bluuebunny/crossref_metadata_2025 huggingface dataset:
Sound propagation and speech transmission in a branching underground tunnel
Authors: Imaizumi Hiroyuki , Kunimatsu Sunao , Isei Takehiro
Published: July 2002

The characteristics of sound propagation and speech transmission along a tunnel with a “T” intersection were investigated. At receivers within sight of the sound source, low frequencies were mainly attenuated around the intersection than high frequencies. At receivers out of sight of the source, high frequencies were extensively attenuated. The overall pattern of sound attenuation along the different sections of tunnel, which was calculated by the conical beam method, agreed well with the measurements in this study. Numerical calculations of reflected and diffracted waves with minimum transmission paths in a two-dimensional plane showed that reflected waves were the primary contributors to sound fields out of sight of the source. The articulation scores measured at receivers within sight of the source were high, and most of the confusion concerned syllables that could easily be misheard, even if there were a high signal-to-noise ratio. The types of syllable confusions observed at the receivers out of sight of the source appeared to have been caused by the greater deterioration in speech signals along this part of the tunnel, especially at high frequencies. The evaluation by rapid speech transmission indices (RASTI) appeared to be overestimated at the receivers out of sight of the source. Taking into account the early decay times of impulsive sound and the calculation procedures used in RASTI, it is concluded that speech intelligibility may not have been evaluated correctly by RASTI.
Product Form of Kernel Functions for Nonlinear Viscoelasticity of PVC Under Constant Rate Stressing
Authors: Findley W. N. , Onaran K.
Published: July 2002

Determination of all the kernel functions for multiple integral representation of creep is very involved. In this paper the kernel functions were assumed to have a product form, such as f2(t−τ1,t−τ2)=f2(t−τ1)f2(t−τ2). The validity of this assumption was tested by experiments on a poly(vinyl chloride) plastic tube subjected to constant rates of stressing in combinations of tension and torsion. Some experiments also included abrupt changes in stress. Application of the theory to several complex experiments is illustrated. Agreement between theory and experiment is generally satisfactory, so the assumption seems adequate for the type stress histories investigated.
Fundamentals of False-Twist Texturing of Thermoplastic Continuous Filament Yarns
Authors: Smith R. L. , Pieters R. , Morrison M. E.
Published: July 2002

This paper describes the state of development for false-twist texturing of thermoplastic continuous filament yarns. Supply yarn parameters are shown to significantly affect the textured product. Quantitative and qualitative information is given to describe these effects. The thermodynamic and crystallization rate parameters are presented for nylon 6, nylon 66, and polyethylene-terepthalate. Equations are given for calculation of temperature-time profiles in yarns during texturing. Both the fundamentals of twisting using spindle or friction twisters are summarized. The effect of process variables on twist distribution and crimp rigidity are presented. Finally, experiments are described which show how force-elongation curves for textured nylon 6 can be made similar to nylon 66. Recommendations for future work are discussed. Ways are needed to improve the dye uniformity and reduce barré from textured yarns in piece-dyed fabrics. More information should be reported on the effect of processing constants (tension and temperature gradients) on crystallization rate phenomena and structural changes during texturing. Basic information on the effect of yarn and process constants on friction twisting with the many commercial units needs reported. The final goal of this fundamental work should be a mathematical model, which rigorously describes the texturing process. With this model, yarn and machinery manufacturers could optimize their products more fully for the use of the texturing mills.
Elevated Temperature Creep of Polyurethane under Nonlinear Torsional Stress with Step Changes in Torque
Authors: Lai J. S. Y. , Findley W. N.
Published: July 2002

Constant stress experiments, recovery, and multi-step creep tests in torsion in the nonlinear range were performed at different temperatures up to 160 °F. It was found that the results could be described by a power function of time whose exponent was independent of stress and temperature. Most of the temperature effect and most of the nonlinearity were found in the coefficient of the time-dependent term. The nonlinearity was described by the multiple integral representation, and the changes in stress were adequately predicted by the modified superposition method, except at the highest temperatures.
Correlation and Molecular Interpretation of Data Obtained in Elongational Flow
Authors: Hudson N. E. , Ferguson J.
Published: July 2002

Elongational and shear flow experiments on solutions of polybutadiene in dekalin and polyacrylonitrile in dimethyl formamide have been examined. It has been found that by using the total strain in elongation rather than strain rate the data obtained at different rates of extrusion and take-up rate in the elongational flow experiments can be correlated. The use of the concept of total strain can be shown to allow the data to be considered in terms of constant macromolecular entanglement. Moreover, by plotting the variation of the normalized elastic modulus in elongation, Ḡn=G/Ḡ0, against the normalized elongational viscosity, η̃n=η̃/3η0, it becomes possible to obtain the total strain at which the elongational response of a polymer solution changes from mainly viscous to mainly elastic. The results have been considered in terms of a set of constitutive equations developed by Marrucci et al. Remarkable similarity exists between their theoretical predictions and the experimental results, in elongational flow, on the above solutions. These are discussed on the molecular level and it is proposed that the anomalous situation that exists between the proposal that chain entanglement decreases and the change in response of the fluid from viscous to elastic as elongation progresses, can be resolved. This is achieved by postulating the existence of a network of very-long-lifetime entanglements between the macromolecules.
Determination of shear rate and viscosity from batch mixer data
Authors: Bousmina M. , Ait-Kadi A. , Faisant J. B.
Published: July 2002

A general analysis allowing the determination of shear rate and viscosity from batch mixer rotor speed and torque data is presented. The batch mixer was represented by two effective adjacent sets of concentric cylinders exerting the same torque as that obtained from the batch mixer. The effective internal radius was determined through a general procedure for calibration using non-Newtonian fluid. The effective equivalent internal radius, Ri, was determined for different polymers and processing conditions. The results revealed that Ri is a universal quantity practically insensitive to the nature and to the rheological behavior of the fluid under mixing. In the case of small gaps, it was found that there is a special position in the gap where the effective internal radius, the shear rate and viscosity are independent of rheological characteristics of the fluid under mixing. This validates the Newtonian approximation previously used by Goodrich and Porter to extract the shear rate-viscosity dependence from batch mixer data. The technique was tested on seven different amorphous and semicrystalline polymers and the results were found to be in reasonable agreement with the data obtained independently with cone-and-plate and capillary rheometers. Contributions of both shear stress between the two cylinders and the stress generated at the wall were evaluated. The latter was found predominant.
Characterizing the Language Used to Discuss Death in Family Meetings for Critically Ill Infants
Authors: Barlet Margaret H. , Barks Mary C. , Ubel Peter A. , Davis J. Kelly , Pollak Kathryn I. , Kaye Erica C. , Weinfurt Kevin P. , Lemmon Monica E.
Published: October 2022

Importance

Communication during conversations about death is critical; however, little is known about the language clinicians and families use to discuss death.

Objective

To characterize (1) the way death is discussed in family meetings between parents of critically ill infants and the clinical team and (2) how discussion of death differs between clinicians and family members.

Design, Setting, and Participants

This longitudinal qualitative study took place at a single academic hospital in the southeast US. Patients were enrolled from September 2018 to September 2020, and infants were followed up longitudinally throughout their hospitalization. Participants included families of infants with neurologic conditions who were hospitalized in the intensive care unit and had a planned family meeting to discuss neurologic prognosis or starting, not starting, or discontinuing life-sustaining treatment. Family meetings were recorded, transcribed, and deidentified before being screened for discussion of death.

Main Outcomes and Measures

The main outcome was the language used to reference death during family meetings between parents and clinicians. Conventional content analysis was used to analyze data.

Results

A total of 68 family meetings involving 36 parents of 24 infants were screened; 33 family meetings (49%) involving 20 parents (56%) and 13 infants (54%) included discussion of death. Most parents involved in discussion of death identified as the infant’s mother (13 [65%]) and as Black (12 [60%]). Death was referenced 406 times throughout the family meetings (275 times by clinicians and 131 times by family members); the words die, death, dying, or stillborn were used 5% of the time by clinicians (13 of 275 references) and 15% of the time by family members (19 of 131 references). Four types of euphemisms used in place of die, death, dying, or stillborn were identified: (1) survival framing (eg, not live), (2) colloquialisms (eg, pass away), (3) medical jargon, including obscure technical terms (eg, code event) or talking around death with physiologic terms (eg, irrecoverable heart rate drop), and (4) pronouns without an antecedent (eg, it). The most common type of euphemism used by clinicians was medical jargon (118 of 275 references [43%]). The most common type of euphemism used by family members was colloquialism (44 of 131 references [34%]).

Conclusions and Relevance

In this qualitative study, the words die, death, dying, or stillborn were rarely used to refer to death in family meetings with clinicians. Families most often used colloquialisms to reference death, and clinicians most often used medical jargon. Future work should evaluate the effects of euphemisms on mutual understanding, shared decision-making, and clinician-family relationships.
Rh‐Catalyzed CH Functionalization with Allenes
Authors: Singh Anurag , Volla Chandra M.R.
Published: October 2022

Recent years have witnessed the emergence of allenes as valuable coupling partners in transition metal‐catalyzed CH activation due to their unique reactivity. Carbometalation of the allene plays a key role in controlling the reactivity pattern by selective formation of either M‐π‐allyl or M‐alkenyl intermediate. Among the different metal catalysts, rhodium complexes have proved to be particularly efficient in illustrating the reactivity of various kinds of allenes for generating assortments of products. Annulation reactions with allenes were also well recognized for the construction of diverse array of biologically and pharmaceutically relevant heterocyclic moieties. In this article, we summarized various Rh‐catalyzed CH activation reactions involving allenes as coupling partners with selected examples and provided the reaction mechanism wherever necessary.
Asymmetric Addition of Inert CH Bond to Carbonyls, Imines, and Electron‐Deficient Alkenes
Authors: Vasamsetty Laxmaiah , Wang Jun
Published: October 2022

The nucleophilic addition of organometallic reagents to aldehydes, ketones, imines, and electron‐deficient alkenes is one of the most classic and useful methods to construct organic compounds. Normally, prehalogenation of substrates and the use of stoichiometric amounts of metals to prepare air and moisture‐sensitive organometallic reagents are inevitable. Along with the flourish of CH activation in the last two decades, transition metal‐catalyzed direct addition of inert CH bonds to polar multiple bonds (e.g. CO and CN) has aroused great interest of chemists for its superior atom and step economy. Though great success has been accomplished in this area, controlling the stereoselectivity of such reactions is still a big challenge. In this article, we would like to provide an overview of the advances in transition metal‐catalyzed asymmetric addition of CH bond to carbonyls, imines, and electron‐deficient alkenes, which may assist the development of this field. It is divided into three sections, (i) asymmetric addition of CH bond to carbonyls, (ii) asymmetric addition of CH bond to imines, and (iii) asymmetric addition of CH bond to electron‐deficient alkenes. The discussion of each reaction mainly consists of strategies used to control stereochemistry, selected examples of products with reaction outcomes, and reaction mechanism.
Rhodium‐Catalyzed Enantioselective CH Functionalization Using Chiral Cp Ligands
Authors: Dethe Dattatraya H. , Beeralingappa Nagabhushana C. , Singha Chirantan
Published: October 2022

Asymmetric CH functionalization is one of the most step‐ and atom‐economical approaches that provide efficient access to synthetically valuable enantiopure compounds. In this context, various novel transition metal‐catalyzed enantioselective CH functionalizations have been explored from the past few years to construct chiral molecules. The design of Cp

x

ligands and their application toward transition metal‐catalyzed CH functionalization reactions in an enantioselective manner is highly privileged. In this article, recent progress in the Cp

x

Rh‐catalyzed directing group‐assisted enantioselective CH functionalization reaction has been discussed.
Ru(II)‐Catalyzed CH Functionalization with Olefins and Alkynes
Authors: Logeswaran Ravichandran , Jeganmohan Masilamani
Published: October 2022

The cross‐dehydrogenative coupling reaction of substituted organic molecules with alkenes and alkynes has emerged as one of the most important synthetic organic chemistry reactions to construct structurally complex carbon‐based molecules. This article summarizes significant advances in chelation‐assisted ruthenium(II)‐catalyzed CH bond functionalization such as alkenylation, alkylation, and annulation via deprotonation pathway over the last decade.
Ru‐Catalyzed CH Activations with Oxidizing Directing Groups
Authors: Luo Yanshu , Xia Yuanzhi
Published: October 2022

Transition metal‐catalyzed CH bond activation has emerged as a powerful and ideal method for organic synthesis in recent decades. To avoid the use of over‐stoichiometric oxidant, the concept of oxidizing directing group was introduced for different catalytic systems. Recently, such strategy has been widely employed in the ruthenium‐catalyzed reactions, enabling novel CH functionalization under relatively mild conditions. In this article, progress in the recent development of the Ru‐catalyzed CH activations with oxidizing directing groups was summarized according to different types of internal oxidants. Major findings in the research field, mechanistic information from experimental or theoretical studies, and possible role of the internal oxidant were introduced according to literature reports.
Iron‐Catalyzed CH Activation/Functionalization to Form CC Bonds
Authors: Neidig Michael L. , Bhatia Shilpa , DeMuth Joshua C.
Published: October 2022

Iron‐catalyzed CH activation has attracted great interest over the past couple of decades as a promising technique to establish CC bond‐forming functionalities for complex molecule design. The motivation behind this trend can be attributed to the low cost, minimal toxicity, and rich oxidation chemistry afforded by iron. The synthetic utility of iron catalysis for CH activation/functionalization was widely recognized following the development of an iron‐catalyzed CH activation system that facilitated the cross‐coupling of a CH bond with an organometallic reagent under oxidative conditions. Following this seminal approach, iron‐catalyzed CH activation has been widely explored to establish CC bonds across a variety of functionalities. This article underscores the evolution of CC bond‐forming iron‐catalyzed CH activation by providing several examples across a broad range of CH functionalizations including alkylation, alkenylation, alkynylation, allylation, arylation, and annulation that involve CH‐activated organoiron species through the reaction of a substrate CH bond with an iron catalyst. An additional section of this article is dedicated to highlighting the key mechanistic insights into iron‐catalyzed CH functionalization, a field that is largely underdeveloped yet invaluable toward the rational development of the next generation of systems in iron‐catalyzed CH activation/functionalization.
Copper and Iron‐Promoted Decarboxylative CH Functionalization
Authors: Li Lian‐Hua , Liang Yong‐Min
Published: October 2022

The decarboxylative CH functionalization, as the combination of CH bond activation and decarboxylation, represents a great potential and is one of the eye‐catching key methods for organic syntheses. These reactions show good tolerance to many functional groups. Among the recent advances in decarboxylation processes, to some extent, copper‐ and iron‐promoted strategies occupy significant roles.
Copper‐Catalyzed CH Functionalization: CC Bond Construction via Cross Dehydrogenative Coupling (CDC)
Authors: Morja Mayur I. , Chauhan Prakashsingh M. , Chikhalia Kishor H.
Published: October 2022

The direct CH activation path has rationalized the preparation of functionalized molecules by minimizing the number of synthetic steps, and the processes are more atom economic. One such strategy, cross‐dehydrogenative coupling (CDC) reaction is an expedient synthetic protocol for direct CH functionalization including the construction of CC and CX (X = O, S, N, etc.) bonds. In the past years, considerable advancement has been made in the CC bond formation by using different hybrid CH (sp3, sp2, and sp) substrates via the CDC reaction. Particularly, copper‐catalyzed CDC reactions have attracted considerable attention because copper is an abundant, inexpensive, and environmentally benign metal. This article efforts to provide a comprehensive understanding of the development of cross‐dehydrogenative CC coupling via copper catalysis, as well as its mechanism and application in synthetic chemistry.
Copper‐Catalyzed CN Bond Formation by CH Functionalization
Authors: Wang Zhen , Shi Tao , Zhang Honghua
Published: October 2022

Copper‐catalyzed CN bond formation by CH functionalization has gained increasing attention in recent years, but no review systematically and comprehensively summarizes the references in this field. Herein, we summarized the advances in this field covering literatures from 2008 to 2020, and classified this summary into sp
2
CH functionalization and sp
3
CH functionalization. For each example, the reaction conditions, substrate scope, yield, and if possible, the mechanistic scheme are displayed, and sometimes are compared with similar reactions. At last, the development prospect of this domain is definitely expected to be bright.
Copper‐Catalyzed sp
2
CH Bond Functionalization
Authors: Jain Nidhi , Kaur Ramandeep , Sharma Arun
Published: October 2022

The use of sp
2
CH bonds as key functional groups has been realized by transition metal‐mediated CH bond activation and functionalization. In this regard, copper‐catalyzed CH activation has emerged as an environmentally benign and economically attractive approach in modern synthetic organic chemistry. Copper salts serve as versatile catalysts for oxidative coupling reactions and are often proposed to serve as a one‐electron oxidant to promote the single‐electron transfer process. This article discusses the recent advances in the copper‐catalyzed sp
2
CH functionalization achieving CC, CN, CO, CS, and CX bond formation via direct CH activation as well as directing group‐assisted activation strategy. An understanding of the mechanism of these reactions involving organocopper intermediates is crucial to promote the discovery of efficient and highly selective catalytic systems.
Copper‐Catalyzed sp
3
CH Bond Functionalization
Authors: Karjee Pallab , Sarkar Tanumay , Talukdar Kangkan , Shah Tariq A. , Das Bijay K. , Punniyamurthy Tharmalingam
Published: October 2022

Transition metal‐catalyzed CH functionalization provides an appealing strategy for the transformation of simple substrates into complex molecules with structural diversity. Despite the indispensable advances of CH functionalization developed to date, most of the methodologies demanded the use of expensive 4d and 5d transition metals. On the other hand, because of the low toxicity, less expensive, and one of the most abundant 3d row metals, copper progressively possesses a promising metal for the development of CH functionalization. Herein, we present the diverse array of copper‐based expedient C(sp
3
)H functionalization for the construction of directed and nondirected CC, CN, CO, CS, and Chalogen bonds.
Copper‐Catalyzed CH Functionalization Intermediates and Mechanisms
Authors: Hoover Jessica M.
Published: October 2022

CH functionalization reactions enable the efficient introduction of functionality in place of ubiquitous CH bonds. In particular, copper catalysts have seen rapid development and synthetic applications in recent years due, in part, to their ability to easily access multiple oxidation states and intermediates in varied mechanistic pathways. In this article, the predominant mechanistic intermediates and manifolds for Cu‐catalyzed CH activation reactions are presented.
Copper‐Catalyzed CC Bond Formation via CH Functionalization of N‐Heterocycles
Authors: Hore Soumyadip , Singh Abhijeet , Singh Ravi P.
Published: October 2022

The transition metal‐catalyzed CH bond functionalization has been achieved by various catalytic processes, among which copper‐catalyzed reactions have emerged as an environmentally benign and economical alternative. Here, an attempt has been made to collate all the seminal reactions based on CH functionalization to construct CC bond since 2012. This article discusses the evolution of this field from its nascent stages, where strategies for simple activation of sp, sp
2
, and sp
3
CH bonds of pronucleophiles were explored, to the more recent site‐selective reactions. In past decades, many bidentate ligands, for example amino acids, diamines, fused pyridines, oxazolidinones, and amides have transformed the Cu‐catalyzed coupling reactions into a practical and versatile synthetic tool. While the examples have been described with details about reaction conditions, some insight into the mechanistic pathways has also been presented.
Nickel‐Catalyzed Remote CH Bond Functionalization
Authors: Pradhan Suman , Chatterjee Indranil
Published: October 2022

The CH bond is one of the important structural units found in organic compounds. The functionalization of this ubiquitous CH bond has a significant meaning in the field of organic transformation in order to attain several biologically active drug molecules and complex molecular frameworks. Among these activation processes, distant and selective activation of the unactivated CH bond possesses significant challenges as well as rewards. Taking advantage of a functional group present in the molecule, functionalization at the remote position can be achieved. Transition‐metal catalysis is widely applied to perform such remote activation. However, nickel, a first‐row transition metal, shows its great applicability toward this kind of transformation. In this article, the concept of remote bond functionalization is discussed along with various nickel‐catalyzed seminal reports.
Oxidizing and Transformable Directing Groups in CH Functionalization
Authors: Ren Jie , Cui Xiuling
Published: October 2022

Transition metal‐catalyzed direct CH activation has been developed as a powerful strategy for the rapid construction of molecular complexity. The ubiquity and strength of CH bonds present major challenges toward the realization of CH transformations: selectivity and efficiency. The directing groups (DGs) resolved the regioselectivity and improved the catalytic activity of metal. However, they always left a chemical trace in the products, which limited the structural diversity. Hence, the development of multifunctional DGs in CH transformations comprised a central issue recently. This article focuses on the recent progress on the multifunctional DGs in transition metal‐catalyzed CH transformations, including oxidizing, migratable, and transformable DGs, which realize a highly atom‐economical process, incorporate the DGs in the final products, and enrich structural diversity of the products. We expect that these strategies will stimulate further innovative studies thought modifying DGs and developing a novel function of DGs, resulting in the discovery of efficient methods for the synthesis of complex molecules.
C(sp
2
)H Functionalization Guided by Intrinsic Functional Groups
Authors: de Carvalho Renato L. , de Oliveira Joyce C. , da Cruz Kimberly C. T. , Wood James M. , da Silva Júnior Eufrânio N.
Published: October 2022

CH activation has proven to be one of the most versatile synthetic strategies developed so far for the functionalization of sp
2
centers, due to the large variety of reaction conditions available to the practitioner including choice of catalyst, oxidant, additives and also directing group. Regarding the latter, one possibility is to use an intrinsic directing group. These are functional groups resident in the substrate containing a pair of nonbonding electrons, which can interact with the metal center of a catalyst and therefore control the site of CH activation. The use of a directing group that is intrinsic to the molecule is advantageous, as additional synthetic steps are not required for its installation and removal. The implementation of this directing group strategy is therefore guided by the structure of the desired compound and the coordinating ability of heteroatoms within it.
Transition Metal‐Catalyzed CH Bond Activation/Functionalization of Phosphines
Authors: Dixneuf Pierre H. , Soulé Jean‐François
Published: October 2022

Trivalent‐phosphorus‐containing molecules, especially phosphines, are currently used as a ligand in transition metal catalysis. Historically, it was thought that phosphine CH bonds were almost not reactive, but recent examples have demonstrated that it is possible to functionalize them easily under proper conditions. These methods use various Pd, Ir, Ru, and Rh transition metals and native P(III)‐atom as directing groups allowing the regioselective late‐stage functionalization of phosphine ligands. Interestingly, some modified phosphines have outperformed their parent ones in transition metal cross‐coupling reactions. This article summarized the different approaches for the P(III)‐directed CH bond functionalizations.
Heterogeneous CH Functionalization Approaches with Palladium Catalysts
Authors: Mandal Tanmoy , Bhandari Anirban , Choudhury Joyanta
Published: October 2022

Over the last few decades, considerable development in the field of homogeneous transition metal‐catalyzed CH functionalization has been achieved. Nonrecyclable homogeneous catalyst continues to be a major limitation in the field. Heterogenization of homogeneous catalysts allows reusability, making the systems economically and ecologically sustainable. The development of suitable Pd‐based heterogeneous catalysts is an active area of research motivated by the success of the Pd‐based homogeneous catalyst. This article summarizes the Pd‐based heterogeneous platforms for CH functionalization. The article has been divided into two broad sections: (i) Pd‐complex‐based heterogeneous catalysts and (ii) Pd nanoparticles‐based heterogeneous catalysts. Both sections are further divided into sub‐sections based on the supporting platforms used for anchoring the metal. In each section, the efficiency, site selectivity, and reusability of the Pd‐based catalysts are summarized.
Earth Abundant 3d Transition Metals (Fe, Co, Ni) for Nondirected CH Borylation
Authors: Kamitani Masahiro
Published: October 2022

Organoboron reagents are important synthetic intermediates that are often used in the Suzuki–Miyaura cross‐coupling reaction. Versatile and efficient chemical reactions that are capable of introducing a boryl group to an arbitrary organic molecule on demand are essential for the synthesis of new organoboron reagents. The nondirected CH borylation process generates organoboron reagents from a variety of organic molecules via CH‐to‐CB bond transformations. Further, it is widely used in numerous organic syntheses that are followed by coupling reactions, even though it is less selective than directed CH borylations of specific molecules equipped with a directing group. While nondirected borylations were initially catalyzed by precious metals, methods employing catalysts containing earth‐abundant metals (e.g. Fe, Ni, and Co) have been rapidly emerging over the past decade. This article provides a review of recent literature (from 2010 to early 2021) on earth‐abundant Fe, Ni, and Co catalysts for catalytic CH borylation.
Lanthanum‐ and Cerium‐Mediated CH Activation: Spectroscopy, Structures, and Formation of Metal‐Containing Intermediates
Authors: Cao Wenjin , Yang Dong‐Sheng
Published: October 2022

This article examines vibronic spectra, isomeric structures, and formation of transient metal complexes produced in La‐ and Ce‐mediated CH activation reactions of hydrocarbon compounds in the gas phase. The hydrocarbon compounds include small alkenes, alkynes, and alkadienes. Molecular masses of metal complexes are measured with time‐of‐flight mass spectrometry, vibronic spectra are probed with mass‐analyzed threshold ionization (MATI) spectroscopy, and isomeric structures are determined by comparing experimental and computational vibronic spectra, and plausible reaction pathways for the formation of specific isomers are investigated by quantum chemical calculations.
Metal‐Free Radical CH Functionalization via Aldehyde Auto‐Oxidation
Authors: Paul Subhasis , Biswas Promita , Guin Joyram
Published: October 2022

Oxidative functionalization of CH bond involving free‐radical intermediate offers a great opportunity for selective conversion of abundant chemicals to value‐added materials under mild conditions with remarkably high functional group tolerance. Accordingly, radical‐mediated synthesis receives considerable interest in pharmaceutical, agrochemicals, and polymer sciences. Numerous effective strategies for the functionalization of CH bonds through free‐radical intermediate have been developed. Despite these advancements in radical CH functionalization chemistry, the generation of free‐radical intermediate via oxidative homolytic activation of unactivated CH bond under sustainable conditions remains challenging. In this connection, the auto‐oxidation of organic compounds that enables selective generation of reactive free‐radical intermediate upon exposure of organic compounds to O
2
is of particular attraction. The auto‐oxidation of organic feedstocks has already been applied in the industrial production of commodity chemicals such as phenols and terephthalic acid. Nevertheless, the utilization of aerobic oxidation of chemical feedstocks in organic synthesis under reagent‐free conditions is very rare, particularly for small‐scale synthesis of functionalized molecules. Recently, a significant advancement in aerobic radical functionalization of CH bond using aldehyde auto‐oxidation has been achieved. This article provides an overview of the current development on selective functionalization of CH bond using aldehyde auto‐oxidation that proceeds via a radical pathway under reagent‐free conditions.
Platinum‐Catalyzed CX (X = O, B, Cl, Si) Bond Formation Through CH Functionalization
Authors: Huo Shouquan , Li Yumin
Published: October 2022

Low temperature and selective oxidation of unactivated alkanes through CH activation such as direct methane oxidation is a great challenge in chemical transformations, especially in the industry scale, and platinum has played a major role in the field. This article outlines significant achievements in the platinum‐catalyzed methane oxidation including the Shilov reaction and the Periana‐Catalytica system which provide one of the most promising approaches to the challenge. In addition to methane oxidation, some synthetically useful reactions have been developed under improved Shilov conditions, notably the terminal or regioselective CH oxidation of alkyl groups in various substrates. Platinum‐catalyzed CH borylation and silylation reactions are also discussed. Platinum‐catalyzed borylation of CH bonds of sterically congested arenes and fluorinated arenes is particularly noteworthy and it also complements the iridium chemistry in terms of chemo and regioselectivity.
Gold‐Catalyzed C(sp
2
)H Functionalization under Au(I)/Au(III) Catalysis
Authors: Urvashi XXXXXXXX , Singh Pallavi , Patil Nitin T.
Published: October 2022

Among the newer approaches to transition metal‐catalyzed CH functionalization, Au(I)/Au(III) catalysis has emerged as a powerful synthetic tool for the construction of carbon–carbon and carbon–heteroatom bonds. The orthogonal reactivity pattern of gold catalysts as compared to other transition metal catalysts provides an excellent opportunity for the development of new modes of CH functionalization. The rapid enhancement in the field of gold‐catalyzed CH functionalization is complemented by the development of several strategies for achieving the typically arduous Au(I)/Au(III) redox cycle. This article documents all the examples of C(sp
2
)H functionalization under Au(I)/Au(III) catalysis reported so far.
Catalytic Enantioselective CH Borylation
Authors: Xu Liang , Song Peidong , Li Pengfei
Published: October 2022

Organoboron compounds have proven to be versatile building blocks in the synthesis of natural products, organic materials, or drugs. The stereospecific transformations of optically active organoboron compounds, which represent an interesting class of enzyme inhibitors and have been used as marketed drugs themselves, potentially afford chiral products that are in growing demand for the screening of pharmaceutically active candidates. This amplifies the necessity to develop efficient and practical strategies to deliver enantioenriched organoboron compounds. Encouraged by this surging demand, an increasing number of racemic direct CH borylation reactions, which have been developed as a step and atom‐economic approach to borylated products, have evolved into their asymmetric versions based on elegantly designed chiral ligand and catalytic strategies. Herein, a brief summary of these breakthroughs is presented, especially emphasizing their connections with the racemic prototypical transformations. We expect that such introduction will inspire more efficient strategies in this field, enabling a more convenient access of chiral organoboron compounds.
Synthesis of Fused Heterocycles via Transition Metal‐Catalyzed CH Functionalization
Authors: Usuki Yoshinosuke , Satoh Tetsuya
Published: October 2022

This article focuses on synthesis of nitrogen‐containing or oxygen‐containing fused heterocyclic natural products through transition metal‐catalyzed CH functionalization. With highlighting some recent achievements in this field, a current state analysis on this synthetic methodology will be contributed.
CH Activation of Indoles
Authors: Kowalczyk Rafał , Mittal Lalit S.
Published: October 2022

Tremendous advances in transition metal‐catalyzed CH functionalization of the indole scaffolds have been recently reported. Great efforts have been devoted to the directing group strategy development in selectivity achievement overriding both the inherent reactivity of the indole scaffold and the activation of C2/C3H bonds. This article aims to highlight the elegant methods enabling the direct arylation, alkenylation, alkylation, and alkynylation along with the introduction of heteroatoms into indole scaffold via selective metal‐catalyzed CH activation strategies.
Transition Metal‐Catalyzed Site‐Selective CH Bond Arylation of Arenes/Heteroarenes Using Quinone Diazides
Authors: Bera Satabdi , Samanta Rajarshi
Published: October 2022

Transition metal‐catalyzed direct introduction of phenol/naphthol moieties into the arene/heteroarene CH bonds has been studied using quinone diazides. Generally, the reactions proceed via CH insertions of metal carbenes or migratory insertion of metal carbenes. These arylation reactions are further discussed and extended with selected scope, limitations, and plausible mechanism. Interesting enantioselective reactions to provide stereogenic centers and axial chirality are also described. In this article, the summarized progress in the field of site‐selective arylations into CH bonds of arenes/heteroarenes using quinone diazide class of compounds under transition metal catalysis has been described.
Regio‐Selective CH Functionalization of 7‐Azaindoles
Authors: Kannaboina Prakash , Das Parthasarathi
Published: October 2022

The 7‐azaindole is an important building block in several pharmaceutically important compounds. To develop synthetic, elegant techniques for the functionalization of 7‐azaindole core continues to be an active area of research due to its powerful medicinal properties. There have been significant advances in metal‐catalyzed functionalization of the 7‐azaindole moiety. A collective account of these reactions is presented in this article to showcase the existing landscape of CH functionalization of 7‐azaindoles, to create interest in this field for further development and propagate this strategy for ring substitution reactions of 7‐azaindole systems.
Manganese‐Catalyzed CH Functionalization of Heterocycles
Authors: Liu Zheyuan , Dang Yanfeng
Published: October 2022

Manganese is one of the most prominent candidates for catalysis in looking for novel reactivity, owing to its less toxic, inexpensive, and earth‐abundant nature. In recent decade, manganese‐catalyzed CH functionalization of heterocycles has emerged as a powerful and efficient method in chemical synthesis. These strategies mainly involve CH addition to unsaturated substrates, cascade CH activation/cyclization, and CH alkylation/arylation, which have found great applications in the biochemistry and natural product synthesis. This section summarizes the main advancements of manganese‐catalyzed CH functionalization of heterocycles in homogeneous catalysis.
Iridium‐Catalyzed Asymmetric CH Functionalization
Authors: Shibata Takanori , Pan Shiguang
Published: October 2022

Iridium catalysis is one of the major synthetic protocols in CH functionalization. In particular, it has been used to realize significant achievements in enantioselective transformations. This article describes Ir‐catalyzed enantioselective reactions initiated by CH bond cleavage. Various CH alkylations using alkenes are mainly discussed as an atom‐economical strategy. As a recent advancement, the introduction of heteroatom functionality by CH activation, such as CH borylation, silylation, and amidation, is also mentioned.
Ruthenium‐Catalyzed Asymmetric CH Functionalization
Authors: Xu Xue , Cui Xin
Published: October 2022

Owing to their cost‐effectiveness among precious metals and easy preparation, ruthenium catalysts have been developed as one class of the major tools for catalytic CH functionalization with a diversified scope of pathways. During the recent decades, asymmetric catalytic systems by chiral ruthenium catalysts have been actively explored for the production of enantiomerically enriched products from inert CH bonds. Through the atom/group transfer pathways, asymmetric hydroxylation, amination, and alkylation reactions of CH bonds have been developed based on the design of various new ligands and catalysts. On the other hand, ruthenium catalysis via metal‐assisted CH cleavage and ruthenacycle intermediates has recently been shown successfully in their asymmetric versions with different strategies. In this article, the development of ruthenium‐catalyzed asymmetric CH bond functionalization reactions will be reviewed. Atom/group transfer pathways are summarized according to the reaction types, including hydroxylation, amination, and alkylation. Subsequently, ruthenium(0)‐catalyzed asymmetric CH functionalization and the more recent ruthenium(II)‐catalyzed asymmetric CH activation reactions are discussed. The structure and properties of the ligands or the ruthenium‐catalysts, which play a decisive role in the control of stereoselectivity, are classified and discussed in each type of reactions.
Asymmetric CH Functionalization of Ferrocene
Authors: Jin Zhong
Published: October 2022

Since the milestone discovery of its sandwich‐type scaffold in the early 1950s, ferrocene and its related organometallic compounds have received enormous interest from chemistry, biology, and material communities. The rigid molecular architecture and aromaticity make them relatively stable and applicable as catalysts or ligands for the diverse organic transformations. To date, a wide range of synthetic methodologies for this unique family of organometallic compounds have been developed, given their widespread application in organic synthesis. Among them, the recent direct CH functionalization catalyzed by transition metals provided an atom‐ and step‐economical approach to the structurally diverse ferrocene derivatives. In particular, transition metal‐catalyzed asymmetric CH functionalization of ferrocene has proven an efficient, enantioselective strategy for the synthesis of planar‐chiral ferrocenes. In this article, the recent progress on direct asymmetric CH functionalization of ferrocene derivatives is summarized.
Synthesis of Heteroatom Stereocenters by Enantioselective CH Functionalization
Authors: Cao Zhen , Tang Wenjun
Published: October 2022

Enantioselective CH functionalization is one of the most straightforward and efficient approaches to access synthetically valuable chiral molecules. Only recently, transition metal‐catalyzed enantioselective CH functionalization has been explored to construct heteroatom stereocenters, providing molecules with heteroatom stereocenters that cannot be accessed otherwise. This article aims to provide a recent update toward the construction of heteroatom stereocenters through enantioselective CH functionalization including desymmetrization approach and resolution approach. The content is categorized according to the formed stereogenic atoms including P, Si, S‐stereocenters.
Iron‐Catalyzed Benzylic CH Functionalization
Authors: Zhou Lulu , Gao Yanqun , Huang Qiping , Wu Hao , Han Wei
Published: October 2022

Among diverse CH bonds, direct functionalization of the benzylic position is particularly fascinating but a challenging process for synthetic chemists because alkyl arenes are abundant, cheap, and stable and at the same time suffer from issues of selectivity, functional group compatibility, and inclination toward over oxidation in benzylic CH functionalization. Among various transition metals, iron ideally conforms to the spirit of element strategy initiative. Hence, iron‐catalyzed benzylic CH functionalization has emerged as an area of significant interest to researchers. We will endeavor to highlight the recent advances in iron‐catalyzed benzylic CH functionalization for constructing CC, CN, and CO bonds. We hope that this review will be useful for synthetic organic chemists and inspire further discoveries in the interesting iron‐catalyzed CH functionalization area.
Ruthenium‐Catalyzed Benzylic CH Functionalization
Authors: Sreedharan Ramdas , Muthuvel Karthick , Gandhi Thirumanavelan
Published: October 2022

The activation and functionalization of the benzylic CH bond by transition metal catalysts have gathered much attraction owing to their occurrence in agrochemicals, pharmaceuticals, and fine chemicals. Among the various active metal catalysts, ruthenium gained upper hand, as they are comparatively economic as well as show versatile catalytic activity. Ruthenium efficiently activates the benzylic C(sp
3
)H bond and effects alkylation, arylation, allylation, vinylation, cyanation, silylation, amination, amidation, and oxidation reactions.
Pd‐Catalyzed Benzylic CH Functionalization
Authors: Thorat Raviraj A. , Jain Saket , Parganiha Devendra , Kumar Sangit
Published: October 2022

Palladium‐catalyzed benzylic CH functionalization has enormous application in industry and academia. Conventional methods have limited scope and selectivity toward functionalization attributed to the very high reactivity of benzylic position particularly benzylic anion. This article discusses the current development of palladium‐catalyzed benzylic CH functionalization involving CC, CO, CN, and CF bond formation which not only tame the reactivity of benzylic anion but also enables its reaction with a large variety of substrates. Some of the applications such as construction of biologically, pharmaceutically, and agrochemical relevant organic molecules have been discussed. This article summarizes palladium‐catalyzed benzylic CH functionalization in a comprehensive way.
Selective Functionalization of BH Bond of
o
‐Carboranes
Authors: Cao Ke , Zhang Cai‐Yan , Wu Ji , Yang Junxiao
Published: October 2022

Icosahedral carboranes are a class of carbon–boron molecular clusters with three‐dimensional aromaticity, which have growing applications in functional materials, boron neutron capture therapy agents, organometallic, and coordination chemistry. To further expand the application of
o
‐carboranes, the functionalization of
o
‐carboranes with diverse groups and controllable regioselectivity has been a challenging subject as the 10 BH bonds are not fully equal and have a slight difference in reactivity. In the past six years, transition metal‐catalyzed BH activation has been proved to be a powerful tool to accomplish the regioselective functionalization of
o
‐carboranes and achieved much advancement in this field. This article summarizes recent advances around BH activation.
Photocatalytic Continuous‐Flow Methods for CH Functionalization
Authors: Pieber Bartholomäus
Published: October 2022

Photocatalysis provides many strategies for the direct functionalization of CH bonds through various mechanisms. All of these reactions require efficient irradiation of the reaction mixture, which limits the use of traditional batch techniques. Continuous flow chemistry, on the contrary, is ideally suited for such transformations due to the small reactor dimensions, which ensure efficient irradiation of the entire reaction mixture. This leads to reduced reaction times, higher selectivities, and provides a straightforward opportunity to scale such transformations to synthetically useful quantities. The enabling technology also offers precise control of the reaction time and temperature to ensure high reproducibility. Moreover, flow setups enable the straightforward and efficient use of gaseous reagents due to the high interfacial area of biphasic reaction mixtures in flow reactors. The stoichiometry of gases can be precisely controlled using mass flow controllers and their solubility in the liquid phase can be increased using higher system pressures, thereby accessing reactions that are otherwise difficult or impossible to realize. This article summarizes and discusses the applications of flow chemistry for photocatalytic CH functionalization.