There are several reports of lactam cyclizations, but most yield less-substituted lactam rings. Therefore, diastereoselective cyclization to yield highly substituted lactams is one of the challenges in this field. We therefore propose a strategy involving the reactions of α-halocarboxamides with E/Z-mixed internal olefins here. An Fe/triphos catalyst system is effective in reactions between α-bromocarboxamides and internal olefins to form trans lactams with quaternary carbons. Control experiments reveal that the reaction involves a radical process. This reaction may be useful in the field of pharmaceuticals, as γ-lactam moieties constitute the core structures of numerous drugs and natural alkaloids.