Synthesis of dinitro-substituted furans, thiophenes, and azoles

Direct nitration of the corresponding mononitro furans with fuming nitric acid, thiophenes with acetyl nitrate, and thiazoles with trifluoroacetyl nitrate, gave dinitro-substituted furans, thiophenes, and thiazoles. The nitrations of 2-alkylthiophenes with 3 and 5 molar equivalents of acetyl nitrate, generated in situ, are discussed. Reactions of the mononitro furans with fuming nitric acid gave 1,1,5,5-tetrasubstituted dihydrofurans as by-products. Treatment of 5-methyl-4-nitroisoxazole with hydrazine or its methyl or phenyl derivative, followed by oxidation of the corresponding 4-amino-5-nitro-1H-pyrazoles with hydrogen peroxide (50%) gave 4,5-dinitro-1H-pyrazoles. A safe one-pot synthesis of 1-alkyl-3,5-dinitro-1H-[1, 2,4]triazoles was developed from dicyandiamide.