Abstract Reflux of isopropenyl acetate with an excess of AlCl 3 in 1, 2-dichloroethane affords 3, 5-diacetyl-2, 6-dimethyl-4 H-pyran-4-one in 17% yield. The mild acidic cleavage of the latter (2% HCl, 20° C, 16 h) gives 3-acetyl-2, 6-dimethyl-4 H-pyran-4-one in 87% yield,