Abstract: Two improved methods were worked out for the preparation of α,β-dimethylanhy-dracetonebenzil (Ⅰ) by condensation of benzil with 3-pentanone in the presence of KOHasthe catalyst.In method 1, the condensation was carried out with a 3 h stirring in ethanol atroom temperature.After keeping the reaction vessel to stand at room temperature for 3days, the product Ⅰ_Aobtained was demonstrated to be a mixture of two pairs of enan-tiomers.But in method 2, the solvent was changed from ethanol to benzene with an additionof suitable amount of polyethyIene glycol PEG-400.After refluxing the mixture for 3 h, theproduct Ⅰ_A'obtained was proved only one pair of enantiomers.When Ⅰ_A and Ⅰ_A'were de-hydrated by heating with Ac₂O-H₂SO₄ separately, both of them formed the same compound3, 4-dipheny1-2, 5-dimethyl cyclopentadienone (Ⅱ).The constituents of Ⅰ_A'Ⅰ_A'and Ⅱwere confirmed mainly by ¹H NMRand IR.Finally, it was suggested that Ⅰ_Abe c0nsistedof about equal amount of dl-erythro-Ⅰ and dl-threo-Ⅰ,while Ⅰ_A'is only dl-erythro-Ⅰ.

Key words: α, β-Dimethylahydracetonebenzil, Erythro-Form, Threo-Form