The combination of SmI2 and the conjugate base of triethylurea (TEU-) has been shown to favor the cyclization of unsaturated halides over direct reduction to a much greater extent than other SmI2-based reductants. Aryl, heteroaryl, and alkyl halides (X = Br, Cl, F) readily undergo heterocyclization and carbocyclization in the presence of SmI2/TEU-.