Benzenediazonium Tetrafluoroborate‐Catalyzed Formal [3 + 3] Cyclization of 4‐Hydroxycoumarins With Propargylicalcohols

A formal [3 + 3] cycloaddition of 4‐hydroxycoumarins with propargylicalcohols was established under mild conditions. This strategy utilizes diazonium tetrafluoroborate as the Lewis acid catalyst and provides a practical approach for delivering pyranocoumarin derivatives in moderate to high yield. The structure of the cycloadduct was unequivocally confirmed by single‐crystal x‐ray diffraction. The potential synthetic applications of this strategy were also highlighted by the scale‐up experiment and further synthetic transformation.