Tetrahedron Letters
Volume 58, Issue 9,
1 March 2017
, Pages 803-824
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Abstract
A significant number of reactions have appeared in the literature regarding cross dehydrogenative coupling (CDC) reactions over the years. This review aims to cover the advances in the area of C
C bond formations via CDC reactions in the last six years (2011–2016). For the sake of brevity, the review has been subdivided into four major parts (i) sp3 – sp3, (ii) sp3 – sp2, (iii) sp2 – sp2 and (iv) sp3/sp2 – sp bond forming reactions. The reactions are discussed based on the principal catalyst system used, i.e. metal based, non-metal based or photocatalyst. Wherever necessary, the uniqueness of the methods has been shown by highlighting the substrate scope, along with proposed mechanisms.
Introduction
Carbon-carbon bond forming reactions have always been of primary interest for an organic chemist. The need to innovate, and discover new CC bond forming reactions is an on-going process.1 Methods developed should ideally comply with three important guidelines: (i) the method should make use of readily available starting materials, (ii) non-toxic reagents or catalysts should be employed, and (iii) the reaction should be performed under mild reaction conditions. It is challenging to develop such ideal methods and development of such methods have a long-lasting impact in modern organic chemistry, to achieve the synthesis of complex molecular targets in the shortest possible synthetic routes. A majority of CC bond forming reactions involve (pro-) electrophilic and (pro-) nucleophilic partners as the starting materials (Scheme 1),2 and in a few cases, they manifest in the form of radical reactions3 and pericyclic reactions.4
The term coupling is used when two molecules combine to form a new bond with the aid of catalyst/s, the majority being transition metals.5 These reactions are versatile and are useful for synthesizing several complex molecules in short synthetic sequences which otherwise may need multistep procedures. In view of the same, the importance of the coupling reaction has been acknowledged with the Nobel Prize in the year 2010.6
A majority of traditional CC bond forming reactions employ functionalized starting materials as their precursors (Scheme 1). Although transition metal catalyzed cross-coupling reactions and metathesis7 reactions have revolutionized the modern CC bond forming reactions, they require pre-functionalized starting materials. These reactions generally require the coupling partner to possess leaving groups8 such as Br, I, OTf, SiR3, SnR3, BR2, etc. These methods require additional steps to prepare functionalized starting materials, thereby, making them inefficient and unattractive. A direct CH functionalization9 is always desirable, as it does not require functionalization of starting materials (Scheme 1).
An ideal atom-economical protocol for the formation of CC bond would be by the removal of hydrogen atoms from two carbon atoms of two different molecules or from the same molecule. In this direction, there have been continuous efforts to overcome the limitations of using pre-functionalization coupling partners, for developing novel CC bond forming reactions by employing readily available starting materials, which are not pre-functionalized.10 Nonetheless, transition metal catalyzed reactions have partially overcome the limitations faced by traditional methods. In this perspective, direct CH functionalization reactions are sought after by means of direct oxidation of the CH bond to generate an active species. Since, CH bonds are ubiquitous in nature, selective functionalization of the required CH bond is a difficult task.
Also, CH bonds are fairly inert11 and thermodynamically stable compared to other commonly encountered bonds in organic compounds. Selective activation of CH bond in the presence of other reactive non-CH bonds is an additional challenge, and there has been a continued effort for developing such selective functionalization. In this regard, the concept of cross-dehydrogenative coupling (CDC) offers a unique way of CC or CX (X=heteroatom) bond forming reactions (Scheme 2).10 This simple and elegant CDC strategy involves (i) coupling two sp3 CH bonds; or (ii) coupling sp3 CH bond with sp2 CH bond; or (iii) coupling sp3 CH bond with various nucleophiles. This tandem oxidative coupling of CH bonds employs simple un-functionalized precursors as the starting materials and thereby reducing the extra step for synthesizing functionalized starting materials. Although, the reaction is termed as CDC, molecular hydrogen is not the by-product of these transformations. The two hydrogen atoms are removed by the mediation of a base (or solvent or counter-ion) or an oxidising agent (Scheme 3).
The first CDC reaction reported was the homodimerization of terminal alkynes in the presence of a stoichiometric amount of Cu(OAc)2. This reaction is referred to as the Eglinton reaction,12 and was reported in 1956 (Scheme 4). Within 10years, Glaser and Hay reported the same conversion using catalytic amount of Cu and molecular oxygen as an oxidant.13 However, these types of reactions were limited to electron-rich systems only.
Almost a decade later, Moritani and Fujiwara14 reported a Pd-catalyzed coupling reaction of arenes with alkenes as the coupling partners, without employing any pre-functionalized precursors, such as, aryl or alkenyl halides (Scheme 5). This is an early example of oxidative coupling of two different molecules and hence two different CH bonds. CDC reactions gained momentum in early 2000, due to the excellent work done in this area and spearheaded by the groups of Murahashi15 and Li.16, 17
The functionalization of CH bonds by CDC reactions have been achieved by using a variety of catalysts, and performing the reaction with various coupling partners such as phosphites,15 indoles,18 nitriles,15(a), 15(b), 15(c), 17(d), 19 nitroalkanes,20 activemethylenes,21 etc.,22, 23 Most of the CDC reactions use metal-oxo complexes or low valent transition metal catalysts22, 23, such as, Ru, Cu, Fe, V, Au, Pt, Ir etc., along with a suitable oxidant, which serves to generate the electrophilic coupling partner. A few non-metal catalysts such as 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ),3(a), 3(c) phenyl iodine diacetate (PIDA)20b or phenyl iodine bis-trifluoroacetate (PIFA), benzoyl peroxide (BPO),20d and photocatalysts, such as, Eosin Y20e and Rose Bengal20f are also employed for various CDC reactions. The oxidants generally used are O2, hydrogen peroxide (H2O2), tert-butyl hydroperoxide (TBHP), tert-butyl peroxide (TBP).
Section snippets
The review
The aim of this review is to cover only the recent progress in CDC reactions for CC bond formation, which have been reported in the last six years (2011–2016). Depending on the nature of the hybridization of the carbon atom, the review is classified into, (i) sp3 – sp3, (ii) sp3 – sp2, (iii) sp2 – sp2, and (iv) sp3/sp2 – sp bond forming reactions. Metal-catalyzed oxidative Heck-type reactions can be classified as CDC. However, due to the vast number of reports in that area, they have not been
CDC involving Csp3
Csp3 bond formation
The Csp3Csp3 bond forming reactions are catalyzed by, (i) salts and complexes of Cu, Fe, Pd, and Ir, or (ii) by non-metallic agents like iodine and its derivatives, and (iii) photocatalysts. Besides this, asymmetric bond forming reactions are also reported by employing metal catalysts.
Conclusion
CDC reactions are complementary to traditional coupling methods. Traditional methods require pre-functionalization of starting materials, whereas, CDC reactions overcome that limitation.10 CDC reactions are the closest to an ideal reaction that researchers have reached, with respect to the conservation of steps and atom economy. Over several years, a number of research groups have been involved in exploration of this fertile area and this foray has resulted in the generation of several
Acknowledgments
The authors gratefully acknowledge the Indian Institute of Science, Bangalore, for journal access and literature search tools. Authors thank co-workers of the group who contributed to some of the chemistry described in the review. We thank V. Lanke for proofreading. BVV, JD, KRB, and YS thank CSIR, New Delhi, for scholarships. The authors also thank IISc, SERB (NO. SB/S1/OC-56/2013), CSIR (No 1/245/10-EMR-II and No 02(226)/15/EMR-II) and RL Fine Chem for supporting the research.
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A detailed theoretical investigation into the mechanism of the cobalt (II) catalyzed O-arylation reaction of phenols with aryl iodides has been carried out with the aid of the Density Functional Theory method at the UB3LYP-D3 level of theory. The naturally occurring amino acid, l-valine was taken as the ancillary ligand for modeling the reaction mechanism. A tetrahedral, l-valine ligated cobalt (II) phenoxide complex in the quartet state, was found to be the active catalytic species. Unlike the Cu-catalyzed C-X (X=O, S, N) cross-coupling and Co-catalyzed C
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(Video) Sonogashira Coupling Reaction| Sonogashira Coupling Reaction Mechanism| With Problems| CSIR-NET GATE
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FAQs
What are the examples of cross coupling reaction? ›
Cross-coupling reactions are important for the production of pharmaceuticals, examples being montelukast, eletriptan, naproxen, varenicline, and resveratrol. with Suzuki coupling being most widely used. Some polymers and monomers are also prepared in this way.
Which is the famous coupling reaction? ›Other notable examples of such coupling reactions include: The Wurtz reaction. The Pinacol coupling reaction. Glaser coupling.
What are cross-coupling reactions used for? ›Cross-coupling reactions stand among the most important reactions in chemistry [1,2]. Nowadays, they are a highly valuable synthetic tool used for the preparation of a wide variety of organic compounds, from natural and synthetic bioactive compounds to new organic materials, in all fields of chemistry [3].
What is the difference between coupling and cross coupling reaction? ›Coupling reactions are used for the formation of various conjugated polymers by using metal catalysts. For the production of various natural products, coupling reactions are used. Cross-coupling reactions are used for the preparation of monomers and polymers.
Which of the following metals is most commonly used for cross-coupling reactions? ›While palladium and nickel are the most often used metals for catalysis of cross-coupling reactions involving Grignard and organozinc reagents <B-1998MI227>, other transition metals (Cu, Fe, Co) can also be used.
What was the first cross-coupling reaction? ›Metal catalyst
The first nickel catalyzed cross-coupling reaction was reported by Percec and co-workers in 1995 using aryl mesylates and boronic acids.
34 Palladium-catalyzed C-C coupling reactions
This effect has been used in many coupling and polymerization processes.
Classical cross-coupling reactions are named on the basis of the type of nucleophile used. For example, a reaction that utilizes an organoborane nucleophile is known as a Suzuki-Miyaura reaction, while a reaction that involves an organozinc nucleophile is called a Negishi reaction.
What is the most famous chemical reaction? ›Photosynthesis is the most important chemical reaction in the biosphere, as it is the prerequisite for all higher life on earth.
What is dehydrogenative coupling reaction? ›Abstract. Cross-dehydrogenative coupling (CDC) is a process in which, typically, a C–C bond is formed at the expense of two C–H bonds, either catalyzed by metals or other organic compounds, or via uncatalyzed processes.
What is the name of the carbon carbon coupling reaction? ›
Pinacol coupling reaction: A pinacol coupling reaction is an organic reaction in which a carbon-carbon bond is formed between the carbonyl groups of an aldehyde or a ketone in presence of an electron donor in a free radical process. The reaction is also known as a vicinal diol.
What catalyst is used in coupling reactions? ›Palladium Catalysts [Cross-coupling Reaction using Transition Metal Catalysts]
Which coupling is best and why? ›Diaphragm couplings are great all-rounder shaft couplings. They can accommodate parallel misalignment as well as high angular and axial misalignment. They also have high torque capabilities and can transmit torque at high speeds without the need for lubrication.
What are the three types of coupling? ›The different types of coupling are: Common-mode impedance (galvanic) coupling. Capacitive coupling. Inductive coupling.
What are the two main types of coupling? ›Couplings fall into two main categories: Material Flexing and Mechanical Flexing. The material flexible types obtain their flexibility from stretching or compressing a resilient material, such as rubber, or from the flexing of thin metallic discs or grid.
What is palladium catalyzed cross coupling used for? ›Pd-catalyzed cross-coupling reactions that form C–N bonds have become useful methods to synthesize anilines and aniline derivatives, an important class of compounds throughout chemical research.
What is the most common use for transition metals? ›Transition metals are always used in industries as catalysts for various reactions. Iron mixed with Manganese and Chromium (both elements are also transition metals) gives Steel. Steel is used for construction purposes, building cars and aircraft, etc. Nickel is used in producing stainless steel.
What is the difference between cross coupling and CH activation? ›However, the cross coupling reaction requires extra procedures for preparing organic halides (or triflates) compounds, and organic boron or metal compounds. On the other hand, the C-H bond activation can reduce these procedures, thus making this reaction a cost-effective and eco-friendly system.
What is cross-coupling in organic chemistry? ›A cross-coupling reaction in organic synthesis occurs when two fragments are joined together with the aid of a metal catalyst.
What is Buchwald Hartwig cross-coupling? ›The Buchwald–Hartwig reaction is a cross-coupling reaction where arylamines or heteroarylamines (pyridineamines) are formed by the reaction of an aryl halide or triflate including heteroaryl (pyridines) halide or triflate with a primary or secondary amine in the presence of a palladium metal catalyst and a base.
What is the catalyst for CC bond formation? ›
The most common C–C-bond-forming reaction in organic chemistry is most likely the aldol addition. (5) In nature, this reaction is catalyzed by aldolases which perform the reversible and stereoselective addition of a donor to an acceptor.
Which enzyme is involved in splitting or formation of CC bond? ›P450 Reactions. Many of the reactions discussed here, both C-C bond forming and C-C bond breaking, are catalyzed by P450 enzymes.
What is the difference between Suzuki and stille coupling? ›Mechanism of the Suzuki Coupling. One difference between the Suzuki mechanism and that of the Stille Coupling is that the boronic acid must be activated, for example with base. This activation of the boron atom enhances the polarisation of the organic ligand, and facilitates transmetallation.
Why does reaction coupling occur? ›Coupling occurs when the energy released by an exergonic reaction is linked to an endergonic reaction. The three phosphates of ATP are energetically bound to the main structure (nucleoside- adenosine).
Which is the king of chemical reaction? ›Hence, Sulphuric acid ( H 2 SO 4 ) is known as king of chemicals.
What are the 3 most important chemical reactions? ›There are three main types of chemical reactions important in human physiology, synthesis (anabolic), decomposition (catabolic) and exchange.
What is the fastest chemical reaction in the world? ›Within a fraction of a trillionth of a second, H2O+ gives up a proton to another water molecule, creating hydronium (H3O+) and a hydroxyl (OH) radical. Scientists had long known of this reaction, with a first sighting in the 1960s when scientists at Argonne first detected the electron ejected from water by radiolysis.
What is the dehydrogenative coupling of silanes? ›The dehydrogenative coupling of silanes is a reaction type for the formation of Si-Si bonds. Although never commercialized, the reaction has been demonstrated for the synthesis of certain disilanes as well as polysilanes. These reactions generally require catalysts.
What are the examples of carbon-carbon bond reaction? ›Some examples of reactions which form carbon–carbon bonds are the aldol reaction, Diels–Alder reaction, Grignard reaction, cross-coupling reactions, the Michael reaction and the Wittig reaction.
Which reaction involves one CC and CO bond formation? ›The aldol reaction forms β-Hydroxyketones from carbonyl compounds. This reaction forms C-C bonds and C-O bonds (C attaches to a hydroxy group).
What are examples of carbon-carbon bond forming reactions? ›
Some examples of reactions which form carbon–carbon bonds are aldol reactions, Diels–Alder reaction, the addition of a Grignard reagent to a carbonyl group, a Heck reaction, a Michael reaction and a Wittig reaction.
What is Lindlar's catalyst What is it used for? ›The catalyst is used for the hydrogenation of alkynes to alkenes (i.e. without further reduction into alkanes). The lead serves to deactivate the palladium sites, further deactivation of the catalyst with quinoline or 3,6-dithia-1,8-octanediol enhances its selectivity, preventing formation of alkanes.
Which is the most common catalyst used for polymerization? ›Ziegler–Natta catalyst is a type of catalyst made from a mixture of chemical compounds that are mainly used in the synthesis of polymers belonging to 1-alkenes such as alpha-olefins which are hydrocarbons containing a double carbon-carbon bond.
What are the commonly used catalyst for the Fischer Tropsch synthesis? ›Catalysts considered for Fischer-Tropsch synthesis are based on transition metals of iron, cobalt, nickel and ruthenium.
What is the most commonly used coupling? ›The most common type of coupling used in AF amplifiers is R-C coupling. This is because: The frequency response of the RC amplifier provides constant gain over a wide frequency range, hence most suitable for audio applications. It used the resistor and the capacitor which are not expensive so the cost is low.
Which type of coupling is least preferred? ›Coupling between modules can be ranked in the order of strongest (least desirable) to weakest (most desirable) as follows: Content Coupling, Common Coupling, External Coupling, Control Coupling, Stamp Coupling, Data Coupling.
Which type of coupling is suitable for most applications? ›Universal joint or Hooke's joint
As the name suggests, this type of coupling can be used anywhere. The universal joint can transmit power even at high parallel or angular misalignments.
- Highest Level of Coupling (Unacceptable) Content Coupling.
- High Levels of Coupling (Undesirable but Possibly Unavoidable) Common Coupling. External Coupling.
- Moderate Levels of Coupling (Acceptable) Control Coupling.
- Low Coupling (Desirable) Stamp Coupling. ...
- Lowest Level of Coupling.
- Reference.
Common coupling is one of the forms of coupling in which two or more modules share some global data such as global data structures. Different modules read from and write their data to a common global field that has some information regarding the operations to be performed is an example of common coupling.
Why is coupling necessary? ›The primary reason for using a coupling is to connect the drive shaft to the driven shaft. It is difficult to manufacture a machine connected with one-piece shaft instead of using a coupling.
What are the four levels of coupling? ›
Levels of Coupling
Coupling can be low / loose / weak or high / tight / strong. Tight coupling translates into ripple effects when making changes, as well as code that is difficult to understand. It tends to propagate errors across modules, when one module behaves incorrectly.
However there are two main types of couplings (Fig 1) which are (i) rigid couplings, and (ii) flexible couplings. Rigid couplings are used for shafts having no misalignment.
What are examples of energy coupling? ›The sodium-potassium pump is an example of energy coupling. The energy derived from exergonic ATP hydrolysis is used to pump sodium and potassium ions across the cell membrane. The hydrolysis of one ATP molecule releases 7.3 kcal/mol of energy (∆G = −7.3 kcal/mol of energy).
What are examples of coupled reactions in cellular respiration? ›The final step of respiration uses oxygen as a driving force to create energy in the form of ATP. As a result, O2 gas is reduced to H2O. So, the glucose and O2 created by photosynthesis is used in respiration to make CO2 and water - the materials needed in photosynthesis. In this way, these two reactions are coupled.
What is an example of energy coupling in biology? ›Energy Coupling in Sodium-Potassium Pumps
For example, transmembrane ion pumps in nerve cells use the energy from ATP to pump ions across the cell membrane and generate an action potential. The sodium-potassium pump (Na+/K+pump) drives sodium out of the cell and potassium into the cell.
Energy Coupling is the linkage between chemical reactions such that one reaction generates energy (that is, transforms it into a readily usable form, especially ATP) whereas the other reaction utilizes that energy or, rather, that energy drives the other reaction forward.
How is glycolysis an example of energy coupling? ›This is a coupled reaction, in which phosphorylation of glucose is coupled to ATP hydrolysis. The free energy of ATP hydrolysis (an energetically favorable reaction) fuels the glucose phosphorylation (an energetically unfavorable reaction).
Why is coupling process important? ›In organic chemistry, coupling reactions occur when two fragments are joined together with the aid of a metal catalyst to form a variety of reactions. Because transition metal catalysts increase reaction rate without altering its thermodynamics, they are commonly used as catalysts in chemical reactions.
Which two types of reactions are often coupled in cells? ›Anabolism and catabolism
Two types of metabolic reactions take place in the cell: 'building up' (anabolism) and 'breaking down' (catabolism).
The coupled reaction is required to facilitate the production of free energy (ATP) in the human cell simultaneously with the other exergonic metabolic reactions so that ATP can be used by the human cell when required.
What are the 3 reactions that occur during cellular respiration and where do they occur in the cell? ›
There are three main steps of cellular respiration: glycolysis, the citric acid cycle, and oxidative phosphorylation. Glycolysis takes place in the cytosol, the citric acid cycle occurs in the mitochondrial matrix, and oxidative phosphorylation occurs on the inner mitochondrial membrane.
What is cross coupling in biology? ›Cross-coupling reactions represent a class of synthetic transformations that involve the combination of an organometallic reagent (that has a main group metal atom in most of cases) with an organic electrophile in the presence of groups 8–10 metal catalysts to achieve a C–C, C–H, C–N, C–O, C–S, C–P, or C–M bond ...
Which molecule is most responsible for energy coupling in cells? ›ATP (Adenosine tri-phosphate) is an important molecule found in all living things. Think of it as the “energy currency” of the cell.
Why is energy coupling important for living organisms? ›In order to conserve energy, a change in the state of the system must be coupled to a change in the surroundings which increases the work potential of a part of the surroundings (work is performed on the surroundings, or a separate system undergoes a change in state with +DG).
What is palladium catalyst? ›The Pd catalyst is an effective heterogeneous catalyst for carbon–carbon (C–C) coupling reactions, such as the Heck reaction and Suzuki–Miyaura reaction, affording good to high yields. In these reactions, the catalyst was easily recovered and reused five times without significant activity loss.