Electrochemically induced CH functionalization using bromide ion/2,2,6,6-tetramethylpiperidinyl-N-oxyl dual redox catalysts in a two-phase electrolytic system

• Electrocatalytic CH bond functionalization of tetrahydroisoquinolines is reported.
• The transformation is mediated by a bromide ion/TEMPO dual redox catalyst system.
• The transformation is conducted in a two-phase electrolytic medium.
• The mechanism is proposed to proceed via a sequence of oxidation and addition reactions involving water as a nucleophile.
• The procedure features wide substrate scope, the use of mild reaction conditions.

The electrochemical oxidative functionalization of benzylic CH bonds, mediated by a dual bromide ion/2,2,6,6-tetramethylpiperidinyl-N-oxyl (TEMPO) redox catalyst system in a two-phase electrolytic medium, has been explored using cyclic voltammetry (CV) and preparative electrolysis techniques. The results show that electron transfer between TEMPO+ and a neutral substrate occurs with an efficiency that depends upon the presence of a base. The preparative scale electrolysis led to the formation of dihydro-isoquinolinones, isochromanone and xanthenone in moderate to excellent yields. On the basis of the CV analysis and preparative electrolysis results, a reaction mechanism is proposed.