Electrochemical Oxidation Enables Radical Dearomative Spiroannulation to 2H‐Spiro[benzofuran‐3,9′‐fluoren]‐2‐one

Abstract

Developing pragmatic strategies for accessing functional benzofuran‐2‐ones from 3‐([1,1'‐biphenyl]‐2‐yl)benzofuran remains an enduring challenge. Herein, we have achieved a highly discriminating electrochemical oxidative dearomative spiroannulation of 3‐([1,1'‐biphenyl]‐2‐yl)benzofuran, culminating in the synthesis of 2H‐spiro[benzofuran‐3,9'‐fluoren]‐2‐one derivatives. By harnessing the electrophilic intermediates of benzofuryl radical cations supported by DFT calculations, we attain exceptional regioselectivity while eliminating the need for stoichiometric oxidants. Mechanistic investigations reveal a sequence of events involving the benzofuran radical cation, encompassing the capture of H2O, nucleophilic arene attack, and subsequent deprotonation, ultimately yielding the final benzofuran‐2‐ones.