Preparation of Phenazine N5,N10-Dioxides. Effects of Benzofuroxan Substituents in the Outcome of their Expansion Reaction with Phenolates

It is well known that phenolate anions react with benzo[1,2-c]1,2,5-oxadiazole N-oxides (benzofuroxans) to afford phenazine N,N-dioxide derivatives. These are obtained through an heterocycle expansion process by reaction of the corresponding 1,2,5-oxadiazole system with the phenolate carbanion generated in basic medium attacking one of the heterocyclic nitrogen (Figure 1). When substituted benzofuroxans and phenolates are used, the reactions yield a mixture of 6and 9or 7and 8-isomers.