Currently, the chemistry of organofluorine compounds is a leading and rapidly developing area of organic chemistry. Fluorine present in a molecule largely determines its specific chemical and biological properties. This thematic issue covers the trends of organofluorine chemistry that have been actively developed in Russia the last 15 – 20 years. The review describes nucleophilic substitution and heterocyclization reactions involving fluorinated arenes and quinones and skeletal cationoid rearrangements in the polyfluoroarene series. The transformations involving CF3-substituted carbocations and radical cations are considered. Heterocyclization and oxidative addition reactions of trifluoroacetamide derivatives and transformations of the organic moiety in polyfluorinated organoboranes and borates with retention of the carbon – boron bond are discussed. Particular attention is devoted to catalytic olefination using freons as an efficient synthetic route to fluorinated compounds. The application of unsymmetrical fluorine-containing N-heterocyclic carbene ligands as catalysts for olefin metathesis is demonstrated. A variety of classes of organofluorine compounds are considered, in particular, polyfluorinated arenes and 1,2-diaminobenzenes, 1-halo-2-trifluoroacetylacetylenes, α-fluoronitro compounds, fluorinated heterocycles, 2-hydrazinylidene-1,3-dicarbonyl derivatives, imines and silanes. The potential practical applications of organofluorine compounds in fundamental organic chemistry, materials science and biomedicine are outlined. The bibliography includes 1019 references.

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Chemo- and regiocontrolled syntheses of pyrazoles and pyridones are presented on the basis of 4-pyrones. A novel approach towards highly functionalized 3,4'-bipyrazoles has been developed by using reactions of ethyl 5-acylcomanoates with hydrazines. The acid-promoted double cyclocondensation allows switching of the structure of the pyrazole rings easily through changing both the nature of hydrazine and the reaction conditions. The transformation of 4-pyrones with phenylhydrazine in EtOH at -20 °C leads to hydroxypyridones as monoaddition products which can be used as precursors for the preparation of pyridone and pyrazole derivatives. A novel rearrangement of 2-hydroxypyridone to pyrazolyl-1,3-diketones in DMSO was found. The structure and regiochemistry of bipyrazoles were confirmed by X-ray analysis and 2D NMR experiments.

An expedient synthesis of a series of 2-pyrones, bearing a CF 3 group at the 6-position and aryl group at position 4, from readily available aryl-4,4,4-trifluorobutane-1,3-diones, PCl 5, and sodium diethyl malonate is described.

Ethyl 2-(dimethylamino)methylene-3-oxobutanoate Diethyl oxalate 4-Oxo-4H-pyran-2,5-dicarboxylic acid 4-Oxo-1-phenyl-1,4-dihydropyridine-2,5-dicarboxylic acid a b s t r a c tThe reaction of ethyl 2-(dimethylamino)methylene-3-oxobutanoate with diethyl oxalate in the presence of sodium hydride in THF gave diethyl 4-oxo-4H-pyran-2,5-dicarboxylate, from which 4-oxo-4H-pyran-2,5-dicarboxylic and 4-oxo-1-phenyl-1,4-dihydropyridine-2,5-dicarboxylic acids and their derivatives were obtained in good yields.Ó 2013 Elsevier Ltd. All rights reserved.Chelidonic acid, a c-pyrone compound with the structure shown in Figure 1, is a naturally occurring compound that is widely distributed among many plants. 1 It is contained in the rhizomes of Chelidonium majus L. at quite high concentrations, and has multiple pharmacological effects including mild analgesic, antimicrobial, oncostatic, and central nervous system sedation. 2 In addition, chelidonic acid and chelidamic acid were the most potent inhibitors of glutamate decarboxylase from rat brain, 3 and may attenuate allergic reactions by inhibition of caspase-1 activity. 4Unlike well-studied diethyl chelidonate, 5 diethyl 4-oxo-4H-pyran-2,5-dicarboxylate (diethyl isochelidonate), is much less known. Furthermore, none of the isomeric 4-pyrone dicarboxylic acids I-III has been recorded in the literature (Fig. 1). Diethyl isochelidonate was mentioned for the first time in 2012 in the patent literature, c-Pyrone derivatives bearing electron-withdrawing carbonylcontaining substituents at the 2-and 5-positions have, surprisingly, been poorly investigated, probably due to the limited number of methods available for their preparation. 6,7 At the same time, these compounds are an important class of c-pyrones which can serve as the starting materials for the syntheses of a broad range of heterocyclic systems due to the presence of five electrophilic centers in their molecules (the C-2, C-4 and C-6 atoms of the pyrone system, and the carbonyl carbons of the 2-COR and 5-COR 0 groups). The diverse range of properties of these compounds is due to the fact that, being highly reactive geminally activated push-pull alkenes with a good leaving group at the a-and a 0 -carbon atoms, whose role is played by the enolate anion, they acquire the ability to undergo additional transformations related to c-pyrone ring-opening and heterocyclizations.The present Letter describes an improved synthesis of diethyl isochelidonate (1), which consists of the Claisen condensation of ethyl 2-(dimethylamino)methylene-3-oxobutanoate with diethyl oxalate in the presence of sodium hydride. Moreover, the synthesis 0040-4039/$ -see front matter Ó

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