Journal
ANGEWANDTE CHEMIE-INTERNATIONAL EDITION
Volume 59, Issue 15, Pages 6115-6121Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/anie.202000252
Keywords
cobalt; cyclizations; polycycles; reaction mechanisms; terpenoids
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Funding
- National Institutes of Health through NIH R01 grant [GM-129264]
- NSF Graduate Research Fellowship
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A novel Co-II-catalyzed polyene cyclization was developed that is uniquely effective when performed in hexafluoroisopropanol as the solvent. The process is presumably initiated by metal-catalyzed hydrogen-atom transfer (MHAT) to 1,1-disubstituted or monosubstituted alkenes, and the reaction is remarkable for its tolerance of internal alkenes bearing either electron-rich methyl or electron-deficient nitrile substituents. Electron-rich aromatic terminators are required in both cases. Terpenoid scaffolds with different substitution patterns are obtained with excellent diastereoselectivities, and the bioactive C20-oxidized abietane diterpenoid carnosaldehyde was made to showcase the utility of the nitrile-bearing products. Also provided are the results of several mechanistic experiments that suggest the process features an MHAT-induced radical bicyclization with late-stage oxidation to regenerate the aromatic terminator.
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