Synthesis of some 8-substituted 5-deazaflavins

Treatment of 8-fluoro-3,10-dimethyl-5-deazaflavin (Ia) with ethyl cyanoacetate in ethanol in the presence of potassium carbonate gave the corresponding 8-(1-cyano-1-ethoxycarbonylmethyl)-5-deazaflavin, which was converted into 3,8,10-trimethyl-5-deazaflavin by refluxing in aqueous dimethylformamide. Treatment of Ia with sodium azide in ethanol yielded 8-azido-3,10-dimethyl-5-deazaflavin (V). Compound V was converted into the corresponding 8-amino-, 8-acetamido-, and 8-benzamido-5-deazaflavins by heating in high boiling alcohols, acetic anhydride, and benzoic anhydride, respectively. Fusion of compound V with dimethyl acetylenedicarboxylate yielded 4,5-bis(methoxycarbonyl)-1-(3,10-dimethyl-5-deazaflavin-8-yl)-1,2,3-triazole.