Diels-Alder Reactions of [2.2]Paracyclophane-1-ene and [2.2]Paracyclophane-1,9-diene with 3,6-Disubstituted 1,2,4,5-Tetrazines

Abstract

[2.2] Paracyclophan-1-ene (1) and [2.2] paracyclophane-1,9-diene (6) apparently act as dienophiles with inverse electron demand and smoothly react with dimethyl 1,2,4,5-tetrazine-3,6-dicarboxylate (2a) at room temperature forming dihydropyridazine adducts, which are dehydrogenated to the pyridazino-anellated [2.2] paracyclophanes 5a and 8a, respectively. The molecular structure of 5a is determined by X-ray crystal-structure analysis. Under more rigorous conditions, phenyl-substituted derivatives 5b and 8b are obtained from 1 and 6, respectively, with 3,6-diphenyl-1,2,4,5-tetrazine. Compounds 1 and 6 are less reactive dienophiles than other strained cyclic olefins as shown by kinetic measurements.