A novel Co(III)-catalyzed oxidative annulation of aromatic aldehydes with internal alkynes for accessing isocoumarins is described, which is achieved by oxidation, weak chelation-assisted C-H bond functionalization, and annulation cascades with excellent functional group compatibility, high atom economy, and step efficiency. By using environmentally benign and inexpensive poly(ethylene glycol)-400 (PEG-400), the Co/Cu/PEG-400 system could be recycled and reused.
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