Transition Metal-Diene Complexes in Organic Synthesis, Part 22.The Iron-Mediated Quinone Imine Cyclization: A General Route to 3-Hydroxycarbazoles

Abstract

Electrophilic aromatic substitution of 4-methoxyarylamines 2by the tricarbonyliron-complexed cyclohexadienylium cations 1leading to the iron complexes 3 is described. Chemoselectiveoxidation of the arylamine moiety of the complexes 3 to the quinoneimine and iron-mediated quinone imine cyclization using appropriate oxidizingreagents (activated manganese dioxide or thallium(III) trifluoroacetate) ledto the tricarbonyliron-complexed 4b,8a-dihydrocarbazol-3-ones 5.Demetalation of 5 with trimethylamine N-oxideat room temperature occurred with concomitant aromatization of the organicligand and provided a broad access to the 3-hydroxy-9H-carbazoles 7.