Abstract
Two exocyclic and endocyclic olefin tautomers of chromone phosphonates were obtained in good to excellent yields at different temperatures by utilizing an N-heterocyclic carbene catalyst in the intramolecular reactions between the formyl group and alkynylphosphonates. The exocyclic olefins can isomerize to the endocyclic derivatives completely when treated with a thiazolium salt precatalyst and potassium carbonate at 30 °C for three to five hours. In addition, the chromone phosphonate derivatives were also applied in the one-pot synthesis of benzopyranopyridine phosphonates in moderated yields.
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