Vinylphosphonium salt

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. 

Activated Acetylenes. The reaction of triphenylphosphine with phenylacetylene has been investigated in more detail.The rearrangement has been shown to proceed via the vinylphosphonium salt (30). 

B. 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. 

Vinylphosphonium salts are reactive as dienophiles as a result of the EWG character of the phosphonium substituent. The D-A adducts can be deprotonated to give ylides that undergo the Wittig reaction to introduce an exocyclic double bond. This sequence of reactions corresponds to a D-A reaction employing allene as the dienophile.71... 

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... 

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... 

From Sodium Azide and Vinylphosphonium Salts Phosphonium salts of the types 4 and 5 react with sodium azide in aqueous solution to give v-triazoles in high yield. The proposed mechanism (Scheme 13) involves nucleophilic attack at the carbon jS-tothe phosphorus, followed by cyclization with displacement of triphenyl-phosphine. 

The reaction of 4-(dichloromethylene)-2-phenyl-5(477)-oxazolone 400 and tri-phenylphosphine affords the vinylphosphonium salt 401, from which Al-benzoyl (triphenylphosphoranylidene)ketenimine 403 is obtained by hydrolytic ring opening of 401 and subsequent treatment of 402 with triethylamine (Scheme 7.129). 

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). 

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... 

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... 

The influence of substituents on both the phosphorus and vinyl groups was investigated (see Scheme 11). Vinylphosphonium salts (137) undergo cycliza-... 

A convenient route to the 1,3-selenazole nucleus uses a polyfunctional reagent such as the vinylphosphonium salt (110), which with sodium hydrogen selenide gives the ylide (111) (Scheme 33). Cyclization of (111) yields the phosphonium derivative (112). A variety of compounds have been prepared by this method [182-184],... 

The use of traditional condensation reactions continues to be reported with vinylphosphonium salts and iV-sulfonylanilines (Equation 128) <1997M927>. 

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