Synthesis, Structure, and Spectral Properties of Bis(pyrrol‐2‐yl)pyridines

Abstract

Abstract 2,6‐Bis(pyrrol‐2‐yl)pyridine ( 4 ), 2‐(pyrrol‐2‐yl)‐6‐[2‐(1‐vinylpyrrol‐2‐yl)]pyridine ( 5 ), 2,6‐bis[2‐(1‐vinylpyrrol‐2‐yl)]pyridine ( 6 ), 2,6‐dimethyl‐3,5‐bis[2‐(1‐vinylpyrrol‐2‐yl)] pyridine ( 9 ), 3‐acetyl‐2,6‐dimethyl‐5‐[2‐(1‐vinylpyrrol‐2‐yl)]pyridine ( 10 ), and 2,6‐dimethyl‐3‐(pyrrol‐2‐yl)‐5‐[2‐(1‐vinylpyrrol‐2‐yl)]pyridine ( 11 ) have been synthesized from the oximes of the corresponding diacetylpyridines in a one‐pot procedure by treatment with acetylene in MOH/DMSO systems (M = Li, K) at 80–140 °C under pressures of 25–30 atm, thus illustrating the applicability and general character of the reaction for synthesis of diverse dipyrrole‐pyridine assemblies and their N ‐vinyl and acetyl derivatives. A stable 4· DMSO complex with bifurcated NH ··· O ··· HN bonding has been isolated and its X‐ray structure determined. Quantum chemical analysis at the B3LYP/6‐311G* level shows that the cis‐cis conformation of 4 is most stable, with the cis‐trans and trans‐trans forms accordingly less favorable by 3.2 and 7.8 kcal mol –1 . Activation barriers of cis‐cis ‐to‐ cis‐trans and cis‐trans ‐to‐ trans‐trans dynamics are 8.3 and 9.5 kcal mol –1 , respectively, which means that internal rotation of the pyrrole rings in 4 is essentially hindered. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)