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Asymmetric Photocatalysis by Intramolecular Hydrogen‐Atom Transfer in Photoexcited Catalyst–Substrate Complex
Author(s) -
Zhang Chenhao,
Chen Shuming,
Ye ChenXi,
Harms Klaus,
Zhang Lilu,
Houk K. N.,
Meggers Eric
Publication year - 2019
Publication title -
angewandte chemie
Language(s) - English
Resource type - Journals
eISSN - 1521-3757
pISSN - 0044-8249
DOI - 10.1002/ange.201905647
Subject(s) - intramolecular force , catalysis , rhodium , photochemistry , hydrogen atom , chemistry , substrate (aquarium) , photocatalysis , reaction mechanism , enone , stereochemistry , organic chemistry , alkyl , oceanography , geology
Abstract 3‐(2‐Formylphenyl)‐1‐pyrazol‐1‐yl‐propenones undergo an asymmetric photorearrangement to benzo[ d ]cyclopropa[ b ]pyranones with up to >99 % ee , which is catalyzed by a bis‐cyclometalated rhodium catalyst in the presence of visible light. Mechanistic experiments and DFT calculations support a mechanism in which a photoexcited catalyst/substrate complex triggers an intramolecular hydrogen‐atom transfer followed by a highly stereocontrolled hetero‐Diels–Alder reaction. In this reaction scheme, the rhodium catalyst fulfills multiple functions by 1) enabling visible‐light π→π* excitation of the catalyst‐bound enone substrate, 2) facilitating the hydrogen‐atom transfer, and 3) providing the asymmetric induction for the hetero‐Diels–Alder reaction.