Curcumin is a natural product displaying a broad range of biological activities, including anticancer properties. It is, however, poorly absorbed by the human body and, as a so-called pan-assay interference compound, it exhibits non-specific activity leading to false positive results in biological assays. Nonetheless, different structural modifications of the curcumin scaffold have previously shown to lead to an improved biological and specificity profile without losing antiproliferative activity. In that respect, recent research in our group culminated in unprecedented benzothiazepane-based hit molecules with promising biological and drug-like properties. In the present hit expansion study, 14 new 2-aryl-4-(4-aryl-2-oxobut-3-en-1-ylidene)benzothiazepanes were successfully synthesized through the implementation of various aromatic ring modifications and subsequently tested for cancer cell cytotoxicity using eight different cancer cell lines, revealing useful structure-activity relationship insights for this new class of compounds.