Synthesis of 2 H ‐chromeno[4,3‐ b ]pyridine‐2,5(1 H )‐diones and related heterocycles via the erlenmeyer‐ploechl reaction

1,2‐Dihydro‐5 H ‐[1]benzopyrano[4,3‐ b ]pyridine‐2,5‐diones 4a‐j were synthesized from 4‐alkylamino‐coumarin‐3‐carbaldehydes 1 and 5(4 H )‐oxazolinones (azalactones) derived from N ‐acetylglycine ( 2a ) and hippuric acid ( 2b ). The intermediates 3 ( 3j isolated only) underwent spontaneous recyclization via opening of the azalactone and successive formation of the fused 2‐pyridones 4 . Attempts to synthesize the selected 2 H ‐chromeno[3,4‐ f ]‐1,7‐naphthyridine 6 by Vilsmeier reaction of 4e failed. Instead, N ‐deacetylation took place, followed by formylation of the amino group to the formamidine 7a . In addition, pyranopyridine 9a was obtained by condensation of the 3‐formyl‐2‐pyridone 8 with the azalactone derived from 2a and acetic anhydride.