Development of a General Procedure To Access Recoverable Solid-Supported Photocatalysts for Use in Organic Synthesis.

The often high cost of bespoke transition-metal-containing and organic photocatalysts inspires the development of a practical and green method by which photocatalysts can be recovered and reused through multiple reaction iterations. Herein, we showcase a general method to access novel solid-supported photocatalysts (SSPCs) that are recoverable by simple filtration. Proof-of-concept SSPCs were successfully utilized in two representative photoredox-catalyzed transformations with recycled catalysts showing no loss in activity in iterative reaction runs. Additionally, the viability of one of these SSPCs in a multi-gram scale reaction was demonstrated with the development of an easily replicated flow system.

Photoredox Cyanomethylation of Indoles: Catalyst Modification and Mechanism.

The direct cyanomethylation of indoles at the 2- or 3-position was achieved via photoredox catalysis. The versatile nitrile synthon is introduced as a radical generated from bromoacetonitrile, a photocatalyst, and blue LED as a light source. The mechanism of the reaction is explored by determination of the Stern-Volmer quenching constants. By combining photophysical data and mass spectrometry to follow the catalyst decomposition, the catalyst ligands were tuned to enable synthetically useful yields of radical coupling products. A range of indole substrates with alkyl, aryl, halogen, ester, and ether functional groups participate in the reaction, affording products in 16-90% yields. The reaction allows the rapid construction of synthetically useful cyanomethylindoles, products that otherwise require several synthetic steps.

Milled Dry Ice as a C1 Source for the Carboxylation of Aryl Halides.

The use of carbon dioxide as a C1 chemical feedstock remains an active field of research. Here we showcase the use of milled dry ice as a method to promote the availability of CO2 in a reaction solution, permitting practical synthesis of arylcarboxylic acids. Notably, the use of milled dry ice produces marked increases in yields relative to those obtained with gaseous CO2, as previously reported in the literature.

Water-Soluble Iridium Photoredox Catalyst for the Trifluoromethylation of Biomolecule Substrates in Phosphate Buffered Saline Solvent.

The development of a water-soluble iridium catalyst enables the trifluoromethylation of polar small molecules and peptides in DMSO solution or aqueous media. The reaction was optimized in a microtiter plate format under ambient air, using commercial Langlois reagent as a CF3 radical source, blue LEDs for excitation, and using DPBS as solvent to provide up to 60% CF3- peptide.