Flavin Photocatalysts for Visible-Light [2+2] Cycloadditions: Structure, Reactivity and Reaction Mechanism
| Authors | |
|---|---|
| Year of publication | 2018 |
| Type | Article in Periodical |
| Magazine / Source | CHEMCATCHEM |
| MU Faculty or unit | |
| 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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