Phosphoranes, cleavage

Phosphorane 343 is interesting from another point of view as it represents a formal trapping product of the species 345 resulting from cleavage of one C—CO bond in cyclopropenone claimed earlier (p. 56). 

When an aminophosphonium species is used with an aryl lithium reagent, cleavage of the amino functionality from phosphorus is observed, producing the parent phosphine.10 This reaction has been used to prepare stable phosphoranes from aminophosphonium species using dilithium reagents (Figure 5.6).10 It should be noted that the... 

The importance of equilibria in the chemistry of pentacoordinated phosphorus arises from the possibility of passing from a given structure to another, even if the latter has a totally different molecular geometry and distribution of electrons, by a mere shift of hybridization. This has important consequences on the chemical properties of phosphoranes and on the possibilities of interconversion of isomers by bond rupture and recombination processes akin to regular true stereomutations, i.e. without bond cleavage. 

The phosphorane 70 can also undergo stereomutation without bond cleavage by the Berry process (Berry pseudorotation with the PH bond as pivot) or by the Ramirez process... 

This example illustrates the importance of the tautomeric P(III) P(V) equilibrium yielding the same result as a stereomutation without bond cleavage. In view of their importance in phosphorane chemistry, we shall therefore study the following equilibria P(III)—P(V), P(IV) P(V), P(V)—P(V) and (Vl) P(V)l... 

The phosphites 3 and 4 are oxidized by chlorine and bromine to furnish stable covalent phosphoranes. No Arbuzov reaction was observed. The trichlorophosphorane 5 can be reacted with again to form a spirophosphorane 7 which is hydrolyzed without ring cleavage to give an extremely stable hydroxyphosphorane or a phosphoraneoxide anion . . ... 

On the basis of these findings a new level had been reached, from which a very efficient pursuit of the stereochemical and other questions pertinent to those classes of compounds became possible. In this respect, the key reaction consisted in the protolytic cleavage of phosphate ion 57 to give 2-biphenylyl-bis-2,2 -biphenylylene-phosphorane 25 d. On the assumption that 57 very probably had an octahedral structure, it was then hoped that the fate of the optical activity on protolytic cleavage of optically active forms of this ion would also enable some conclusions on the stereochemistry of the resulting phosphorane 25 d to be made. The resolution of 57 could readily be achieved with methylbrucinium iodide and finally yielded the optically active potassium salts K-57 with = 1930 and [M] = 10164° 66). 

As can be seen from the following scheme, cleavage of the optically active ate-complex 57 with protons should lead to a chiral, optically active phosphorane, B, provided this has a rigid trigonal-bipyramidal configuration. 

In electrophilic reactions bis-2,2 -biphenylylene-organylarsoranes react like the corresponding phosphoranes exclusively under cleavage of one arsafluorene system i2i,i23) tjjUS reflecting the presence of considerable ring strain at least for the pentavalent state. 

The double bond is transformed into an aldehyde first. Bishydroxylation and oxidative cleavage creates the aldehyde. Aldehydes can be transformed into alkynes by a special phosphorane. 

The [(aryldiazenyl)methylene](tripheny])phosphoranes 1 afford in good yields the quina-zolin-4(3//)-one derivatives 2 via a facile thermally promoted rearrangement, withN=N bond cleavage and elimination of triphenylphosphane. ... 

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