“One-Pot” Synthesis of γ-Pyrones from Aromatic Ketones/Heteroarenes and Carboxylic Acids

Abstract

Despite the various attractive properties of γ-pyrones, there are still some deficiencies in their synthetic approaches such as lower atom economy, multistep processes, and prefunctionalization of the reagents. In this work, an efficient and simple (CF3CO)2O/CF3SO3H-mediated “one-pot” approach was realized to produce γ-pyrones by applying aromatic ketones/heteroarenes and carboxylic acids as the starting materials. The target products were isolated in moderate to excellent yields. The reaction mechanism was studied by density functional theory calculational methods. The results of experimental and theoretical investigations not only helped us explain the reason of high selectivity formation of β-diketones but also proved that 1,3,5-ketones might be important intermediates for the cyclization to afford γ-pyrones.

Dithioallyl Cations in Stereoselective Dearomative (3 + 2) Cycloadditions of Benzofurans: Mechanism and Synthetic Applications

“…A tert-butyl group did perform well as this is sterically blocking the formation of such orthoallylation side products. A strongly electron-withdrawing group, such as a nitro group, completely shuts down all reactivity (viz., 19). The cyclopentannulated adduct 20 was helpfully crystalline, and this allowed us to confirm the regioselectivity for dialkylbenzofuran substrates in this reaction, which was previously only possible via NMR spectral analysis.…”

“…As already mentioned, this can be rationalized by the weaker carbocation stabilization by the oxygen lone pairs as compared to that of the indole nitrogen. Electrophilic aromatic alkylations and acylations of benzofurans are usually nonregioselective and are known to give mixtures of C2 and C3 alkylation products, 18,19 while some examples of C2-selective benzofuran alkylations are indeed known. 20 In this regard, it is interesting to note that in our previous study of indole substrates, we observed a strong effect of protecting groups on the indole N−H moiety (Scheme 4).…”

Study of the dehydroacetic acid homolog by IR, Raman spectroscopy, and DFT

“…The neopentyl derivative of dehydroacetic acid 3-(3,3-dimethylbutanoyl)-4-hydroxy-6-neopentyl-2H-pyran-2-one (1) has been obtained by CF 3 SO 3 H/(CF 3 CO) 2 O activated acylation of carboxylic acids according to [12]. The white product has the crystalline powder form (melting point 77 − 78° C).…”

Synthesis of γ-Pyrones and N-Methyl-4-pyridones via the Au Nanoparticle-Catalyzed Cyclization of Skipped Diynones in the Presence of Water or Aqueous Methylamine

“…2 Apart from this approach, a series of synthetic methodologies for the synthesis of γ-pyrones (or 4pyrones) have been developed through the years. The most important include Ag(I)- 3 or Au(I) 4 -catalyzed cyclization of 3,5-dioxo-6-ynoates, Claisen-type cyclization of enaminodiones, 5 Au-catalyzed reaction between diazodicarbonyl compounds and vinyl ethers, 6 acid-catalyzed condensation between aromatic ketones and carboxylic acids, 7 condensation of acylated Meldrum's acid with vinyl ethers, 8 reaction between the enolate of 4-methoxy-2-buten-2-one and suitable acyl substances, 9 cyclization of ketene dithioacetals with acyl chlorides, 10 condensation of β-keto esters or acids in the presence of triflic anhydride, 11 Rh-catalyzed reaction between allylic alcohols and α,β-unsaturated aldehydes, 12 and more recently, Bu 3 P-catalyzed tandem reaction between diynones and allylic alcohols. 13,14 In addition, skipped diynones appear as versatile precursors for the formation of γ-pyrones via hydration followed by intramolecular cyclization.…”