DUAL FORMATION OF BETA DIKETONES FROM METHYLENE KETONES AND ACETIC ANHYDRIDE BY MEANS OF BORON TRIFLUORIDE . IMPROVED METHOD OF SYNTHESIS OF CERTAIN BETA DIKETONES

Evidence is presented that the formation of β diketones from methylene ketones and acetic anhydride by means of boron trifluoride involves, not only direct C acetylation of the ketone, but also O acetylation of the ketone and C acetylation of the resulting ketone enol ester. The O acetylation is catalyzed by proton acid formed as the byproduct in the C acetylation of the ketone. Certain intermediate ketone enol esters, β diketone enol esters, and boron difluoride complexes were isolated. Acetophenone, however, apparently undergoes only C acetylation. The relative proportions of the methyl and methylene derivatives of methyl methylene ketones were found to be dependent, not only on the structure of the ketone, but also on the conditions employed for effecting the acetylation. Several β diketones were prepared conveniently by use of the boron trifluoride-diacetic acid complex which is available commercially. © 1969, American Chemical Society. All rights reserved.