Electrochemically induced chain reactions: the addition of fluorene and indene to aromatic aldehydes initiated by electrochemical reduction

Abstract

The electrochemical reduction at −30 °C of 2,6-dichlorobenzaldehyde (1a), benzaldehyde (1b), and terephthalaldehyde (2) in tetrahydrofuran with tetrabutylammonium perchlorate as supporting electrolyte, under an argon atmosphere and in the presence of fluorene or indene, gives carbinols resulting from the addition of fluorene or indene and requires only a catalytic amount of electricity. The chain reaction is initiated by proton abstraction from fluorene or indene by a base electrogenerated by reduction of the aldehyde and the propagation involves the addition of the carbanion to the aldehyde followed by regeneration of the nucleophile by proton transfer from the proton donor to the alkoxide anion (base-catalyzed addition). The voltammetric behavior of the aldehydes in the absence and in the presence of fluorene or indene is also presented. Key words: electrochemical reduction, aromatic aldehydes, addition of fluorene (indene), base catalysis, chain reaction.