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Metal‐Free CC Coupling Reactions with Tetraguanidino‐Functionalized Pyridines and Light
Author(s) -
Stang Simone,
Kaifer Elisabeth,
Himmel HansJörg
Publication year - 2014
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201304987
Subject(s) - chemistry , pyridine , homolysis , pyridinium , photochemistry , dication , alkyl , radical , bond cleavage , medicinal chemistry , metal , reaction rate constant , ion , organic chemistry , kinetics , catalysis , physics , quantum mechanics
Herein we report on metal‐free CC coupling reactions mediated by the pyridine derivative 2,3,6,7‐tetrakis(tetramethylguanidino)pyridine under the action of visible light. The rate‐determining step is the homolytic NC bond cleavage of the initially formed N ‐alkyl pyridinium ion upon excitation with visible light. The released alkyl radicals subsequently dimerize to the CC coupling product. 2,3,6,7‐Tetrakis(tetramethylguanidino)pyridine, which is a strong electron donor ( E 1/2 (CH 2 Cl 2 )=−0.76 V vs. ferrocene) is oxidized to the dication. For alkyl=benzyl and allyl, relatively high first‐order rate constants of 0.23±0.03 and 0.13±0.03 s −1 were determined. Regeneration of neutral 2,3,6,7‐tetrakis(tetramethylguanidino)‐pyridine by reduction allows to drive the process in a cycle.