electrochemical reduction of 3-cyano-1-methyl-pyridinium iodide, a nicotinamide dinucleotide model compound

3-Cyano-1-methylpyridinium iodide (1) exhibits one polarographic wave at pH values below 11 (E1/2 = -0.87 V vs. SCE). Electrolysis at the plateau potential of this wave, involving a one-electron uptake, leads to the formation of a mixture of four dimeric products, unambiguously identified as two diastereoisomer pairs: 3,3′-dicyano-1,1′-dimethyl-1,1′,4,4′-tetrahydro-4, 4′-bipyridines 2 and 3, and 3,3′-dicyano-1,1′-dimethyl-1,1′,6,4′-tetrahydro-6, 4′-bipyridines 4 and 5.