New synthetic approaches for the construction of difluoromethylated architectures

Fluorinated compounds play a vital role in the fields of agrochemicals, pharmaceuticals, and materials science because of their unique lipophilicity, permeability, and metabolic stability. Among all such appealing fluorine-containing functional groups, the difluoromethyl group has attracted considerable attention owing to its outstanding chemical and physical properties. It has been used as a lipophilic hydrogen bond donor and a bioisostere of thiol, hydroxy, or amino groups. The excellent properties of the CF2H group have motivated many chemists to develop effective strategies for the selective incorporation of the CF2H group into target molecules. Over the past decades, a variety of efficient, atom-economical, and facile methods have been discovered for the difluoromethylation of organic substrates. This review summarizes the developments in different types of difluoromethylations, which could be classified into the following categories: radical difluoromethylation, transition metal-catalyzed difluoromethylation, and nucleophilic and electrophilic difluoromethylation.

Fifty Shades of Phenanthroline: Synthesis Strategies to Functionalize 1,10-Phenanthroline in All Positions

1,10-Phenanthroline (phen) is one of the most popular ligands ever used in coordination chemistry due to its strong affinity for a wide range of metals with various oxidation states. Its polyaromatic structure provides robustness and rigidity, leading to intriguing features in numerous fields (luminescent coordination scaffolds, catalysis, supramolecular chemistry, sensors, theranostics, etc.). Importantly, phen offers eight distinct positions for functional groups to be attached, showcasing remarkable versatility for such a simple ligand. As a result, phen has become a landmark molecule for coordination chemists, serving as a must-use ligand and a versatile platform for designing polyfunctional arrays. The extensive use of substituted phenanthroline ligands with different metal ions has resulted in a diverse array of complexes tailored for numerous applications. For instance, these complexes have been utilized as sensitizers in dye-sensitized solar cells, as luminescent probes modified with antibodies for biomaterials, and in the creation of elegant supramolecular architectures like rotaxanes and catenanes, exemplified by Sauvage's Nobel Prize-winning work in 2016. In summary, phen has found applications in almost every facet of chemistry. An intriguing aspect of phen is the specific reactivity of each pair of carbon atoms ([2,9], [3,8], [4,7], and [5,6]), enabling the functionalization of each pair with different groups and leading to polyfunctional arrays. Furthermore, it is possible to differentiate each position in these pairs, resulting in non-symmetrical systems with tremendous versatility. In this Review, the authors aim to compile and categorize existing synthetic strategies for the stepwise polyfunctionalization of phen in various positions. This comprehensive toolbox will aid coordination chemists in designing virtually any polyfunctional ligand. The survey will encompass seminal work from the 1950s to the present day. The scope of the Review will be limited to 1,10-phenanthroline, excluding ligands with more intracyclic heteroatoms or fused aromatic cycles. Overall, the primary goal of this Review is to highlight both old and recent synthetic strategies that find applicability in the mentioned applications. By doing so, the authors hope to establish a first reference for phenanthroline synthesis, covering all possible positions on the backbone, and hope to inspire all concerned chemists to devise new strategies that have not yet been explored.

Promoting Photocatalytic Direct C-H Difluoromethylation of Heterocycles using Synergistic Dual-Active-Centered Covalent Organic Frameworks

Difluoromethylation reactions are increasingly important for the creation of fluorine-containing heterocycles, which are core groups in a diverse range of biologically and pharmacologically active ingredients. Ideally, this typically challenging reaction could be performed photocatalytically under mild conditions. To achieve this separation of redox processes would be required for the efficient generation of difluoromethyl radicals and the reduction of oxygen. A covalent organic framework photocatalytic material was, therefore, designed with dual reactive centers. Here, anthracene was used as a reduction site and benzothiadiazole was used as an oxidation site, distributed in a tristyryl triazine framework. Efficient charge separation was ensured by the superior electron-donating and -accepting abilities of the dual centers, creating long-lived photogenerated electron-hole pairs. Photocatalytic difluoromethylation of 16 compounds with high yields and remarkable functional group tolerance was demonstrated; compounds included bioactive molecules such as xanthine and uracil. The structure-function relationship of the dual-active-center photocatalyst was investigated through electron spin resonance, femtosecond transient absorption spectroscopy, and density functional theory calculations.

Divergent Construction of Thiochromanes and N-Arylbutanamides via Arylthiodifluoromethyl Radical-Triggered Cascade of Alkenes

A strategy utilizing silver-catalyzed oxidative decarboxylation radical cascade cyclization of arylthiodifluoroacetic acids with alkenes for the simple and efficient preparation of difluoromethylated thiochromanes and 2,2-disubstituted-N-arylbutanamides derivatives has been developed. This approach includes good functional group tolerance, easily accessible starting materials, and operational simplicity.

Photoredox Catalysis-Enabled C-H Difluoromethylation of Heteroarenes with Pentacoordinate Phosphorane as the Reagent

Difluoromethylated heterocyclic compounds have found broad applications in numerous bioactive molecules. Herein, we report photoredox catalysis-induced direct C-H difluoromethylation of heterocycles by using bis(difluoromethyl) pentacoordinate phosphorane (PPh3(CF2H)2, 1) as the reagent. A variety of heterocycles, such as quinoxalin-2(1H)-one, thiophene, indole, and coumarin, are readily tailored with a difluoromethyl group. The method is featured as transition-metal-free by using an organic compound Erythrosin B as the catalyst and O2 as the oxidant.

A Review on Synthetic Approaches of Phenanthridine

Abstract:

The phenanthridine family is widely found in medicinal chemistry and material science because of the biological activity and its presence in a variety of significant natural products and synthetic dye stuffs. The phenanthridine has many clinical applications, for e.g., being used as an anticancer agent, possessing antibacterial, antiprotozoal, pharmaceutical, and optoelectronic properties. Many methods have been reported for the synthesis of phenanthridine and phenanthridine alkaloids, such as Pd catalyzed C-C bond formation, a reaction involving C-H activation, radical, microwave-assisted, transition metal-catalyzed, one-pot cascade, benzyne mediated, photochemical, hypervalent iodine promoted methods, etc. Here, we have summarized the literature data from 2014 to the present concerning novel or improved synthetic approaches.

TMSCFX2 (X = Cl, Br) as halofluorocarbene sources for the synthesis of halofluorocyclopropanes

TMSCFX2 (X = Cl, Br; TMS = trimethylsilyl) have been developed as halofluorocarbene (CFX, X = Cl, Br) precursors for [2+1] cyclopropanation with alkenes. Structurally diverse halofluorocyclopropanes were obtained in good to excellent yields. It was found that the reactivity order of the three halofluorocarbene reagents (TMSCF2Br, TMSCFCl2, and TMSCFBr2) in halofluorocyclopropanation with 1,1-diphenylethylene can be very different under different reaction conditions.

Silver-Mediated Methoxylation of Aryl C(sp2)–H Bonds Directing by DMEDA

The first example of silver-mediated phosphine-promoted methoxylation of aryl C(sp2)–H bonds with the commercially available reagent for the preparation of alkyl aryl ethers has been developed. This protocol is characterized by mild reaction conditions, broad substrate scope, and high regioselectivity.

Tandem radical cyclization for the construction of 1-difluoroalkylated isoquinolines via Cu catalyzed and visible light-promoted pathways

A Cu/B₂pin₂ system promoted cyclization for the synthesis of 1-difluoroalkylated isoquinolines with vinyl isocyanides and bromodifluoroacetic derivatives in moderate to good yields was reported.