A new series of 9‐substituted‐4,10‐dimethylpyrano[2,3‐f]cinnolin‐2‐ones (5a, 5b, 5c, 5d, 5e, 5f, 5g, 5h, 5i, 5j, 5k, 5l, 5m) were synthesized via intramolecular cyclization of the respective acyl amidrazone derivatives (4a, 4b, 4c, 4d, 4e, 4f, 4g, 4h, 4i, 4j, 4k, 4l, 4m), catalyzed by polyphosphoric acid. Compounds (4a, 4b, 4c, 4d, 4e, 4f, 4g, 4h, 4i, 4j, 4k, 4l, 4m) were synthesized through direct interaction of coumarin‐7‐yl hydrazonoyl chloride (3) with the corresponding cyclic sec‐amines in the presence of triethylamine. The structures of the new compounds were confirmed by elemental analyses, NMR, and MS spectral data. The antitumor activity of compounds 5a, 5b, 5c, 5d, 5e, 5f, 5g, 5h, 5i, 5j, 5k, 5l, 5m was evaluated in vitro on breast cancer cell line (MCF‐7) by a cell viability assay utilizing the tetrazolium dye 3‐(4,5‐dimethylthiazol‐2‐yl)‐2,5‐diphenyltetrazolium bromide. Among the compounds tested, compounds 5d, 5f, 5k, and 5h showed potential anti‐MCF‐7 activity and were able to reduce the viability after 72 h to less than 50%.