First Total Synthesis of the Cytotoxic Carbazole Alkaloid Excavatine‐A and Regioselective Annulation to Pyrano[2,3‐a]carbazoles and [1,4]Oxazepino[2,3,4‐jk]carbazoles

We describe the first total synthesis of the cytotoxic carbazole alkaloid excavatine‐A. The carbazole framework was constructed through double C–H bond activation of a diarylamine by using our palladium(II)‐catalyzed oxidative cyclization. Treatment of the intermediate 8‐hydroxycarbazoles with prena...

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Bibliographic Details
Published in:European journal of organic chemistry 2017-06, Vol.2017 (22), p.3288-3300
Main Authors: Brütting, Christian, Kataeva, Olga, Schmidt, Arndt W., Knölker, Hans‐Joachim
Format: Article
Language:English
Subjects:
Activation
Additives
Alkaloids
Carbazoles
Chemical reactions
Cytotoxicity
Organic chemistry
Oxazepines
Palladium
Reaction time
Regioselectivity
Selectivity
Synthesis
Total synthesis
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Summary:We describe the first total synthesis of the cytotoxic carbazole alkaloid excavatine‐A. The carbazole framework was constructed through double C–H bond activation of a diarylamine by using our palladium(II)‐catalyzed oxidative cyclization. Treatment of the intermediate 8‐hydroxycarbazoles with prenal and different additives led either to pyrano[2,3‐a]carbazoles or to [1,4]oxazepino[2,3,4‐jk]carbazoles. The pyran annulation was investigated to determine the influence of substitution pattern, additives, and reaction time on the selectivity. We describe the first total synthesis of the 2,8‐dioxygenated carbazole alkaloid excavatine‐A. Reaction of the intermediate 8‐hydroxycarbazoles with prenal under Brønsted acid catalysis afforded [1,4]oxazepino[2,3,4‐jk]carbazoles, whereas a combination of Lewis and Brønsted acid led to pyrano[2,3‐a]carbazoles.
ISSN:1434-193X
1099-0690
DOI:10.1002/ejoc.201700515