2-Methylcyclopentane-1,3-dione reacts with chloromethyl vinyl ketone to give 2-methyl-2-(4-chloro-3-carbonylbutyl)cyclopentane-1,3-dione, chlorohydrin I or epoxide II as the main product depending on the concentration of Et3N used. X-ray anal. of I shows that the configuration of epoxide in II is b. The homologous epoxide III, prepared in a similar way is shown to be a b-epoxide.

Key words: TRIETHYL AMINE P, X-RAY DIFFRACTION ANALYSIS, ETHYL ACETATE, STEROIDS, NAPHTHALENONE P, SINGLE CRYSTALS, EPOXIDE, INDENE P, CONFIGURATION, BETA DIKETONES