Synthetic routes, characterization, electrochemical and spectral properties of p-substituted N-phenylpyrroles

A series of p-substituted N-phenylpyrroles, including 4-(1H-pyrrol-1-yl)phenol (1), 1-(4-methoxyphenyl)-1H-pyrrole (2), 1,1'-benzene-1,4-diylbis(1H-pyrrole) (4), 1,1'-biphenyl-4,4'diylbis(1H-pyrrole) (5) and 1-(4-bromophenyl)-1H-pyrrole (3), was prepared by means of a modified Clauson-Kaas method. Two new symmetrically and asymmetrically end-capped pyrrole thiophenes, namely 1-[4-(thiophen-2-yl)phenyl]-1H-pyrrole (6) and 1,1'-(bithiophen-5,5''-diyldibenzene-4,1-diyl)bis(1H-pyrrole) (7) were synthesized by using 3 as a building block and the Stille method as cross-coupling reaction. For both methods, the chemical yields ranged from 36 to 81% and the desired products were characterized by H-1 and C-13 NMR, IR, and mass spectrometry. Electrochemical properties and UV-visible absorption spectra were also investigated in order to evaluate the substituent electron-donor effects on the physicochemical parameters.