Pyrano[4,3‐b]pyran‐2,5‐diones, 1. – Convenient Synthesis of Pyranopyrano‐quinolinetriones
Reaction of malondiamides 1 with malonyl chloride (5) leads to 2,5‐dioxo‐2H,5H1‐pyrano[4,3‐b]pyrans 7, which readily react with diazomethane to give the corresponding methyl ethers 8. Thermically induced cyclisation of 8 affords 7,12‐dihydro‐2H,5H1‐pyrano[2′,3′ :4,5]pyrano [2,3‐b]quinoline‐2,5,12‐triones 9. Acidic hydrolysis of 9 yields 4H1‐pyrano[2,3‐b]quinoline‐4,5(10H)1‐diones 10, while basic hydrolysis of 9 gives 4‐hydroxy‐2(1H)1‐quinolinones 11.