Pyridinium ylides, 1,3-dipolar cycloaddition

Pyridinium ylides will undergo dipolar cycloaddition reactions the topic has been reviewed (B-76M120601). 

Cyanides can react with 1-aminopyridinium salts to give 2-substituted triazolopyridines, possibly via the pyridinium ylide. With 1-aminopyridinium iodide and cyanide ion the intermediate 4-cyanopyridine reacts with the aminopyridinium salt to give 2-(4-pyridyl)triazolopyridine (45).51 When acetonitrile or benzonitrile are used, 2-methyl- and 2-phenyltriazolo-pyridines are obtained.58 60 The reaction is thought to involve a dipolar cycloaddition of the N- mi nopyridine with the nitrile, as shown in Eq. (4). 

A review on die inter- and intra-molecular cycloaddition of oxidopyridiniums and pyridinium ylides has appealed.117 The known 1,3-dipolar cycloaddition of 1 -methyl-4-phenyl-3-oxidopyridinium with electron-deficient dipolarophiles has been used to produce tropenones which can be transformed into 6- and 7-substituted 3-phenyltropanes, analogues of cocaine.118... 

Mechanistically, this sequence can be rationalized by initial alkynone formation upon coupling of acid chloride 7 and aUcyne 4 furnishing the alkynone 8, which now can act as a dipolarophile (Scheme 18). The amount of triethylamine is sufficient to deprotonate the l-(2-oxoethyl)pyridinium bromide 25 giving rise to the zwitter-ionic pyridinium ylide 27, an allyl-type dipole suitable for the subsequent 1,3-dipolar cycloaddition to give the dihydroindolizine 28. Under either aerobic or anaerobic conditions in the final cycloaddition step oxidative aromatization directly furnishes the desired indolizines 26. 

The overall sequence of carbenoid generation/ylide formation/[3-l-2]-cycloaddition or rearrangement was explored in the synthesis of a series of 1,3-triazine derivatives. Thus, 1,3-dipolar cycloaddition of the pyridinium ylide derived from 2-(3-diazo-2-oxopropylthio)pyridine gives a 1,3-thiazine ring incorporated into the polycyclic system (Scheme 21) (93JOC1144). 

T14687>. The 1,3-dipolar cycloaddition of pyridinium ylides with a,P-unsaturated aldehydes or ketones in the presence of tetrakis-pyridme cobalt dichromate gives 1-acylindolizidines <97SC1395>. Similarly, pyridinium dicyanomethylides react with cyclooctyne to produce indolizidines <97JHC203>. 

Indolizines have been made via carbene addition to 2-vinylpyridine or dipolar addition of pyridinium ylides. 3-substituted indolizines have been obtained in a one step procedure from reaction of chlorocarbenes with 2-vinylpyridine (94CC509). Microwave irradiation has been used in 1,3-dipolar cycloaddition of pyridinium dicyanomethylide with alkynes <94H(38)785>. 

An oxidative one step synthesis of aromatic indolizine (91) by 1,3-dipolar cycloaddition of pyridinium ylides with alkenes was reported (Scheme 51) (93JCS(P1)2487). 

Bayazit, M. K., and Coleman, K. (2009). Fluorescent single-walled carbon nanotubes following the 1,3-dipolar cycloaddition of pyridinium ylides,/ Am. Chem. Soc., 131, pp. 10670-10676. 

Apart from the more routine uses, cycloaddition to the olefinic bond of diphenyl-cyclopropenone (211) has led to the quadricyclanone (277) from (298). The first apparent 1,3-dipolar cycloadditions of pyridinium ylides (299) to cyclopropenones... 

Differently substituted pyrrolidine rings can be obtained by the 1,3-dipolar cycloaddition of pyridinium ylides 42 on SWCNTs that afford indolizine derivatives such as compound 43 (09JA10670,14MI99). 

The effect of solvent nature on the reactions of pyridinium ylides with (E)-l,2-di(alkylsulfonyl)-l,2-dichloroethene has been investigated. It has been found that in aprotic solvents these reactions take place as a 1,3-dipolar cycloaddition followed by double elimination with the formation of substituted l,2-di(alkylsulfonyl)indolizines. 

The 1,3-dipolar cycloaddition reaction of pyridinium ylides (40) with 3-alkenyl oxindoles (41) yielded spiro-cycloadducts (42) related to oxindole alkaloids, such as strychnofoline (Scheme 12). The one-pot 1,3-dipolar cycloaddition of 3-arylsydnones with a,/ -unsaturated ketones formed 1,3,4-trisubstituted pyrazoles in refluxing dry dimethylbenzene. ... 

One of the simplest ways to produce substituted indolizines is by 1,3-dipolar cycloaddition. These procedures allow the use of readily available pyridine rings and simple substrates to construct the fused heterocyclic core in only two steps and, in some cases, one pot. It is important to note that the reactivity profiles of the 1,3-dipolar species and the dipolarophile are greatly dependent on the steric and electronic nature of each reaction component. In general, electron-poor dipolarophiles bearing limited steric encumbrance work best in this reaction paradigm. As some intermediate pyridinium ylides exhibit stability at ambient or cold temperatures, these intermediates can be isolated, which allows rapid generation of substituted indolizines in parallel. An example reaction is described in eq... 

Cycloaddition Reactions. The reaction of pyridinium, iso-quinolinium, and benzimidazolinium 7V-ylide with fluorovinyl tosylate 1 gives cyclic monofluorinated adducts in moderate yield (eq 6). The reaction mechanism is thought to involve initial 1,3-dipolar cycloadditon of the TV-ylide to 1, followed by elimination of both tosic and hydrofluoric acid. ... 

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