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Electrochemical oxidation of 2,4,5‐triaryl‐substituted pyrroles. II . Oxidative dimerization of 4,5‐diphenyl‐2‐mesitylylpyrrole
Author(s) -
Silvestri G.,
Gambino S.,
Filardo G.,
Petruso S.,
Caronna S.,
Sprio V.
Publication year - 1989
Publication title -
journal of heterocyclic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.321
H-Index - 59
eISSN - 1943-5193
pISSN - 0022-152X
DOI - 10.1002/jhet.5570260244
Subject(s) - chemistry , dimer , electrochemistry , pyrrole , monomer , medicinal chemistry , derivative (finance) , selectivity , photochemistry , organic chemistry , polymer chemistry , catalysis , electrode , polymer , financial economics , economics
2,4,5‐Triaryl‐substituted pyrroles lead, upon chemical or electrochemical oxidation, to an intermediate β‐β'‐dimer, which, in the course of the reaction, undergoes further oxidation to a tetracyclic derivative. To improve the selectivity towards the uncyclized dimer the oxidation of a triarylpyrrole in which the ortho positions of the phenyl group in position 2 are hindered by the presence of methyl groups was attempted. The cyclization was hindered, but an α‐β'‐dimer was obtained as the major product. An unexspected isomeric α‐β'‐dimer, in which the mesitylyl group is shifted into the β position of the pyrrole ring which undergoes the oxidation, was obtained in minor amounts. Electroanalytical data indicate that the process goes through the formation of a monomeric radical cation, followed by a slow chemical reaction.