Complementary Photocatalytic Toolbox: Control of Intramolecular endo- versus exo-trig Cyclizations of α-Phenyl Olefins to Oxaheterocyclic Products

Abstract

The regioselectivity of the intramolecular cyclization of bifunctional α-phenyl alkenes can be controlled simply by the choice of the organic chromophore as the photocatalyst. The central photoredox catalytic reaction in both cases is a nucleophilic addition of the hydroxy function to the olefin function of the substrates. N,N-(4-Diisobutylaminophenyl)phenothiazine catalyzes exo-trig cyclizations, whereas 1,7-dicyanoperylene-3,4,9,10-tetracarboxylic acid bisimides catalyze endo-trig additions to products with anti-Markovnikov regioselectivity. We preliminarily report the photoredox catalytic conversions of 11 representative substrates into 20 oxaheterocycles in order to demonstrate the similarity, but also the complementarity, of these two variants in this photoredox catalytic toolbox.

Photoredox Catalytic Access to N,O‐Acetals from Enamides by Means of Electron‐Poor Perylene Bisimides

“…They form stable radical anions and dianions which were used in photochemistry [12] . The chromophore was further improved for its photocatalytic use by the 2,6‐di iso propylphenyl substituents at the imide nitrogens to enhance solubility in MeCN [13] and by the two cyano substituents at the core to make it even more electron‐poor. N , N ‐di‐(2,6‐di iso propyl)‐1,7‐dicyano‐perylen‐3,4,9,10‐tetracarboxylic acid imide ( PBI1 , Figure 2) has been successfully applied in the nucleophilic addition of alcohols to styrenes, turned out to give higher yields than the mesityl acridinium, [14] and the acid‐free synthesis of acetals from silylenol ethers and aldehydes [15] .…”

Reductive Activation of Aryl Chlorides by Tuning the Radical Cation Properties of N‐Phenylphenothiazines as Organophotoredox Catalysts

“…The tunability of organophotoredox catalysts is a prerequisite to adjust their applicability to distinct organic reactions. [23] Nphenylphenothiazines [19,[22][23][24] based on the core structure 1 fulfill this requirement in principle through their modular structure, as they can be modified at the core or at the phenyl substituents to vary the optoelectronic properties and adapt the photoredox properties to the particular synthetic problem. The introduction of dialkylamino substituents in the para position on the phenyl ring give strongly negative redox potentials.…”