Synthesis of Functionalized 4H-Pyrano[3,2-c]pyridines from 4-Hydroxy-6-methyl-2-pyridone and Their Reactions. Unexpected New Routes to 3,3′-Benzylidenebis[4-hydroxy-6-methyl-2(1H)-3-pyridinone]s

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Abstract
The reaction of 4-hydroxy-6-methyl-2-pyridone 1 with benzylidenemalononitriles in an ethanolic solution containing a catalytic amount of piperidine and α-cyanoacrylic esters in pyridine affords the corresponding 4H-pyrano[3,2-c]pyridines. However, it’s reaction with 3-(cyanomethylene)-2-indolinones gives either 2-amino-3-quinolinecarbonitriles or ethyl 2-amino-5′,6′-dihydro-7′-methyl-2,5′-dioxospiro-[indoline-3,4′-[4H]-pyrano[3,2-c]pyridine-3′-carboxylate. In contrast, the reaction of 1 with 3-aryl-2-cyano-2-propenethioamides affords 3,3′-benzylidenebis[4-hydroxy-6-methyl-2(1H)-3-pyridinone]s. The reaction of the obtained 4H-pyrano[3,2-c]pyridines with acetic anhydride affords the corresponding fused system.

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