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

Hans-Joachim Knölker; Michael Bauermeister; Jörn-Bernd Pannek; Marcus Wolpert

doi:10.1055/s-1995-4430

Synthesis 1995; 1995(4): 397-408
DOI: 10.1055/s-1995-4430

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

Hans-Joachim Knölker^* , Michael Bauermeister, Jörn-Bernd Pannek, Marcus Wolpert

^*Institut für Organische Chemie, Universität Karlsruhe, Richard-Willstätter-Allee,D-76131 Karlsruhe, Germany, Fax +49(721)698529

Abstract

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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.

tricarbonyliron complexes - electrophilic substitution - iron-mediated quinone imine cyclization - 3-hydroxycarbazoles - 4b,8a-dihydrocarbazol-3-ones

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