Selenium heterocycles XLIV. Syntheses of 8,9‐dihydro‐1,2,3‐thiadiazolo[4,5‐a]‐4,7‐dihydroxynaphthalene and 1,2,3‐selenadiazolo[4,5‐a]‐4,7‐dimethoxynaphthalene

The reaction of thionyl chloride with the semicarbazone 2 gave 4,5-dihydro-6,9-dihydroxynaphtho-[1,2-d][1,2,3]thiadiazole (3) instead of 4,5-dihydro-6,9-dimethyoxynaphtho[1,2-d][1,2,3]thiadiazole (4). Selenium dioxide oxidation of compound 2 gave 4,5-dihydro-6,9-dimethyoxynaphtho[1,2-d][1,2,3]selenadiazole (5). Oxidation of compound 5 with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone afforded 6,9-dimethyoxynaphtho[1,2-d][1,2,3]selenadiazole (6).