Unexpected oxidation of a substituted benzo[a]phenazine: oxidative cleavage of a double bond and formation of a macrolactone

Peroxidation of the phenazine of β-lapachone using m-ClC₆H₄CO₃H/CH₂Cl₂ furnished a macrolactone with a rigid 10-membered ring, and the corresponding N-oxide, originating from the oxidative cleavage of the aromatic double bond at the site of fusion of the dihydropyrane moiety with the phenazine component. A third compound, a dihydrobenzophenazine-5-one, was also generated probably by hydrolysis of an intermediate epoxide-acetal or α-hydroxy-hemiacetal formed at the same site. All of the new compounds were fully characterized by X-ray diffractometry and spectroscopic methods.