A Naphthalene with Unusual Bond Alternation Made by Annelation with Bicyclo[2.1.1]hexene Units:Aromaticity and Reactivity

摘要

The issue of aromaticity of cyclic pi-conjugated systems has been the subject of long-lasting discussion from both theoretical and experimental points of view.Naturally,the aromaticity is affected by the extent of bond alternation.Siegel and Stanger showed by theoretical calculations the effect of annelation with strained sigma-frameworks to bring about the bond alternation in benzene.In experimental studies,Vollhardt has utilized annelation with ben-zocyclobutadiene systems,while Siegel has used annelation with highly strained bicyclo[2.l.l]hexene (abbreviated as BCH) units to transform the structure of benzene into cyclohexatriene-like geometry (i.e.,1).Annelation with strained frameworks tends to elongate the bond endocyclic to the strained system and to give a double bond character to the exocyclic bonds.