Synthesis of 5H‐[1]benzopyrano[4,3‐b]pyridin‐5‐ones containing an azacannabinoidal structure

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Abstract
Starting from 7‐alkoxy‐4‐aminocoumarins 5,6,8,12, and 13 as key intermediates, this paper describes two different methods for the preparation of azacannabinoidal 5H[1]benzopyrano[4,3‐b]pyridin‐5‐ones 24–27, 38, and 39 containing typical structural requirements for ZNS activity. First, Michael addition of 6 and 8 to the double bonds of alkyl vinyl ketones 14 and 15 resulted in a mixture of tetrahydropyridines 24–27 and fused pyridines 20–23 the latter of which were reduced by sodium cyanoborohydride to give the target compounds 24–27. The second, pyridine ring closure was accomplished by a combination of Vilsmeier acetylation and formylation resulting in fused 4‐chloropyridines 31–33 followed by reduction.