a series of primary alkyl halides. Doubly P-chiral ditertiary bis(phosphane oxides) are also obtained from these metallated secondary phosphane oxides by treatment with electrophiles based on straight-chain, tartrate-derived, and bishalomethylarene dihalides. In general, the bis-phosphane oxides are obtained in good yields. However, when the α,ω-dihalide bears an embedded heteroatom (O or Si), yields are diminished. The enantiomeric purity of each of the products was assessed through admixture with (R(p))- and (S(p))-tert-butyl(phenyl)phosphanylthioic acids and measurement of the tert-butyl resonances in the ¹H-NMR spectra. In all cases, the act of metallation of the enantiomerically pure secondary phosphane oxide followed by its alkylation is not accompanied by detectable racemization. This method for preparing P-chiral tertiary phosphane oxides is therefore more straightforward than those described previously.