Abstract
AbstractConventional photoredox catalytic additions of alcohols to olefins require additives, like thiophenol, to promote back electron transfer. The concept of “photozymes” assumes that forward and backward electron transfer steps in a photoredox catalytic cycle are controllable by substrate binding to photocatalytically active peptides. Accordingly, we synthesized a short tripeptide modified with 1,7‐dicyano‐perylene‐3,4 : 9,10‐tetracarboxylic acid bisimide as photoredox catalyst. This peptide undergoes an unconventional photoredox catalytic cycle with the radical anion and dianion of the perylene bisimide‐peptide as intermediates. The photoredox catalytic reactions with α‐phenyl styrenes as substrates require remarkably low catalyst loadings (0.5 mol%) and give the methoxylation products in high yields. The concept of “photozymes” for photoredox catalysis has significant potential for other photocatalytic reactions, in particular with respect to enantioselective photocatalysis.
Highlights
Peptides, especially those with only less than ten amino acids, are an established type of catalysts for important classes of organic reactions, including oxidations, reductions, group transfers, like acylations, additions and CÀ C-bond formation, in particular aldol reactions.[1]
We investigated the photocatalysis with substrate 2 by UV/ Vis absorption spectroscopy in order to get deeper insights why the photocatalytic reactions with P1 do not need thiophenol, in contrast to those with 1.[16]. Remarkably, the UV/Vis absorbance of a reaction solution of P1 (25 μM in MeOH) in the presence of substrate 2 (3 mM) shows after a very short time of irradiation (2 min) the nearly complete conversion to the two-electronreduced radical dianion P12À according to its spectroscopic signature with a characteristic maximum at 605 nm (Figure 6)
We show by this work that both the fast forward and, more importantly, the slow backward electron transfer steps are controllable by substrate binding to photocatalytically active peptides (“photozymes”)
Summary
Barriers of reactions by alternative pathways that are not accessible by the conventional thermal approach.[4]. As organic photoredox catalysts to convert aromatic alkenes to products with Markovnikov- and anti-Markovnikov orientation, respectively. Forward and backward electron transfer might be controllable by substrate binding to photocatalytically active peptides. We call these peptides “photozymes” and established this new concept by short proline-rich peptides modified with 1-(N,N-dimethylamino)pyrene as photoredox active chromophore, such as P0, that catalyze nucleophilic additions of alcohols to α-phenyl styrenes to products with Markovnikov orientation (Figure 1). We provide important mechanistic insights how this “photozyme” work efficiently without thiophenol as additive reagent
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