The scope, generality, and mechanism of the Dess-Martin periodinane-mediated cyclization reaction of unsaturated anilides discovered during the total synthesis of the CP-molecules (phomoidrides A and B) are delineated. A plethora of heterocyclic compounds are accessible by employing gamma,delta-unsaturated amides (derived from anilines and carboxylic acids), urethanes, or ureas (derived from isocyanates and allylic alcohols and amines) as substrates. Optimization of the reaction led to room-temperature conditions, while isotope labeling studies allowed a mechanistic rationale for this cascade reaction.