Thiophosphonium Salts

From tertiary phosphine sulphides and alkyl halides, quasi phosphonium compounds are formed (9.411). If trialkyl phosphites are reacted with sulphenyl chlorides in the presence of SbCls, thiophosphonium salts can be isolated (9.489). Reaction (9.490) occurs spontaneously and goes to completion in a few days. 

Spiro cations in which four sulphur atoms are linked directly to the central phosphorus atom, are formed in reactions 

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In the direct synthesis of thiophosphonium salts, the oxidizing agent can be a disulphide using either constant-current electrolysis (c.c.e) conditions or by simple addition with benzoic acid433 (reaction 122). 

The widespread use of achiral or racemic chlorophosphines 27 in synthetic phosphorus chemistry (PClPh2 in particular is an ubiquitous diphenylpho-sphinating agent) contrasts with their rare application in P-stereogenic chemistry. The reason is the lack of methods to produce enantioenriched P-stereogenic chlorophosphines and their marked tendency to racemise. Indeed, the first example of enantiomerically enriched chlorophosphine was reported by Ome-lanczuk in 1992, who prepared (5)-P(/-Bu)PhCl in 49% ee by decomposition of an optically emiched thiophosphonium salt. The same compound has been prepared more recently, albeit in low ee, by kinetic resolution. ... 

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