Phosphonium salts modification

Phosphonium Salt—Urea Precondensate. A combination approach for producing flame-retardant cotton-synthetic blends has been developed based on the use of a phosphonium salt—urea precondensate (145). The precondensate is appUed to the blend fabric from aqueous solution. The fabric is dried, cured with ammonia gas, and then oxidized. This forms a flame-resistant polymer on and in the cotton fibers of the component. The synthetic component is then treated with either a cycUc phosphonate ester such as Antiblaze 19/ 19T, or hexabromocyclododecane. The result is a blended textile with good flame resistance. Another patent has appeared in which various modifications of the original process have been claimed (146). Although a few finishers have begun to use this process on blended textiles, it is too early to judge its impact on the industry. 

The phosphonium salt method works best with nucleophilic olefins [//, 12, 16, 17, 18, 19] (Table 1 and equations 1-3) and has been used m mechanistically important studies of difluorocarbene additions to norbornadienes [20 21, 22, 23] that provided the first example of a concerted homo-l,4-addition (equation 4) A recent modification uses catalytic 1,4,7,10,13,16 hexaoxacyclooctadecane (18-crown-6) to shorten reaction times and increase yields with less nucleophilic olefins [12] (Table 1) Neither procedure, however, compares with the use of phenyl(tri-f1uoromethyl)mercury or (trifluoromethyl)trimethyltin reagents [efficient reactions with less nucleophilic olefins (equations 3 and 5) and cyclic dienes [24, 25] (equations 6 and 7)... 

Another modification of the Hantzsch thiazole synthesis afforded C-4 thiazolylmethyl phosphonium salts (49). These ylids could then undergo Wittig condensations to furnish a wide variety of 2,4-disubstituted thiazoles <96TL983>. 

Allenyl- and propargyl-phosphonium salts have also been used as precursors of heterocyclic compounds in the presence of various functionalized nucleophiles279, via the intermediacy of vinylphosphonio compounds however, an ylide extrusion has been sometimes observed815,816, depending on the nature of the functions in the nucleophile (reaction 250). Allenylphosphonium salts are able to add such weak CH acids as in ketones, even in absence of basic catalysts817,818, without any modification of the keto group (reaction 251). 

Although solution-based cyclization of linear peptides can be achieved with a slight excess of uronium salt without detectable N-terminal modification, on-resin cyclizations may be accompanied by significant guanidino formation. In such cases the use of phosphonium salts such as PyBOP or PyAOP (Section 3.7), which do not produce these side products, may be advantageous. 

Similar types of alkylation have been applied in syntheses of other steroidal side-chains, including that of 22-trans-26,27-dinorergosta-5,22-dien-3j8-ol (387), a novel marine sterol. In addition, the Wittig reaction has been used to prepare various possible polyene intermediates in phytosterol biosynthesis. The aldehydes (389) and (390) were prepared (Scheme 26) from stigmasterol acetate (388b) by modification of a known procedure. These aldehydes were then alkylated with a variety of ylides derived from phosphonium salts, leading to a series of polyenes (391) and (392). ... 

Phase transfer catalysis and the use of crown ethers are also of particular advantage in alkanenitrile synthesis (Table 1). Usually quaternary ammonium and phosphonium salts serve quite well as catalysts. Another modification is represented by the use of a solid catalyst, which is insoluble in the two-phase system, for instance alumina or anion-exchange resins (triphase catalysis). Crown ethers again capture the cations and generate naked cyanide ions in fairly nonpolar solvents, leading to exceptionally mild reaction conditions. 

Schlosser s modification" of the Wittig reaction produced the phosphonium salts 1137 in excellent yield. 

This synthetic method has two steps the first step involves synthesising the polymer and the second includes modification with active groups. Some monomers generally used to form the backbone of homopolymers or copolymers include vinyl benzyl chloride, methyl methacrylate, 2-chloroethyl vinyl ether, vinyl alcohol and maleic anhydride. The polymers are then activated by anchoring antimicrobial groups, such as phosphonium salts, ammonium salts or phenol groups, via quaternisation, chloride substitution or anhydride hydrolysis. 

A modification to this reaction can be seen in the reaction of a dicarbonyl equivalent, acyl-vinyl-phosphonium salt. Reaction of the phosphonium salt with an appropriately functionalized formamidine provides the imidazole phosphonium salt. The imidazole phosphonium salt can be further functionalized to an intermediate used to synthesize the cimetidine, an H2-receptor histamine antagonist used to treat ulcers. 

An important modification of the Wittig reaction that involves phosphonate esters has the advantage of being highly stereoselective. The use of phosphonate esters rather than phosphonium salts is illustrated in the accompanying equations ... 

The modification of phosphonium salts is also a possibility to make available new derivatives. Hence, a series of azoles was added to the triple bond of triphenyl-phenylethynyl phosphonium bromide to aflbrd new products (Scheme 65). ... 

NaH stirred ca. 45 min. at 65-70° under Ng in excess dimethyl sulfoxide until Hg-evolution is complete, allowed to react with 1 equivalent of ethyl triphenyl-phosphonium bromide, then with 0.85 equivalent of benzophenone 1,1-di-phenyl-l-propene. Y 97.5%.—The reactivity of the methylsulfinyl carbanion (formed by reaction of NaH with dimethyl sulfoxide), which is even more basic than the trityl anion, is sufficient to convert phosphonium salts into ylides thereby permitting a simple and convenient modification of the Wittig reaction. E. J. Gorey and M. Ghaykowsky, Am. Soc. 8A, 866 (1962) / -diketones from carboxylic acid esters and ketones (s. Synth. Meth. 6, 737), sym. ) -diketones, s. J. J. Bloomfield, J. Org. Chem. 27, 2742 (1962). 

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