Phosphinoselenoic acids

The reaction of carbodiimides with phosphonothioic and phosphinothioic acid as well as phosphonoselenoic and phosphinoselenoic acids " proceed in a similar manner. 

This method was also used for the preparation of P-chiral phosphinoselenoic amides (Rp,5)-61 and (Sp,S)-62 (Scheme 19). Enantiomerically pure amides 61,62 were synthesized by reaction of racemic phosphinoselenoic chlorides rac-60 with opticaUy-active lithium amides. Two diastereomers of (Rp,S)-61 and (Sp,S)-62 were formed in a nearly equal ratio in high yields, and the two diastereomers were successfully separated by column chromatography on silica gel. The absolute configuration of phosphinoselenoic amide (/ p,S )-61 was determined by X-ray analysis. Using this reaction, enantiomerically pure salts of phosphinoselenoic acid 63 and P-chiral phosphinoselenoic chlorides ( )-(5)-60 were prepared (Scheme 20) [45, 46]. 

The deselenonation of phosphinoselenoic acids by dimethyl sulfoxide (DMSO) (39) proceeds exothermically, whereas the corresponding reaction with phosphinothioic acids requires heating at 100°. The reactivity of the P=X bond is proportional to the softness disparity of the two adjoining atoms. 

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