Additions to Vinylphosphonium Salts

Additions to Vinylphosphonium Salts.—Sodium alkoxides react with vinylphosphonium salts (110) to give alkoxy-olefins (111) which can be hydrolysed to known jS-dicarbonyl compounds.  

Thiazolylmethylphosphonium salts (112) are formed in the reaction of vinylphosphonium salts (113) with thiourea or thioacetamide, showing that the initial attack is beta to the phosphonium grouping to give an intermediate immonium ylide. 

Additions to Vinylphosphonium Salts. Two reports of the reaction of -mercaptoketones with triphenylvinylphosphonium bromide in the presence of base to yield 2,5-dihydrothiophens (86) have appeared. - 

Vinylphosphonium salts such as (87), which bear a leaving group in the -position, can give, by reaction with acyloins in the presence of base, good yields of furans via the isolable 2-ethoxy-2,5-dihydrofurans.  

Triphenylvinylphosphonium bromide undergoes cydoaddition with a variety of dienes to give phosphonium salts, e.g. (90).  

Addition of sodium azide to arylethynyltriphenylphosphonium salts in DMF gives the phosphonium ylides (91) which can be hydrolysed to l-iT,2,3-triazoles by aqueous base.  

Miscellaneous. The phosphonium salt (92) has been shown to be an excellent reagent for the carboalkenylation of carbonyl compounds. For example, the sodium enolate (93) and (92) give a cyclic product (94) which is thought to arise from a stabilized ylide by cyclization via an intramolecular Wittig reaction. 

Additions to Vinylphosphonium Salts.— The addition of triphenylvinyl-phosphonium bromide to a number of active methylene compounds has been studied. A correlation was observed between the acidity of the active methylene species and the ease of formation of 2 1 adducts. 

Pyrazolinyltriphenylphosphonium salts (88) can be prepared by 1,3-dipolar addition of excess diazomethane to triphenylvinylphosphonium salts. Thermolysis of (88) gave phosphonium salts (89) by elimination 

Purines, pyrimidines, and nucleosides, for example cytidine, condense with the vinylphosphonium salt (92) to yield (93), which on treatment with alkali eliminate triphenylphosphine.  

MisceUaneous.—The carbanions (94), formed from the reaction of the corresponding phosphonium salt with sodium ethoxide and the sodium salt of t-butyl hydroperoxide, decompose in a number of ways. Migration of a phenyl group to oxygen yields the phosphine oxide (95) and formation of the alkyl ethyl ethers may be due to the intermediacy of a carbene, which is trapped by solvent.  

Cyclopropyl ketones (96) have been formed in moderate yield from the esters of 3-hydroxypropylphosphonium salts by treatment with potassium t-butoxide. The acidity and enolization of several j8-ketophosphonium salts have been investigated and discussed in detail. -  

The use of vinylphosphonium salts in heterocyclic synthesis continues to be exploited. The kinetically controlled reactions of the / -acylvinylphosphonium salts (143) with 2-aminopyridine lead to the salts (144) similar reactions occur with 2-aminopyrimidine and cytosine. Under conditions where thermodynamic control prevails, the salts (145) are formed predominantly, resulting from a Dimroth rearrangement of (144).136 

The reaction of a-mercaptocarbonyl compounds [e.g. (148)] with buta-l,3-dien-l-yltriphenylphosphonium salts unexpectedly leads to 3-vinylthiophens,138 whereas reaction with vinylphosphonium salts results in the formation of c/ -2,5-dialkyl-2,5-dihydrothiophens (149).139 

A number of addition reactions to the salt (150) have been reported.140 With azide ion, the ylide (151) is formed. Diels-Alder addition of cyclopentadiene occurs to form isomeric adducts (152). With thioamides, a mixture of the salts (153) and (154) results, and with, e.g., 2-aminopyridine, the salt (155) is formed. 

Miscellaneous. The reaction of the aminophosphonium salt (156) with thiols and alkoxides affords a convenient, high-yield, single-step synthesis of unsymmetrical thioethers.141 The key intermediate is the alkoxyphosphonium salt (157), which undergoes nucleophilic attack by RS- at the alkoxy carbon. 

The formation of /7-nitro-AW-dimethylaniline (in addition to the expected p-nitrophenyl ether) in the reaction of nitrophenate ion with the alkoxyphosphonium salts (158) indicates the intermediacy of the relatively stable interconverting phos-phoranes (159). Loss of dimethylamide ion gives the salt (160), which subsequently undergoes SurAr reactions.142 

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Additions to Vinylphosphonium Salts. Vinyltriphenylphosphonium bromide reacts with the enolate (141) to give a one-stage synthesis of the tricyclic ketone (142) (Scheme 6).135... 

Electrochemically-promoted reversible interconversion of alkyltriphenyl-phosphonium salts and the related ylides has been shown to occur in the presence of benzophenone oxime O-methyl ether as a mediator, providing an example of electrochromism. Nucleophilic addition to vinylphosphonium salts has again been widely used as a means of generating ylides, and for the synthesis of heterocyclic systems" New developments include the catalysis of addition of... 

A widely applicable cyclization method discovered by Schweizer is based on a nucleophilic addition to vinylphosphonium salts followed by an intramolecular Wittig reaction <64JA2744>. The... 

There is a report describing intramolecular, stereoselective cyclopropanations by utilizing the ylide reaction Preparation of tricyclic compounds, such as 24, has been accomplished by intramolecular reaction of phosphorous ylide generated in situ by addition of enolate anion to vinylphosphonium salt (equation 82) . Optically active... 

The photocycloaddition of 2tf-azirines to electron-deficient olefins produces d -pyrrolines as primary photoproducts. Some of the dipolarophiles used include acrylic esters, acrylonitriles, fumaric and maleic esters, methyl allenecarboxylate, norbornene, and l,2-dicyanocyclobutene. Similarly, styrenes and vinylpyridines undergo smooth photocycloaddition to 2H-azirines. Addition of acetylene derivatives to the transient nitrile ylide gives 2H-pyrroles (18, 20) which rearrange to pyrroles (19) if the C-2 atom is monosubstituted. 3-Phenyl-2/f-azirines have been found to cycloadd to vinylphosphonium salts and to vinyl sulfones. The initial adducts (22 and 24) undergo ready loss of the phosphorous or sulfur substituent to give 2H-pyrroles (23 and 25). ... 

The use of a vinylphosphonium salt as the source of the QQ fragment instead of the more commonly employed 1,2-dicarbonyl substrate is illustrated by the pyrrole synthesis in Scheme 79b (8UOC2570). A particularly interesting feature is the intramolecular Wittig reaction with an amide carbonyl group. A very useful synthesis of pyrroles depends upon the addition of the anion of p-toluenesulfonylmethyl isocyanide (TOSMIC) to a,/3-unsatur-... 

The reaction of triphenylphosphine and dimethyl acetylenedicarboxylate (DMAD) in the presence of either 2-, 3-, or 4-aminophenol and 2-amino-3-hydroxypyridine gives a vinylphosphonium salt which undergoes Michael addition to give a range of highly functionalized heterocyclic systems <2002T6895>. 

The same kind of addition can be carried out on the ethynylphosphonium salt 26, generated in situ from the 1,2-vinylenebisphosphonium salt 25, and, depending on the experimental conditions, the vinylphosphonium salt produced can eventually undergo a second addition of YH to produce the / -acetalized or-thioacetalized salt. The same type of /Mieterosubstituted vinylphosphonium salt can also undergo an acidic hydrolysis that leads to the ketonic salt itself335 (reaction 74). 

Two standard routes to y-functional phosphonium salts with electron-withdrawing groups consist in using the corresponding Michael alkenes to achieve either halide substitution in the -position to the functional group, in order to obtain y-functional vinylphosphonium salts, or Michael addition in the presence of acid to produce the y-functional alkylphosphonium salt (reaction 85). 

Diarylpyrroles have been constructed from a-amidonitriles and vinylphosphonium salts. The reaction presumably proceeds by nucleophilic addition to the vinylphosphonium salt followed by cyclization via an intramolecular Wittig reaction. Elimination of HCN accounts for the final aromatization (equation 118) (81JOC2570). 

Vinylphosphonium salts accept nucleophiles by addition in a Michael reaction to form phosphoranes, which may subsequently react with a carbonyl group to form an alkene (see Scheme 10). This reaction, discovered by E. E. Schweizer in 1964,80 was developed into a widely applicable cycliza-tion method.81 The reaction of 2-formyIpyrrole with vinyltriphenylphos-phonium bromide to give 87% of 3/f-pyrrolizine (1) is among the first to... 

Nitroalkenes, vinyl sulfones and vinylphosphonium salts have been shown as good Michael acceptors for 2-lithio-l,3-dithiane derivatives. Nitroalkene sugar derivative 246 has been used as electrophile for the synthesis of branched-chain cyclitols397 - 399. Seebach and Langer studied the addition to simple nitroalkenes using the chiral solvent (,S ,.S )-DDB (247) with some degree of diastereoselectivity400,401. 

Reactions of Phosphines. - 1.2.1 Nucleophilic Attack at Carbon. Treatment of the unsaturated y-lactone (177) with tributylphosphine results in selective relacement of chlorine to form the phosphonium salt (178). Reactions of phosphines with alkynes have continued to attract interest. A palladium-catalysed addition of triphenylphosphine to unactivated terminal alkynes in the presence of methanesulfonic acid provides a route to the vinylphosphonium salts (179). This reaction fails with methyldiphenylphos-... 

Reactions of Phosphines. - 1.2.1 Nucleophilic Attack at Carbon. Interest has continued in developing the synthetic applications of the 1 1 adducts of tertiary phosphines with dialkyl acetylenedicarboxylate esters. Protonation of the initial adduct from triphenylphosphine by phthalimide, followed by nucleophilic addition of the nitrogen of the resulting imido anion to the intermediate vinylphosphonium salt, has given the stabilised ylide system (189). ° Similar reactions with isatin and 3-chlorotetrahydrofuran-2,4-dione have given the yl-... 

Stable phosphorus ylides (50) and (51) have been prepared from the reaction of electron-deficient acetylenic esters, such as dialkyl acetylenedicarboxylates or alkyl propiolates and triphenylphosphine in the presence of 3-chlorotetrahyd-rofuran-2,4-dione (Scheme 10). These reactions are thought to proceed via vinylphosphonium salt intermediates which undergo Michael addition with the conjugate base of the CH-acid. Similar methodology has been used to prepare phosphonium ylide (52) from triphenylphosphine, isatin (indoline-2,3-dione) and dimethyl acetylenedicarboxylate. " ... 

Nucleophilic addition then occurs to give the vinylphosphonium salts (143), some of which are able to undergo a further addition of nucleophile. The French group has also discovered a new reaction of arylphosphonium salts with t-butyl-lithium, in which the t-butyl carbanion undergoes nucleophilic addition to an aryl group to form ylides, e.g., (144), which then undergo Wittig reactions... 

Addition to Double Bonds. Compared with other alkylsul-fenylating agents, addition of dimethyl(methylthio)sulfonium trifluoromethanesulfonate to double bonds is less frequently used. Treatment of olefins with the reagent followed by the addition of triphenylphosphine gave 2-methylthioalkylphosphonium salts in high yields, which could be converted into vinylphosphonium salts or vinyl phosphine oxides (eq 9). ... 

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