Electrochemically induced chain reactions. Reactions of aromatic aldehydesinduced by electrogenerated bases

The electrochemical reduction of aromatic aldehydes (ArCHO) such as 2-napht haldehyde (1), 4-dimethylaminobenzaldehyde (2), 3-methoxybenzaldehyde (3) a nd 2-pyrrole carboxaldehyde (4) in N,N-dimethylformamide with tetrabutylamm onium hexafluorophosphate as supporting electrolyte, under an argon atmosph ere and in the presence of protons donors (AH(2)) such as fluorene (FlH(2)) or indene (InH2), gives products such as (ArCH=A) and/or [ArCH(AH)(2)] (AH = FlH or InH). Three consecutive chain reactions are initiated by proton a bstraction from fluorene or indene by a base electrogenerated by the reduct ion of ArCHO. The propagation steps of the first chain reaction involves ad dition of AH(-) to ArCHO and protonation of the resulting alcoholate with r egeneration of AH(-) to give the carbinol ArCH(OH)AH. The second chain reac tion is the base-catalyzed dehydration of ArCH(OH)AH to ArCH=A. The third i s the addition of AH(-) to ArCH=A, giving ArCH(AH)(2) with regeneration of AH(-).