Facile synthesis and characterization of novel bis(2-S-alkylpyridines) and bis(3-aminothieno[2,3-b]pyridines) incorporating 1,3-diarylpyrazole moiety

Abstract

ABSTRACT3-(4-Hydroxyphenyl)-1-phenyl-1H-pyrazole-4-carbaldehyde (1) is condensed with acetophenone to afford the corresponding unsaturated carbonyl compound 4 whose potassium salt is reacted with 1,4-dibromobutane to afford the bis-unsaturated carbonyl compound 3. Both carbonyl compounds 3 and 4 are reacted with 2-cyanoethanethioamide, through Michael addition reaction followed by cyclocondensation, to prepare the starting materials bis(pyridine-2(1H)-thione) derivative 5 and pyridine-2(1H)-thione derivative 8. Two synthetic routes to synthesize the target materials 7 and 14 are described to get the most efficient method for preparation and maximum yield%. The first route came from the direct alkylation of the bis(pyridine-2(1H)-thione) derivative 5 using iodomethane (6a) and benzyl chloride (6b) to afford the corresponding bis(2-S-alkylpyridine) derivatives 7a,b. The reaction of 5 with halo-containing compounds 10a–d to synthesize the target materials bis(3-aminothieno[2,3-b]pyridine) derivatives 14a–d failed under various reaction conditions. The second route involves the reaction of pyridine-2(1H)-thione derivative 8 with 6a,b and 10a–d to afford the corresponding 2-S-alkylpyridine derivatives 9a,b and 3-aminothieno[2,3-b]pyridine derivatives 13a–d, through the formation of 2-S-alkylpyridine derivatives 12a–d followed by a Thrope-Ziegler reaction, whose potassium salts reacted with 1,4-dibromobutane to afford the corresponding target materials 7a,b and 14a–d, respectively. The structures of target molecules were elucidated using elemental analyses and spectral data.