Vinyl azides reactions

Vinyl azide Reaction conditions Azirine yield, % Other reaction products Ref... 

Another type of intramolecular interaction that could be classed as neighbouring group participation occurs in the thermolysis of vinyl azides (reactions 61 and 62) and other olefinic azides such as... 

The overwhelming majority of vinyl azide reactions involve the expulsion of molecular nitrogen and subsequent reorganization of the remainder of the molecule. Such decompositions may be initiated thermally or photochemically. Azirines are frequently isolated from the reaction mixtures, but a great variety of other products, including nitriles, dihydropyrazines, indoles and isoxazoles have also been obtained. 

Azides are generally stable in the presence of bases and nucleophilic displacement of the azido group is uncommon, but displacements have been observed on a few vinyl azides. Reaction of j8-azidovinyl phenyl ketone 73 (R = H) with piperidine gave phenyl -2-piperidino-vinyl ketone (119) and reaction of the same azide with sodium hydroxide in aqueous methanol gave the dimethyl acetal 120 . 

In most cases it is easy to rationalize the products obtained from vinyl azide reactions which do not involve the loss of molecular niaogen. For example, the substitution of the azido group by a nucleophilic reagent in the 2-azidovinyl ketone 73 (R = H) and the )3-dicyanovinyl... 

A novel method for preparing amino heterocycles is illustrated by the preparation of 2-amino-5-methylthiophene (159). In this approach vinyl azides act as NH2 equivalents in reaction with aromatic or heteroaromatic lithium derivatives (82TL699). A further variant for the preparation of amino heterocycles is by azide reduction the latter compounds are obtained by reaction of lithio derivatives with p- toluenesulfonyl azide and decomposition of the resulting lithium salt with tetrasodium pyrophosphate (Scheme 66) (82JOC3177). 

A mechanism for this reaction involving nucleophilic attack of the ylide on the cyanide group and formation of the P=N linkage via a four-centred intermediate was formulated. The structure of this phosphazene was confirmed by its synthesis from the vinyl azide, Ph(N3)C=CHPh, and triphenylphosphine. Phosphoranes stabilized by electron-withdrawing... 

Vinyl azides decompose to 3H-azirines. This reaction has been reviewed recently 247). 

Elimination of HI, which in the presence of an excess of IN3 can form hydrazoic acid, followed by its addition to the vinyl azides can give an intermediate triazide 75. The same compound could arise directly by substitution of one iodine atom by an azido group. The intermediate 75 has been considered to undergo a transannular reaction with homolytic cleavage of the weak C—I bond to form the radical 76, which loses a nitrogen atom to a radical 77. Combination of the two radicals leads to the 2-tetrazene 74 (equation 77). 

Vinyl azides have been prepared via the reaction of sodium azide with 1-((V-acetyl-/V-nitrosoamino)alkan-2-ols [16]. The reaction proceeds via the initial formation of the carbene (see Section 7.1). 

An intramolecular counterpart of this reaction is the cyclization (Scheme 17) of anions derived from vinyl azides the neutral azides fail to cyclize, presumably because the cyclic tautomer (the triazole) is not aromatic, whereas the anion is. 

Vicinal dihalo compounds, dehalogena-tion of, 7-10 Vinyl amines, 98 Vinyl ammonium hydroxides, 97 Vinyl azides, 277 Vinyl carbazole, 98 V-Vinyldimethylamine, 103 Vinylidene chloride, reaction with sodium /8-alkoxyalcoholates, 56, 58... 

Thermolysis of certain vinylic azides gives rise to cyano compounds. Representatives of this interesting class of reactions (zwittazido cleavage) [97] are outlined in the following. The fragmentation is predicated by a p-atom which can assume an acceptor role readily. 

Photogenerated nitrenes can undergo cycloaddition with alkenes intermolecular reaction leads to aziridine products (5.38), and intramolecular reaction in vinyl azides gives azirines (5.39). The bicyclic azirine from phenyl azide has not been isolated, but it is the intermediate that best accounts for the formation of a substituted azepine when this azide is irradiated in the presence of a secondary amine (5.401. 

Azirines are also made by carbene addition to nitriles (89 — 90) and by thermal or photochemical (68JA2869) elimination of N2 from vinyl azides (e.g. 91 — 92). Vinyl azides are prepared by the Hassner reaction (68JOC2686, 71ACR9), where iodine azide is first added to an alkene and the resultant (3-iodoazide is dehydrohalogenated with base (Scheme 37) (86RTC456). 

Reactions of Vinyl Azides G. L abbe, Angew. Chem., Int. Ed. Engl., 1975, 14, 775-782. Cyclic Hydroxylamines Review of Preparative Methods and Properties R. T. Coutts and A. M. K. El-hawari, Heterocycles, 1974, 2, 669-743. 

The formation of 34 from 33 in the reaction of Scheme 42 is explained by a rapid intramolecular cycloaddition of the initially formed vinyl azide followed by loss of nitrogen.200... 

Vinyl azides follow the same course of reaction when treated with dimethylsulfoxonium ylide in dimethyl sulfoxide at room temperature for 12 hr and high yields of clean 1-vinyltriazolines are obtained.378... 

A reaction mechanism in which the / carbon of the vinyl azide attacks the N-N double bond of the triazolinedione to give an intermediate which cyclizes with loss of nitrogen to the triazoline has been proposed (Scheme 3).6... 

Irradiation of vinyl azides also produces 1-azirines. In some instances it may be the method of choice since the reaction can be carried out at low temperature and little polymerization of the azirines occurs. 

Kurtz and Sheehter48 have observed similarly that irradiation of 3,4,5-triphenylisoxazole gives AT-phenylbenzoylphenylketenimine, 3-benzoyl-2,3-diphenyl-l-azirine, and 1,4,5-triphenyloxazole. The formation of the azirine and ketenimine from this reaction and from the decomposition of vinyl azides would suggest a similarity in mechanism. 

One of the best known reactions of 1-azirines is the acid/catalyzed hydrolysis to aminoketones. Since the Neber reaction also accomplishes this same synthetic end, this reaction may appear to have little practical value. This is not the situation because with the Neber reaction there is no control over the aminoketone that will be obtained from a given ketone. For example, when oxime (127) derived from benzyl methyl ketone (126) is subjected to the Neber reaction aminoketone 128 is obtained.59 The amino function is substituted for the most acidic a-hydrogen. The isomeric aminoketone (132) that could not be prepared by the Neber reaction can be formed by the hydrolysis of 1-azirine (131). The synthesis of this 1-azirine has been accomplished from allyl benzene (129) through vinyl azide (130) using iodine azide.22... 

FIGURE 25. The heterogeneous gas-phase dehydrochlorination of /1-chloroethyazide on solid potassium rm-butoxide yielding vinyl azide, and the subsequent thermal decomposition of the latter to 27/-azirine. The double-oven apparatus is equipped with cold traps for the by-product tert-butyl alcohol and the end product 2/7-azirine. The PES ionization patterns of the pure compounds were used for optimization of the reaction conditions. Reproduced by permission of Verlag der Zeitschrift der Naturforschung from Reference 215... 

Aryl azides may also be prepared from the corresponding halide, using azide ions197,198. Vinyl azides are prepared, in high yields, by reaction of chlorides with sodium azide in aqueous acetone208. Cyano and ester functional groups are unaffected by the reaction conditions. 

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