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Ortho effect in the Bergman cyclization: interception of p-benzyne intermediate by intramolecular hydrogen
Tarek A Zeidan1, Mariappan Manoharan, Igor V Alabugin
1Department of Chemistry and Biochemistry, Florida State University, Tallahassee, FL 32306-4390, USA.
Abstract:
Intramolecular hydrogen atom (H-atom) abstraction from the o-OCH3 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.
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