Flavin Photocatalysts for Visible-Light [2+2] Cycloadditions: Structure, Reactivity and Reaction Mechanism

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Authors

MOJR Viktor PITROVA Gabriela STRAKOVA Karolina PRUKALA Dorota BRAZEVIC Sabina SVOBODOVA Eva HOSKOVCOVA Irena BURDZINSKI Gotard SLANINA Tomáš SIKORSKI Marek CIBULKA Radek

Year of publication 2018
Type Article in Periodical
Magazine / Source CHEMCATCHEM
MU Faculty or unit

Faculty of Science

Citation
Web Full Text
Doi http://dx.doi.org/10.1002/cctc.201701490
Keywords cycloaddition; energy transfer; natural products; photochemistry; reaction mechanisms
Description New photocatalysts from the flavin family were found to mediate the [2+2] photocycloaddition reaction. 3-Butyl-10-methyl-5-deazaflavin (3a) and 1-butyl-7,8-dimethoxy-3-methylalloxazine (2e), if irradiated by visible light, were shown to allow an efficient (Phi approximate to 3-10%) intramolecular cyclisation of various types of substrates including substituted styrene dienes and bis(aryl enones), considered as electron-rich and electron-poor substrates, respectively, without any additional reagent. The versatility of the procedure was demonstrated by the cyclisation of photosensitive cinnamyl (E)-3-iodoallyl ether. Structure-activity studies found alloxazine 2e was more active than 7-monosubstituted (R = Cl, Br and MeO) alloxazines. The introduction of chlorine and bromine atom on the deazaflavin skeleton did not enhance the catalytic efficiency of 3a. A detailed electrochemical and spectroscopic study explains the reaction mechanism proceeding through energy transfer from the flavin excited triplet state to the diene followed by its cyclisation.
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