Described herein are phenylsulfonamido-benzofuran derivatives, and pharmaceutically acceptable salts thereof. Also provided are pharmaceutical compositions, methods, uses, and kits involving compounds of Formulae (I), (II), (III), (IV), (V), or (VI) for treating and/or preventing proliferative diseases (e.g. cancers, inflammatory diseases, and autoimmune diseases) in a subject. The compounds and pharmaceutical compositions as described herein inhibit at least one protein of the BCL-2 family in a biological sample or subject to treat and/or prevent a proliferative disease. In certain embodiments, compounds described herein are selective inhibitors of MCL-1, a BCL-2 family member protein.