Ortho effect in the Bergman cyclization: interception of p-benzyne intermediate by intramolecular hydrogen abstraction

Tarek A Zeidan; Mariappan Manoharan; Igor V Alabugin

doi:10.1021/jo051857n

Ortho effect in the Bergman cyclization: interception of p-benzyne intermediate by intramolecular hydrogen abstraction

J Org Chem. 2006 Feb 3;71(3):954-61. doi: 10.1021/jo051857n.

Authors

Tarek A Zeidan¹, Mariappan Manoharan, Igor V Alabugin

Affiliation

¹ Department of Chemistry and Biochemistry, Florida State University, Tallahassee, FL 32306-4390, USA.

PMID: 16438507
DOI: 10.1021/jo051857n

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.