Phosphonium betaines

Wong, Y.S., Paik, Fl.N., Chieh, P.C., and Carty, A.J., Two-carbon three-electron ligands. Phosphonium-betaine complexes via nucleophilic attack by phosphites on a o-rc-acetylide di-iron hexacarbonyl derivative, /. Chem. Soc., Chem. Commun., 309, 1975. 

Stereochemical information on the mode of cyclodehydration of unsymmetrical diols to cyclic ethers could obviously have important consequences regarding useful, preparative routes to chiral cyclic ethers of high enantiomeric purity. For example, dioxyphos-phorane promoted cyclodehydration of a chiral diol can, in principle, give the enantiomeric ethers by either of two stereochemi-cally distinct routes. Separate stepwise decomposition of oxy-phosphonium betaines, A and B, although proceeded by a number of equilibria could ultimately afford a nonracemic mixture of cyclic ethers. 

Trialkylphosphines and carbon disulfide give adducts (304) which react with alkynoic acids to form the phosphonium betaines (305). The latter can be converted into 1,3-dithiole-4-carboxylic acids (306) (76BCJ1996). DMAD can also be used in this reaction (79JOC930). 

During the past twelve months a number of new phosphonium betaines and zwitterions has been reported. Reaction of ylides with acylisocyanates or acylisothiocyanates in methanol proceeds via a cyclization yielding pyrimidine substituted triphenylphosphonium salts (5) which can be converted into the corresponding betaines. The crystal structures of triphenylphosphonium-car-boxylate betaines 6 and 7 have been reported. Betaines 6 and 7 were obtained... 

A delicate balance of steric and electronic effects at phosphorus controls the course of decomposition of the phosphonium betaines (151) that may be generated in protic solvents. Electron-withdrawing heteroaryl substituents e.g. 2-furyl and 2-thienyl) promote intramolecular collapse of the betaine to form the normal Wittig products, as also does enclosure of the phosphorus in the ring-strained dibenzophospholium system. Except in such cyclic systems, both electron-donating and bulky groups e.g. o-tolyl and t-butyl) reduce the rate of intramolecular collapse and allow a dehydra-... 

Olefins with electrophilic substituents, but not those with electron-donating substituents, add tertiary phosphines 61 the phosphonium betaines first formed stabilize themselves under some circumstanes by forming their tautomers, the alkylidenephosphoranes. Thus, for example, the ylide (5) is obtained in more... 

In the first step, acid-catalyzed azomethine formation (113 115) takes place. In the second step, the phosphonium salt 115 is deprotonated to give the P-yhde 116, which (in analogy to an aza-WiTTic reaction) undergoes intramolecular nucleophihc addition to the imine function. The resulting phosphonium betaine 117 eliminates PPh3, thus establishing the indole system 114. 

A phosphoniodefluorination reaction of 2,5,6,7,8-pentafluoro-l,4-naphthoquinone was described for the synthesis of 5,6,7,8-tetrafluoro-1,4-naphthoquinone phosphonium betaines which were recognized as potential inhibitors of tumoral cell growth and also as cell-protecting antioxidants (Scheme 2). ... 

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