Electrochemical Synthesis of Heterocyclic Compounds. XI. Annelation of Coumarin Ring via Cathodic Reduction of 3-Nitrocoumarin Derivatives

Annelation of the coumarin ring was performed via cathodic reduction of 3-nitrocoumarin derivatives (1-4) by controlled potential. The reduction of 3-nitro-4-aminocoumarin, 1, gave 3,4-diaminocoumaDin, 5, and subsequent treatment with formic acid furnished tlie novel 4H [1] benzopyrano [3,4-b] imidazole-4-on ring system 6. The condensation of 5 with trifluoracetic acid anhydride, acetic acid anhydride, and benzil gave products 7, 8 and 9, respectively. The reduction of 3-nitro-4-carbetoxymethylthiocoumar.in, 2, gave the cyclic product 3H, 5H [1] benzopyrano[3,4-b]l,4-thiazine (2H)-3,5-dion, 10. The r.eduction of 3-nitro-4-(2-formylphenoxy)coumarin, 3, and subsequent intramolecular condensation of amino derivative 11 gave the novel SH [1] benzopyrano[3,4-b]l,4-benzoxazepin-8-on ring system 13. The same compound 13 was obtained through reduction of 3-ruitro-4-chlorcoumarin, 4, to 3-amino-4-chlorocoumarin, 12, acid and subsequent ·condensation of 12 with salicylaldehyde.