dimerization occurs by an acid catalysed aldol-typecondensation, while the anhydrides act as dehydrating agents converting the initially formed dimeric ketol to the β,γ-unsaturated ketone 4. Formation of dimeric ketone 4 was also observed when the α-bromoketone 8 was treated with zinc and ethyl chlorocarbonate. In the presence of zinc and zinc chloride however, ketone 8 yielded the dimeric β-diketone 12