Phenyl-Carbonyl Coupling Reactions Promoted by Samarium Diiodide and Hexamethylphosphoramide

By mediation of samarium diiodide and hexamethylphosphoramide, benzaldehydes and acetophenones underwent self- and cross-couplings to give the products having linkages at the para-carbons of phenyl rings and the carbonyl groups. The phenyl-carbonyl coupling of 2,5-dimethoxybenzaldehyde generated a Sm(III)-enolate intermediate, which was trapped by alkyl halides in a stereospecific manner to give uncommon 1,4-dialkyl-2,5-cyclohexadiene-1-carboxaldehydes. The benzaldehydes bearing tethered carbonyl chains proceeded with intramolecular phenyl-carbonyl couplings to afford fused benzocycles.