Cathodic deprotonation of 5-substituted isoxazoles

The regularities of electroreduction of 5-substituted isoxazoles are studied by examining their cyclopropyl and phenyl derivatives. It is found that this process proceeds on a steel electrode according to the mechanism of direct cathodic deprotonation and is accompanied by the removal of a proton from the 3rd position of the isoxazole ring with the formation of a corresponding carbanion, which is readily isomerized to enolate anion of an open type. The same mechanism is realized also in the electroreduction of 5-substituted isoxazoles on cathodes with a high overpotential of hydrogen evolution (C, Hg). An alternative process, namely, an indirect cathodic deprotonation of 5-substituted isoxazoles, can be realized with the use of MeOH or t-BuOH as the prebases.