Trifluoroacetic Anhydride as an Activator in the Acylation of Aryl Methyl Ketones with Carboxylic Acids
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luoroacetic Anhydride as an Activator in the Acylation of Aryl Methyl Ketones with Carboxylic Acids E. A. Shokovaa,*, V. A. Tafeenkoa, and V. V. Kovaleva a
Faculty of Chemistry, Moscow State University, Moscow, 119991 Russia *e-mail: [email protected] Received July 1, 2018; revised February 13, 2020; accepted February 14, 2020
Abstract—Trifluoroacetic anhydride was used as an efficient activator of the acylation of aryl methyl ketones with carboxylic acids in the presence of Brønsted and Lewis acids (SF3SO3H, MeSO3H, 4-MeC6H4SO3H·H2O, BF3·Et2O). In all cases, the products were the corresponding β-diketones. In the reactions in the presence of boron trifluoride–diethyl ether complex, the products were isolated as BF2-chelates with high yields. Keywords: 1,3-diketones, acylation, trifluoroacetic anhydride, carboxylic acids, aryl methyl ketones, acid catalysis
DOI: 10.1134/S1070428020100164 β-Dicarbonyl compounds constitute one of the most important classes of organic compounds and are widely used as key building blocks in organic synthesis. They also exhibit various kinds of biological activity, including antitumor, antiviral, anti-inflammatory, antioxidant, and antimicrobial activities, as well as a broad spectrum of ionophoric properties [1–4]. We previously reported [5] for the first time the synthesis of β-keto acids directly from carboxylic acids without preliminary activation of the latter. Carboxylic acids containing branched alkyl groups [such as 3.3-dimethylbutanoic, 2-methylbutanoic, and 2-(adamantan1-yl)acetic acids] in the system trifluoroacetic anhydride (TFAA)/trifluoromethanesulfonic acid undergo self-acylation to produce the corresponding β-dicarbonyl compounds. Trifluoroacetic anhydride readily reacts with carboxylic acids to give mixed anhydrides, acyl trifluoroacetates, thus playing the role of an activatng agent. Trifluoromethanesulfonic acid used as catalyst favors enolization of carbonyl compounds and enhances the acylating activity of acyl trifluoroacetates. Using the system TFAA/CF3SO3H we have developed a simple and efficient procedure for the preparation of
β-diketones widely needed in organic synthesis and synthesized heterocyclic compounds from arenes and carboxylic acids by one-pot reactions [6, 7]. The goal of the present work was to find out whether TFAA can be used as an activating agent in the synthesis of β-diketones in the presence of other acid catalysts that are more accessible than trifluoromethanesulfonic acid. The substrates were aromatic methyl ketones: acetophenone (1a) and 2-acetylthiophene (1b). Apart from CF3SO 3H, Brønsted acids, namely methanesulfonic acid (MeSO3H) and p-toluenesulfonic acid (TsOH·H2O), and a Lewis acid, boron trifluoride–diethyl ether complex (BF3·Et2O) were used as catalysts. Acetophenone (1a) reacted with 3.3-dimethylbutanoic acid (2a) in TFAA in the presence of MeSO3H or TsOH·H2O (reactant molar ratio 1a–2a–TFAA–catalyst = 1:1:6:1) to give β-diketone 3a, as in the presence of trifluoromethanesulfonic acid [6] (Scheme 1). The maximum yields
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