A cyanoborohydride‐promoted radicalcyclization methodology has been developed to access α‐chlorolactams in a simple and efficient way using NaBH3CN and trichloroacetamides easily available from allylic and homoallylic secondary amines. This methodology allowed the synthesis of a library of α‐chlorolactams (mono‐ and bicyclic), which were tested for herbicidal activity, trans‐3‐chloro‐4‐methyl‐1‐(