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Synthesis of 1,1′‐ and 2,2′‐Bicarbazole Alkaloids by Iron(III)‐Catalyzed Oxidative Coupling of 2‐ and 1‐Hydroxycarbazoles

2017; Wiley; Volume: 24; Issue: 2 Linguagem: Inglês

10.1002/chem.201704554

1521-3765

Christian Brütting, Raphael F. Fritsche, Sebastian K. Kutz, Carsten Börger, Arndt W. Schmidt, Olga Kataeva, Hans‐Joachim Knölker,

Alkaloids: synthesis and pharmacology

Abstract We describe the synthesis of 1,1′‐ and 2,2′‐bicarbazoles by oxidative homocoupling of 2‐ and 1‐hydroxycarbazoles. The oxidative coupling using catalytic amounts of F 16 PcFe can be applied to both groups of substrates. Although F 16 PcFe generally provides the best yields for the synthesis of 1,1′‐bicarbazoles, di‐ tert ‐butyl peroxide affords better results for the 2,2′‐bicarbazoles. In our study, we have achieved the first syntheses of the biscarbalexines A–C, bisglybomine B, 2,2′‐dihydroxy‐7,7′‐dimethoxy‐3,3′‐dimethyl‐1,1′‐bicarbazole, bispyrayafoline C, and bisisomahanine. The iron‐catalyzed coupling of koenigine led to an improved synthesis of 8,8′′‐biskoenigine and afforded an unprecedented decacylic product. Oxidative coupling of 1‐hydroxycarbazoles led to bisclausenol, and to the first total syntheses of bismurrayafoline B and D.