Proline‐Rich Short Peptides with Photocatalytic Activity for the Nucleophilic Addition of Methanol to Phenylethylenes

Abstract

Short proline‐rich peptides were synthesized and modified with 1‐(N,N‐dimethylamino)pyrene by copper(I)‐catalyzed cycloaddition. They perform photoredox catalysis of the nucleophilic addition of methanol to 1,1‐diphenylethylene derivatives into products with Markovnikov orientation. The common additive triethylamine is avoided because forward and backward electron transfer is controlled by substrate binding. A free carboxylic function in the substrate allows more precise substrate binding and defines the electron transfer path better than the unspecific exciplex formation with the substrate bearing a carboxylic ester. A proline‐type turn is an advantage for photoredox catalysis, but a proline‐induced helix is not required. This is the first successful example for introducing secondarily structured peptides to photoredox catalysis.

N-Arylphenothiazines as strong donors for photoredox catalysis – pushing the frontiers of nucleophilic addition of alcohols to alkenes

“…The principal problem of this type of photoredox catalytic cycle is that the back-electron transfer cannot compete with the initial electron transfer because both components, 1 +· and 13 −· , are formed only in stationary low concentrations. In the past, we used electron mediators as additives (triethylamine) [19,26] or peptides with substrate-binding sites [31–32] to overcome this problem. For the current work, we propose a radical ion pair in a solvent cage that undergoes an extremely fast proton transfer followed by the intracage back-electron transfer, since triethylamine is no longer needed (vide infra).…”

Photoinduced Organic Reactions by Employing Pyrene Catalysts

“…The same research group achieved the nucleophilic addition of methanol to phenylethylene 24 without an electron shuttle by using proline-bearing short peptides Py7 that contain the 1-( N , N -dimethylamino)pyrene ( Py6 ) moiety (Scheme 10 ). 14 Peptides with proline linkers of different chain lengths were prepared and tested as photoredox catalysts. Forward and backward electron transfers can be tuned by binding the carboxylic acid or ester groups of 24 with the guanidine or amide moieties of Py7 via hydrogen bonding and/or electrostatic interactions.…”

Photo- and electro-chemical strategies for the activations of strong chemical bonds

“…The Wagenknecht group published a series of papers on Markovnikov addition of alcohols to olefins under highly photoreducing conditions. [160][161][162] Aiming for a redshifted and more photoreducing PTH derivative, the authors designed and tested a new series of N-arylphenothiazines, with N-(para-dialkylaminophenyl)phenothiazines performed well in the reductive activation of olefins (Scheme 58). 162 The photoexcited PTH1 and PTH2 derivatives were able to reduce unactivated olefin 202 to its radical anion 204 by SET.…”