1.3.2- Oxazaphospholidines ring opening

An X ray examination of the product from the interaction of (2B,4fi,5S)-(-)-3,4-dimethyl-2-phenyl-1,3,2-oxazaphospholidine 2-oxide with an aryl Grignard reagent has demonstrated that ring opening occurs with retention of configuration at phosphorus in accord with Inch s work, but at variance with that of Koizumi, and also in stereochemical opposition to that displayed by acyclic analogues (Mislow). Acid catalyzed alcoholysis of the acyclic phosphinic amide... 

TABLE 3. Ring opening in 1,3,2-oxazaphospholidine 2-sulphides by Grignard reagents... 

Reactions between the 1,3,2-oxazaphospholidines 613 (X = O) and alkoxide ions are even more remarkable in that ring opening occurs with preferential P—N rather than P—O bond cleavage, and with inversion of configuration at phosphorus, cf. 613 618 . The... 

Scheme 27 Stereodivergent ring-opening of 2-phenyl oxazaphospholidines 88...

The opening of oxazaphospholidine rings (/ p)-122 with tert-butyllithium occurred diastereoselectively with retention of absolute configuration on the phosphorus atom, affording the borane complex of aminophosphine (Rp)-124 [67, 68]. The reaction possibly proceeds via formation of chiral o X -phosphenium cation 126, which was obtained from (Sc)-chlorophosphine 125 and then isolated as borane complex 127 (Scheme 38). 

Leon T, Riera A, Verdaguer X (2011) Stereoselective synthesis of F-stereogenic aminophosphines ring opening of bulky oxazaphospholidines. J Am Chem Soc 133 5740-5743... 

Scheme 4.50 Ring opening and acidolysis of unprotected oxazaphospholidine 116.

Chloride is a better leaving group than alkoxide or aroxide, whereas the latter outpaces dialkylamides. Phosphorus-bound heterosubstituents, if cleverly selected, can be displaced stepwise (Scheme 1-Al). Thus, adding an alkyllithium in three consecutive steps to 2-chloro-3-methyl-l,3,2-oxazaphospholidine (51), first the halogen is substituted selectively, next the five-membered ring (of 52) is opened by rupture of the P-0 bond, and eventually the nitrogen-attached side chain (of 53) is substituted to afford the final phosphine. 

---