Over the last decade, substantial research has led to the introduction of an impressive number of efficient procedures which allow the selective construction of CC bonds by directly connecting two different CH bonds under oxidative conditions. Common to these methodologies is the generation of the reactive intermediates in situ by activation of both CH bonds. This strategy was introduced by the group of Li as cross-dehydrogenative coupling (CDC) and discloses waste-minimized synthetic alternatives to classic coupling procedures which rely on the use of prefunctionalized starting materials. This Review highlights the recent progress in the field of cross-dehydrogenative C sp 3C formations and provides a comprehensive overview on existing procedures and employed methodologies.

A pharmaceutical industry viewpoint on how the fundamental laws of photochemistry are used to identify the parameters required to implement photochemistry from lab to scale. Parameters such as photon stoichiometry and light intensity are highlighted within to inform future publications. Photochemistry employs photons to drive chemical transformations. Traditional approaches rely on the direct excitation of bonds with light 1,2. In contrast, photoredox catalysis uses a photosensitizer to facilitate electron transfer, generating reactive intermediates under mild conditions 3. From a pharmaceutical industry point-of-view, photochemistry is a powerful tool to access highenergy intermediates that can provide novel reactivity and enables new disconnections, allowing target-and diversity-oriented synthesis to be explored 4. Photochemistry is extensively used within medicinal chemistry projects, but has not yet been extensively employed for the commercial manufacture of pharmaceutical agents 5. The scientific community has published new and exciting photochemical methods, but in our experience these transformations can be challenging to reproduce 3,6. We believe that this difficulty results from an under-emphasized importance of fundamental photochemical concepts, which renders translation of methods between setups challenging. Most authors try to describe the key features of the photochemical system used in their experiments; however, the description may not be completely sufficient to ensure reproducibility in a different lab or comparable reactor system. It can be quite common to find little technical detail about the equipment setup in the Supplementary Information and many summaries fall short of fully characterizing the photo-physical properties of their setup. We believe that careful characterization and description of the photochemistry equipment is essential; more systematic and better documented experimentation will enable greater mechanistic understanding, leading to facile identification of the key scale-up factors. From a review of the fundamentals of photochemistry, we will detail the minimum information to include in any photochemistry-related publication. This will enable the chemistry community to more readily assess and adopt photochemical transformations. We will then look toward the future of photochemistry for a manufacturing system that applies this technology. Grotthuss-Draper law Light must be absorbed by a chemical substance for a photochemical reaction to occur. Photon absorption excites a molecule from its ground state to an excited state. Chemical substances only absorb at specific wavelengths, so it is critical that the right wavelength is selected for the desired transformation.

Potassium (trifluoromethyl)trimethoxyborate is introduced as a new source of CF(3) nucleophiles in copper-catalyzed trifluoromethylation reactions. The crystalline salt is stable on storage, easy to handle, and can be obtained in near-quantitative yields simply by mixing B(OMe)(3), CF(3)SiMe(3), and KF. The trifluoromethylation reagent allows the conversion of various aryl iodides into the corresponding benzotrifluorides in high yields under mild, base-free conditions in the presence of catalytic quantities of a Cu(I)/1,10-phenanthroline complex.

Molecular editing such as insertion, deletion, and single atom exchange in highly functionalized compounds is an aspirational goal for all chemists. Here, we disclose a photoredox protocol for the replacement of a single fluorine atom with hydrogen in electron-deficient trifluoromethylarenes including complex drug molecules. A robustness screening experiment shows that this reductive defluorination tolerates a range of functional groups and heterocycles commonly found in bioactive molecules. Preliminary studies allude to a catalytic cycle whereby the excited state of the organophotocatalyst is reductively quenched by the hydrogen atom donor, and returned in its original oxidation state by the trifluoromethylarene.

A new procedure for the photoredox-mediated conjugate addition of radicals that can be conveniently generated from α-amino acids to DNA-tagged Michael acceptors and styrenes is presented. This C(sp )-C(sp ) coupling tolerates a broad array of structurally diverse radical precursors, including all of the 20 proteinogenic amino acids. Importantly, this reaction proceeds under mild conditions and in DNA-compatible aqueous media. Furthermore, the presented reaction conditions are compatible with DNA, making this reaction platform well suited for the construction of DNA-encoded libraries. The scope and limitations of the chemistry are discussed herein along with proposals for how this methodology might be used to construct DNA-encoded libraries.

A new catalytic manifold that merges photoredox with nickel catalysis in aqueous solution is presented. Specifically, the combination of a highly active, yet air-stable, nickel precatalyst with a new electron-deficient pyridyl carboxamidine ligand was key to the development of a water-compatible nickel catalysis platform, which is a crucial requirement for the preparation of DNA-encoded libraries (DELs). Together with an iridium-based photocatalyst and a powerful light source, this dual catalysis approach enabled the efficient decarboxylative arylation of α-amino acids with DNA-tagged aryl halides. This C(sp 2 )−C(sp 3 ) coupling tolerates a wide variety of functional groups on both the amino acid and the aryl halide substrates. Due to the mild and DNA-compatible reaction conditions, the presented transformation holds great potential for the construction of DELs. This was further evidenced by showing that well plate-compatible LED arrays can serve as competent light sources to facilitate parallel synthesis. Lastly, we demonstrate that this procedure can serve as a blueprint toward the adaptation of other established nickel metallaphotoredox transformations to the idiosyncratic requirements of a DEL.

A mild Ru/Ni dual catalytic desulfinative photoredox C-C cross-coupling reaction of alkyl sulfinate salts with aryl halides has been developed. The optimized catalyst system, consisting of Ru(bpy)Cl, Ni(COD), and DBU, smoothly mediates the coupling of a diverse set of secondary and primary nonactivated alkyl sulfinate salts with a broad range of electron-deficient aryl bromides, electron-rich aryl iodides, and heteroaryl bromides under irradiation with blue light. The procedure is ideal for late-stage introduction of alkyl groups on pharmaceutical intermediates, and the C-C cross-coupling reaction allowed the rapid synthesis of caseine kinase 1δ inhibitor analogues via a parallel medicinal chemistry effort.

Pd-catalyzed intermolecular aerobic dehydrogenative aromatizations have been developed for the arylation of amines with nonaromatic ketones. Under optimized reaction conditions, primary and secondary amines are selectively arylated in good yields with cyclohexanones and 2-cyclohexen-1-ones in the presence of a Pd-catalyst under an atmosphere of molecular oxygen.