Vinylphosphonium salts, synthesis

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 photocycloaddition of arylazirines with a variety of multiple bonds proceeds in high yield and provides a convenient route for the synthesis of five-membered heterocyclic rings. Some of the dipolarophiles include azodicarboxylates, acid chlorides, vinylphosphonium salts and p-quinones. 

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... 

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... 

In a similar manner, alkynes can undergo sequential carbometallation reactions, previously illustrated in equation (32).136 It is possible to combine carbocupration of alkynes with the use of a Michael acceptor as electrophile when that electrophile is a vinylphosphonium salt, carbocupration can be coupled to Wittig alkenation to result in a stereospecific synthesis of dienes via a one-pot, four-component, four carbon-carbon bond-forming reaction sequence.302... 

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. 

An alternative route to ylide synthesis via a-deprotonation is the abstraction of a proton from the y-po-sition of a vinylphosphonium salt (equation 10). Complications may arise, however, if the phosphonium salt carries a good leaving group in the P-position so that a vinylphosphonium salt may be formed, or if a P-proton is so acidic that a Hofmann elimination is favored. " ... 

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 one step bicycloannulation sequence as applied in the total synthesis of cycloseychellene 9 using a vinylphosphonium salt is also shown. 

Synthesis of E-allylamines from vinylphosphonium salts, phthalimide aldehydes (via a Wittig reaction) (see 1st edition). 

Preparation. - A range of 1,3-dithianylphosphonium salts (218) has been prepared in the course of further studies of sulfur lone pair anomeric effects in these systems.Conventional quatemization reactions have been used in the synthesis of the salt (219) and a range of polymer-supported phosphonium salts (220). A new efficient route to salts of the type (221) has been developed. The of>-azolylalkylphosphonium salts (222) are readily accessible from the reactions of the corresponding a>-bromoalkylphosphonium salts and azoles. Routes to vinylphosphonium salts, e.g., (223), continue to be explored, and their reactivity utilised in the synthesis of phosphonium salts bearing heterocyclic substituents, e.g., (224). The betaine (225) has been... 

A new method of fluoro-olefin synthesis involves initial reaction of the ylide-salt (60) with perfluoroacyl fluorides to give vinylphosphonium salts (61), rather than the acylation products. Alkaline hydrolysis of (61) gives ( )-fluoro-alkenes (Scheme 8). The reaction of non-stabilized ylides with chlorodifluoro-... 

Phosphoranylideneaminoquinones, e.g. (20), have been prepared in good to excellent yields by the reaction of phosphines with [2,l]benzisoxazole-4,7-quinones, e.g. (19)." A safer alternative to the vinyl azide-based synthesis of (N-vinylimino)phosphoranes (21) has been reported (Scheme 1)." N-(AlkyIthiomethyl)iminophosphoranes (23) have been synthesised from the benzotriazole-substituted iminophosphorane (22) and used without isolation to provide routes to N-alkylthiomethyl-imines, -amides, and -ureas. Tetraazolyl-substituted ylides (25) and (26) are the products of the reaction of vinylphosphonium salts (24) with excess sodium azide." The novel 1,2-1 -azaphosphete (28), which is potentially antiaromatic, has been prepared by the reaction of the azide... 

Scheme 9.13). The process starts with a Michael reaction of a keto-thiol with a vinylphosphonium salt. The Michael adduct is then reacted under the usual conditions of the Wittig synthesis to form a dihydrothiophene. This is easily oxidized (dehydrogenated) to the thiophene with the mild agent chloranil, which is reduced to tetrachlorohydroquinone. 

Phosphorus Nucleophiles. Triphenylphosphine is an effective nucleophile for reacting with the bridged sulfonium ion in high yield. The phosphonium salts generated eliminate MeSH upon reaction with base, such as l,8-diazabicyclo[5.4.0]undec-7-ene, resulting in a synthesis of vinylphosphonium salts. If NaOH is used, a vinylphosphine oxide is generated. 

Michael addition of l-lithio-2-methoxycarbonylprop-2-enyl phenyl sulphide to acrylates gives 3-(phenylthio)cyclopentadienones, while addition to aldehydes is followed similarly by cyclization to furan-2-ones. Further uses of vinyl sulphides in syntheses of cyclic compounds include an efficient pentannelation procedure (Scheme 12), cyclization of )i (3-phenylthio-2-methylprop-2-enyl)-)ff-keto-esters to 3-(phenylthio)cyclohexanones, using TFA, and an aromatic substitution reaction [HOCPhjCCSEt)—CHj - 3-phenyl-2-(ethylthio)indene] that involves attack at the yff-carbon atom of the vinyl sulphide moiety, promoted by acid-catalysed dehydration. l-(Phenylthio)vinylphosphonium salts PhSC(=CH PPh3 X , have been advocated for use in the synthesis of cyclopentanone by condensation with... 

An investigation of the synthesis of allylamines via vinylphosphonium salts (Schweizer reaction), has displayed its generality for their preparation in high stereochemical purity. Thus, the reaction between phthalimide, vinyltri-n-butylphosphonium bromide, and an aldehyde in the presence of sodium hydride gives the H-imide (8), from which the free -allylamines can be liberated (Scheme 10). Ketones do not react. 

Synthesis of Thiophens by Ring-closure Reactions.—A new general method for the preparation of alkylated 2,5-dihydrothiophens (3), through the reaction of o -mercapto-ketones (1) or a-mercapto-aldehydes with vinylphosphonium salts... 

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