Synthesis of Novel Bithiophene-Substituted Heterocycles Bearing Carbonitrile Groups

Symmetrical and unsymmetrical bithiophene-substituted heterocycles bearing carbonitriles including imidazo[1,2-a]pyridine, benzimidazole, and pyridine derivatives have been synthesized via different synthetic protocols. The bithiophene bis-imidazo[1,2-a]pyridine derivatives 3a,b were achieved in three steps starting from 2-acetyl-5-bromothiophene. Suzuki coupling reaction of 2a with 5-formylthiophen-2-ylboronic acid forms the formyl derivative 5, which by condensation with 3,4-diaminobenzonitrile in the presence of sodium bisulfite furnishes the unsymmetrical bithiophene derivative6. The bis-benzimidazole derivative 8 was obtained via hexabutylditin-mediated homocoupling of 5-bromothiophene-2-carboxaldehyde, while the benzimidazole derivatives 12a,b were prepared via the formyl derivatives 11a,b, a product of Velsmier formylation reaction of 10a,b. Two synthetic protocols for the aryl/hetaryl-2,2′-bithiophene derivative 14 have also been presented. In addition, the guanyl hydrazones of bithiophenes, 16 and 17, were prepared from bis(tri-n-butylstannyl)-2,2′-bithiophene through a Stille coupling reaction followed by a condensation step.