Catalytic arylation of furan-2-carbaldehyde with arenediazonium salts was studied. The yields of 5-arylfuran-2-carbaldehydes were found to depend on the solvent, catalyst, and anion in the arenediazonium salt. Redox catalysis and generation of aryl radicals are not sufficient conditions for the reaction to occur. The reaction is successful only under conditions ensuring formation of complex intermediates. A mechanism involving two Cu 2+ ↔ Cu + catalytic series and generation of furan-2-carbaldehyde was proposed.Interest in arylation of furan derivatives is largely determined by prospects in searching for biologically active substances among compounds of the furan series. Many furan derivatives are used as medicines [1,2]. Such medicines as Nitrafudan, Dantrolene, Clodanolene, and Azimilide contain an arylfuran fragment. Numerous arylfuran compounds exhibit versatile biological activity [2][3][4][5]. A convenient method for the synthesis of arylfurans is copper-catalyzed arylation of furan derivatives with arenediazonium salts according to Meerwein [4,[6][7][8][9][10][11][12]. These reactions were reported mainly for 2-substitued furans which underwent arylation at the 5-position (Scheme 1). furan derivatives follows a mechanism similar to one of the above reactions. In the first case, the reaction is redox catalytic, and it involves intermediate copper complexes [14,15], while in the second radical arylation occurs [7,13]. The ESR and polarographic data indicated generation of a radical adduct (arylfuryl radical) [16,17], and radical mechanism of the process was proposed.We performed a series of experiments on the arylation of furfurol with a view to elucidate in detail mechanism of this reaction. The following modes of generation of aryl radicals were tried: decomposition of N-nitrosoacetanilide, decomposition of diazonium salts in alkaline medium, on heating, and in the presence of potassium iodide, thermal and catalytic decomposition of diaryliodonium salts, reduction of diazonium salts with ascorbic acid, and their electrochemical reduction. The reagents and conditions were selected in such a way that the formation of intermediate complexes by the catalyst [Cu(I) or Cu(II)] with furfurol and diazonium salt be either favored or completely excluded.Using 4-nitrobenzenediazonium chloride (Ia) as an example we examined decomposition of diazonium salt in the presence of furfurol in alkaline medium (Gomberg reaction conditions) and on heating (Scheme 2). In the first case, 5-(4-nitrophenyl)furan-2-carbaldehyde (IIa) was obtained in 9% yield, and in the second case the yield of IIa was 11.5%. In both cases, the reactions were accompanied by considerable tarring. Standard Meerwein reaction conditions ensure 50-60% yield of aldehyde IIa. In the reaction of fur-

The standard enthalpies of combustion, formation, fusion, and sublimation of crystalline furan 2 carboxylic and 3 (2 furyl) 2 propenoic acids are determined by experimental methods and recalculated to 298 K. The possibility of using additive calculation schemes based on the principle of group contributions to calculate the standard enthalpies of vaporization and formation of substances with similar combinations of functional fragments in the gas phase is analyzed.

No abstract

No abstract

No abstract