Cyclic phosphonium salts synthesis

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). 

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. 

TABLE 25. Synthesis of cyclic compounds from vinylic phosphonium salts and carbonyl-containing nucleophiles... 

The reactivity and use in organic synthesis of l,3,2,>l5-dioxaphospholanes has been presented230. Further details on various topics can be found in the following reviews Gloede (1988)344 Markovskii et a/.342, work prior to 1987 on linear equilibria between phosphoranes and phosphonium salts and Polezhaeva and Cherkasov340, results obtained prior to 1982 with cyclic derivatives. 

Redox systems involving R2P and R2PX substituted benzenes and biphenyls have been studied by cyclic voltammetry and ESR spectrometry. The successive addition of one electron has been postulated25. The formation of a free radical on one-electron reduction has been confirmed by the observation of an ESR signal showing splittings from 31P. The synthesis of phosphonium salts in nearly quantitative yields from phosphane has also been established. 

Through steric hindrance and conjugative effects, these ionic phosphonium salts are very stable to hydrolysis. This, coupled with the lipophilic nature of the cation, results in a very soft, loosely bound ion pair, making materials of this type suitable for use as catalysts in anionic polymerization [8 - 13]. Phosphazene bases have been found to be suitable catalysts for the anionic polymerization of cyclic siloxanes, with very fast polymerization rates observed. In many cases, both thermodynamic and kinetic equilibrium can be achieved in minutes, several orders of magnitude faster than that seen with traditional catalysts used in cyclosiloxane polymerization. Exploiting catalysts of this type on an industrial scale for siloxane polymerization processes has been prevented because of the cost and availability of the pho hazene bases. This p r describes a facile route to materials of this type and their applicability to siloxane synthesis [14]. 

Carbodiphosphoranes (bistriorgano)phosphoranylideneniethanes, hexaorganocarbodiphosphoranes) may be generated from suitable phosphonium salt precursors by dehydrohalogenation or dehalogena-tion. Since the first synthesis of hexaphenylcarbodiphosphorane, a series of symmetrical, unsymmetri-cal, mixed alkyl/phenyl, cyclic and difunctional carbodiphosphoranes have been prepared. Compounds synthesized until 1984 have been listed. 

The key step in a new synthesis of cyclic ketones by House and Babad is cyclization with potassium t-butoxide in f-butanol of a phosphonium salt of type (8) to a cyclophosphorane (9). The reaction is considered to be related to a Dieckmann condensation. When n = 2-4 yields are 52-84%. 

At first sight, the synthesis of Z-38 by the Wittig reaction seems too risky. The phosphonium salt 39 has a more acidic proton (C02H) than the one we want to remove to make the ylid, and the aldehyde 40 not only also has an acidic proton (OH), but it prefers to remain as the cyclic hemia-cetal 41 so that there is no carbonyl group at all. 

The Julia olefin synthesis is rather like the Wittig reaction with a sulfone instead of a phosphonium salt but with one other important difference the elimination step is stereoselective and both dia-stereoisomers of the intermediate can give the same isomer of the alkene. Treatment of the sulfone 147 with a strong base gives the anion 148 (or a metal derivative) that combines with an aldehyde to give a diastereomeric mixture of adducts 149. Elimination by various methods gives, in open chain compounds, mostly -150 but, in cyclic compounds, mostly the Z-alkene.29... 

Sardnaxanthin (230), a Cso-carotenoid containing two cyclic y end groups with an additional Cs-unit was first prepared as a racemate [100], For the synthesis of the optically active compound the C20 + C10 + C20 = C50 strategy was chosen. For the synthesis of the C2o-phosphonium salt 231, the key building block of the synthesis, camphoric acid (144) was selected as starting material [101] (Scheme 51). 

By Miscellaneous Routes.—The synthesis of cyclic phosphine oxides from a,co-dibromides and tetraphenyldiphosphine has been described (Scheme 5). The intermediate phosphonium salts are converted into the... 

The catalytic activity of phosphonium salts in the synthesis of cyclic carbonates (e.g., propylene carbonate from propylene oxide and carbon dioxide) was found to be greatly enhanced by their immobilization onto silica that itself had no catalytic effect. The discipline of ionic liquids keeps developing dynamically. Phosphonium ionic liquids have received much less attention than ammonium salts in the past, but the situation is changing. Triphenylalkyl-, tetraalkyl- and functionalized-phospho-nium tosylates (Fig. 11) that exhibit melting points mostly above 100 °C were introduced and characterized. 

Bertrand et al. have introduced a stable acyclic a-aminophosphonium salt. Only basic phosphines, such as tris(dimethylamino)phosphine, allow for the synthesis of stable aminophosphonium salts. The species mentioned gave upon deprotonation with butyllithium the corresponding C-amino phosphorus ylide (Scheme 100/1). In contrast, two cyclic a-amino phosphonium salts were found to be stable despite the presence of weakly basic triarylphosphine moieties. The key intermediates were dicationic aldiminium salts that on treatment with sodium tert-butylate afforded the cyclic a-aminophosphonium salts under discussion (Scheme 100/2 and 3). In Scheme 100/2, the carbenoid intermediate involved is also shown. On treatment with LiHMDS or BuLi, the stable phosphonium salts were converted to the corresponding P-ylides (Scheme 100/2 and 3). In the second example, the cyclic ylide was transformed to a phosphinoarylenamine derivative via a carbenoid intermediate (Scheme 100/3). ... 

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