2A-Azirines

It is known that unsaturated three-membered nitrogen heterocycles display tautomerism involving nonaromatic and antiaromatic (i.e., Air systems) forms. In all cases, the nonantiaromatic tautomer is the most stable 1-azirine la and 1-diazirine 2a. Nonetheless, antiaromatic tautomers are known, for instance, triazirines 3. 

Similiar to the case of bicyclo[4.1.0]heptatriene (2a), the proposed31 bi-cyclic intermediate (2b) in the ring expansion of lb has never been directly observed. However, the analogous azirines, formed by photolysis of 1- and 2-naphthyl azides, have been characterized by IR (Scheme 13)47 and both trapping48 3,6,0 and IR spectroscopic characterization484 of substituted derivatives... 

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