The chemistry of cyclic π-systems surrounded by rigid σ-frameworks: Blending a σ-flavor into the aromatics

Abstract

Unique new properties are expected for the cyclic π-systems when they are completely surrounded by rigid σ-frameworks. From this viewpoint, a series of π-conjugated cyclic systems composed of five- to eight-membered rings fully annelated with bicyclo[2.2.2]octene units were prepared by reductive cyclization of α,ω-dibromides of bicyclo[2.2.2]-octene-2,3-diyl oligomers (n=3,4,5) as the key step. Not only the steric effects but both the inductive and σ-π conjugative electronic effects of the σ-frameworks were found to greatly stabilize the π-system especially when it bore the positive charge. These hydrocarbons were also characterized by readiness in undergoing reversible one-electron red-ox process. Thus, not only the closed-shell ionic species but also the open-shell states seem to be stabilized by the presence of bicyclic a-frameworks. © 1993 IUPAC