The photoredox catalytic cycle with an electron‐deficient perylene bisimide (PBI) runs as long as green light is provided. The substrate silylenolethers and aldehydes enter the cycle, are oxidized to their radical cations and converted to acetals and ketals, which leave the cycle as products. Acid catalysts are not needed. Ketal and acetal groups protect the carbonyl compounds like helmets. More information can be found in the Research Article by H.‐A. Wagenknecht and D. Steuernagel (DOI: 10.1002/chem.202203767).
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.
Acetals and ketals are among the most important protecting groups for carbonyl compounds. A new method for acetalization and ketalization by means of photoredox catalysis has been developed. A biscyanolated perylene bisimide is used as an electron-poor photocatalyst, together with green light (525 nm LED). Silylenolethers derived from aldehydes react efficiently to give acetals in good to excellent yields. A broad substrate range was shown with respect to both the aldehydes and the alcohols. The functional group tolerance is high; in particular, acid-and hydrogen-labile protecting groups are tolerated. Aldehydes can also be directly and selectively converted into the respective acetals. Only ketones must be converted to their silylenolethers before ketalization. This photocatalytic method works without any use of acids or photoacids, and does not need any additives or H-atom transfer reagents. Hence, it broadens the substrate scope and repertoire of photoredox catalysis with respect to carbonyl chemistry.
A new method activates CCl 3 F by means of photoredox catalysis and functionalizes alkenes by the CCl 2 F group. N-phenylphenothiazine is used as strongly reducing organophotocatalyst. The photoredox catalytic approach combines the productive disposal of this ozone depleting material and greenhouse gas with the synthesis of potentially useful organic compounds, complements the concept of atom transfer radical addition, and allows for the first time direct synthetic access to the CCl 2 F group as structural motif. The substrate scope is broad and the multifunctionalized class of products allows for a variety of following-up transformations.
What is the most significant result of this study?A new photocatalytic method for the acetalization and ketalization of aldehydes and silylenolethers was developed that uses only a biscyanolated perylene bisimide as photocatalyst in substoichiometric amounts and green light from LEDs. The tolerance of functional groups is remarkably high; in particular, acid-labile Boc groups are tolerated. This is due to the fact that the method does not require the use of any acids, photoacids or H-atom transfer reagents as additives.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.