Phosphonium salts cyclic

Quite a number of cyclic phosphonium salts have been prepared over the years. We have not generally included compounds here which contain fewer than three potential binding sites in a ring unless they are mentioned as by-products in another reaction. Horner, Kunz and Walach have utilized the well-known alkylation approach to prepare cyclic phosphonium salts containing four phosphorus atoms. The formation of the cyclic tetraphosphonium salts is shown below in Eq. (6.14). 

The cyclic phosphonium salts 140,141,143,145, and 146 so obtained are evidence for the mechanism of the oxaphospholic cyclization and especially for the main role of the tertiary carbocation formation during the process. The additional data which support this assumption, come from the investigation of the same reaction, but with different substrate, i.e., dimethyl(l,2-hexadienyl)phosphine oxide 147. In this case, the reaction mechanism involved formation of secondary carbocation that gives oxaphosphole product 148 only in 10% yield (Scheme 60) [124],... 

On reacting the same substrates with phenylsulphenyl- and with phenylselenenyl bromides, relatively stable cyclic phosphonium salts 74 were obtained (Scheme 29) [82],... 

Preparation.—The hydroxyalkylphosphines (106) (obtained by the cleavage of THF or tetrahydropyran with lithium diorganophosphides) are converted in good yield into the cyclic phosphonium salts (107), (108) on treatment with hydrogen bromide followed by a weak base.108... 

Most of the pKa values for the phosphonium salts have been determined by potentio-metric measurements in the case of / -ketophosphonium salts562 (Table 13). The acidity of these phosphonium salts depends not only on the R and R groups of the carbonyl chain, but also on the other substituents linked to the phosphorus562 564. Particularly for the cyclic phosphonium salts, the pKa value can vary significantly depending on the different steric and electronic (even transannular) effects on the phosphorus atom564 ... 

Preparation, properties and reactions of phosphonium salts TABLE 19. Stereochemistry of the alkaline hydrolysis of cyclic phosphoniums salts... 

Further examples in which pentacoordinate phosphorus intermediates are implicated are the reactions of phosphonium salts. The cyclic phosphonium salt (161) shows a rate enhancement of 1300 1 in alkaline hydrolysis relative to either its six-membered or acyclic analogues (65ACS931). Ring strain relief in going from (163) to (164) seems to account for the higher rate of formation of the favoured intermediate (163 see Scheme 19). 

We have simulated the steric course of the alkaline hydrolysis of chiral five- (12) and six- (13) membered cyclic phosphonium salts, whose reaction kinetics and product stereochemistries had been studied previously by Marsi and coworkers (14,15). For this purpose, we determined the absolute configuration of the phospholan-ium iodide (12), and the x-ray structures of the related phos-thorinanium salts, 4 and (13). 

Some Cyclic Phosphonium Salts and Their Relation to the Stereochemical Course of Base Hydrolysis. 

A cyclic phosphonium salt fJ) was obtained, in addition to other products, when red phosphorus was treated with 1,4-diiodobutane at 210 °C for 3 h in the presence of catalytic amounts of iodine Alkylation of elemental phosphorus with hydrocarbon halides are summarized in Table 1. 

The reaction between triarylmethyl perchlorates and triarylphosphines gives the triarylmethyl salts (117) in good yield. The oxoalkylphosphonium salts (118) have been prepared from the reaction of methylenetriphenylphosphorane with esters. The cyclic phosphonium salts (119) arise from the cycloaddition of allyldiphenyl-phosphine to nitrilimines. ... 

The reaction between 1,8-bis(bromomethyl)naphthalene and Ph2PSiMe2 affords a cyclic phosphonium salt (1), which can be rearranged with Me2P=CH2 to give the cyclic ylide (2). 

Ring enlargement via hydrolysis of cyclic phosphonium salts obtained by alkylation (acylation) of cyclic phosphines. 

The corresponding phosphenium ion reacts quite differently. With dimethylbutadiene, a spiro-cyclic phosphonium salt is the only product <83JA7443,83JA7444,86IC740). 

Cyclic phosphonium salts (66) have been prepared by the reaction of substituted vinylphosphines with nitrilimines. Cyclization of the intermediate betaine with triethylammonium chloride is prevented by the presence of strong electron-accepting groups on the a carbon, in which case stable azo-ylides (67) are isolated. 

A number of cycloaddition reactions involving allene derivatives as dienophiles have been recorded. Allene itself reacts only with electron-deficient dienes but allene carboxylic acid or esters, in which a double bond is activated by conjugation with the carboxylic group, react readily with cyclopentadiene to give 1 1 adducts in excellent yield. For example, the allene 12 gave, with very high yield and selectivity, the cycloadduct 13, used in a synthesis of (-)-P-santalene (3.19). An allene equivalent is vinyl triphenylphosphonium bromide, which is reported to react with a number of dienes to form cyclic phosphonium salts. These can be converted into methylene compounds by the usual Wittig reaction procedure (3.20). 

Methylphosphonous dichloride and butadiene react to give a cyclic phosphonium salt (6.170) which on subsequent hydrolysis produces an equimolecular mixture of the two isomers (6.886). If either pure isomer is heated at 175°C with some NaOMe, an approximate equimolecular mixture of the 2- and 3-phospholene is obtained. By suitable choice of conditions, the McCormack method can be made to yield either phospholene isomer. In some cases the use of PCI3 favours one isomer while PBrj favours the other. Phospholenes can be formed from oxophosphines by cycloaddition... 

For references see Williams, R. V. Lin, X. New ketene equivalents for the Diels-Alder reaction. Vinyl sulfoxide cycloaddition. /. Chem. Soc., Chem. Commun. 1989, 1872-1873. Ruden, R. Bonjouklian, R. Cycloaddition of vinyl triphenyl-phosphonium bromide. New synthesis of cyclic phosphonium salts. Tetmhedron Lett. 1974, 15, 2095-2098. Ranganathan, S. Ranganathan, D. Mehrotra, A. K. Nitroethylene as a versatile ketene equivalent. Novel one-step preparation of prostaglandin intermediates by reduction and abnormal Nef reaction. J. Am. Chem. Soc. 1974, 96, 5261-5262. Kozikowski, A. P. Floyd, W. S. Kuniak, M. P. 1,3-Diethoxycarbonylallene an active dienophile and ethoxycar-bonylketene equivalent in the synthesis of antibiotic C-nucleosides. J. Chem. Soc., Chem. Commun. 1977, 582-583. 

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