P V Oxazaphospholidines

In the last section several oxazaphospholidine oxides, obtained by oxidation of the P(III) precursor with t-BuOOH, have already been described. There is also one report by Juge and co-workers in which they prepare oxazaphospholidine oxides and sulfides by in situ deboronation/oxidation of oxazaphospholidine boranes. This section illustrates some more derivatives, prepared directly from P(V) species and ephedrine. Chronologically, these types of compounds were studied earlier than the corresponding P(III) counterparts. Nowadays oxazaphospholidine boranes, not oxides, are the most important precursors used to prepare enantiopure phosphorus ligands. However, apart from historic interest, ephedrine-derived oxazaphospholidine oxides, sulfides and selenides occupy an important place in the study of phosphorus stereochemistry and conformational analysis. Only a few examples are described here. 

The yields vary considerably (7-91%) and so do the diastereoselectivities (0-84% de), although they tend to be low. Even worse, it was found that they depend upon the exact conditions of the reaction and on the purification method, although the separation of the epimers is often possible. No crystal structures have been reported and the absolute configuration of the products was determined by thorough NMR analysis and comparison with previously reported data on similar compounds. 

Treatment of 37 with LDA affords rearranged product 38 in a 85% yield, with retention of configuration at the phosphorus atom. More recently Buono and co-workers came to the same conclusion with similar substrates. 

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