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Gadolinium Photocatalysis: Dearomative [2+2] Cycloaddition/Ring‐Expansion Sequence with Indoles
Author(s) -
Ma Jiajia,
Schäfers Felix,
Daniliuc Constantin,
Bergander Klaus,
Strassert Cristian A.,
Glorius Frank
Publication year - 2020
Publication title -
angewandte chemie international edition
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.831
H-Index - 550
eISSN - 1521-3773
pISSN - 1433-7851
DOI - 10.1002/anie.202001200
Subject(s) - regioselectivity , cycloaddition , chemistry , ring (chemistry) , indole test , cyclobutane , photocatalysis , excited state , photochemistry , combinatorial chemistry , lanthanide , stereochemistry , organic chemistry , catalysis , physics , ion , nuclear physics
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.