Phosphonium salts sulphurated

The bis-phosphonium salt (156) has been condensed with various dialdehydes to give potentially aromatic and anti-aromatic systems, while fully unsaturated 11- (158), 12- (159), and 13-membered (160) sulphur heterocycles have been prepared as shown. These showed no appreciable ring current and are presumably non-planar. 

The sulphur atom of alkyl(thioalkyl)phosphonium salts forms a new onium centre on triethyloxonium tetrafluoroborate alkylation in nitromethane848,849 (thiocetals see above). Phosphonium ketene acetals are potential alkylating agents for phosphorus dithioic acid anions in non-aqueous, aprotic and aqueous media and in phase-transfer catalysis conditions296 (reaction 263). It is suggested that onium ketene acetals react by nucleophilic attack on the methyl group of the acetal. 

A mixture of isomers of 7-chloro-7-methoxynorbomene gives an isomeric mixture of phosphonium salts (66) and (67) on reaction with triphenyl phosphine in liquid sulphur dioxide at — 60 °C. Both salts can be converted into the non-classical dication (68). The salt (67) isomerizes to (66) at temperatures above —14 °C. ... 

Acyloxy-phosphonium salts (16.4) are cyclized to a 2-bcnzopyran on heating in toluene with t-butyl methoxide. The acyl group may be provided by a reagent rather than have been attached to the oxygen or sulphur atom in this example, the thiophenol is treated with the acid chloride-TEA in boiling toluene. 

A series of new phosphazo-phosphonium salts [(R3P=N) PF4 ] PF6, where R = Me or Ph and n = 1—3, has been characterized as the product from reactions between the PFg-ether adduct and silyliminophosphoranes R3P=NSiMc3/ while the latter compounds, with S4N4, yield phosphazo-cyclotrithiazenes (50) by elimination of sulphur and (Me3Si)2N2S. ... 

Indoles and Carbazoles. - Formation. 2-Arylindoles (132) are formed by intramolecular Wittig reaction of the phosphonium salts (131). The hydroxamic acids PhN(OH)COCH2COR (R = alkyl or aryl) cyclize in boiling toluene to mixtures of indoles (133) and 3-isoxazolones (134). Irradiation of a solution of o-iodoaniline and the potassium enolate of acetone affords 2-methylindole. The enamino-ketone (135) cyclizes photochemically to 1,2-dimethylindole (136) with elimination of acetaldehyde/ The styrene derivative (137), obtained by the action of Meerwein s acetal, Me2NCH(OMe)2, on o-nitrotoluene, yields 1-hydroxyindole on treatment with zinc/ Azidobenzocyclobutanes (138 R = Me, Ph, or CH2Ph) are converted into indoles (133) by the action of concentrated sulphuric acid/ ... 

The units 49 and 50 used in the synthesis of vitamin A are also used in many ways in carotenoid syntheses and are produced industrially in large scale. p-Ionone (17) can be converted into vinyl-p-ionol (51) by ethynylation to 52 and partial hydrogenation [42]. This conversion is also achieved in one step by 1,2-addition of vinylmagnesium chloride 55[43]. The two routes are, in principle, equivalent, and which one is used in practice is decided by conditions on site. In this example, the main considerations are the availability of acetylene (4) and vinyl chloride, operating experience, and permits for handling these materials. The Ci5-phosphonium salt 49 is formed directly from 51 by the action of triphenylphosphine and acid [44,45]. A step involving labile P-ionylidene-ethyl halide is thus avoided. Crystalline (lE,9E)-49 is obtained in excellent yield by reaction of 51 with triphenylphosphine and sulphuric acid in isopropanol/heptane [46]. 

Crystalline 59 which is primarily in the (all- )-form is obtained in a similar manner to the preparation of the Ci5-phosphonium salt 49 described above, by reacting vitamin A acetate (26) with triphenylphosphine (54) and sulphuric acid in isopropanol/heptane [62]. Aqueous solutions of 59 are obtained when vitamin A is reacted with triphenylphosphine (54) and sulphuric acid in methanol, the solution of 59 is washed with heptane to remove lipophilic byproducts and the solvent is removed by steam injection in a stripping column [63]. The process is especially suitable for utilizing mother liquors from the crystallization of vitamin A acetate (26). 

The unique chemistry exhibited by vinyl phosphonium salts and sulphur ylides is married in a versatile synthesis of disubstituted cyclopropanes (Scheme 1), and... 

Fusion of phenyl (and other aryl) tertiary oxides with NaOH at 200-300°C gives sodium diphenylphosphinate directly (6.124) while with nitric acid, the phosphoryl group acts as a meta director, and with sulphuric acid a phosphonium salt can be formed (6.123). 

Fluorophosphoranes can be obtained from phosphonous and phosphinous halides by reactions with arsenic or antimony obtained with KHF2 (6.518). Some phosphinous halides react with sulphur compounds to give phosphinothioites (9.420), with phenyl azide to give monophosphazenes (7.447), and with ylids fluorides (6.504, 6.505). Hydrofluorophosphoranes produces phosphonium salts (6.377). Phosphonous and phosphinous halides can be condensed to form polyphosphines or cyclic derivatives (6.660, 6.666,6.680,6.684), or reacted to give P-P linkages (6.737). 

Simple optically active phosphines can be converted back into phosphonium salts without any change of configuration if benzyl or alkyl halides are used (reversal of Equation 13.57). Oxidation to phosphine oxides with hydrogen peroxide or sulphurisation to phosphine sulphides with elemental sulphur also proceeds with retention of configuration. On the other hand, racemisation or complete inversion occurs if oxidation is carried out with diethyl peroxide. Halogenation to a phosphonium compound followed by hydrolysis results in inversion (13.63). 

Butyllithium is an unsuitable base on account of its sensitivity to air and moisture. In the process the phosphonium salt precursor (formed from the alcohol, Ph3P and hydrogen halide), together with aldehyde in methanol, are treated with methanolic sodium methoxide at — 30 C. After reaction the solution is neutralized with dilute sulphuric acid, the Vitamin A ester extracted into a hydrocarbon solvent and isolated after removal of solvent by distillation. 

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