Metal‐Free CC Coupling Reactions with Tetraguanidino‐Functionalized Pyridines and Light

Herein we report on metal‐free C?C 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 N?C bond cleavage of the initially formed N‐alkyl pyridinium ion upon excitation with visible light. The released alkyl radicals subsequently dimerize to the C?C coupling product. 2,3,6,7‐Tetrakis(tetramethylguanidino)pyridine, which is a strong electron donor (E_1/2(CH₂Cl₂)=?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.