Vinyl azides Hassner reaction

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). 

Hassner and Belinka118 generated primary enamines in situ by reaction of vinyl azides 67 with alkyl lithium derivatives and converted them to ketones (equation 45). 

The synthesis of vinyl azides by regiospecific elimination of hydrogen iodide from vicinal iodoazides has been developed by Hassner and co-workers and constitutes the only noteworthy example of the directing effect of the azido group on elimination reactions. 

The photodecomposition of vinyl azides is of interest as a potential synthetic route to the highly stre-ined azirine ring system. Smolinsky was the first to prepare compounds of this class by the pyrolysis of vinyl azides (39) and Hassner and Fowler have shown that the corresponding photo-reaction also produces 1-azirines (40) in excellent yield. Three possible mechanisms were proposed by these authors, one involving a nitrene intermediate 41. 

Of all the methods available to generate this 1,3-dipole, the photochemical generation of nitrile ylides from 2tf-azirines offers the greatest opportunity for structural variation. The 2/f-azirine ring can be readily prepared in large quantities using either the vinyl azide route developed by Hassner and coworkers or the modified Neber reaction sequence. 3-Aryl-2 -azirines (15) can also be obtained in good yields by reaction of alkylidene phosphoranes... 

Not only azirines but also nitriles were obtained in thermal reactions of vinyl azides (see, for example. Schemes 5.15 and 5.17). Hassner and coworkers summarized some rules, ° which allow to expect the former or latter products after loss of dinitrogen from enazides. The 1-azidocyclopentadiene 202 tnmed ont to be highly unstable because fragmentation to furnish the nitrile 203 was observed already at room temperature (Scheme 5.24). On the other hand, the isomer 204 was isolated as a relative stable lemon-yellow solid, which was converted to the indole 205 by reflnxing in toluene or irradiation in chloroform. In some cases, the formation of cyano compounds from vinyl azides was... 

Just like the aryl azides 2, the vinyl azides 11 are more reactive in their cycloadditions with active methylene compounds than are alkyl azides. In 1970, Alfred Hassner et al. developed a general synthetic approach to 1-vinyl-1,2,3-triazoles 12 and 14, (Scheme 4.4) [6] by the cycloaddition of active methylene compounds 10 or 13 with vinyl azides 11 (or their precursors, the P-haloalkyl azides), in the presence of 1 equiv. of an alkoxide (NaOMe). Decarboxylation of the l- dnyl-5-substituted l,2,3-triazole-4-carboxylic acids 14 synthesized from the reaction of ethyl acetoacetate or ethyl benzoylacetate with vinyl and P-haloalkyl azides led to 1-vinyl-5-substituted 1,2,3-triazoles in almost quantitative yield [6]. 

Hassner and co-workers have shown that the intramolecular azide-alkene cycloaddition reactions of azido vinyl j8-lactams primarily lead to cis fused triazolines. The triazoline 61, fused to a 6-membered ring, was formed exclusively as the cis-fused isomer and decomposed on treatment with silica gel to imine 66. On the other hand, the 8-membered ring fused triazoline 63 which was isolated as a cis trans mixture, on exposme to sUica, produced only aziri-... 

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