Synthesis of new 2 H ,4 H ‐benzopyrano[3,4‐ b ]yridine‐1,3,5‐trione derivatives via carbon suboxide

The new 2 H ,4 H ‐[1]benzopyrano[3,4‐ b ]pyridine‐1,3,5‐trione derivatives 10a‐f were prepared in the following three steps: first the preparation of new N ‐( tert ‐butoxycarbonyl)‐3‐amino‐2 H ‐1‐benzopyran‐2‐one derivatives 5a‐f by reaction of coumarin‐3‐carboxylic acids and diphenylphosphorylazide, then hydrolysis of 5a‐f with gaseous hydrogen chloride to give the corresponding amines 7a‐f , and finally the preparation of 10a‐f by reaction of 7a‐f and carbon suboxide in the presence of a Lewis acid.