期刊
CHEMISTRY-A EUROPEAN JOURNAL
卷 25, 期 22, 页码 5658-5663出版社
WILEY-V C H VERLAG GMBH
DOI: 10.1002/chem.201900587
关键词
C-C coupling; C-H activation; homogeneous catalysis; nitrogen heterocycles; radicals
资金
- Netherlands Organization for Scientific Research (NWO TOP-Grant) [716.015.001]
- University of Amsterdam (Research Priority Area Sustainable Chemistry)
- National Science Foundation (Graduate Research Fellowship Program, NSF-NWO-GROW-project) [DGE-1419118]
Radical cyclization via cobalt(III)-carbene radical intermediates is a powerful method for the synthesis of (hetero)cyclic structures. Building on the recently reported synthesis of five-membered N-heterocyclic pyrrolidines catalyzed by Co-II porphyrins, the [Co(TPP)]-catalyzed formation of useful six-membered N-heterocyclic piperidines directly from linear aldehydes is presented herein. The piperidines were obtained in overall high yields, with linear alkenes being formed as side products in small amounts. A DFT study was performed to gain a deeper mechanistic understanding of the cobalt(II)-porphyrin-catalyzed formation of pyrrolidines, piperidines, and linear alkenes. The calculations showed that the alkenes are unlikely to be formed through an expected 1,2-hydrogen-atom transfer to the carbene carbon. Instead, the calculations were consistent with a pathway involving benzyl-radical formation followed by radical-rebound ring closure to form the piperidines. Competitive 1,5-hydrogen-atom transfer from the beta-position to the benzyl radical explained the formation of linear alkenes as side products.
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