Objective: This study involved the synthesis of new Schiff bases and 1,3-oxazepine derivatives from the baclofen drug and study the anticancer activities. Methods: Baclofen was initially reacted with aromatic aldehydes to create Schiff base derivatives (Ia–Ib), which were then closed in the next step using anhydrous acids to form oxazepine derivatives (IIa–IId). Results: The title compounds were synthesized successfully and identified using FT-IR, 1H NMR, and 13C NMR spectroscopy. Additionally, compound (IIc)’s (3-(4-chloro-phenyl)-4-[2-(4nitro-phenyl)-4,7-dioxo-4,7-dihydro-[1,3] oxazepin-3-yl]butyric acid) anticancer activity was assessed using MTT assay against FTC-133 (thyroid cancer) compared with WRL-68 (normal cell line). Discussion: The results showed that the viability of the FTC-133 cell was found to be greatest at 12.5 g/mL (96.52 ± 0.70) and lowest at 400 g/mL (35.378 ± 5.07). The effect of compound (IIc) on the normalizing of the WRL-68 cell line resulted in an IC50 for 62.39 ϻg/mL. Conclusions: It has been found that the compound (IIc) has good efficiency against thyroid cancer (FTC-133).
