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
