Despite advances in breast cancer treatments, recurrence, and metastasis still occur. Phytochemicals and their derivatives are promising as alternative anticancer agents. Coumarin derivatives have demonstrated anticancer activity in various tumor cells. 3-isopropyl-4-methyl-5,7-dihydroxycoumarin (C13) is a new semi-synthetic coumarin with inhibitory activity against Taq DNA polymerase in vitro, making it an attractive target for cancer research. Additionally, chalcone derivatives combined with halogens and O-benzyl groups have shown significant antitumor effects in oral squamous cell carcinoma and colon cancer, respectively. However, the biological activity of novel chalcones modified by chlorine (JS23) and O-benzyl groups (X2) remains unknown. Searching for new antineoplastic alternatives, we studied the antitumor effects of three natural derivatives—C13, JS23, and X2—in human MCF-7 breast cancer cells. Cells were exposed to serum-free media containing these derivatives at concentrations ranging from 0 to 50 μM for 24, 48, and 72 h. The compounds were dissolved in dimethyl sulfoxide (DMSO), and cells treated with 1% DMSO for 48 h were used as negative controls. Cell viability was assessed by MTT assay. Ki-67 immunostaining, TUNEL, senescence-associated β-galactosidase, and wound healing assays were performed on C13-treated cells. C13 and X2 significantly inhibited cell viability with the same IC50 value (25 μM) in a dose- and time-dependent manner, although X2 reached this pattern at 30 μM. JS23 exhibited the strongest cytotoxic activity in a dose-dependent but time-independent manner (IC50=10.03 μM). C13-treated cells at IC50 concentration showed a Ki-67 proliferation index of 43.01%, an apoptotic mean value of 0.21, dose-dependent induction of senescence, and significant cell migration inhibition after 6 to 72 h of treatment in a dose-independent manner. These natural derivatives could represent promising alternatives to current breast cancer therapies.