Synthesis and spectroscopic properties of rotamers in the series of 2-(fluoroaryl)-4-substituted pyrroles

A mild, simple and efficient method for the synthesis of ortho, meta and para-fluoroaryl substituted pyrroles was discovered. It was found by NMR spectroscopy, that ortho-fluoroaryl substituted pyrroles exist in the form of inhibited conformational isomers (rotamers). Intramolecular interaction of the hydrogen atom of the pyrrole ring and the fluorine atom in the ortho-position of the aryl substituent leads to the appearance of two sets of signals in the H-1 and C-13 NMR spectra. Based on the combination of 2D HMBC and HSQC NMR spectroscopy, as well as temperature dependent NMR experiments in DMSO and CDCl3 we conclude that the ratio of obtained rotamers is permanent and does not depend from the temperature.

Automated summary

A mild, simple, and efficient method for the synthesis of ortho, meta, and para-fluoroaryl substituted pyrroles was discovered. Through NMR spectroscopy, it was found that ortho-fluoroaryl substituted pyrroles exist as inhibited conformational isomers, with intramolecular interactions between the hydrogen and fluorine atoms. The ratio of obtained rotamers was determined to be constant regardless of temperature, based on 2D HMBC and HSQC NMR spectroscopy.