Nitrilimines reaction with

The reaction is illustrated by the intramolecular cycloaddition of the nitrilimine (374) with the alkenic double bond separated from the dipole by three methylene units. The nitrilimine (374) was generated photochemically from the corresponding tetrazole (373) and the pyrrolidino[l,2-6]pyrazoline (375) was obtained in high yield 82JOC4256). Applications of a variety of these reactions will be found in Chapter 4.36. Other aspects of intramolecular 1,3-dipolar cycloadditions leading to complex, fused systems, especially when the 1,3-dipole and the dipolarophile are substituted into a benzene ring in the ortho positions, have been described (76AG(E)123). 

Most 1,3,4-oxadiazoles are thermally stable (unlike many A -l,3,4-oxadiazolines, see Section 4.06.6.2) and high temperatures are needed to induce ring cleavage. At 700°C oxadiazolinones (12) lose carbon dioxide to form a nitrilimine which undergoes further reaction, with loss of nitrogen. For example, 4-phenylbut-l-en-3-yne was formed on heating oxadiazolinone (12 R = ethynyl)... 

Reaction of nitrilimines 26 with 1-substituted-1-methylhydrazines 27 yielded the acyclic adducts 28. Thermal cyclization of adducts gave tetrahydro-l,2,4,5-tetrazines 29 in 70-80% yields. Dihydro-1,2,4,5-tetrazines 30 were obtained (22-25% yield) upon elimination of formaldehyde from tetrahydrotetrazines 29a <03SC1245>. 

Thanks to the ready availability of nitriles, their reaction with nitrilimines is a useful method for the preparation of bistriazoles, e.g. (189) and (190) in Scheme 89. 

The intermediate l-aza-2-azoniallene cations can undergo 1,3-dipolar cycloaddition reactions with inverse electron demand [119]. Thus, oxidation of a A -phenyl hydrazone in the presence of pyridine leads to the formation of a. y-triazolo[4,3-a]-pyridinium salt by attack of pyridine as a nucleophile on the intermediate nitrilimine [Eq. (17)] [120]. Other examples are reported by Jugelt [121]. 

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