P V Secondary Diazaphospholidines

Natural L-aspartic acid can be transformed in several steps into triamine 19, which reacts smoothly with phosphorus trichloride to yield diastereomerically pure 20. This triaminophosphine is stable in neutral or mildly acidic aqueous conditions but, interestingly, it suffers a SN2-type hydrolysis upon purification by sihca gel column chromatography with wet ethyl acetate, yielding the desired secondary diaminophosphine oxide in 60% of overall yield from 19. The absolute configuration of the phosphorus atom (i ) could be unequivocally determined by crystallographic analysis.  

The synthetic route has been extended for the preparation of several analogues, listed in Table 3.8. 

DIAPHOX ligands are in general air- and moisture-stable since 21 is only formed in minute amounts. P NMR in CDCI3 shows, however, that 

0-Z)M(trimethylsilyl)acetamide (BSA, a strong silylating agent) shifts this equilibrium towards the P(III) tautomer 22 These type of compounds are excellent ligands for Pd and Ir centres and have been used in challenging enantioselective allylic substitution reactions.  

---