We report the design and synthesis of porous organic polymers (POPs) based on N-phenylphenothiazine (PTH), which typically requires ultraviolet-light irradiation, as a class of purely organic, stable, and reusable visible-light heterogeneous photocatalysts. The extended π-conjugation and polymeric networks not only enhance visible-light absorption but also accelerate the reaction rates. More intriguingly, the switchable bromoalkylation and cyclopropanation of unactivated terminal alkenes could be achieved by simply tuning the solvents under PTH-POP catalysis. The flexible manipulation of the resultant products further demonstrates its synthetic utility. 

Phenylphenothiazine-Based Porous Organic Polymers as Visible-Light Heterogeneous Photocatalysts for Switchable Bromoalkylation and Cyclopropanation of Unactivated Terminal Alkenes

Intermolecular cyclopropanation of mono-, di-, and trisubstituted olefins with α-bromo-β-ketoesters and α-bromomalonates under organophotocatalysis is reported. The reaction displays broad functional group tolerance, including substrates bearing acids, alcohols, halides, ethers, ketones, nitriles, esters, amides, carbamates, silanes, stannanes, boronic esters, as well as arenes, and furnishes highly substituted cyclopropanes. The transformation may be performed in the presence of air and moisture with 0.5 mol % of a benzothiazinoquinoxaline as organophotocatalyst. Mechanistic investigations, involving Stern–Volmer quenching, quantum yield determination, and deuteration experiments, are carried out, and a catalytic cycle for the transformation is discussed.

https://pubs.acs.org/doi/pdf/10.1021/jacs.2c11680

Intermolecular Organophotocatalytic Cyclopropanation of Unactivated Olefins

A three-component reaction for the synthesis of substituted anilines by a gold(i)-catalyzed domino reaction was developed. Cationic gold catalysts selectively and sequentially activated two different alkynes, which were involved in pyrrole synthesis and subsequent Diels-Alder reaction. The sequential formal (3 + 2) annulation/Diels-Alder reaction of three components provided a variety of substituted anilines in a modular fashion. Moreover, utility of the aniline products was demonstrated by derivatization to substituted benzoxazines, which are pharmaceutically important heterocycles.

Synthesis of substituted anilines via a gold-catalyzed three-component reaction

Visible‐Light‐Mediated Cyclopropanation: Recent Progress

Intramolecular activation of imidate with cationic gold(I) catalyst: A new benzylation reaction of alcohols

A mild photoredox-catalyzed intramolecular cyclopropanation of alkenes with α-bromo-β-keto esters in an aqueous medium was developed. The sequential reaction process comprising the intramolecular radical addition of α-bromo-β-keto esters to olefins under photoredox catalysis, and subsequent cyclization to form cyclopropane proceeds in one-pot under exceptionally mild conditions at room temperature in the presence of 2,6-lutidine. A broad range of substrates consisting of various alkenes and both base- and acid-sensitive functionalized esters were feasible under the reaction conditions, resulting in a wide range of functionalized bicyclic cyclopropanes.

Photoredox-catalyzed intramolecular cyclopropanation of alkenes with α-bromo-β-keto esters

A gold-catalyzed introduction of various terminal alkynes to acetals was investigated. Extensive optimization of the reaction conditions revealed that thermally stable cationic gold catalysts bearing bulky ligands such as 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene 3-1H-benzo[d][1,2,3]triazolyl gold trifluoromethanesulfonate (IPrAu(BTZ-H)OTf) were particularly suitable for the reaction. Additionally, significant solvent effects were observed. Ether solvents such as tetrahydrofuran (THF), cyclo pentyl methyl ether (CPME), and 1,4-dioxane were effective for the reaction. Studies on the scope of substrates and alkynes indicated that various alkynes and acetals were feasible to provide a wide range of propargylic ethers.

Miyu Furuta

Papers

Photoredox-catalyzed intramolecular cyclopropanation of alkenes with α-bromo-β-keto esters

Synthesis of Propargylic Ethers by Gold-Mediated Reaction of Terminal Alkynes with Acetals.