CYCLOHEPTATRIENE NORCARADIENE EQUILIBRIUM IN DIMETHYL TRANS-3,8-DIHYDROHEPTALENE-3,8-DICARBOXYLATE

Diels-Alder cycloadditions of dienophiles, such as 4-phenyl-1,2,4-tria zoline-3,5-dione, dimethyl acetylenedicarboxylate, dimethyl fumarate, diethyl azodicarboxylate, maleic anhydride, benzyne and p-benzoquinone , to dimethyl trans-3,8-dihydrohexalene-3,8-dicarboxylate (4) have bee n investigated, and monoaddition products (9)-(16) have been isolated. It has been shown that a second addition to this system occurs only w ith singlet oxygen and with benzyne. Furthermore, it has been establis hed that the second addition is retarded because of the strain in the cycloheptatriene molecule. The anti bicyclic endoperoxides (21)-(25) f ormed have been converted, either on heating or in a Co(tpp)-catalysed reaction, into the corresponding bisepoxides (27)-(31).