Molecular Oxygen as a Redox Catalyst in IntramolecularPhotocycloadditions of Coumarins

Oxygen as a catalyst! While oxygen is usually excluded in nonoxidative photochemical reactions, the photocycloaddition of 3-(alk-4-en-1-yl)-substituted coumarins greatly benefits from the presence of O 2, which was shown to act as a redox catalyst, preferentially in combination with the common antioxidant 3,5-di-tert-butyl-4-hydroxytoluene (BHT). Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.This work was supported by the Universitat zu Koln and the Fonds der Chemischen Industrie. We thank Dr. S. Neufeind and Dipl.-Chem. A. M. Heinsch fur stimulating discussions.Kranz, DP.; Griesbeck, AG.; Alle, R.; Pérez Ruiz, R.; Neudörfl, JM.; Meerholz, K.; Schmalz, H. (2012). Molecular Oxygen as a Redox Catalyst in IntramolecularPhotocycloadditions of Coumarins. Angewandte Chemie International Edition. 51(24):6000-6004. doi:10.1002/anie.201201222S60006004512