The Transacylation between β-Diketone and Ester in the Presence of Aluminum Chloride
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概要
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The reaction of acetylacetone with an equivalent of phenyl benzoate in the presence of 2 equivalents of aluminum chloride in nitrobenzene afforded benzoylacetone (26% yield), dibenzoylmethane (4%), and phenyl acetate (37%), together with small amounts of phenolic ketones at 45°C. The total yield, based on the acyl groups introduced into the β-diketones, is similar to the yield of the ester newly formed. Such a similarity, suggestive of a transacylation, was also observed both on the use of <I>p</I>-nitrophenyl benzoate and on the treatment of benzoylacetone with phenyl benzoate or on that of dibenzoylmethane with <I>p</I>-nitrophenyl acetate. The non-formation of triacylmethanes is a strong evidence for the transacylation reaction, in which β-diketones and some esters exchange acyl groups directly. The analogous treatment of acetylacetone with α-naphthyl benzoate produced phenolic ketones, such as 2-acetyl- and 4-acetyl-1-naphthol, and the same benzoylated ketones as above in yields of 30 and 32% respectively. The considerably higher ratio of the 2-acetyl to the 4-acetyl isomer than that from the Fries rearrangement of α-naphthyl acetate indicates that another transacylation is accompanied by a rearrangement proceeding through complexes different from those in the Fries rearrangement.
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