Deoxygenative Deuteration of Carboxylic Acids with D2 O

Improved Electrochemical Peptide Synthesis Enabled by Electron-Rich Triaryl Phosphines

While remarkable progress has been made in the development of peptide medicines, many problems related to peptide synthesis remain unresolved. Previously, we reported electrochemical peptide synthesis using a phosphine as a potentially recyclable coupling reagent. However, there was room for improvement from the point of view of reaction efficiency, especially in the carboxylic acid activation step and the peptide bond formation step. To overcome these challenges, we searched for the optimal phosphine. Among phosphines with various electronic properties, we found that electron-rich triaryl phosphines improved the reaction efficiency. Consequently, we successfully performed electrochemical peptide synthesis on sterically hindered and valuable amino acids. We also synthesized oligopeptides that were challenging with our previous method. Finally, we examined the effect of substituents on the phosphine cations, and gained some insights into reactivity, which will aid researchers designing reactions involving phosphine cations.

A Modified Arbuzov-Michalis Reaction for Selective Alkylation of Nucleophiles

The alkylation of nucleophiles is among the most fundamental and well-developed transformations in chemistry. However, to achieve selective alkylation of complex substrates remains a nontrivial task. We report herein a general and selective alkylation method without using strong acids, bases, or metals. In this method, the readily available phosphinites/phosphites, in combination with ethyl acrylate, function as effective alkylating agents. Various nucleophilic groups, including alcohols, phenols, carboxylic acids, imides, and thiols can be alkylated. This method can be applied in the late-stage alkylation of natural products and pharmaceutical agents, achieving chemo- and site-selective modification of complex substrates. Experimental studies indicate the relative reactivity of a nucleophile depends on its acidity and its steric environment. Mechanistic studies suggest the reaction pathway resembles that of the Arbuzov-Michalis reaction.

Photoredox-Catalyzed Phosphine-Mediated Successive Deoxygenation of Sulfonyl Oxime Salts Enables Anti-Markovnikov Hydrothiolation of Alkenes

Stable and easy-to-handle sodium salts of sulfonyl oximes were first identified to proceed via visible-light-driven phophine-mediated successive deoxygenation to realize the anti-Markovnikov hydrothiolation of alkenes, which could serve as an odorless sulfur source. Mechanistic studies revealed that the key thiyl radical intermediate could be generated in situ from the sulfonyl oxime anion via a phosphine-mediated fragmentation and a sequential deoxygenation process. Notably, a wide range of alkenes, including acrylamides, acrylates, vinyl ketones, vinyl sulfones, and acrylonitriles, are competent substrates for this protocol, which is highly beneficial for the construction of structurally diversified organosulfur compounds.

Electrocatalytic reductive deuteration of arenes and heteroarenes

The incorporation of deuterium in organic molecules has widespread applications in medicinal chemistry and materials science1,2. For example, the deuterated drugs austedo3, donafenib4 and sotyktu5 have been recently approved. There are various methods for the synthesis of deuterated compounds with high deuterium incorporation6. However, the reductive deuteration of aromatic hydrocarbons-ubiquitous chemical feedstocks-to saturated cyclic compounds has rarely been achieved. Here we describe a scalable and general electrocatalytic method for the reductive deuteration and deuterodefluorination of (hetero)arenes using a prepared nitrogen-doped electrode and deuterium oxide (D2O), giving perdeuterated and saturated deuterocarbon products. This protocol has been successfully applied to the synthesis of 13 highly deuterated drug molecules. Mechanistic investigations suggest that the ruthenium-deuterium species, generated by electrolysis of D2O in the presence of a nitrogen-doped ruthenium electrode, are key intermediates that directly reduce aromatic compounds. This quick and cost-effective methodology for the preparation of highly deuterium-labelled saturated (hetero)cyclic compounds could be applied in drug development and metabolism studies.

Nickel-Catalyzed Highly Selective Radical C-C Coupling from Carboxylic Acids with Photoredox Catalysis

Controlling the cross-coupling reaction between two different radicals is a long-standing challenge due to the process occurring statistically, which would lead to three products, including two homocoupling products and one cross-coupling product. Generally, the cross-coupling selectivity is achieved by the persistent radical effect (PRE) that requires the presence of a persistent radical and a transient radical, thus resulting in limited radical precursors. In this paper, a highly selective cross-coupling of alkyl radicals with acyl radicals to construct C(sp2)-C(sp3) bonds, or with alkyl radicals to construct C(sp3)-C(sp3) bonds have been achieved with the readily available carboxylic acids and their derivatives (NHPI ester) as coupling partners. The success originates from the use of tridentate ligand (2,2' : 6',2''-terpyridine) to enable radical cross-coupling process to Ni-mediated organometallic mechanism. This protocol offers a facile and flexible access to structurally diverse ketones (up to 90 % yield), and also a new solution for the challenging double decarboxylative C(sp3)-C(sp3) coupling. The broad utility and functional group tolerance are further illustrated by the late-stage functionalization of natural-occurring carboxylic acids and drugs.

Generation of alkyl and acyl radicals by visible-light photoredox catalysis: direct activation of C-O bonds in organic transformations

Alkyl and acyl radicals play a critical role in the advancement of chemical synthesis. The generation of acyl and alkyl radicals by activation of C-O bonds using visible-light photoredox catalysis offers a mild and environmentally benign approach to useful chemical transformations. Alcohols, carboxylic acids, anhydrides, xanthates, oxalates, N-phthalimides, and thiocarbonates are some examples of alkyl and acyl precursors that can produce reactive radicals by homolysis of the C-O bond. These radicals can then go through a variety of transformations that are beneficial for the construction of synthetic materials that are otherwise difficult to access. This study summarizes current developments in the use of organic photocatalysts, transition-metal photoredox catalysts, and metallaphotocatalysts to produce acyl and alkyl radicals driven by visible light.

Photoinduced Catalyst-Free Deuterodefunctionalization of Aryltriazenes with CDCl3

A photoinduced deuterodetriazenation of aryltriazenes with CDCl3 under catalyst-free conditions is reported. The reactions featured simple operation, ecofriendly conditions, readily available reagents, inexpensive D sources, precise site selectivity, and a wide range of substrates. Since aryltriazenes could be readily synthesized from arylamine, this protocol can be used as a general method for easily and accurately incorporating deuterium into aromatic systems by using CDCl3 as a D source.

Electrocatalytic Hydrogenation Using Palladium Membrane Reactors

Hydrogenation is a crucial chemical process employed in a myriad of industries, often facilitated by metals such as Pd, Pt, and Ni as catalysts. Traditional thermocatalytic hydrogenation usually necessitates high temperature and elevated pressure, making the process energy intensive. Electrocatalytic hydrogenation offers an alternative but suffers from issues such as competing H2 evolution, electrolyte separation, and limited solvent selection. This Perspective introduces the evolution and advantages of the electrocatalytic Pd membrane reactor (ePMR) as a solution to these challenges. ePMR utilizes a Pd membrane to physically separate the electrochemical chamber from the hydrogenation chamber, permitting the use of water as the hydrogen source and eliminating the need for H2 gas. This setup allows for greater control over reaction conditions, such as solvent and electrolyte selection, while mitigating issues such as low Faradaic efficiency and complex product separation. Several representative hydrogenation reactions (e.g., hydrogenation of C=C, C≡C, C=O, C≡N, and O=O bonds) achieved via ePMR over the past 30 years were concisely discussed to highlight the unique advantages of ePMR. Promising research directions along with the advancement of ePMR for more challenging hydrogenation reactions are also proposed. Finally, we provide a prospect for future development of this distinctive hydrogenation strategy using hydrogen-permeable membrane electrodes.

Photoredox-Catalyzed Hydroacylation of Azobenzenes with Carboxylic Acids

Acyl hydrazides are widely found in bioactive compounds and have important applications as versatile synthetic intermediates. In the current report, a photoredox-catalyzed hydroacylation of azobenzenes was disclosed with carboxylic acids as the acylation reagent, affording a variety of N,N'-disubstituted hydrazides. The process possesses the advantages of mild reaction conditions, broad substrate scope, and high efficiency. Preliminary mechanistic investigation indicated that the addition of an acyl radical to the azo compound should be involved.

Precision Deuteration in Search of Anticancer Agents: Approaches to Cancer Drug Discovery

Cancer chemotherapy has been shifted from conventional cytotoxic drug therapy to selective and target-specific therapy after the findings about DNA changes and proteins that are responsible for cancer. A large number of newer drugs were discovered as targeted therapy for particular types of neoplastic disease. The initial discovery includes the development of the first in the category, imatinib, a Bcr-Abl tyrosine kinase inhibitor (TKI) for the treatment of chronic myelocytic leukemia in 2001. But the joy did not last for long as the drug developed a point mutation within the ABL1 kinase domain of BCR-ABL1, which subsequently led to the discovery of many other TKIs. Resistance was observed for newer TKIs a few years after their launching, but the use of TKIs in life-threatening cancer therapy is considered as far better compared with the risks of disease because of its target specificity and hence less toxicity. In search of a better anticancer agent, the physiochemical properties of the lead molecule have been modified for its efficacy toward disease and delay in the development of resistance. Deuteration in the drug molecule is one of such modifications that alter the pharmacokinetic properties, generally its metabolism, as compared with its pharmacodynamic effects. Precision deuteration in many anticancer drugs has been carried out to search for better drugs for cancer. In this review, the majority of anticancer drugs and molecules for which deuteration was applied to get better anticancer molecules were discussed. This review will provide a complete guide about the benefits of deuteration in cancer chemotherapy.

Highly effective and selective FeBr3-promoted deuterium bromination/cyclization of 1,n-enynes

A highly effective and selective FeBr3-promoted deuterium bromination/cyclization of 1,n-enynes is reported. On the one hand, the Lewis acid FeBr3 as a catalyst promotes cyclization of 1,n-enynes to afford deuterium heterocyclic frameworks with high efficiency. On the other hand, FeBr3 serves as the bromine source (with D2O as the deuterium source) to promote the formation of the desired deuterated pyrrole derivatives containing alkenyl bromide groups. This protocol provides an effective pathway to afford deuterated alkenyl brominative compounds as (Z)-isomers with high yields and selectivity, offering a new method for introducing 2H into organic compounds.

Regioselective Thiol-yne Reaction of Thiol with ((Methyl-d3)sulfonyl)ethyne: Synthesis of (2-((Methyl-d3)sulfonyl)vinyl)sulfides

Herein, we have developed a new method for the synthesis of ((methyl-d3)sulfonyl)ethyne, which is cost-effective and environmentally friendly and can be synthesized at the gram level. As an ideal thiol-yne reagent, it can be reacted with various types of thiols to afford (Z)- and (E)-type vinyl sulfides under different conditions with high selectivity. In addition, it can complete the conformational transition from Z- to E-type products under suitable conditions, and can also carry out further derivatization smoothly. The deuterium content of all products was greater than 99%. The preliminary mechanistic studies support the visible light-mediated radical course, and herein provide a novel and efficient synthetic strategy for the direct introduction of deuterated methyl groups, enriching the methods for the construction of C-S bond-containing compounds.

Photocatalytic Umpolung Strategy for the Synthesis of α-Amino Phosphine Oxides and Deuterated Derivatives

Direct, economical, and green synthesis of deuterated α-amino phosphine oxides remains an elusive challenge in synthetic chemistry. Herein, we report a visible-light-driven umpolung strategy for synthesizing deuterated α-amino phosphine oxides from isocyanide using 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene as the photocatalyst and D2O as the deuterium source. Moreover, the streamlined and sustainable methodology can be applied in the modification of amino acids, natural products, and drugs. The strong antiproliferative activity of the desired products indicates that the method could provide a novel privileged scaffold for antitumor drug development.

Photocatalytic Phosphine-Mediated Thioesterification of Carboxylic Acids with Disulfides

Herein, a practical and effective synthesis of thioesters from readily available carboxylic acids and odorless disulfides was developed under photocatalytic conditions. This approach involves phosphoranyl radical-mediated fragmentation to generate acyl radicals and allows for incorporation of both S atoms of the disulfides into the desired products. In addition to batch reactions, a continuous-flow reactor was employed, enabling rapid thioester synthesis on a gram scale. Preliminary experimental mechanistic studies and the rapid synthesis of dalcetrapib are also demonstrated.

Umpolung trifluoromethylthiolation of alcohols

Herein we develop a metal-free umpolung dehydroxytrifluoromethylthiolation of alcohols with commercially available PPh3 and N-trifluoromethylthiophthalimide within 30 minutes. This protocol shows excellent functional group tolerance and high regioselectivity. The dehydroxytrifluoromethylthiolation of a series of natural products and drugs further demonstrates its practicality. Preliminary mechanistic studies suggest that PPh3 is responsible for deoxygenation and the key trifluoromethylthiophosphonium ion may be hydrolyzed by H2O in solvent.

Visible-Light Enabled Dehydroxylative Alkylation of α-Hydroxy Carboxylic Acid Derivatives via C-O Bond Cleavage

A novel visible-light photoredox strategy is reported for the efficient dehydroxylative alkylation of a wide array of α-hydroxy carboxylic acid derivatives using diaryl boron radical. The reaction features readily accessible starting materials, broad substrate scope with excellent functionality tolerance. Preliminary mechanistic studies reveal that the spin-center shift process is responsible for the C-O bond activation, which is promoted by the diaryl boron radical generated from bench-stable and commercially available tetraphenyl borate (NaBPh4 ).

Regioselective Hydrodeoxygenation of α-Diketones with Phosphites under Visible-Light Catalysis

Novel regioselective hydrodeoxygenation of α-diketones with phosphites as the deoxygenation reagent was realized via visible-light photoredox catalysis. Broad substrate scope and high functional group compatibility were obtained. Unsymmetric α-diketones were selectively reduced at the carbonyls of higher electrophilicity. This unique regioselectivity compared with available methods makes it a practical complementary approach for the monohydrodeoxygenation of α-diketones.

Deuterium- and Electron-Shuttling Catalysis for Deoxygenative Deuteration of Alcohols

A practical and precise method for visible-light-promoted deoxygenative deuteration of common aliphatic alcohols using D2O as the deuterium source is reported. Upon intermediacy of xanthate anions, a variety of primary, secondary, and tertiary alcohols can be facilely transformed into deuterioalkanes with excellent D-incorporation at predicted sites. The deoxygenation and deuteration sequence is catalyzed by in situ formed deuterated 2-mercaptopyridine, which plays dual roles as a deuterium atom transfer catalyst and an electron shuttle as well.

Photocatalytic 1,2-Phosphorus-Migrative [3 + 2] Cycloaddition of Tri(t-butyl)phosphine with Terminal Alkynes

Tri(t-butyl)phosphine and terminal alkynes undergo 1,2-phosphorus-migrative [3 + 2] cycloaddition in the presence of a proton source under photocatalytic conditions. The reaction exhibits broad functional group tolerance and affords substituted cyclic phosphonium salts, which are amenable to further derivatization by Wittig olefination. Theoretical studies suggest that the phosphorus 1,2-migration of a β-phosphonioalkyl radical proceeds through a phosphine radical cation-alkene complex as a pseudointermediate, and the two fragments in the intermediate are bound to each other through multiple noncovalent interactions.

Thiol-promoted intermolecular cyclization to synthesize 1,2,4-oxadiazoles including tioxazafen under transition metal-free conditions

A simple and efficient one-pot intermolecular annulation reaction for the synthesis of 1,2,4-oxadiazoles from amidoximes and benzyl thiols has been developed, in which benzyl thiols act as not only reactants but also organo-catalysts. The control experiments proved that thiol substrates could facilitate the dehydroaromatization step. High yield, functional group diversity and transition metal-free, extra oxidant-free, and mild conditions are the important practical features. Moreover, this protocol provides an effective alternative method for the synthesis of a commercially available broad-spectrum nematicide, tioxazafen.

Selective multifunctionalization of N-heterocyclic carbene boranes via the intermediacy of boron-centered radicals

The selective difunctionalization of N-heterocyclic carbene (NHC) boranes with alkenes has been achieved via decatungstate and thiol synergistic catalysis. The catalytic system also allows stepwise trifunctionalization, leading to complex NHC boranes with three different functional groups which are challenging to prepare by other methods. The strong hydrogen-abstracting ability of the excited decatungstate enables the generation of boryl radicals from mono- and di-substituted boranes for realizing borane multifunctionalization. This proof-of-principle research provides a new chance for fabricating unsymmetrical boranes and developing boron-atom-economic synthesis.

Visible-light-induced reactions of methylenecyclopropanes (MCPs)

Diverse, visible-light-induced transformations of methylenecyclopropanes (MCPs) have been reported in recent years, attracting significant attention from synthetic chemists. As readily accessible strained molecules, MCPs have sufficient reactivity to selectively generate different target products, through reactions with various radical species upon visible-light irradiation under regulated reaction conditions. These transformations can be classified into three subcategories of reaction pathway, forming ring-opened products, cyclopropane derivatives, and alkynes. These products include pharmaceutical intermediates and polycyclic/heterocyclic compounds that are challenging to obtain using traditional methods. This review summarizes the recent advancements in this field.

Photocatalytic Deuterium Atom Transfer Deuteration of Electron-Deficient Alkenes with High Functional Group Tolerance

Due to its mild reaction conditions and unique chemoselectivity, hydrogen atom transfer (HAT) hydrogenation represents an indispensable method for the synthesis of complex molecules. Its analog using deuterium, deuterium atom transfer (DAT) deuteration, is expected to enable access to complex deuterium-labeled compounds. However, DAT deuteration has been scarcely studied for synthetic purposes, and a method that possesses the favorable characteristics of HAT hydrogenations has remained elusive. Herein, we report a protocol for the photocatalytic DAT deuteration of electron-deficient alkenes. In contrast to the previous DAT deuteration, this method tolerates a variety of synthetically useful functional groups including haloarenes. The late-stage deuteration also allows access to deuterated amino acids as well as donepezil-d₂ . Thus, this work demonstrates the potential of DAT chemistry to become the alternative method of choice for preparing deuterium-containing molecules.

Triflylpyridinium Enables Rapid and Scalable Controlled Reduction of Carboxylic Acids to Aldehydes using Pinacolborane

Building up new and efficient methods for the controlled conversion of carboxylic acids to aldehydes is important. Herein, we report a rapid, modular and scalable method for the conversion of carboxylic acids to aldehydes using pinacolborane at ambient temperature, in which a triflylpyridinium reagent is used. The conversion of carboxylic acid to intermediate acylpyridinium by triflylpyridinium is new. A binary pyridine-coordinated boronium complex is generated after reduction. The unprecedented reduction of the acylpyridinium by HBpin opens up a practically direct synthesis of aldehydes from carboxylic acids. Theoretical studies indicate that the reduction of acylpyridinium requires a lower activation free energy than that of the product aldehyde. The synthetic advantage of this protocol is further highlighted by the scalable synthesis of aldehyde via continuous flow process. Configuration retention for chiral acids are presented in those syntheses.

Catalytic asymmetric deuterosilylation of exocyclic olefins with mannose-derived thiols and deuterium oxide

Metal-free, photoinduced asymmetric deuterosilylation of exocyclic olefins has been achieved using a mannose-derived thiol catalyst.

Catalytic Vilsmeier-Haack Reactions for C1-Deuterated Formylation of Indoles

The Vilsmeier-Haack reaction is a powerful tool to introduce formyl groups into electron-rich arenes, but its wide application is significantly restricted by stoichiometric employment of caustic POCl₃. Herein, we reported a catalytic version of the Vilsmeier-Haack reaction enabled by a P(III)/P(V)═O cycle. This catalytic reaction provides a facile and efficient route for the direct construction of C1-deuterated indol-3-carboxaldehyde under mild conditions with stoichiometric DMF-d7 as the deuterium source. The products feature a remarkably higher deuteration level (>99%) than previously reported ones and are not contaminated by the likely unselective deuteration at other sites. The present transformation can also be used to transfer other carbonyl groups. Further downstream derivatizations of these deuterated products manifested their potential applications in the synthesis of deuterated bioactive molecules. Mechanistic insight was disclosed from studies of kinetics and intermediates.

Visible-Light-Induced Acylative Coupling of Benzoic Acid Derivatives with Alkenes to Dihydrochalcones

A strategy was developed for the visible-light-induced photocatalytic synthesis of dihydrochalcone via the deoxygenation and coupling of benzoic acid derivatives with alkenes using diphenyl sulfide as the O-transfer reagent. Under mild photoredox conditions, a series of dihydrochalcone derivatives were produced in moderate to good yields. A mechanism for the visible-light-induced free-radical coupling was proposed on the basis of the control experiments. The protocol provides a new strategy the generation of acyl radicals from carboxylic acids and the synthesis of dihydrochalcones.

Dehydroxylative Arylation of Alcohols via Paired Electrolysis

Nonactivated alcohols along with arene compounds are used in electrochemical dehydroxylative arylation for constructing C(sp³)-C(sp²) bonds. The P^III reagent undergoes single-electron anodic oxidation to form its radical cation, which reacts with the alcohol to produce an alkoxytriphenylphosphine radical. Through spontaneous β-scission of the phosphoranyl radical, the C-O bond is cleaved to form an alkyl radical species, which couples with the radical anion generated by cathodic reduction of the electron-poor arene to afford the dehydroxylative arylated product.

Site-selective deuteration at the α-position of enals by an amine and bis(phenylsulfonyl)methane co-catalyzed H/D exchange reaction

An amine and bis(phenylsulfonyl)methane co-catalyzed hydrogen-deuterium exchange (HDE) method via a Michael-retro-Michael pathway for site-selective introduction of deuterium at the α-position of enals using D₂O as a deuterium source has been achieved. The mild, operationally simple protocol allows for high yielding and high level deuterium incorporation (up to 99%) for structurally diverse aromatic-derived enals and dienals.

Photoredox Catalytic Phosphine-Mediated Deoxygenation of Hydroxylamines Enables the Construction of N-Acyliminophosphoranes

The chemistry of phosphoranyl radicals has received increasing attention in recent years. Here, we report the generation of amidyl radicals through photocatalytic deoxygenation of hydroxylamines with triphenylphosphine. This methodology offers a novel and convenient route to a diverse range of N-acyliminophosphoranes in moderate to good yields under visible-light photoredox conditions. Fluorescence quenching experiments suggest that the excited-state of the organic photocatalyst (4CzIPN) was oxidatively quenched by a Cu(II) salt.

Radical deuteration

Deuterated chemicals are becoming irreplaceable in pharmaceutical engineering, material science and synthetic chemistry. Many excellent reviews have discussed acid/base-dependent or metal-catalyzed deuteration reactions, but radical deuterations have been discussed less. With the development of radical chemistry, there has been a rapid growth in radical deuterium-labelling technology. Diverse mild, cheap and efficient strategies for deuterium atom installation have been reported, and this review summarizes the recent achievements of radical deuteration classified by the reaction types.

Recent Advances in Employing Catalytic Donors and Acceptors in Electron Donor-Acceptor Complex Photochemistry

Electron donor-acceptor (EDA) complexes provide a means to initiate radical reactions under visible light irradiation using substrates that do not absorb visible light individually. Catalytic approaches to complex formation are vital for advancing this synthetic strategy as it decouples the complexation and photogeneration of radicals from substrate functionalization, a limitation inherent to stoichiometric approaches that restricts structural diversity. This Synopsis highlights recent developments in EDA complex photochemistry in which either the donor or acceptor are employed catalytically.

Palladium-Catalyzed Synthesis of C-1 Deuterated Aldehydes from (Hetero) Arenes Mediated by C (sp2)-H Thianthrenation

A palladium-catalyzed deuterated formylation of aryl sulfonium salts is prepared conveniently from readily available arenes, which enables the expedient synthesis of a series of structurally diverse C-1 deuterated aldehydes with 96%-99% deuterium incorporation. The easy to handle and cost-effective DCOONa provides a deuterium source, which can be introduced onto the formyl units with excellent selectivity under the palladium-catalytic redox neutral conditions. This catalytic route can accomplish the direct late-stage C-H functionalization of bioactive molecules and natural product derivatives assisted by C (sp²)-H thianthrenation. Moreover, on the basis of this practical approach, several deuterated drugs and analogues could be prepared with excellent levels of deuterium incorporation.

Highly selective single and multiple deuteration of unactivated C(sp3)-H bonds

Selective deuteration of unactivated C(sp3)-H bonds is a highly attractive but challenging subject of research in pharmaceutical chemistry, material science and synthetic chemistry. Reported herein is a practical, highly selective and economical efficient hydrogen/deuterium (H/D) exchange of unactivated C(sp3)-H bonds by synergistic photocatalysis and hydrogen atom transfer (HAT) catalysis. With the easily prepared PMP-substituted amides as nitrogen-centered radical precursors, a wide range of structurally diverse amides can undergo predictable radical H/D exchange smoothly with inexpensive D2O as the sole deuterium source, giving rise to the distal tertiary, secondary and primary C(sp3)-H bonds selectively deuterated products in yields of up to 99% and excellent D-incorporations. In addition to precise monodeuteration, this strategy can also achieve multideuteration of the substrates contain more than one remote C(sp3)-H bond, which opens a method to address multi-functionalization of distal unactivated C(sp3)-H bonds.

Synthesis of C-1 Deuterated 3-Formylindoles by Organophotoredox Catalyzed Direct Formylation of Indoles with Deuterated Glyoxylic Acid

Direct formylation of feedstock indoles with newly developed, cost-effective deuterated glyoxylic acid as formylation agent under visible light and air (O₂) as terminal oxidant has been developed. An isatin byproduct produced from the corresponding indole reactant serves as a facilitator for the formylation process. The simple, mild, metal- and oxidant-free protocol enables the synthesis of structurally diverse C1-deuterated 3-formylindoles with broad functional group tolerance and late-stage functionalization at a high level of D-incorporation (95-99%).

Rhodium-Catalyzed Deuterated Tsuji-Wilkinson Decarbonylation of Aldehydes with Deuterium Oxide

The recent surge in the applications of deuterated drug candidates has rendered an urgent need for diverse deuterium labeling techniques. Herein, an efficient Rh-catalyzed deuterated Tsuji-Wilkinson decarbonylation of naturally available aldehydes with D₂O is developed. In this reaction, D₂O not only acts as a deuterated reagent and solvent but also promotes Rh-catalyzed decarbonylation. In addition, decarbonylative strategies for the synthesis of terminal monodeuterated alkenes from α,β-unsaturated aldehydes are within reach.

Deoxygenative gem-difluorovinylation of aliphatic alcohols

An unprecedented deoxygenative gem-difluorovinylation of aliphatic alcohols using α-trifluoromethyl alkenes is achieved under photocatalytic conditions. Inexpensive Ph₃P acts as an efficient O-atom transfer reagent to facilitate the deoxygenation of alcohols for the generation of reactive alkyl radical species. Remarkable features of this reaction include mild conditions, simple operation and broad scope. The synthetic utility of this reaction was validated by the success of two-step one-pot reactions, scale-up synthesis and chemoselective monodeoxygenation of diols.

Visible light-induced deoxygenation/cyclization of salicylic acid derivatives and aryl acetylene for the synthesis of flavonoids

A visible-light-induced photocatalytic strategy for the synthesis of flavonoids has been developed through the deoxygenative/cyclization reaction of salicylic acid derivatives with aryl acetylene using diphenyl sulfide as an O-transfer reagent. Based on the controlled experiments, the mechanism of visible-light-induced free radical coupling cyclization was proposed. The protocol obtained 51 flavonoids in good yields and has been successfully applied to the synthesis of some natural flavones.

Decarboxylative tandem C-N coupling with nitroarenes via SH2 mechanism

Aromatic tertiary amines are one of the most important classes of organic compounds in organic chemistry and drug discovery. It is difficult to efficiently construct tertiary amines from primary amines via classical nucleophilic substitution due to consecutive overalkylation. In this paper, we have developed a radical tandem C-N coupling strategy to efficiently construct aromatic tertiary amines from commercially available carboxylic acids and nitroarenes. A variety of aromatic tertiary amines can be furnished in good yields (up to 98%) with excellent functional group compatibility under mild reaction conditions. The use of two different carboxylic acids also allows for the concise synthesis of nonsymmetric aromatic tertiary amines in satisfactory yields. Mechanistic studies suggest the intermediacy of the arylamine–(TPP)Fe(III) species and might provide a possible evidence for an S_H2 (bimolecular homolytic substitution) pathway in the critical C-N bond formation step.

Aromatic tertiary amines are versatile building blocks in organic synthesis. In this article, the authors report on an iron-catalysed reaction for the decarboxylative C-N coupling from carboxylic acids and nitroarenes, leading to non-symmetric tertiary aromatic amines.

Visible light-promoted synthesis of ureas and formamides from amines and CO2

A divergent visible-light-induced Ph₃P-promoted method for the synthesis of ureas and formamides from amines and CO₂ is reported. Without external additions, a range of ureas could be directly accessed under ambient temperature and pressure. Using triisopropylsilanethiol as the hydrogen source, formamides could be produced.

Programmable iodization/deuterolysis sequences of phosphonium ylides to access deuterated benzyl iodides and aromatic aldehydes

Herein, a tunable iodization/deuterolysis protocol for phosphonium ylides by employing D₂O as the deuterium source was designed. Notably, this process could be manipulated by tuning the base, thus leading to two valuable deuterated building blocks - benzyl iodides and aromatic aldehydes with broad substrate scope, good functional group compatibility and excellent deuteration degree. Concise syntheses of a series of deuterated drug analogues have been achieved based on the developed deuteration reaction platform.

C-H deuteration of organic compounds and potential drug candidates

C-H deuteration has been intricately developed to satisfy the urgent need for site-selectively deuterated organic frameworks. Deuteration has been primarily used to study kinetic isotope effects of reactions but recently its significance in pharmaceutical chemistry has been discovered. Deuterium labelled compounds have stolen the limelight since the inception of the first FDA-approved deuterated drug, for the treatment of chorea-associated Huntington's disease, and their pharmacological importance was realised by chemists, although surprisingly very late. Various approaches were developed to carry out site-selective deuteration. However, the most common and efficient method is hydrogen isotope exchange (HIE). This review summarises deuteration methods of various organic motifs containing C(sp²)-H and C(sp³)-H bonds utilizing C-H bond functionalisation as a key step along with a variety of catalysts, and exemplifies their biological relevance.

Effects of digestion duration on energy efficiency, compost quality, and carbon flow during solid state anaerobic digestion and composting hybrid process

This study investigated the effects of anaerobic digestion duration on methane yield, net energy production, and humification of compost during solid state anaerobic digestion (SSAD) and composting hybrid process for food waste treatment. Carbon flow and balance were used to evaluate organic methanation and humification inclination of carbon in the whole SSAD and aerobic composting system. Results showed that SSAD for 15 (AD-15) and 21 days (AD-21) could increase net energy production and degraded organic matter contained in the mixtures to achieve high biological stability. The cumulative net energy production between the AD-15 and AD-21 treatments was not significantly different, which was 8.3% higher than that in SSAD for 30 days (AD-30). Furthermore, digestate (AD-15 and AD-21) composting for 3 days reached maturity and absence of phytotoxic substances. Carbon fixed into humus of the AD-21 treatment (11.6%) was not significantly different from that of AD-15 (12.0%). However, the total amount of carbon fixed into compost in AD-15 was 6.6% higher than that in AD-21. Moreover, the CO₂ -C loss of the AD-15 treatment (22.9%) was slightly higher than that of AD-21 (20.6%). Thus, AD-21 treatment achieved the most effective use of carbon during SSAD and composting hybrid process for food waste treatment. These results could provide valuable insights for the effective management of food waste in practice.

Arylboronic Acid Deborylation Deuteration via Synergistic Thiol, Lewis Base, and Photoredox Catalysis

A mild method for the deborylation deuteration of arylboronic acids with D₂O, mediated by the synergistic combination of a thiol, a Lewis base, and photoredox catalysis, is reported. This reaction showed a broad substrate scope, excellent deuterium incorporation, and functional group tolerance. Therefore, this method is practical for the site-selective D-labeling of bioactive molecules and drug molecules.