TRANSITION METAL-DIENE COMPLEXES IN ORGANIC-SYNTHESIS .22. THE IRON-MEDIATED QUINONE IMINE CYCLIZATION - A GENERAL-ROUTE TO 3-HYDROXYCARBAZOLES

Electrophilic aromatic substitution of 4-methoxyarylamines 2 by the tr icarbonyliron-complexed cyclohexadienylium cations 1 leading to the ir on complexes 3 is described. Chemoselective oxidation of the arylamine moiety of the complexes 3 to the quinone imine and iron-mediated quin one imine cyclization using appropriate oxidizing reagents (activated manganese dioxide or thallium(III) trifluoroacetate) led to the tricar bonyliron-complexed 4b, 8a-dihydrocarbazol-3-ones 5. Demetalation of 5 with trimethylamine N-oxide at room temperature occurred with concomi tant aromatization of the organic ligand and provided a broad access t o the 3-hydroxy-9H-carbazoles 7.