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Angew Chem Int Ed Engl. 2019 Oct 7;58(41):14462-14466. doi: 10.1002/anie.201905647. Epub 2019 Aug 30.

Asymmetric Photocatalysis by Intramolecular Hydrogen-Atom Transfer in Photoexcited Catalyst-Substrate Complex.

Author information

1
Fachbereich Chemie, Philipps-Universität Marburg, Hans-Meerwein-Straße 4, 35043, Marburg, Germany.
2
Department of Chemistry and Biochemistry, University of California, Los Angeles, CA, 90095-1569, USA.

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.

KEYWORDS:

Diels-Alder; asymmetric catalysis; hydrogen atom transfer; photochemistry; rhodium

PMID:
31469211
DOI:
10.1002/anie.201905647

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