A cascade thermal isomerisation of cyclobutane di-(carbomethoxy) Δ2-1,2,3-triazolines with intramolecular 1,3-dipolar cycloreversion as the key step

Unprecedented thermal isomerisation of the strained ∆2-1,2,3-triazolines led to the formation of products possessing a novel 1,2,7-triaza-[3.3.0]octa-2-ene ring system incorporated in a norbornane framework. Experimental evidence and quantum chemical calculations have been used to support a postulated reaction mechanism involving as the first step, a rare example of intramolecular 1,3-dipolar cyclo-reversion. Subsequently, several steps involving 1,3-dipolar ring closure, hydrogen shifts and an intramolecular addition are postulated leading to the observed product of this deep-seated isomerisation. The influence of changing substituents on the product outcome of this novel reaction cascade was also studied.