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. Herein, we describe a formal [3 + 3] cycloaddition of 4-hydroxycoumarins with propargylicalcohols catalyzed by benzenediazonium tetrafluoroborate as the Lewis acid catalyst for the synthesis of pyranocoumarins under mild conditions.image