Halophosphonium salts 66 —

Halophosphonium salt formation, immediately followed by its transformation to enoxyphosphonium, takes place in the reaction of tertiary phosphines with the positive halogen of some secondary a-haloketones. Indeed, the reaction, which can also lead to a 2-oxoalkylphosphonium salt by a classical SN2 reaction (route a), is oriented to the enoxyphosphonium salt (route b) by different factors459-461 (reactions 131) an increasing steric hindrance on the phosphine and/or the carbon linked to the halogen, or an increasing stability of the enolate and an increasing electrophilicity of the halogen. 

Halophosphonium salts are the useful precursors for the preparation of heteropho-sphonium by ligand exchange, although some relatively stable alkoxyphosphonium salts... 

In the formation of halophosphonium salts, the chlorophosphine alkylation occurs easily with diverse alkyl halides40 5fl-c. Generally, the reaction proceeds without any solvent or in CH2C12, with a Lewis acid such as A1C13, especially in the case of PC13 or RPC12 (reaction 143). Finally in heterophosphonium synthesis by the alkylation of... 

The cyclic phosphinate (96) has been isolated from the reaction of dichloro(methyl)phosphine with the ethoxycarbonylimine derived from hexafluoroacetone. Treatment of trichloro(organo)phosphonium-hexafluorophosphate salts with dichloro(diethylamino)phosphine results in the halophosphonium salts (97). Some reactions of dichloro(-)menthylphosphine have been reported.As usual, nucleophilic displacement reactions of halogenophosphines have received attention as routes to new systems of interest as ligands.Of particular interest in this connection is a report of the synthesis of the phosphorus-functionalised calixarenes (98). Only one chlorine atom of dichloro(phenyl)-phosphine is replaced on treatment with an excess of dicyclohexylamine, enabling the stepwise synthesis of the chiral aminophosphines (99), described as air-stable solids. 

Two moles of methylenetriphenylphosphorane are reacted with one mole of a dihalogen compound. In the first step methylenetriphenylphosphorane is C-alkylated yielding an to-halophosphonium salt, which subsequently reacts with a second mole of methylenetriphenylphosphorane forming a transylidation equilibrium with methyltriphenylphosphonium halide and an w-halogenated ylide. This compound undergoes intramolecular C-alkylation, in the course of which the resulting exocyclic phosphonium salt... 

The Wittig reaction makes use of the ylide derived by removal of hydrogen halide from a halophosphonium salt. Thus, as shown in Equation 9.59, treatment of... 

Weigand, J.J., Burford, N., Davidson, R.J., Cameron, S. and Seelheim, R, New synthetic procedures to catena-phosphorus cations Preparation and dissociation of the first cyclo-phosphino-halophosphonium salts, J. Am. Chem. Soc. 131 (49), 17943-17953 (2009). 

In connected work, a polystyrene-supported phosphine oxide vwis converted into synthetically useful polymeric halophosphonium salts by reaction with oxalyl chloride/bromide (Scheme 61). " ... 

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