A method of synthesizing 2-iminoindolines using samarium diiodide (SmI2) is reported. In the presence of tert-butyl alcohol, treatment of carbodiimides bearing alpha,beta-unsaturated carbonyl moieties with a stoichiometric amount of SmI2 afforded 2-iminoindolines in moderate to high yields. The products were isolated after Boc protection of the amidine moieties. This reaction proved to be applicable to lactams and acyclic/cyclic esters as substrates.