Recent advancements in metal-catalyst-free multicomponent radical sulfonylation of alkynes.

Vinyl sulfones are crucial building blocks in synthetic chemistry and core structural units of pharmaceutically active molecules, thus extensive investigations have been conducted on the construction of these skeletons. In contrast to the classical synthetic approaches, the radical sulfonylation of alkynes for producing vinyl sulfones has garnered considerable interest because of its mild conditions and high efficiency. Radical sulfonation of alkynes typically begins with the sulfonyl radical attacking the alkynes, followed by further functionalization. Moreover, the association of metal-catalyst-free systems with multicomponent reactions (MCRs) offers an environmentally friendly pathway for efficiently constructing complex scaffolds from readily available partners. However, there is no comprehensive review summarizing the advancements in metal-catalyst-free multicomponent radical sulfonylation of alkynes. Hence, we provide a categorical overview based on the objects of sulfonylation of alkynes (hydrosulfonylation, carbosulfonylation, aminosulfonylation, oxysulfonylation, sulfosulfonylation, selenosulfonylation, and iodosulfonylation), along with interpretations of the reaction mechanisms.

Dual Nickel/Photoredox-Catalyzed Arylsulfonylation of Allenes.

The nickel/photoredox dual catalysis system is an efficient conversion platform for the difunctionalization of unsaturated hydrocarbons. Herein, we disclose the first dual nickel/photoredox-catalyzed intramolecular 1,2-arylsulfonylation of allenes, which can accurately construct a C(sp2)-C(sp2) bond and a C(sp3)-S bond. The reaction exhibits excellent chemoselectivity and regioselectivity, allowing modular conformations of a diverse series of 3-sulfonylmethylbenzofuran derivatives. Control experiments showed that the bipyridine ligand is crucial for the formation of a stable σ-alkyl nickel intermediate, providing the possibility for sulfonyl radical insertion. Meanwhile, the electrophilic sulfonyl radical facilitates further oxidative addition of the σ-alkyl nickel intermediate and inhibits addition with allenes. In addition, control experiments, cyclic voltammetry tests, Stern-Volmer experiments, and density functional theory calculations afford evidence for the Ni(0)/Ni(I)/Ni(II)/Ni(III) pathway in this 1,2-arylsulfonylation.

Metal-catalyzed Markovnikov-type selective hydrofunctionalization of terminal alkynes.

Metal-catalyzed highly Markovnikov-type selective hydrofunctionalization of terminal alkynes provides a straightforward and atom-economical route to access 1,1-disubstituted alkenes, which have a wide range of applications in organic synthesis. However, the highly Markovnikov-type selective transformations are challenging due to the electronic and steric effects during the addition process. With the development of metal-catalyzed organic synthesis, different metal catalysts have been developed to solve this challenge, especially for platinum group metal catalysts. In this perspective, we review homogeneous metal-catalyzed Markovnikov-type selective hydrofunctionalization of terminal alkynes according to the classified element types as well as reaction mechanisms. Future avenues for investigation are also presented to help expand this exciting field.

Copper-Catalyzed Radical Relay 1,3-Carbocarbonylation across Two Distinct C═C Bonds.

The radical relay provides an effective paradigm for intermolecular assembly to achieve functionalization across remote chemical bonds. Herein, we report the first radical relay 1,3-carbocarbonylation of α-carbonyl alkyl bromides across two separate C═C bonds. The reaction is highly chemo- and regioselective, with two C(sp3)-C(sp3) bonds and one C═O bond formed in a single orchestrated operation. In addition, the synthesis method under mild conditions and using inexpensive copper as the catalyst allows facile access to structurally diverse 1,3-carbocarbonylation products. The plausible mechanism is investigated through a series of control experiments, including radical trapping, radical clock experiments, critical intermediate trapping, and 18O labeling experiment.

Photoinduced Copper-Catalyzed Aminoalkylation of Amino-Pendant Olefins.

The combination of photo and copper catalysts has emerged as a novel paradigm in organic catalysis, which provides access to the acceleration of chemical synthesis. Herein, we describe an aminoalkylation of amino-dependent olefins with maleimides through a cooperative photo/copper catalytic system. In this report, the strategy allows the generation of a broad complex of functionalized nitrogenous molecules including oxazolidinones, 2-pyrrolidones, imidazolidinones, thiazolidinones, pyridines, and piperidines in the absence of an external photosensitizer and base. The approach is achieved through a photoinduced Cu(I)/Cu(II)/Cu(III) complex species of nitrogen nucleophiles, intermolecular radical addition, and hydrogen atom transfer (HAT) processes. The plausible mechanism is investigated by a series of control experiments and theoretical tests, including radical scavenging experiments, deuterium labeling experiments, ultraviolet-visible absorption, and cyclic voltammetry (CV) tests.

Recent advances in radical-mediated intermolecular (4 + 2) cycloaddition.

(4 + 2) Cycloaddition plays an important role in the synthesis of versatile carbocyclic/heterocyclic compounds with its high atom- and step-economy. Additionally, with mild conditions and indispensable functional group compatibility, the radical reaction has been recognized as a useful tool in organic chemistry. Given the enormous impact of radical-mediated (4 + 2) cycloaddition processes and their promising applications, we summarize and highlight the recent works in this attractive area. On the basis of the types of radicals that initiate different (4 + 2) cycloaddition processes, we classify them into processes involving alkenyl cations or alkenyl radicals, aryl radicals, acyl radicals, alkyl radicals, and heteroatom radicals, and this review places special emphasis on the reaction design and mechanisms, which will stimulate future developments in radical-mediated intermolecular (4 + 2) cycloaddition.

Applications of sulfonyl hydrazides in radical cyclization of alkenes.

Radical cyclization is regarded as a powerful and promising strategy for the assembly of diverse important cyclic structures because of its high atom- and step-economy. As excellent radical acceptors, alkenes offer two potential directions, pushing the research domain of radical cyclization. In this context, as a radical precursor, sulfonyl hydrazide plays an important role in accomplishing radical cyclization of alkenes in a facile and efficient way. This review focuses on the applications of sulfonyl hydrazides in radical cyclization of alkenes, which generally has two radical conversion modes, sulfonyl radicals and sulfoxide radicals. In particular, the section of sulfonyl radicals consists of eight parts containing aromatic rings, alkenes, alkynes, cyanides, aldehydes, carboxylic acids, amides, and small ring compounds, according to the objects of cyclization after addition with alkenes. Within each category, representative instances are presented and discussed in terms of their general mechanistic perspectives when needed.

Photoredox and Copper Dual-Catalyzed Cyclization of Alkyne-tethered α-Bromocarbonyls.

The synergistic systems of photoredox and copper catalyst have already appeared as a novel formation of green synthetic chemistry, which open new avenues for chemical synthesis applications. We describe a novel strategy for the cyclization of alkyne-tethered α-bromocarbonyls initiated by the cleavage of C(sp3 )-Br bond via the collaboration of photoredox and copper catalyst. The present protocol exhibits mildness using economical copper catalyst and visible-light at room temperature. The gram-scale and sunlight irradiation experiments proceeded smoothly to show the practicality of the methodology. It is notable that the newly generated oxygen in the product originates from H2 O.

Chemodivergent Tandem Radical Cyclization of Alkene-Substituted Quinazolinones: Rapid Access to Mono- and Di-Alkylated Ring-Fused Quinazolinones.

Chemodivergent tandem radical cyclization offers exciting possibilities for the synthesis of structurally diverse cyclic compounds. Herein, we revealed a chemodivergent tandem cyclization of alkene-substituted quinazolinones under metal- and base-free conditions, this transformation is initiated by alkyl radicals produced from oxidant-induced α-C(sp3 )-H functionalization of alkyl nitriles or esters. The reaction resulted in the selective synthesis of a series of mono- and di-alkylated ring-fused quinazolinones by modulating the loading of oxidant, reaction temperature, and reaction time. Mechanistic investigations show that the mono-alkylated ring-fused quinazolinones is constructed by the key process of 1,2-hydrogen shift, whereas the di-alkylated ring-fused quinazolinones is mainly achieved through crucial steps of resonance and proton transfer. This protocol is the first example of remote second alkylation on the aromatic ring via α-C(sp3 )-H functionalization and difunctionalization achieved by association of two unsaturated bonds in radical cyclization.

Radical bicyclization of 1,6-enynes with sulfonyl hydrazides by the use of TBAI/TBHP in the aqueous phase.

A novel 5-exo-dig/6-endo-trig bicyclization of 1,6-enynes with sulfonyl hydrazides in the aqueous phase using the cheap and available tetrabutylammonium iodide (TBAI)-tert-butyl hydroperoxide (TBHP) combined system is reported. The resulting reaction of diverse nitrogen- and oxygen-polyheterocycles displays high chemical selectivity, high step-economy, and a moderate substrate scope. Moreover, iodosulfonylation can be realized by modulating the structure of the 1,6-enynes.

Metal- and Base-Free Radical Cascade Cyclization/Hydrolysis of CN-Containing 1,6-Enynes with Ethers to Access Polyheterocycles.

A convenient and straightforward approach for the radical cascade cyclization/hydrolysis of CN-containing 1,6-enynes with simple ethers under metal- and base-free conditions is described. This strategy provides a variety of valuable ethers-substituted polyheterocycles via the construction of three C-C bonds, one C=O bond, and two new six-membered rings within a single procedure. The resulting products can smoothly undergo follow-up conversions to various useful scaffolds. The methodology shows excellent functional group tolerance, high step- and atom- economy, and mild reaction conditions, which can be further scaled up to gram quantity in a satisfactory yield.

Fe-Catalyzed Selective Formal Insertion of Diazo Compounds into C(sp)-C(sp3) Bonds of Propargyl Alcohols: Access to Alkyne-Substituted All-Carbon Quaternary Centers.

The construction of all-carbon quaternary centers, especially those containing an alkyne-substituted framework, represents an important challenge in organic synthesis. Here we present a novel Fe-catalyzed selective formal insertion of diazo compounds into C(sp)-C(sp3) bonds of propargyl alcohols under mild conditions that enables the streamlined construction of alkyne-substituted all-carbon quaternary centers. This unique strategy starts with in situ generation of an ester group in the presence of carboxylic acids, followed by insertion of metal-carbene into C(sp)-C(sp3) bonds, which may open up a new reaction mode for exploring metal-carbene insertion into acyclic C-C bonds.

The polychloromethylation/acyloxylation of 1,6-enynes with chloroalkanes and diacyl peroxides through dual-role designs.

The novel polychloromethylation/acyloxylation of 1,6-enynes with chloroalkanes and diacyl peroxides through dual-role designs has been developed to prepare 2-pyrrolidinone derivatives with polychloromethyl units with the use of an inexpensive copper salt under mild conditions. This strategy includes two dual-role designs, not only improving atomic utilization but also allowing a cleaner process. The wide substrate scope and simple reaction conditions demonstrate the practicability of this protocol.

Cyclization/hydrolysis of 1,5-enenitriles initiated by sulfonyl radicals in the aqueous phase in the presence of the I2/TBHP system.

A novel cyclization/hydrolysis of 1,5-enenitriles for the synthesis of valuable pyrrolidine-2,4-diones in the aqueous phase using I2 as the catalyst and tert-butyl hydroperoxide (TBHP) as the oxidant is reported. In the presence of the I2/TBHP system, sulfonyl hydrazides produce sulfonyl radicals, which undergo radical addition, intramolecular cyclization, hydrogen abstraction, and hydrolysis to give the final products. The use of the inexpensive and environmentally friendly I2/TBHP catalytic oxidation system in the aqueous phase makes it a benign and sustainable strategy.

Visible-Light-Catalyzed Tandem Radical Addition/1,5-Hydrogen Atom Transfer/Cyclization of 2-Alkynylarylethers with Sulfonyl Chlorides.

A novel visible-light-catalyzed tandem radical addition/1,5-hydrogen atom transfer/cyclization cascade of 2-alkynylarylethers with sulfonyl chlorides in 2-methyltetrahydrofuran was developed under photocatalyst- and additive-free conditions. This reaction relies on unique energy transfer and solvent-radical relay strategies to generate sulfonyl radicals for the preparation of a series of sulfonyl-functionalized dihydrobenzofurans in moderate to high yields catalyzed by visible light or solar radiation.

Sleep patterns and potential risk factors for disturbed sleep quality in patients after surgery for infective endocarditis.

BACKGROUND: The current study aimed to investigate the sleep quality of patients after valve replacement surgery due to infective endocarditis and identify risk factors for disturbed sleep post hospitalisation. METHODS: Eighty patients were assessed postoperatively using subjective scale measures, the Pittsburgh sleep quality index (PSQI) and the Epworth sleepiness scale, and an objective measure, actigraphy. Scale measures were assessed approximately 2 weeks and 6 months after surgery. Actigraphy monitoring was performed for 2 consecutive weeks during hospitalisation. Logistic regression was used to identify risk factors for disturbed sleep. RESULTS: The study population (n = 80) had an average age of 42.8 ± 14.2 years, and 67.5% were male. The median sleep efficiency was 85.3% in week 1 and 86.8% in week 2. The frequency of awakenings was significantly higher in week 1 (20.0 times vs. 19.3 times, p = 0.017). The scale measures showed significant improvement in sleep by 6 months after surgery compared to that during hospitalisation. Multivariable logistic regression analysis suggested that the possible risk factors for disturbed sleep 6 months after surgery included age (OR = 1.479, 95%CI 1.140-1.920) and a few parameters of early postoperative disturbed sleep quality (PSQI: OR = 2.921, 95%CI 1.431-5.963; sleep efficiency: OR = 0.402, 95%CI 0.206-0.783; and average duration of awakenings: OR = 0.006, 95%CI 0.000-0.827). CONCLUSIONS: Disturbed sleep quality was witnessed in postoperative patients during hospitalisation and up to 6 months after surgery. Over time, the patients' sleep quality improved significantly. Age and a few early postoperative sleep quality variables were risk factors for disturbed sleep 6 months after surgery.

Recent Advances in Copper-Catalyzed C-N Bond Formation Involving N-Centered Radicals.

C-N bonds are pervasive throughout organic-based materials, natural products, pharmaceutical compounds, and agricultural chemicals. Considering the widespread importance of C-N bonds, the development of greener and more convenient ways to form C-N bonds, especially in late-stage synthesis, has become one of the hottest research goals in synthetic chemistry. Copper-catalyzed radical reactions involving N-centered radicals have emerged as a sustainable and promising approach to build C-N bonds. As a chemically popular and diverse radical species, N-centered radicals have been used for all kinds of reactions for C-N bond formation by taking advantage of their inherently incredible reactive flexibility. Copper is also the most abundant and economic catalyst with the most relevant activity for facilitating the synthesis of valuable compounds. Therefore, the aim of the present Review was to illustrate recent and significant advances in C-N bond formation methods and to understand the unique advantages of copper catalysis in the generation of N-centered radicals since 2016. To provide an ease of understanding for the readers, this Review was organized based on the types of nitrogen sources (amines, amides, sulfonamides, oximes, hydrazones, azides, and tert-butyl nitrite).

Selective divergent radical cyclization of 1,6-dienes with alkyl nitriles.

An efficient, selective, and step economical radical cyclization of 1,6-dienes with alkyl nitriles initiated by α-C(sp3)-H functionalization under the Sc(OTf)3 and Ag2CO3 system is described here. The selective divergent cyclization relies on the substitution effect at the α-position of the acrylamide moiety and nitriles, which is terminated by hydrogen abstraction, direct cyclization with the aryl ring, or further cyclization with the CN bond and hydrolysis, respectively.

The construction of benzimidazo[2,1-a]isoquinolin-6(5H)-ones from N-methacryloyl-2-phenylbenzoimidazoles through radical strategies.

Benzimidazo[2,1-a]isoquinolin-6(5H)-one constitutes a structurally unique class of tetracyclic N-heterocycles that are found throughout a myriad of biologically active natural products, pharmaceutical compounds, and functional materials. Various synthetic routes for the preparation of benzimidazo[2,1-a]isoquinolin-6(5H)-ones have been reported. In particular, the use of N-methacryloyl-2-phenylbenzoimidazoles to construct benzimidazo[2,1-a]isoquinolin-6(5H)-ones through various radical strategies have attracted widespread attention due to the versatility and simple preparation of raw materials, as well as the step-economy and mild reaction conditions. Using representative examples, we highlight significant progress in the synthesis of benzimidazo[2,1-a]isoquinolin-6(5H)-ones, including the selection of the catalytic system, substrate scope, mechanistic understanding, and applications. The contents of this review focus on the development of C-, S-, P-, and Si-centered radical addition-intramolecular cyclization strategies.

Recent progress in the radical α-C(sp3)-H functionalization of ketones.

The direct use structurally simple ketones as α-ketone radical sources for α-C(sp3)-H functionalization is a sustainable and powerful approach for constructing complex and multifunctional chemical scaffolds with diverse applications. The reactions of α-ketone radicals with alkenes, alkynes, enynes, imides, and imidazo[1,2-a]pyridines have broadened the structural diversity and complexity of ketones. Through chosen illustrative examples, we outline the recent progress in the development of methods that enable the radical α-C(sp3)-H functionalization of ketones, with an emphasis on radical initiation systems and possible mechanisms of the transformations. The application of these strategies is illustrated by the synthesis of several biologically active molecules and drug molecules. Further subdivision is based on substrate type and reaction type.