Cyclic phosphoranes stability

A number of preparations of mixed halogenophosphoranes from tervalent phosphorus-fluorine compounds have been reported. For example, acyclic and cyclic fluorine compounds have been converted to phosphoranes, such as (36) and (37), by treatment with chlorine. Similar reactions leading to AA-dialkylaminodichlorodifluorophosphoranes (38) have been described and the stability of (38) to exchange processes commented upon. iVA-Dialkylaminotetraiodophosphoranes (39) have been prepared from AA-dialkylaminodichlorophosphines and lithium iodide, although no detailed physical evidence for the structure of these unusual compounds has yet been reported. The preparation of bis-(A-alkylamino)difluorophosphoranes (4) has been described above (see Section lA). 

The deoxygenation of aryl 2-nitrophenyl sulphides with tervalent phosphorus compounds is analogous to that of the corresponding ethers except that in many cases the anticipated phosphoranes, e.g. (87), are thermally unstable.58 The extra stability of spirophosphoranes allows them to be isolated, e.g. (13), if cyclic phos-phonites are used in deoxygenation.8... 

Formate esters behave as typical carbonyl compounds in reactions with a number of ylides, eliminating phosphine oxide and forming vinyl ethers, e.g. (33).35 Stabilized phosphoranes are able to condense with the carbonyl group of cyclic thioanhydrides (34).38 Quinoline derivatives, e.g. (35), are obtained from the condensation of dicar-boalkoxy-ylides with isocyanates.37 Benzoyl isothiocyanates and keto-phosphoranes give quantitative yields of (36), which are unreactive in Wittig reactions but can be readily oxidized by selenous acid.38 The products obtained from reactions (Scheme 9) with the triazolinedione (37) depend upon the stability of the ylide used.39... 

Attack on Oxygen. Cyclic phosphites or phosphonites (38) react with a-keto-acids to give cyclic acyloxyphosphoranes (39), which have previously been implicated as intermediates in the hydrolysis of phosphoenolpyruvate initial attack on keto-oxygen has been suggested, as shown. Acyclic phosphites gave the Michaelis-Arbusov product (40), presumably because they lack the five-membered ring to stabilize the phosphorane (39). 

A Phosphorus System.—Photoelectron spectroscopy of the bicyclic phosphorane (742) reveals that it exists in the open form (743) in the vapour phase the related radical (744), on the other hand, is stabilized with respect to the mono-cyclic valence isomer... 

---