Synthesis of 5‐fluoro‐2‐methyl‐3‐(2‐trifluoromethyl‐1,3,4‐thiadiazol‐5‐yl)‐4(3H)‐quinazolinone and related compounds with potential antiviral and anticancer activity

The synthesis of ten new substituted 1,3,4‐thiadiazolyl‐4(3H)‐quinazolinones 8–11, 13, 17, and 20–23 is reported. Compounds 8–11 were prepared by condensation of 5‐fluoro‐2‐methyl‐3,1‐benzoxazin‐4‐one (3) and 5‐substituted 2‐amino‐1,3,4‐thiadiazoles 4–7. Compound 13 was obtained by condensation of 5‐fluoro‐2‐methyl‐3,1‐benzoxazin‐4‐one (3) with DL‐α‐amino‐ϵ‐caprolactam (12). Compound 17 was synthesized by condensation of 6‐bromo‐2‐methyl‐3,1‐benzoxazin‐4‐one (16) and 2‐amino‐5‐t‐butyl‐1,3,4‐thiadiazole (5). Compounds 20–23 were obtained by condensation of 5‐chloro‐6,8‐dibromo‐2‐methyl‐3,1‐benzoxazin‐4‐one (19) and 5‐substituted 2‐amino‐1,3,4‐thiadiazoles 4–7, respectively. The substituted 3,1‐benzoxazin‐4‐ones 3, 16, and 19 were obtained in good yield by refluxing the appropriate anthranilic acid, 1,15, and 18 with acetic anhydride (2).