Reactions between Triazolindiones and Equilibrating Forms of Cycloheptatriene Derivatives Featuring 7,7-Spiro and 1,7-Fused Heterocyclic Rings

Nitrile oxide-azaheptafulvene adducts consist of rapidly equilibrating mixtures of fused (1) and spiro (2) isomers, the relative stabilities of which are nicely reproduced by B3LYP/ 6-31G* calculations. The reaction between these compounds and MTAD affords only two diastereomeric adducts. These adducts are formal Diels-Alder products