Photocatalytic Systems with Flavinium Salts: From Photolyase Models to Synthetic Tool for Cyclobutane Ring Opening

Abstract

Two new photocatalytic systems based on flavinium species formed in situ by protonation of riboflavin-tetraacetate (1) with triflic acid or prepared in advance via alloxazine quaternization are presented as effective tools for oxidative cyclobutane ring [2 + 2] cycloreversion using visible light. The system with 1,3-dimethyl-8-trifluoromethylalloxazinium perchlorate (2c) was found to be superior allowing an acid-free mild procedure, which results in the opening of cyclobutanes with high oxidation potential (up to 2.14 V) and/or with sensitive groups (e.g., furan) without side reactions.

Visible Light [2+2] Photocycloaddition Mediated by Flavin Derivative Immobilized on Mesoporous Silica

“…We demonstrated the usefulness of the prepared heterogeneous alloxazine catalyst 2 in the visible light for [2+2] photocycloaddition of various dienes with a special focus on the transformations characterized by lower conversion and/or problematic product isolation under homogeneous conditions. We believe this approach to prepare a solid supported catalyst may be useful for other flavin derivatives for which photocatalytic properties have been of high research interest . It should bring new environmentaly benign photoorganocatalytic procedures.…”

Deazaflavin reductive photocatalysis involves excited semiquinone radicals

“…dFl dF 0 in its oxidised form serves as a light-harvesting antenna in photolyases 29 . Inspired by nature, artificial Fl derivatives as well as flavoenzymes have been applied in photoredox catalysis and photobiocatalysis, mainly in oxidative transformations or in energy transfer processes 6,20,[30][31][32][33][34][35][36][37][38][39][40][41][42][43][44] . Photoenzymatic radical polymerisation employing highly reducing excited FADH* − known from photolyases is rare and a very recent example of a photoreductive process with Fl 45 .…”

Nature is the Cure: Engineering Natural Redox Cofactors for Biomimetic and Bioinspired Catalysis

“…Blue‐light irradiation of flavin induces a dramatic change in its redox properties and a logical application of these notable photophysical properties has been found in the development of photocatalytic systems . Synthetic flavin analogues have been designed and shown to perform a wide range of reactions including aerobic oxidoreductions and cycloreversion . Most of these transformations build on the well documented ability of flavins to react with radicals in oxidative manifolds, and are directly inspired by the involvement of flavin cofactors in enzymes such as photolyase, which repairs UV‐damaged DNA by opening the cyclobutane adducts arising light‐induced pyrimidine dimers [2+2] cycloaddition.…”