Phosphorus-containing leaving groups

Besides glycosyl phosphites and phosphates, a variety of other phosphorus containing leaving groups have been designed and proposed. These are summarized in Table 4.11. 

Phosphorus-containing leaving groups with glycosyl-sulfur linkages such as dithiophosphates and phosphorodiamidimidothioates were discussed in Section 4.3.2.3. 

Tricoordinate phosphorus >P-X compounds containing a suitable leaving group are indispensable in the synthesis of biophosphates and their structural analogues. In contrast to phosphoryl >P(0)-X and thiophosphoryl >P(S)-X, compounds they are spectacularly more reactive in nucleophilic displacements at the phosphorus centre. Westheimer has compared reactions of P compounds with nucleophiles to enzymatic reactions regarding their reactivity [1]. The essential feature of P compounds is their free electron pair with all the structural, stereochemical and mechanistic consequences that follow. P compounds have the structure of a trigonal pyra-... 

Malathion and parathion contain a P=S grouping, exemplifying a further carbonyl analogue, in which phosphorus replaces carbon, and sulfur replaces oxygen. Nevertheless, the same type of chemistry occurs, in which the serine hydroxyl of the insect s acetylcholinesterase attacks this P=S electrophile, followed by expulsion of the leaving group, here a thiolate. The esterified enzyme, however, is not hydrolysed back to the original form of the... 

In addition, there may be an equilibrium in ring-opening polymerizations between onium ions and covalent species. This equilibrium has been observed in the polymerizations of cyclic ethers [29], oxazolines [68], and phosphorus-containing monomers [69], The position of the equilibrium and its dynamics depend on the relative nucleophilicities of the monomer and the counteranion, as well as on the nucleofugacity ot the leaving group. 

Phosphoranes are based on five covalent bonds which utilise 3d orbitals and leave no unbonded electrons on the phosphorus atom. Their reactions are those of electrophiles. Two simple derivatives containing organo groups are. 

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