Three-Component Coupling Reactions of Alkyl Iodides, 1,3-Dienes, and Carbonyl Compounds by Sequential Generation of Radical and Anionic Species with CrCl2

The mild reductant chromium(II) chloride can discriminate between alkyl iodides, alkyl radicals, and allylic radicals. In the presence of CrII the alkyl radical is so long-lived that it can undergo intermolecular addition to a 1,3-diene. Rapid one-electron reduction of the formed allylic radical results in an allylic chromium(II) species, which adds to an aldehyde to afford a three-component coupling product [see, for example, Eq. (a)].