Flavin News: Our Research Activity
Enhancing Flavins Photochemical Activity in Hydrogen Atom Abstraction and Triplet Sensitization through Ring-Contraction
Flavins undergo a fascinating ring-contraction reaction under basic conditions, which leads to so far unexplored new tricyclic molecules. These compounds were found to serve as very stable organic photocatalysts and can mediate both hydrogen atom abstraction and also triplet sensitization after photochemical excitation. Both catalytic activities can be applied in sequential transformations, which we used to directly access disubstituted cyclopentanones from tropolone.
Chemoselective Reduction of Barbiturates by Photochemically Excited Flavin Catalysts
Reductive flavin catalysis enables orthogonal reactivity when compared to the established reducing agent samarium(II) iodide. We show that excited, hydroquinoid flavins selectively reduce barbiturates in hybrid molecules that contain more than one site of potential reduction. This enables chemoselective reductive cyclization reactions which are not possible with samarium(II) iodide.
Photochemical Desaturation and Epoxidation with Oxygen by Sequential Flavin Catalysis
Flavins are active catalysts in a variety of different reactions depending on the conditions applied. In this study, we show that the same flavin catalyst can first perform photochemical oxidation reactions under an argon atmosphere, and subsequently oxygenate substrates when switching the atmosphere to oxygen. We show a series of transformations ranging from Saegusa-Ito oxidations to allylic C-C bond formations in the first step, and halogenation as well as epoxidation for the second reaction.
Enantiodivergent Photochemical Rearrangements Due to Different Coordination Modes at an Oxazaborolidine Lewis Acid Catalyst
In a collaborative study with the Bach and Dreuw groups, we showed that changing the coordination mode of a substrate to Lewis acid catalysts really matters! We could rationalize the strongly enantiodivergent outcome of an oxadi-π-methane rearrangement, which ranged from +92% ee to −45% ee with 2,4-cyclohexadienone substrates.
Molecular Flavin Catalysts for C-H Functionalisation and Derivatisation of Dehydroamino Acids
Quinoid flavin photocatalysts undergo reversible covalent C-C bond formation with diene and dehydroamino acid substrates. These C-C bonds are broken by addition of the persistent radical TEMPO, which results in hydroxylamine products in a catalytic fashion. We show a series of dehydroamino acid substrates and the follow-up chemistry of acylimine products.
Reduced Molecular Flavins as Single-Electron Reductants after Photoexcitation
Flavins are not just oxidants - they are excellent reductants as well! Inspired by the activity of DNA photolyase, Richard successfully searched for conditions to replace the rare-earth reductant samarium(II)iodide by flavin catalysis and discovered a mild procedure using gamma-terpinene as stoichiometric reductant.
Photochemical Deracemization of Chiral Alkenes via Triplet Energy Transfer
This collaborative study with the Bach and Bannwath groups contains an in-depth study of the mechanism of the triplet-sensitised deracemization of axially chiral alkene substrates. Key to understanding the high enantiomeric excess was the analysis of different pathways to the conical intersections in both diastereomeric catalyst-substrates complexes.
Photochemical Deracemization at sp3-Hybridized Carbon Centers via a Reversible Hydrogen Atom Transfer
In a collaboration with the Bach Lab, we were interested in the different molecular geometries of assemblies between hydantoin substrates and a chiral photocatalyst. Fascinatingly, the different binding of enantiomeric substrates allows very efficient deracemization via hydrogen atom transfer (HAT).
Molecular Editing of Flavins for Catalysis
In this Short Review, we give an overview of current strategies in tailoring molecular flavins for specific catalytic applications. We put special emphasis on linking the position of modification to changes in catalyst activity.
Synthetic C‐6 Aminoflavin Catalysts Enable Aerobic Bromination of Oxidation‐Prone Substrates
Our first independent group's research paper describes synthetic flavin catalysts, which allow bromination of tyrosine derivatives and other oxidation-prone substrates. We use inorganic halide salt and capitalize on reactivity that is known with flavoenzymes.
Site‐Selective Nitrene Transfer to Conjugated Olefins Directed by Oxazoline Peptide Ligands
A Fast and Reliable Screening Setup for Homogeneous Catalysis with Gaseous Reactants at Extreme Temperatures and Pressures
Intramolecular [2+2] Photocycloaddition of Cyclic Enones: Selectivity Control by Lewis Acids and Mechanistic Implications
Terahertz Spectroscopy of Tetrameric Peptides
Troponoid Atropisomerism: Studies on the Configurational Stability of Tropone-Amide Chiral Axes
A Stereodynamic Redox-Interconversion Network of Vicinal Tertiary and Quaternary Carbon Stereocenters in Hydroquinone-Quinone Hybrid Dihydrobenzofurans
Supramolecular chirality transfer in stereodynamic catalysts
Investigation of Strain-Promoted Azide–Alkyne Cycloadditions in Aqueous Solutions by Capillary Electrophoresis
Attracting Enantiomers: Chiral Analytes That Are Simultaneously Shift Reagents Allow Rapid Screening of Enantiomeric Ratios by NMR Spectroscopy
Stereodynamic Quinone–Hydroquinone Molecules That Enantiomerize at sp3-Carbon via Redox-Interconversion
By-design enantioselective self-amplification based on non-covalent product–catalyst interactions
Temperature-Controlled Bidirectional Enantioselectivity in Asymmetric Hydrogenation Reactions Utilizing Stereodynamic Iridium Complexes
A stereodynamic phosphoramidite ligand derived from 3,3′-functionalized ortho -biphenol and its rhodium(I) complexen A stereodynamic phosphoramidite ligand derived from 3,3′‐functionalized ortho‐biphenol and its rhodium(I) complex
Rotational Barriers of Substituted BIPHEP Ligands: A Comparative Experimental and Theoretical Study
Stereodynamic tetrahydrobiisoindole “NU-BIPHEP(O)”s: functionalization, rotational barriers and non-covalent interactions
Temperature-Controlled Bidirectional Enantioselectivity in a Dynamic Catalyst for Asymmetric Hydrogenation
Tautomerization-Mediated Molecular Switching Between Six- and Seven-Membered Rings Stabilized by Hydrogen Bonding
CuII-selective bispidine–dye conjugates
5,5′-Diamino-BIPHEP ligands bearing small selector units for non-covalent binding of chiral analytes in solution
Skeleton Decoration of NHCs by Amino Groups and its Sequential Booster Effect on the Palladium-Catalyzed Buchwald-Hartwig Amination
Synthesis of Molecular Gallium Hydrides by Means of Low-Temperature Catalytic Dehydrogenation
Straightforward Synthesis of Poly(dimethylsiloxane) Phases with Immobilized (1R)-3-(Perfluoroalkanoyl)camphorate Metal Complexes and Their Application in Enantioselective Complexation Gas Chromatography