An improved synthesis and some reactions of diethyl 4-oxo-4H-pyran-2,5-dicarboxylate

The Construction of Polycyclic Pyridones via Ring-Opening Transformations of 3-hydroxy-3,4-dihydropyrido[2,1-c][1,4]oxazine-1,8-diones

This work describes the synthesis of 3-hydroxy-3,4-dihydropyrido[2,1-c][1,4]oxazine-1,8-diones, their tautomerism, and reactivity towards binucleophiles. These molecules are novel and convenient building-blocks for the direct construction of biologically important polycyclic pyridones via an oxazinone ring-opening transformation promoted with ammonium acetate or acetic acid. In the case of o-phenylenediamine, partial aromatization of the obtained heterocycles proceeded to form polycyclic benzimidazole-fused pyridones (33-91%).

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

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.

Synthesis of 2,3-Dihydro-4-pyridones and 4-Pyridones by the Cyclization Reaction of Ester-Tethered Enaminones

2,3-Dihydro-4-pyridone skeleton is an important building block in organic synthesis because it features several reaction sites with nucleophilic or electrophilic properties. Herein, we disclose a method for its formation by intramolecular cyclization of ester-tethered enaminones, which can easily be synthesized from readily available materials, such as amines, activated alkynes, and activated alkenes. 2,3-Dihydro-4-pyridones have been isolated in 41-90% yields. We also demonstrate the transformation of these heterocycles into another important class of compounds, 4-pyridones, by utilizing 2,3,5,6-tetrachloro-p-benzoquinone (chloranil) as an oxidizing agent. The latter products were isolated in 65-94% yields.

Normal, Abnormal, and Cascade Wittig Olefinations of α-Oxoketenes

α-Oxoketenes generated in situ by a thermal Wolff rearrangement have been found to participate as 1,2- and 1,4-ambident C-electrophilic/O-nucleophilic reagents towards donor/acceptor carbonyl-stabilized Wittig ylides. This resulted in the very direct and practical syntheses of functionalized allenes by a normal Wittig olefination, 4H-pyran-4-ones by an abnormal Wittig olefination, or 4H-pyranylidenes following a Wittig/abnormal Wittig cascade sequence as a function of the substrates combination employed. Mechanistic experimental and computational studies provided a full rational for these reactivity switches. Some unusual mechanistic features for Lewis acid-free Wittig olefinations were identified in this series such as the involvement of betaine intermediates and some degree of reversibility in the normal Wittig olefination. The abnormal Wittig olefination was fully uncovered.

Thermally induced formal [4+2] cycloaddition of 3-aminocyclobutenones with electron-deficient alkynes: facile and efficient synthesis of 4-pyridones

A thermally induced novel formal [4+2] cycloaddition of cyclobutenones with electron-deficient alkynes under metal-free conditions has been developed. The reaction provides a straightforward and efficient method for the synthesis of 4-pyridone derivatives in a single step.

Bio-based triacetic acid lactone in the synthesis of azaheterocyclesviaa ring-opening transformation

In the present article a new way of converting biobased triacetic acid lactone (TAL) into azaheterocyclic compounds, such as 4-pyridones, pyrazoles, isoxazolines and isoxazoles, has been found through reactive and multifunctional polycarbonyl intermediates.