An inexpensive nontoxic manganese(II)-catalysed dehydrogenative annulation was developed for C–C bond formation. The reaction showed high selectivity and efficiency across a broad substrate scope. Remarkably simple conditions and the ability to conduct gram-scale synthesis underscore this method's utility. To demonstrate the potential of this approach, we tested the drug effects of compound 3n, which showed activity for blocking vascular development. The results of this study will be important for the treatment of eye diseases and tumors caused by vascular proliferation.