Transition metal-free photochemical C-F activation for the preparation of difluorinated-oxindole derivatives

Photoreduction of Trifluoromethyl Group: Lithium Ion Assisted Fluoride-Coupled Electron Transfer from EDA Complex

Photoinduced single-electron reduction is an efficient method for the mono-selective activation of the C-F bond on a trifluoromethyl group to construct a difluoroalkyl group. We have developed an electron-donor-acceptor (EDA) complex mediated single-electron transfer (EDA-SET) of α,α,α-trifluoromethyl arenes in the presence of lithium salt to give α,α-difluoroalkylarenes. The C-F bond reduction was realized by lithium iodide and triethylamine, two common feedstock reagents. Mechanistic studies revealed the generation of a α,α-difluoromethyl radical by single-electron reduction and defluorination, followed by the radical addition to alkenes. Lithium salt interacted with the fluorine atom to promote the photoinduced reduction mediated by the EDA complex. Computational studies indicated that the lithium-assisted defluorination and the single-electron reduction occurred concertedly. We call this phenomenon fluoride-coupled electron transfer (FCET). FCET is a novel approach to C-F bond activation for the synthesis of organofluorine compounds.

Arenethiolate-Catalyzed 1,5-HAT of Aryl Halides: Synthesis of γ-Spirolactams

γ-Spirolactam is a privileged building block that is found in a wide range of natural products and bioactive compounds. Herein, we report an arenethiolate-catalyzed 1,5-HAT of aryl halides to obtain γ-spirolactams through a SET reduction/intramolecular 1,5-HAT/cyclization/HAT process. This protocol features metal-free conditions and a broad substrate scope, furnishing the γ-spirolactams in moderate to excellent yields. Notably, aryl bromides, aryl chlorides and even aryl fluorides are well tolerated in this transformation. A mechanism involving arenethiolate as a SET catalyst is proposed based on DFT calculation.

Nickel-catalysed chelation-assisted reductive defluorinative sulfenylation of trifluoropropionic acid derivatives

Herein we reported a directing-group assisted strategy for nickel-catalysed reductive defluorinative sulfenylation of trifluoropropionic acid derivatives with disulfides in the presence of Zn, involving triple C-F bond cleavage. This process yielded a diverse array of carbonyl-sulfide di-substituted alkenes in moderate to good yields with good functional group tolerance. Specifically, the reactions exhibited high E-selectivity with E/Z ratio up to >99 : 1.

Recent Discovery, Development, and Synthetic Applications of Formic Acid Salts in Photochemistry

The advancement of sustainable photoredox catalysis in synthetic organic chemistry has evolved immensely because of the development of versatile and cost-effective reagents. In recent years, a substantial effort has been dedicated to exploring the utility of formic acid salts in various photochemical reactions. In this context, formates have demonstrated diverse capabilities, functioning as reductants, sources of carbonyl groups, and reagents for hydrogen atom transfer. Notably, the CO2 ⋅- radical anion derived from formate exhibits strong reductant properties for cleaving both C-X and C-O bonds. Moreover, these salts play a pivotal role in carboxylation reactions, further highlighting their significance in a variety of photochemical transformations. The ability of formates to serve as reductants, carbonyl sources, and hydrogen atom transfer reagents reveal exciting possibilities in synthetic organic chemistry. This minireview highlights an array of captivating discoveries, underscoring the crucial role of formates in diverse and distinctive photochemical methods, enabling access to a wide range of value-added compounds.

C-F Activation of Fluorinated Esters Using Photocatalytically Generated Diaminoalkyl Radical

A method for hydrofluoroalkylation of alkenes with trifluoroacetic esters under visible light irradiation affording difluorinated products is described. The reaction involves readily available trimethyltriazinane as a shoichiometric reducing agent, which generates a diamino-substituted alkyl radical serving as a strong electron donor. It is believed that the cleavage of the C-F bond by a triazinane-derived radical involves single electron reduction coupled with fluoride transfer.

Recent Developments on Photochemical Synthesis of 1,n-Dicarbonyls

1,n-dicarbonyls are one of the most fascinating chemical feedstocks finding abundant usage in the field of pharmaceuticals. Besides, they are utilized in a plethora of synthesis in general synthetic organic chemistry. A number of 'conventional' methods are available for their synthesis, such as the Stetter reaction, Baker-Venkatraman rearrangement, oxidation of vicinal diols, and oxidation of deoxybenzoins, synonymous with unfriendly reagents and conditions. In the last 15 years or so, photocatalysis has taken the world of synthetic organic chemistry by a remarkable renaissance. It is fair to say now that everybody loves the light and photoredox chemistry has opened a new gateway to organic chemists towards milder, more simpler alternatives to the previously available methods, allowing access to many sensitive reactions and products. In this review, we present the readers with the photochemical synthesis of a variety of 1,n-dicarbonyls. Diverse photocatalytic pathways to these fascinating molecules have been discussed, placing special emphasis on the mechanisms, giving the reader an opportunity to find all these significant developments in one place.

Recent Advances in C-H Functionalisation through Indirect Hydrogen Atom Transfer

The functionalisation of C-H bonds has been an enormous achievement in synthetic methodology, enabling new retrosynthetic disconnections and affording simple synthetic equivalents for synthons. Hydrogen atom transfer (HAT) is a key method for forming alkyl radicals from C-H substrates. Classic reactions, including the Barton nitrite ester reaction and Hofmann-Löffler-Freytag reaction, among others, provided early examples of HAT. However, recent developments in photoredox catalysis and electrochemistry have made HAT a powerful synthetic tool capable of introducing a wide range of functional groups into C-H bonds. Moreover, greater mechanistic insights into HAT have stimulated the development of increasingly site-selective protocols. Site-selectivity can be achieved through the tuning of electron density at certain C-H bonds using additives, a judicious choice of HAT reagent, and a solvent system. Herein, we describe the latest methods for functionalizing C-H/Si-H/Ge-H bonds using indirect HAT between 2018-2023, as well as a critical discussion of new HAT reagents, mechanistic aspects, substrate scopes, and background contexts of the protocols.

Highlights on U.S. FDA-approved fluorinated drugs over the past five years (2018-2022)

The objective of this review is to provide an update on the fluorine-containing drugs approved by U.S. Food and Drug Administration in the span of past five years (2018-2022). The agency accepted a total of fifty-eight fluorinated entities to diagnose, mitigate and treat a plethora of diseases. Among them, thirty drugs are for therapy of various types of cancers, twelve for infectious diseases, eleven for CNS disorders, and six for some other diseases. These are categorized and briefly discussed based on their therapeutic areas. In addition, this review gives a glimpse about their trade name, date of approval, active ingredients, company developers, indications, and drug mechanisms. We anticipate that this review may inspire the drug discovery and medicinal chemistry community in both industrial and academic settings to explore the fluorinated molecules leading to the discovery of new drugs in the near future.