Journal
ANGEWANDTE CHEMIE-INTERNATIONAL EDITION
Volume 59, Issue 24, Pages 9639-9645Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/anie.202001200
Keywords
[2+2] photocycloaddition; dearomatization; gadolinium; ring-expansion; visible-light photocatlysis
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Funding
- Deutsche Forschungsgemeinschaft (Leibniz Award
- Priority Program LCRMC project) [STR 1186/6-1]
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Lanthanide photocatalysts are much less investigated in synthetic chemistry than rare and expensive late transition metals. We herein introduce Gd-III photocatalysis of a highly regioselective, intermolecular [2+2] photocycloaddition/ring-expansion sequence with indoles, which could provide divergent access to cyclopenta[b]indoles and indolines. A simple and commercially available Gd(OTf)(3) salt is sufficient for this visible-violet-light-induced transformation. The reaction proceeds either through a transient or start-to-end dearomatization cascade and shows excellent regioselectivity (usually >95:5 r.r.), broad scope (59 examples), good functional group tolerance and facile scale-up under mild, direct visible-light-excitation conditions. Mechanistic investigations reveal that direct excitation of the Gd(OTf)(3)/indole mixture gives an excited state intermediate, which undergoes the subsequent [2+2] cycloaddition and cyclobutane-expansion cascade.
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