Electrolysis of N-Heterocyclic Compounds (Part II)

Abstract

Publisher Summary The chapter discusses the electrolytic reactions, in which a heterocyclic system is formed. The reactions will be treated under the following: ring formation reactions, ring contractions, and ring expansions. In the electrolytic formation of heterocyclic systems the role of the current is to bring one or both of the reaction centers to a suitable oxidation state. These reactions may be classified in different ways; they are treated according to the type of bond formed. Ring contractions may occur during reductions or oxidations. A kind of reductive ring expansion is reported, in which benzotriazole is converted to a dihydrobenzo-l,2,4-triazine. The reaction involves the known ring opening of benzotriazole to 2-aminophenylhydrazine by reduction in hydrochloric acid, followed by a condensation with a suitable orthoester; the yields are good and it is probably the most convenient way to prepare derivatives of benzo-1,2,4-triazine. The electrode reactions of heterocyclic compounds, in which a reduction or oxidation of the nucleus takes place, are discussed in the chapter. Ring systems carrying substituents are included if the substituent is not reduced or oxidized, and the redox reactions of the ring are not changed in type by the substituent. Alkyl derivatives of heterocyclic compounds may be oxidized to carboxylic acids, for example, methylpyridines and methylpyridine N-oxides by superoxide ions, generated electrochemically in DMF. Heterocyclic hydroxyl derivatives can be divided into two groups according to whether or not the hydroxyl group is exocyclic.