Acetophenone from benzaldehyde

Benzaldehyde is converted into 2-phenyl-1,3-dithiane with propane-1,3-dithiol and boron trifluoride. Butyllithium deprotonates it at C2, and the anion, equivalent to a benzoyl anion, is methylated with methyl iodide.

Hydrolysis with mercury(II) chloride and calcium carbonate in aqueous acetonitrile releases acetophenone. Overall, the aldehyde carbon has acted as a nucleophile towards methyl iodide, the reverse of its usual behaviour towards methyllithium.