Phosphine oxide alkylation, decarboxylation

Pietrusiewicz and coworkers have developed methods for the synthesis of homochiral phosphine oxides. They play an important role in asymmetric synthesis as chiral ligands for catalysts. The readily prepared (5/ )-ethyl[(menthoxycarbonyl)methyl]phenylphosphine oxide (13) can be deprotonated, alkylated and then decarboxylated to afford the homochiral (/7j,)-alkylethylphenylphosphine oxides (Scheme 12). Pietrusiewicz and Zablocka have also described the synthesis of chirally pure a, 3-unsaturated phosphine oxides. ... 

The alkylation of 38 with menthyl chloroacetate produced a diastereomeric mixture of phosphine oxides 39 and 39. These mixtures could be separated into individual diastereomers in 10 1% yields by fractional recrystallisation in hexane. Each epimer was subjected to hydrolysis to the corresponding acid and subsequent decarboxylation to afford the optically pure methylphosphine oxides 40. Both transformations occurred in very high, often quantitative, yield. This method was an advance because, as seen before, the introduction of encumbered groups by the original Mislow method is cumbersome. Moreover, methylphosphine oxides 40 are key intermediates to prepare diphosphines of the DiPAMP family (see Scheme 2.11). The chemistry of Scheme 2.14 has been used much more recently by Hii and co-workers to prepare series of ami-nohydroxy phosphine oxide ligands by coupling the acid derived from 39 (R = t-Bu) with (-)-norephedrine and (S)-valinol. 

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