Synthesis of a Polycyclic π-Conjugated System Containing an Azulene Unit by the Flash Vacuum Pyrolytic Method. I. Synthesis and Properties of Cyclopent[a]azulenes

Abstract

Abstract 1H- and 3H-cyclopent[a]azulene were synthesized in excellent yields by applying flash vacuum pyrolysis. Their structures were clearly determined. A mixture of 1H- and 3H-cyclopent[a]azulene was completely anionized with methyllithium in THF, but 67% so in ether. Although 1H-cyclopent[a]azulene reacted with dichloroketene to give a [2+2] cycloadduct, 3H-cyclopent[a]azulene reacted with cyclopentadiene to give a [4+2] cycloadduct. These chemical behaviors were predictable according to HMO theory.