Peri-Selective Cycloaddition Reactions of 3-Methoxycarbonyl-2H- cyclohepta[b]furan-2-one with 6,6-Dimethylfulvene

Abstract

Abstract The cycloaddition reaction of 3-methoxycabonyl-2H-cyclohepta[b]furan-2-one with 6,6-dimethylfulvene was carried out under refluxing in ethanol, benzene, or xylene. The [4+2] cycloadduct was formed as a major product in ethanol or benzene together with the minor [8+2] cycloadduct. On the other hand, the [8+2] cycloadduct was formed as a single product in xylene. The [4+2] cycloadduct was completely changed to the [8+2] cycloadduct under refluxing in xylene by a retro–Diels–Alder reaction, a re-cycloaddition reaction followed by spontaneous decarboxylation. The structure of the [8+2] cycloadduct was clearly confirmed by chemical transformation to methyl 3-isopropyl-1H-cyclopent[a]azulene-9-carboxylate which was obtained by the hydride reduction of methyl 3-isopropylidene-3H-cyclopent[a]azulene-9-carboxylate.