1.3.2- Oxazaphospholidine ring

Without additional reagents 1,3-Dipolar cycloaddition with nitrones 1,2,5-Oxazaphospholidine ring... 

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). 

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... 

A serial of related oxazaphospholidine oxides 27-31 were described, revealing that the presence of the second fused ring adjacent to the oxazaphospholidine was essential to obtain high catalytic activity. 

Phosphorus-containing Ring Systems. - A range of new chiral oxazaphospholidine oxides 266 and 267 have been synthesised and used as catalysts in asymmetric reductions of ketones with diborane. Mannich-type cyclisation reactions of 5-amino-3-benzylthio-4-cyano(ethoxycarbonyl)pyrazoles with dichlorophenylphosphine and aromatic aldehydes in the presence of cation exchange resin have been used to prepare a number of 6-oxo-6-phospha-4,5,6-trihydroimidazolo[l,2-b]pyrazoles, e.g. 268. Some of these compounds have herbicidal activity and this report is typical of a number of similar ones in the Chinese literature. A number of metallocycles, e.g. 269, have been reported as products from reactions of transient zirconocene-benzyne intermediates with phosphaimines followed by sulfuration or selenation. ... 

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... 

Amongst five-membered ring compounds examined by diffraction techniques are a series of six 1,3,2-oxazaphospholidines with 2-phenoxy-2-oxo, 2-phenyl-2-oxo-, or... 

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

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. 

It has been shown that the nitrogen atom from the TPG displaces iodine, forming an oxazaphospholidine oxide ring (Scheme 16). ... 

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