A novel CAN‐SiO2‐mediated one‐pot oxidation of 1‐keto‐1,2,3,4‐tetrahydrocarbazoles to carbazoloquinones: Efficient syntheses of murrayaquinone A and koeniginequinone A

One‐pot oxidations of substituted 1‐keto‐1,2,3,4‐tetrahydrocarbazoles ( 1 ) to carbazole‐1,4‐quinones ( 2 ) are efficiently carried out by CAN‐SiO₂‐mediated reaction. This generalized protocol was successfully extended to the synthesis of two naturally occurring carbazoloquinones: murrayaquinone A ( 2b ) and koeniginequinone A ( 2g ). A plausible mechanism for this novel reaction involves formation of a 9‐hydroxy‐2,3,4,9‐tetrahydro‐1H‐carbazole‐1‐one followed by rearrangement to 1‐hydroxycarbazole derivatives, which are further oxidized by cerium (IV) to carbazoloquinones. J. Heterocyclic Chem., (2011).