A concise and efficient approach to polyenic compounds containing important diketone structural fragments is developed from readily available α, β-unsaturated methyl ketones in the presence of copper (II) oxide, iodine, and dimethyl sulfoxide. This is a new carbon– carbon double bond-forming reaction from two methyl sp3 C–H bonds and an attractive route to introduce the SMe group into the molecule from inexpensive dimethyl sulfoxide. ...