Interaction of 5-arylfurfurals with 1-phenyl(4-tolyl)piperazine and sulfur

Abstract

Continuing our research, we investigated the interaction of 5-arylfurfurals with 1-phenyl- or 1-(4-tolyl)piperazine and sulfur under the conditions of the Wilgerodt–Kindler reaction. In both cases, a number of thioamides of 5-arylfuran-2-carboxylic acids containing N-aryl-substituted piperazine moieties were obtained, with high or moderate yields. Benzene was also used as a solvent, but the best results were obtained in the case of the reaction in DMF. The optimal ratio of 5-arylfurfural : sulfur : amine was 1 : 1 : 1,3. The nature of the substituent in the aromatic ring of 5-arylfurfurals does not significantly affect their reactivity. The presence of an aryl substituent in the molecules of substituted piperazines, which reduces their basicity, requires a fairly long reaction (6–8 hours). The reaction was monitored by TLC (eluent – hexane–acetone, 4:1 by volume), as well as by qualitative reactions on the carbonyl group and H 2 S. The structure of the obtained compounds was confirmed by 1 H NMR spectra and elemental analysis. 1 H NMR spectra were recorded on a Bruker Avance 500 instrument with an operating frequency of 500 MHz, solvents – DMSO- d 6 and a mixture of DMSO- d 6 with CCl 4 . Chemical shifts are given relative to the solvent signal (DMSO, 2,50 ppm). General procedure of obtaining thioamides. A mixture of 0,01 mol of 5-arylfurfural, 0,013 mol of 1-phenyl- or 1-(4-tolyl)piperazine and0,32 g(0,01 mol) of powdery sulfur in 20 ml of DMF was heated at a temperature of 80–90 °C and constantly stirring, until the release of hydrogen sulfide stops (6–8 hours). To the cooled reaction mixture was added 100 ml of water, the precipitate was filtered off and recrystallized from ethanol–DMF. Keywords: 5-arylfurfurals, 1-phenylpiperazine, 1-(4-tolyl)piperazine, sulfur, thioamides, Wilgerodt–Kindler reaction.