Transition metal-diene complexes in organic synthesis, Part 22. The iron-mediated quinone imine cyclization: A general route to 3-hydroxycarbazoles

Article abstract of DOI:10.1055/s-1995-4430

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