Room-Temperature Photochemical Copper-Mediated Fluorination of Aryl Iodides.

This report describes a method for the photochemical Cu-mediated fluorination of aryl iodides with AgF via putative aryl radical (Ar•) intermediates. It involves irradiating an aryl iodide with UVB light (λ = 313 nm) in the presence of a mixture of Cu and Cu salts and AgF. Under these conditions, fluorination proceeds at room temperature for substrates containing diverse substituents, including alkoxy and alkyl groups, ketones, esters, sulfonate esters, sulfonamides, and protected amines.

Strategies for the Photocatalytic Generation of Carbanion Equivalents for Reductant-Free C-C Bond Formations.

ConspectusThe use of photocatalysis in organic chemistry has encountered a surge of novel transformations since the start of the 21st century. The majority of these transformations are driven by the generation and subsequent reaction of radicals, owing to the intrinsic property of common photocatalysts to transfer single electrons from their excited state. While this is a powerful and elegant method to develop novel transformations, several research groups recently sought to further extend the toolbox of photocatalysis into the realm of polar ionic reactivity by the formation of cationic as well as anionic key reaction intermediates to furnish a desired product.

Visible-Light-Promoted Metal-Free Synthesis of (Hetero)Aromatic Nitriles from C(sp )-H Bonds*.

The metal-free activation of C(sp )-H bonds to value-added products is of paramount importance in organic synthesis. We report the use of the commercially available organic dye 2,4,6-triphenylpyrylium tetrafluoroborate (TPP) for the conversion of methylarenes to the corresponding aryl nitriles via a photocatalytic process. Applying this methodology, a variety of cyanobenzenes have been synthesized in good to excellent yield under metal- and cyanide-free conditions.

Photocatalytic Reductive Radical-Polar Crossover for a Base-Free Corey-Seebach Reaction.

A metal-free generation of carbanion nucleophiles is of prime importance in organic synthesis. Herein we report a photocatalytic approach to the Corey-Seebach reaction. The presented method operates under mild redox-neutral and base-free conditions giving the desired product with high functional group tolerance.

Photocatalytic carbanion generation from C-H bonds - reductant free Barbier/Grignard-type reactions.

We report a redox-neutral method for the generation of carbanions from benzylic C-H bonds in a photocatalytic Grignard-type reaction. The combination of photo- and hydrogen atom transfer (HAT) catalysis enables the abstraction of a benzylic hydrogen atom, generating a radical intermediate. This radical is reduced by the organic photocatalyst to a carbanion, which is able to react with electrophiles such as aldehydes or ketones, yielding homobenzylic secondary and tertiary alcohols.

Photocarboxylation of Benzylic C-H Bonds.

The carboxylation of sp-hybridized C-H bonds with CO is a challenging transformation. Herein, we report a visible-light-mediated carboxylation of benzylic C-H bonds with CO into 2-arylpropionic acids under metal-free conditions. Photo-oxidized triisopropylsilanethiol was used as the hydrogen atom transfer catalyst to afford a benzylic radical that accepts an electron from the reduced form of 2,3,4,6-tetra(9H-carbazol-9-yl)-5-(1-phenylethyl)benzonitrile generated .

Photocatalytic carbanion generation - benzylation of aliphatic aldehydes to secondary alcohols.

We present a redox-neutral method for the photocatalytic generation of carbanions. Benzylic carboxylates are photooxidized by single electron transfer; immediate CO extrusion and reduction of the formed radical yields a carbanion capable of reacting with aliphatic aldehydes as electrophiles giving the Grignard analogous reaction product.

Photocatalytic Barbier reaction - visible-light induced allylation and benzylation of aldehydes and ketones.

We report a photocatalytic version of the Barbier type reaction using readily available allyl or benzyl bromides and aromatic aldehydes or ketones as starting materials to generate allylic or benzylic alcohols. The reaction proceeds at room temperature under visible light irradiation with the organic dye 3,7-di(4-biphenyl)1-naphthalene-10-phenoxazine as a photocatalyst and DIPEA as sacrificial electron donor. The proposed cross-coupling mechanism of a ketyl- and an allyl or benzyl radical is supported by spectroscopic investigations and cyclic voltammetry measurements.