Ortho Effect in the Bergman Cyclization:Interception of p-Benzyne Intermediate by Intramolecular Hydrogen Abstraction

摘要

Intramolecular hydrogen atom(H-atom)abstraction from the omicron-OCH_3 group effectively intercepts the p-benzyne intermediate in the Bergman cycloaromatization of 2,3-diethynyl-1-methoxybenzene(1)before this intermediate undergoes either retro-Bergman ring opening or external H-atom abstraction.This process leads to the formation of a new diradical and renders the cyclization step essentially irreversible.Chemical and kinetic consequences of this phenomenon were investigated through the combination of computational and experimental studies.