Efficient and scalable synthesis of 3,4-dihydroisoquinolin-1(2H)-ones by benzylic oxidation of tetrahydroisoquinoline derivatives using cerium ammonium nitrate (CAN)

An efficient and scalable method for the synthesis of 3,4-dihydroisoquinolin-1(2H)-ones through benzylic oxidation of tetrahydroisoquinoline derivatives using a catalytic amount of cerium ammonium nitrate (CAN) and a stoichiometric amount of NaBrO3 as oxidants was developed. The reaction is significantly influenced by the substituent groups on the phenyl ring. While electron-withdrawing groups on the phenyl ring can lower the reactivities of the substrates, electron-donating groups on the phenyl ring can dramatically promote the oxidation rate.

Iron-catalyzed selective construction of indole derivatives via oxidative C(sp3)-H functionalization of indolin-2-ones

Considering the importance of developing powerful catalysts and the pharmacophore characteristics of indole derivatives, we describe a switchable approach for the iron-catalyzed oxidative C(sp3)-H functionalization of indolin-2-ones. Selective transformations displayed excellent activity and chemoselectivity using FeCl2 as the catalyst, air as the oxidant, and alcohol as the solvent. By manipulating the reaction conditions, particularly the choice of solvent, catalyst loading, and reaction sequence, a series of valuable indole derivatives, including isatins and symmetrical and nonsymmetrical isoindigos, were selectively synthesized in good to excellent yields. Furthermore, the gram-scale synthesis of compounds with biological anticancer activity under simple conditions highlights their great potential in practical applications.

Blending Aryl Ketone in Covalent Organic Frameworks to Promote Photoinduced Electron Transfer

Aryl-ketone derivatives have been acknowledged as promising organic photocatalysts for photosynthesis. However, they are limited by their photostability and have been less explored for photoinduced electron transfer (PET) applications. Herein we demonstrate a novel strategy to cover the shortage of aryl-ketone photocatalysts and control the photoreactivity by implanting symmetric aryl ketones into the conjugated covalent organic frameworks (COFs). To prove the concept, three comparative materials with the same topology and varied electronic structures were built, adopting truxenone knot and functionalized terephthalaldehyde linkers. Spectroscopic investigation and excited carrier dynamics analysis disclosed improvements in the photostability and electronic transfer efficiency as well as the structure-performance relationships toward N-aryl tetrahydroisoquinoline oxidation. This system provides a robust rule of thumb for designing new-generation aryl-ketone photocatalysts.

Enzyme-Inspired Coordination Polymers for Selective Oxidization of C(sp3)-H Bonds via Multiphoton Excitation

Nature's blueprint provides the fundamental principles for expanding the use of abundant metals in catalysis; however, mimicking both the structure and function of copper enzymes simultaneously in one artificial system for selective C-H bond oxidation faces marked challenges. Herein, we report a new approach to the assembly of artificial monooxygenases utilizing a binuclear Cu₂S₂Cl₂ cluster to duplicate the identical structure and catalysis of the Cu_A enzyme. The designed monooxygenase Cu-Cl-bpyc facilitates well-defined redox potential that initially activated O₂via photoinduced electron transfer, and generated an active chlorine radical via a ligand-to-metal charge transfer (LMCT) process from the consecutive excitation of the in situ formed copper(II) center. The chlorine radical abstracts a hydrogen atom selectively from C(sp³)-H bonds to generate the radical intermediate; meanwhile, the O₂^•- species interacted with the mimic to form mixed-valence species, giving the desired oxidization products with inherent product selectivity of copper monooxygenases and recovering the catalyst directly. This enzymatic protocol exhibits excellent recyclability, good functional group tolerance, and broad substrate scope, including some biological and pharmacologically relevant targets. Mechanistic studies indicate that the C-H bond cleavage was the rate-determining step and the cuprous interactions were essential to stabilize the active oxygen species. The well-defined structural characters and the fine-modified catalytic properties open a new avenue to develop robust artificial enzymes with uniform and precise active sites and high catalytic performances.

Electrochemical α-C(sp3)-H/O-H cross-coupling of isochromans and alcohols assisted by benzoic acid

Isochroman moieties are present in a wide variety of biologically active molecules, but converting isochromans to α-substituted derivatives under mild conditions is challenging. Herein, we report a mild, convenient protocol for synthesis of α-alkoxy isochroman derivatives by means of electrochemical α-C(sp³)-H/O-H cross-coupling reactions of isochromans and alcohols in the presence of benzoic acid, which facilitated the electro-oxidation process and increased the product yield. Various alcohols and isochromans, as well as other structurally similar substrates, gave moderate to high yields of the desired coupling products, and the reaction could be carried out on a gram scale.

Synthesis of New 1,2,3,4-Tetrahydroquinoline Hybrid of Ibuprofen and Its Biological Evaluation

Herein we report the obtaining of 1-(3,4-dihydroquinolin-1(2H)-yl)-2- (4-isobutylphenyl)propan-1-one and its characterization. The newly obtained hybrid and its derivatives (hybrids of ibuprofen with 1,2,3,4-tetrahydroisoquinoline, and piperidine) were screened for their in vitro antioxidant, antitryptic, and inhibition of albumin denaturation activity. The lipophilicity was established using both reversed-phase thin layer chromatography and in silico calculations.

Catalyst-free aerobic radical cascade reactions of o-vinylphenylisocyanides with thiols to access 2-thio-substituted quinolines

We herein report an efficient and green aerobic radical cascade reaction of o-vinylphenylisocyanides with thiols to access a broad range of 2-thio-substituted quinolines without the need for additional catalysts or oxidants.

Selective Degradation of Styrene-Related Plastics Catalyzed by Iron under Visible Light*

Efficient degradation of plastics, the vital challenge for a sustainable future, stands in need of better chemical recycling procedures that help produce commercially valuable small molecules and redefine plastic waste as a rich source of chemical feedstock. However, the corresponding chemical recycling methods, while being generally restricted to polar polymers, need improvement. Particularly, degradation of chemically inert nonpolar polymers, the major constitutes of plastics, suffers from low selectivity and very harsh transformation conditions. Herein, an efficient method was developed for selective degradation of styrene-related plastics under gentle conditions through multiple oxidation of sp³ C-H bonds and sp³ C-C bonds. The procedure was catalyzed with inexpensive iron salts under visible light, using oxygen as green oxidant. Furthermore, simple iron salts could be used to degrade plastics in the absence of solvent under natural conditions, highlighting the potential application of iron salts as additives for degradable plastics.

Advances in silylation and borylation of fluoroarenes and gem-difluoroalkenes via C-F bond cleavage

Organoboron and organosilane compounds are widely used in organic synthesis and pharmaceuticals. In addition, the C-F bond functionalization is a useful tool for the construction of carbon-carbon and carbon-heteroatom bonds. In particular, the late-stage functionalization of bioactive molecules through defluoroborylation and defluorosilylation reactions will provide good opportunities for the development and diversification of new medicinal compounds. Thus, this feature article summarized the methods for the defluorosilylation and defluoroborylation of unreactive monofluoroarenes and gem-difluoroalkenes from 2000 to 2021, which might create some new ideas and will be helpful for further research in this field. These defluoroborylation and defluorosilylation strategies can be applied to synthesize silylated arenes, borylated arenes, silylated fluoroalkenes, and borylated fluoroalkenes, thus providing impressive advantages over traditional methods for the synthesis of organoboron and organosilane compounds in terms of divergent structures.

Molecular oxygen-mediated oxygenation reactions involving radicals

Molecular oxygen as a green, non-toxic and inexpensive oxidant has displayed lots of advantages compared with other oxidants towards more selective, sustainable, and environmentally benign organic transformations. The oxygenation reactions which employ molecular oxygen or ambient air as both an oxidant and an oxygen source provide an efficient route to the synthesis of oxygen-containing compounds, and have been demonstrated in practical applications such as pharmaceutical synthesis and late-stage functionalization of complex molecules. This review article introduces the recent advances of radical processes in molecular oxygen-mediated oxygenation reactions. Reaction scopes, limitations and mechanisms are discussed based on reaction types and catalytic systems. Conclusions and perspectives are also given in the end.

Iron-Catalyzed Diborylation of Unactivated Aliphatic gem-Dihalogenoalkenes: Synthesis of 1,2-Bis(boryl)alkanes

Herein, we report the first example of iron-catalyzed defluoroborylation of unactivated gem-difluoroalkenes, gem-dichloroalkenes, and gem-dibromoalkenes, providing the 1,2-bis(boryl)alkanes in moderate to good yield. This transformation has high regioselectivity, wide substrate scope, and excellent functional group compatibility. Preliminary mechanistic studies indicate that double β-F elimination is involved in the catalytic cycle, and the 1,1-diborylated alkenes might be intermediates in this iron-catalyzed 1,2-diborylation reaction.

Experimental and Computational Studies of the Iron-Catalyzed Selective and Controllable Defluorosilylation of Unactivated Aliphatic gem-Difluoroalkenes

The first iron-catalyzed defluorosilylation of unactivated gem-difluoroalkenes was developed, delivering gem-disilylated alkenes and (E)-silylated alkenes with excellent efficiency. This protocol features good functional group compatibility and excellent regio- and stereoselectivity, enabling the late-stage silylation of biologically relevant compounds, thus providing good opportunities for applications in medicinal chemistry. Preliminary mechanistic studies and DFT calculations reveal that a nucleophilic addition and elimination of the second C-F bond might be involved in the disilylation catalytic system, demonstrating unusual reactivity characteristics of iron catalysis.

A Rh(iii)-catalyzed C–H activation/regiospecific annulation cascade of benzoic acids with propargyl acetates to unusual 3-alkylidene-isochromanones

We developed a new approach to synthesize isochromanones with benzoic acids and propargyl acetates, which introducing an unusual exocyclic C–C double bond at the 3-position with high regioselectivity and moderate to excellent yields.

Iron-catalyzed C–F bond silylation and borylation of fluoroarenes

Iron-catalyzed functionalization of inert bonds has scarcely been documented.

An efficient and practical aerobic oxidation of benzylic methylenes by recyclable N-hydroxyimide

An efficient and practical benzylic aerobic oxidation catalyzed by cheap and simple N-hydroxyimide organocatalyst has been achieved with high yields and broad substrate scope. The organocatalyst used can be recycled and reused by simple workup and only minute amount (1 mol% in most cases) of simple iron salt is used as promoter. Phenyl substrates with mild and strong electron-withdrawing group could also be oxygenated in high yields as well as other benzylic methylenes. Influence of substituents, gram-scale application, catalysts decay and general mechanism of this methodology has also been discussed.

An efficient and practical benzylic aerobic oxidation catalyzed by cheap and simple N-hydroxyimide organocatalyst has been achieved with high yields and broad substrate scope.