Unfused azetes

No unambiguous reactions of unfused azetes have been reported rather, the existence of transient azetes has been inferred from the observation of products which might reasonably be attributed to their further reaction. Separate discussion of reactivity and preparation is, therefore, inappropriate, and apart from a few general comments is deferred to Section 5.09.5.3. 

Extrapolation from the known reactivity of cyclobutadiene would suggest that azetes should be highly reactive towards dimerization and as dienes and dienophiles in cycloaddition reactions and the presence of a polar C=N should impart additional reactivity towards attack by nucleophiles. Isolation of formal dimers of azetes has been claimed as evidence for the intermediacy of such species, but no clear reports of their interception in inter-molecular cycloaddition reactions or by nucleophiles have yet appeared. 

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The only report of an isolable, unfused azete is for trisdimethylaminoazete (304). The flash pyrolysate from triazine (303) contained ca. 30% of an unstable red compound which decomposed on warming to room temperature. The spectral data indicated in (304) were obtained at low temperature and cited as evidence for the azete structure (73AG(E)847). 

Unlike the situation with unfused azetes, there is considerable support from reactivity studies for the existence of benzazetes which can, therefore, be regarded as firmly established. 

Several approaches to unfused azetes have appeared, the most widely used being extrusion of small molecules from heterocyclic precursors. 

The pioneering work of Seybold et al. led to the first isolable unfused azete (30) by the FVT of tris(dimethylamino)triazine (29) (Equation (9)) <73AG(E)847>. The EVT of 4-phenylbenzotriazine... 

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