Enantioselective Organo-Photocatalysis Mediated by Atropisomeric Thiourea Derivatives

Can photocatalysis be performed without electron or energy transfer? To address this, organo‐photocatalysts that are based on atropisomeric thioureas and display lower excited‐state energies than the reactive substrates have been developed. These photocatalysts were found to be efficient in promotin...

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Bibliographic Details
Published in:Angewandte Chemie 2014-05, Vol.126 (22), p.5710-5714
Main Authors: Vallavoju, Nandini, Selvakumar, Sermadurai, Jockusch, Steffen, Sibi, Mukund P., Sivaguru, Jayaraman
Format: Article
Language:English
Subjects:
Asymmetrische Katalyse
Catalysts
Chemistry
Coumarin
Dynamics
Energy transfer
Formations
Hydrogen bonding
Organokatalyse
Photocatalysis
Photocatalysts
Photochirogenese
Photokatalyse
Solar energy
Thioharnstoffe
Thiourea derivatives
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Summary:Can photocatalysis be performed without electron or energy transfer? To address this, organo‐photocatalysts that are based on atropisomeric thioureas and display lower excited‐state energies than the reactive substrates have been developed. These photocatalysts were found to be efficient in promoting the [2+2] photocycloaddition of 4‐alkenyl‐substituted coumarins, which led to the corresponding products with high enantioselectivity (77–96 % ee) at low catalyst loading (1–10 mol %). The photocatalytic cycle proceeds by energy sharing via the formation of both static and dynamic complexes (exciplex formation), which is aided by hydrogen bonding. Organophotokatalysatoren auf der Basis atropisomerer Thioharnstoffe wurden entwickelt. Diese Photokatalysatoren, deren angeregte Energiezustände niedriger liegen als die der reaktiven Substrate, ermöglichen die effiziente [2+2]‐Photocycloaddition 4‐Alkenyl‐substituierter Cumarine. Mit nur 1–10 Mol‐% Katalysator werden die Produkte hoch enantioselektiv erhalten (77–96 % ee).
ISSN:0044-8249
1521-3757
DOI:10.1002/ange.201310940