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Arylmagnesiation of Alkynes Catalyzed Cooperatively by Iron and Copper Complexes
Abstract
Iron and copper complexes cooperatively catalyzed the arylmagnesiation of unfunctionalized alkynes including dialkylacetylenes, where the presence of both iron and copper catalysts is essential for high yields of 2-aryl-1-alkenylmagnesium bromides.
... The most widely used transformations of this type include Zr-catalyzed Negishi methylamination, 1 -3 cycloalumination, 4 -7 Dzhemilev cyclomagnesiation, 8 -13 carbocupration, 14 carbostannylation, 15 carboboration, 16,17 and arylmagnesiation. 18 The carbometallation of alkynes with organozinc reagents is one of the most popular approaches to the synthesis of various functionally substituted alkenes. 19 -28 The considerable interest in the organozinc synthesis of these olefins is, first of all, due to the tolerance of Zn reagents to the presence of heterofuctional substituents in the substrates containing triple bonds. ...
Over the last 10 years, conceptually new results have been obtained in the field of unsaturated organozinc reagents; these results need to be analyzed and integrated. This review systematically considers data on the catalytic carbozincation reactions of alkynes, which give alkenyl organozinc compounds, highly reactive intermediates for the synthesis of functionally substituted olefins. The reactions catalyzed by copper, iron, cobalt, nickel, and rhodium complexes are described. A separate part of the review addresses the catalytic reactions initiated by zirconium and titanium compounds. The reaction conditions are indicated; in some cases, putative reaction mechanisms are discussed.
The bibliography includes 135 references.
... In the past few decades, metal-catalyzed hydroarylation of alkynes has attracted considerable attention because of its fast accessibility to highly functionalized alkenes [1a] . The use of organometallic compounds such as arylmagnesium bromide and tetraphenyltin as arylation reagents enhances the selectivity of hydroarylation [3,4] . Arylboron reagents have drawn considerable attention in recent years because of their advantages, such as good functional group tolerance, ready availability, and air and moiety stability (Fig. 1A) [5] . ...
Transition-metal-catalyzed selective hydroarylation of alkynes represents a state-of-the-art approach in organic chemistry. Herein, we report the reaction of symmetrical 1,3-diynes and arylboronic acids, with Pd(OAc) 2 as the catalyst and PCy 3 as the ligand, affording functionalized enynes in good to excellent yields. Its efficiency is demonstrated by its good functional groups and broad substrate scope. This method offers a general, convenient, and practical strategy for the modular synthesis of multisubstituted enynes. To comprehensively elucidate the mechanism of the Pd-based catalytic system in the hydroarylation of 1,3-diynes, we performed detailed DFT computations for the Pd-catalyzed hydroarylation reaction.
It was found that the Cp2ZrCl2-EtMgBr-catalyzed reaction of 2-alkynylamines with Et2Zn leads to the regio- and stereoselective formation of (2Z)-allylamines in high yield. It has been established that the presence of morpholyl and piperidyl substituents in the structure of propargylamines does not interfere with the regio- and stereoselective 2-zincoethylzincation of the triple bond. Carbocyclization of α,ω-bis(aminomethyl)alkadiynes based on the Cp2ZrCl2-EtMgBr-catalyzed carbozincation reaction with Et2Zn was carried out for the first time. A mechanism for the catalytic 2-zincoethylzincation of α,ω-bis(aminomethyl)alkadiynes was proposed.
Transition metal-catalyzed addition of organometallics to aryl(alkyl)alkynes has been well known to proceed with the regioselectivity in forming a carbon–carbon bond at the alkyl-substituted carbon (β-addition). Herein, the reverse regiochemistry with high selectivity in giving 1,1-diarylalkenes (α-addition) was realized in the reaction of arylboronic acids with aryl(alkyl)alkynes by use of a rhodium catalyst coordinated with a chiral diene ligand, whereas the arylation of the same alkynes proceeded with the usual regioselectivity (β-addition) in the presence of a rhodium/DM-BINAP catalyst. The regioselectivity can be switched by the choice of ligands on the rhodium catalysts. This reverse regioselectivity also enabled the catalytic asymmetric synthesis of phoenix-like axially chiral alkylidene dihydroanthracenes with high enantioselectivity through an α-addition/1,4-migration/cyclization sequence.
The transition metal catalyzed coupling reaction has revolutionized the strategies for forging the carbon‐carbon bonds. In contrast to traditional cross‐coupling methods using pre‐prepared nucleophilic organometallic reagents, reductive coupling reactions for the C−C bonds formation provide some advantages. Because both coupling partners are reduced in the final products using a stoichiometric amount of a reductant, this approach not only avoids the need to use sensitive organometallic species, but also provides an orthogonal and complementary access to classical coupling reaction. Notably, the reductive coupling reactions feature readily available fragments, promote good step economy, exhibit high functional group tolerance and unique chemoselectivity, which have propelled their increasingly popular in the organic synthesis. In recent years, due to the low price, minimal toxicity, and environmentally benign character, iron‐catalyzed carbon‐carbon coupling reactions have garnered significant attention from the organic synthetic chemists and pharmacologists, especially the iron‐catalyzed reductive coupling. This review aims to provide an insightful overview of recent advances in iron‐catalyzed reductive coupling reactions, and to illustrate their possible reaction mechanisms.
A Transition-metal-catalyzed selective hydroarylation of alkynes represents a state-of-the-art approach in organic chemistry. Herein, we report the reaction of symmetrical 1,3-diynes and arylboronic acids, with Pd(OAc)2 as the catalyst and...
The reactions of 1-alkynylphosphines with Et2Zn in the presence of catalytic amounts of Cp2ZrCl2 and EtMgBr proceed regio- and stereoselectively to afford (1Z)-alkenylphosphines. The oxidation and sulfonation of synthesized 1-alkenylphosphines with an aqueous solution of hydrogen peroxide or elemental sulfur give (1Z)-alkenylphosphine oxides and (1Z)-alkenylphosphine sulfides, respectively. A plausible scheme for the Zr—Mg-catalyzed 2-zincoethylzincation of 1-alkynylphosphines was proposed.
It was found that the TaCl5-catalyzed reaction of dialkyl-substituted alkynes with Et3Al results in the regio- and stereoselective formation of tetraalkyl-substituted (Z,E)-hexa-1,3-dienes and (Z)-trisubstituted olefins in a ratio of 2 : 1. TaCl5-catalyzed ethylalumination of 1-alkynylphosphines and 2-alkynylamines with Et3Al was performed for the first time.
The dual‐catalysis tactics where two types of catalysts are connected in one single reaction operation are highly prized in the novel bond constructions that are difficult or unattainable to be achieved with current mono‐catalysis. In recent years, increased emphasis on sustainable catalytic methods on more economic and eco‐friendly processes has shifted the focus to catalysis with earth‐abundant transition metals, such as iron, copper, and so on. As two of the most inexpensive and environmentally friendly metals on earth, the research and development based on either iron or copper catalysis are flourishing, and iron‐copper dual‐catalyzed reactions appeal more and more attention. In this review, we mainly cover the construction of C−C, C−N, C−B, C−P, C−S and C−Sn bonds enabled by iron‐copper dual‐catalysis published in the literature from 2011.
Stereoselective preparation of highly substituted olefins is still a severe challenge that requires well defined elimination precursors. Organoboron chemistry is particularly suited for the preparation of molecules with adjacent stereocenters. As organo boron substrates with leaving groups in β‐position can undergo stereospecific syn‐ or anti‐elimination, this chemistry harbors great potential for the synthesis of complex olefins. In recent years three main strategies emerged, which differ in their approach to the β‐functionalized organoboron elimination precursor. (i) Stereoselective preparation of such elimination precursor can be achieved by addition of a boron‐stabilized anion (d¹) to an aldehyde or ketone (a¹) or diastereoselective 1,3‐rearrangement of suitable boron‐ate‐complexes. Stereospecific methods rely either on (ii) diastereospecific 1,2‐metalate rearrangement of boron‐ate‐complexes that involve opening of appropriate heterocycles or (iii) addition of chiral carbenoids (d¹*) to chiral boronates (a¹*) with a leaving group in α‐position.
The first examples of cyclic (alkyl)(amino)carbene (CAAC) lanthanide (Ln) complexes were synthesized from the reaction of CAAC with Yb[N(SiMe3)2]2 and Eu[N(SiMe3)2]2(THF)2 (THF = tetrahydrofuran). The structures of (CAAC)Yb[N(SiMe3)2]2 (2) and (CAAC)Eu[N(SiMe3)2]2(THF) (3) were determined by X-ray diffraction analysis. Density functional theory calculations of 2 revealed the predominantly ionic bond between the Ln ion and CAAC. Complex 3 enabled catalytic hydrosilylation of aryl- and silylalkenes with primary and secondary silanes in high yields and Markovnikov selectivity.
Allenes are versatile synthons in organic synthesis and medicinal chemistry because of their diverse reactivities. Catalytic 1,4-hydrosilylation of 1,3-enynes may present the straightforward strategy for synthesis of silylallenes. However, the transition-metal-catalyzed reaction has not been successful due to poor selectivity and very limited substrate scopes. We report here the efficient and selective 1,4-hydrosilylation of branched 1,3-enynes enabled by the ene-diamido rare-earth ate catalysts using both alkyl and aryl hydrosilanes, leading to the exclusive formation of tetrasubstituted silylallenes. Deuteration reaction, kinetic study, and DFT calculations were conducted to investigate the possible mechanism, revealing crucial roles of high Lewis acidity, large ionic radius, and ate structure of the rare-earth catalysts.
In industries and academic laboratories, several late transition metal-catalyzed prerequisite reactions are widely performed during single and multistep synthesis. However, besides the desired products, these reactions lead to the generation of numerous chemical waste materials, by-products, hazardous gases, and other poisonous materials, which are discarded in the environment. This is partly responsible for the creation of global warming, resulting in climate adversities. Thus, the development of environmentally benign, cheap, easily accessible, and earth-abundant metal catalysts is desirable to minimize these issues. Certainly, iron is one of the most important metals belonging to this family. The field of iron catalysis has been explored in the last two-three decades out of its rich chemistry depending on its oxidation states and ligand cooperation. Moreover, this field has been enriched by the promising development of iron-catalyzed reactions namely, C–H bond activation, including organometallic C–H activation and C–H functionalization via outer-sphere pathway, cross-dehydrogenative couplings, insertion reactions, cross-coupling reactions, hydrogenations including hydrogen borrowing reactions, hydrosilylation and hydroboration, addition reactions and substitution reactions. Thus, herein an inclusive overview of these reaction have been well documented.
Synergistic catalysis, a type of plural catalysis which utilizes at least two different catalysts to enable a reaction between two separately activated substrates, has unlocked a plethora of previously unattainable transformations and novel chemical reactivity. Despite the appreciable utility of synergistic catalysis, specific examples involving two transition metals have been limited, as ensuring a judicious choice of reaction parameters to prevent deactivation of catalysts, undesirable monocatalytic event(s) leading to side products, or premature termination and other potentially troublesome outcomes present a formidable challenge. Excluding those driven by photocatalytic mechanisms, this review will highlight the reported examples of reactions that make use of two simultaneous catalytic cycles driven by two transition metal catalysts.
The last decades have seen an impressive development of iron complexes involving organophosphorus ligands applied in homogeneous catalyzed hydrometalation of olefins and alkynes. Two main topics will be covered in this JOCSynopsis: (i) an overview of the achievements in the area of iron-catalyzed hydrophosphination and then (ii) hydrosilylation, hydroborylation, and hydromagnesiation reactions promoted by catalysts based on organophosphorus ligands and iron.
Replacing expensive or toxic transition metals with iron has become an important trend in transition metal catalyzed reactions. As an important part of this trend, the stereoselective construction of olefins under iron catalysis is an appealing and prolific research field. This article summarises the recent progress of a wide range of Fe-catalyzed reactions in accessing various stereodefined alkenes, including carbohalogenation, hydro/carbometalation of alkynes (allenes and dienes), alkylation and arylation of stereodefined (pseudo) haloalkenes or alkenyl metals, chelation-assisted C–H activation and other miscellaneous reactions.
The aryl alkene is one of the most ubiquitous molecular scaffolds found in diverse natural products, materials, and pharmaceuticals. Aryl alkenes are also essential synthetic intermediates in both industrial and academic laboratories. Nevertheless, traditional preparative methods have fundamental disadvantages, such as the necessity of lengthy synthetic operations and difficulty in the site‐ and stereoselective construction of multiply substituted derivatives. The development of a more straightforward and site‐ and stereoselective method to prepare aryl alkenes has therefore been an important objective in organic chemistry. A particularly attractive method to synthesize aryl alkenes is transition‐metal‐catalyzed alkyne hydroarylation using aryl donor reagents, which proceeds through the formal addition of Ar–H across the carbon–carbon triple bond of an alkyne. This chapter provides an overview of alkyne hydroarylations catalyzed by homogeneous metal catalysts. The mechanism, selectivity, scope and limitations, and experimental conditions of transition‐metal‐catalyzed alkyne hydroarylations are surveyed according to the aryl donor reagent and its role in the reaction; namely, (1) alkyne hydroarylations using arylmetal reagents (alkyne carbometallation/protonation), and (2) alkyne hydroarylations using aryl halides (reductive Heck reaction).
A stable and efficient PdCl 2 (PPh 3 ) 2 /PEG-400/H 2 O catalytic system for the hydrophenylation reaction of alkynes has been developed. In the presence of 3 mol% PdCl 2 (PPh 3 ) 2 and 2 equiv. of HOAc, the hydrophenylation of both terminal and internal alkynes with sodium tetraphenylborate proceeded smoothly in a mixture of PEG-400 and water at room temperature or 50 °C to afford a variety of phenyl-substituted alkenes in moderate to high yields. The isolation of the products was easily performed by extraction with petroleum ether, and the PdCl 2 (PPh 3 ) 2 /PEG-400/H 2 O system could be readily recycled and reused six times without apparent loss of catalytic activity.
In the last decade, multi‐catalysis has emerged as an excellent alternative to classical methods, rapidly elaborating complex organic molecules while considerably decreasing steps and waste generation. In order to further decrease costs, the application of cheaper and more available iron‐based catalysts has recently arisen. Through these iron‐based multi‐catalytic combinations, greener transformations have been developed that generate complex organic scaffolds from simple building blocks at lower costs. In addition to the decrease in catalysts costs, it was also demonstrated that in many cases, the application of iron complexes could also lead to unique reactivity features, expanding chemist's available toolbox. All the advantages observed in terms of costs and reactivity, should make iron‐based multi‐catalysis one of the leading technology of the future.
Hydrosilylation of alkynes generally yielded vinylsilanes, which are generally inert to the further hydrosilylation because of the steric effects. We report here the first successful dihydrosilylation of aryl‐ and silyl‐substituted internal alkynes enabled by a rare‐earth ate complex to yield geminal bis and tris(silanes), respectively. The lanthanum bis(amido) ate complex supported by an ene‐diamido ligand proved to be the ideal catalyst for this unprecedented transformation, while the same series of yttrium and samarium alkyl and samarium bis(amido) ate complexes exhibited poor activity and selectivity, indicating the significant effects of the ionic size and ate structure of the rare‐earth catalysts.
Hydrosilylation of alkynes generally yield vinylsilanes, which are inert to the further hydrosilylation because of the steric effects. Reported here is the first successful dihydrosilylation of aryl‐ and silyl‐substituted internal alkynes enabled by a rare‐earth ate complex to yield geminal bis‐ and tris(silanes), respectively. The lanthanum bis(amido) ate complex supported by an ene‐diamido ligand proved to be the ideal catalyst for this unprecedented transformation, while the same series of yttrium and samarium alkyl and samarium bis(amido) ate complexes exhibited poor activity and selectivity, indicating significant effects of the ionic size and ate structure of the rare‐earth catalysts.
An operationally simple nickel-catalyzed hydroarylation reaction for alkynes is described. This three-component coupling reaction utilizes commercially available alkynes and aryl bromides, along with water and Zn. An air-stable and easily synthesized Ni(II) precatalyst is the only entity used in the reaction that is not commercially available. This reductive cross-coupling reaction displays a fairly unusual anti selectivity when aryl bromides with ortho substituents are used. In addition to optimization data and a preliminary substrate scope, complementary experiments including deuterium labeling studies are used to provide a tentative catalytic mechanism. We believe this report should inspire and inform other Ni-catalyzed carbofunctionalization reactions.
Iron-catalyzed hydromagnesiation of styrene derivatives offers a rapid and efficient method to generate benzylic Grignard reagents, which can be applied in a range of transformations to provide products of formal hydrofunctionalization. Whilst iron-catalyzed methodologies exist for the hydromagnesiation of terminal alkenes, internal alkynes and styrene derivatives, the underlying mechanisms of catalysis remain largely undefined. To address this issue, and determine the divergent reactivity from established cross-coupling and hydrofunctionalization reactions, a detailed study of the bis(imino)pyridine iron-catalyzed hydromagnesiation of styrene derivatives is reported. Using a combination of kinetic analysis, deuterium labelling and reactivity studies, as well as in situ ⁵⁷Fe Mössbauer spectroscopy, key mechanistic features and species were established. A formally iron(0) ate complex [iPrBIPFe(Et)(CH2=CH2)]− was identified as the principle resting state of the catalyst. Dissociation of ethene forms the catalytically active species which can reversibly coordinate the styrene derivative and mediate a direct and reversible β-hydride transfer, negating the necessity of a discrete iron-hydride intermediate. Finally, displacement of the tridentate bis(imino)pyridine ligand over the course of the reaction results in the formation of a tris-styrene-coordinated iron(0) complex, which is also a competent catalyst for hydromagnesiation.
A directing group‐free, ligand‐promoted palladium‐catalyzed C−H arylation of internal alkynes with simple arenes was developed. Alkenyl chlorides resulting from a 1,4‐chlorine migration or trisubstituted alkenes were produced in moderate to good yields depending on the type of alkyne. A directing‐group‐free, ligand‐promoted palladium‐catalyzed C−H arylation of internal alkynes with simple arenes was developed. Alkenyl chlorides resulting from a 1,4‐chlorine migration or trisubstituted alkenes were produced in moderate to good yields depending on the type of alkyne.
A directing group‐free, ligand‐promoted palladium‐catalyzed C−H arylation of internal alkynes with simple arenes was developed. Alkenyl chlorides resulting from a 1,4‐chlorine migration or trisubstituted alkenes were produced in moderate to good yields depending on the type of alkyne. Ohne dirigierende Gruppe gelingt die ligandunterstützte palladiumkatalysierte C‐H‐Arylierung interner Alkine mit einfachen Arenen. Je nach Art des eingesetzten Alkins werden Alkenylchloride (als Resultat einer 1,4‐Chlorverschiebung) oder trisubstituierte Alkene in mäßigen bis guten Ausbeuten erhalten.
The addition of arylzinc reagents ArZnCl 1 to alkynes 2 was found to be catalyzed by rhodium complexes in the presence of a catalytic amount of zinc chloride. The selectivity in giving 2-arylalkenylzinc species 3 or ortho-alkenylarylzinc species 4, the latter of which is generated through 1,4-Rh migration from alkenyl to aryl in the catalytic cycle, is controlled by the ligands on rhodium. Ligands cod and binap gave 3 and 4, respectively, with high selectivity.
A nickel‐catalyzed synthesis of trisubstituted acrylic acids from alkynes, Grignard reagents, and CO2 is reported. The reaction proceeds through carbomagnesiation of the alkyne with Grignard reagent followed by carboxylation with CO2 under mild reaction conditions in short time. Various unsymmetrical alkynes were transformed into the corresponding acid products in good yields with high stereoselectivity. The key molecule for the present global warming “CO2” must be utilized wherever it applies. Herein, CO2 is used for a nickel‐catalyzed carbomagnesiation of alkynes to produce acrylic acids.
The reaction of arylstannanes ArSnR3 with unfunctionalised alkynes was found to proceed in the presence of a rhodium catalyst and a catalytic amount of zinc chloride to give ortho-alkenylarylstannanes with...
We developed an efficient and straightforward method to prepare tri‐substituted alkenes through palladium‐catalyzed hydroarylation of alkynes with aryl bromides. Diarylacetylenes and alkyl(aryl)acetylenes could be well hydroarylated with various aryl bromides in moderate to excellent yields. Mechanistic studies suggested that alcohol was the reductant to provide hydride through β‐H elimination. Gram scale reaction further demonstrated the practicality and efficiency of the newly developed strategy.
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The iron/diphosphine‐catalyzed annulation of a carboxamide possessing a bidentate directing group with an internal alkyne proceeds in the presence of phenylzinc halide as a base at 40 °C to produce a variety of indenone derivatives. The reaction proceeds through iron‐catalyzed C‐H bond activation of the carboxamide, followed by insertion of the alkyne into the resulting iron intermediate, and cyclization accelerated by the presence of Lewis acidic Zn(II). The reaction of naphthalene and anthraceneamide yields pi‐conjugated indenone derivatives.
Hydrogen Addition
Alkylation and Functionalization
We report here on a chromium-catalyzed addition reaction of an arylmagnesium bromide to an unactivated internal alkyne to afford an ortho-alkenylarylmagnesium bromide. The reaction likely proceeds via insertion of the alkyne into an arylchromium species, alkenyl-to-aryl 1,4-chromium migration, and transmetalation between the resulting arylchromium species and the starting aryl Grignard reagent. The product of this reaction is amenable to a series of electrophilic trapping reactions.
A catalyst system composed of [(C6Me6)RuCl2]2, potassium carbonate/guanidine carbonate, and mesitoic acid efficiently promotes the doubly regioselective C-H hydroarylation of unsymmetrical alkynes. The process involves carboxylate-directed ortho-C-H bond activation followed by regioselective addition to the alkyne C-C triple bond with concerted decarboxylation. This action of the carboxylate as a deciduous directing group ensures exclusive monovinylation with high selectivity for the (E)-1,2-diarylalkene.
A method for the arylboration of 1-arylalkenes with bis(pinacolato)diboron and aryl chlorides or tosylates by cooperative Ni/Cu catalysis has been developed, which affords 2-boryl-1,1-diarylalkanes in high regio- and stereoselectivity. Under the applied conditions, this method is tolerant toward various functional groups, including silyl ether, alkoxycarbonyl, and aminocarbonyl moieties.
We report the elaboration of novel bio-sourced ecocatalysts for the Ullmann coupling reaction. Ecocatalysis is based on the recycling of metals issued from phytoremediation or rehabilitation, and an innovative chemical valorization of the subsequent biomass in the field of catalysis. Here, we describe efficient copper accumulation by plants via phytoextraction and rhizofiltration. These phytotechnologies were revisited to demonstrate a novel potential of these natural resources for green chemistry. Taking advantage of the remarkable ability of the selected plants to accumulate Cu(ii) species into their roots or leaves, the latter can be directly used for the preparation of ecocatalysts, called Eco-Cu®. The formed Eco-Cu® catalysts are thoroughly characterized via ICP-MS, IR studies of pyridine sorption/desorption, TEM, XRD, SM and model reactions, in order to elucidate the chemical composition and catalytic activity of these new materials. Significant differences of properties and activities were observed between Eco-Cu® and conventional Cu catalysts. Eco-Cu® are highly active catalysts in Ullmann coupling reactions with lower Cu quantities compared to known copper catalysts.
A nickel-catalyzed three-component reaction involving terminal alkynes, boronic acids, and alkyl halides is presented herein. Trisubstituted alkenes can be obtained in a highly regio- and stereocontrolled manner by the simultaneous addition of both aryl and alkyl groups across the triple bond in a radical-mediated process. The reaction, devoid of air- and moisture-sensitive organometallic reagents and catalysts, is operationally simple and offers a broad scope and functional-group tolerance.
Chapter 1 describes the importance of ubiquitous metals such as iron for sustainable catalysis, iron-catalyzed C–H bond activation reactions, and the synthesis of fused aromatic compounds via C–H bond activation. The development of iron-catalyzed reactions for the synthesis of fused aromatic compounds is the main topic of this thesis.
Linear fused acenes are important structures for organic semiconductors [1]. Naphthalene is the simplest acene and the [2+2+2] annulation reaction of an aromatic ring with two alkynes via C–H bond activation is an efficient method for synthesizing naphthalenes or other acene structures
Iron-catalyzed C–H bond activation followed by C–C bond formation has received much attention in recent years, motivated by the environmental and economical merits of iron, as well as the scientific challenge in controlling and understanding the reactivity of iron species. This review describes the utilization of iron as a catalyst for directed C–H bond activation, followed by C–C bond formation. Catalytic activation of C(sp2)-H and C(sp3-H) bonds, followed by oxidative reaction with nucleophiles, or reaction with electrophiles is described. Reactions of substrates possessing a directing group are mainly discussed, but other substrates are also presented. Carbon–heteroatom bond formation is also briefly discussed.
[14024-18-1] C15H21O6Fe (MW 353.21)
Controlled multi-carbometalation of alkynes has been envisaged as an efficient synthetic method for dienyl and polyenyl metal reagents, but effective catalyst enabling the transformation has remained elusive. Herein, we report that an iron(II)-N-heterocyclic carbene (NHC) complex (IEt2Me2)2FeCl2 (IEt2Me2 = 1,3-diethyl-4,5-dimethylimidazol-2-ylidene) can serve as precatalyst for the double-carbometalation of internal unsymmetrical alkynes with alkyl Grignard reagents, producing highly substituted 1,3-dienyl magnesium reagents with high regio- and stereo-selectivity. Mechanistic studies suggest the involvement of low-coordinate organoiron(II)-NHC species as the in-cycle intermediates. The strong σ-donating nature of IEt2Me2 and its appropriate steric property are thought the key factors endowing the iron-NHC catalyst fine performance.
The carbometalation and heterometalation of alkenes, alkynes, and allenes are useful methods for building new carbon-metal bonds. As a continuation of volume 1, only the new advents after 1990 in this field are summarized here. Some classic reports as well as mechanisms and applications are presented in detail in this chapter.
As inexpensive and relatively nontoxic metals, Fe and Co are ideal elements for the development of catalysts. Because they have multiple redox states, Fe and Co are also anticipated to have very rich catalytic chemistry. Nonetheless, very little attention has been paid to the catalysis of Fe and Co. The present review surveys reaction conditions, yields and selectivity of the C-C coupling reactions. Possible mechanisms of these intriguing reactions are discussed. Applications of these new reactions to complex molecule synthesis are also described.
Though the synthetic reactions of C-C multiple bonds directly having functional groups are more effective to give functionalized compounds which are easily converted to useful compounds like natural products and drugs, the applicability of this process to functionalized C-C multiple bonds is limited, probably because of the poor compatibility of the reactive metallic portion and the functional group. We focused on the interaction between transition metals and functionalized C-C multiple bonds, and have developed new synthetic methods using the above interaction and its synthetic applications. We discussed the new synthetic methods disclosed by as will be described using iron reagents in detail in this paper.
The hydralumination and subsequent reductive oligomerization of tert-butyl(phenyl)acetylene under the action of diisobutylaluminum hydride were examined. With a 1:1 equivalent ratio of reagents hydralumination proceeded (a) exclusively in a regiospecific cis fashion at 50° ; (b) principally in a trans manner at 110° ; and (c) preponderantly in a bis hydraluminating fashion at 140°. With a 2:1 ratio of alkyne: hydride and prolonged reaction time, the principal hydrolyzed product was cis,cis-1,4-di-tert-butyl-2,3-diphenyl-1,3-butadiene. Finally, by heating the alkyne with a small proportion of hydride, the reduced trimer, cis,cis,cis-1,3,6-tri-tert-butyl-2,4,5-triphenyl-1,3,5-hexatriene, was also obtained upon hydrolysis. The diene and triene were found to undergo conrotatory and, apparently, disrotatory ring closures, respectively. In addition, the clear-cut controlled hetero reductive dimerization of tert-butyl(phenyl)acetylene with a different alkyne, methyl(phenyl)acetylene, was achieved, leading to cis,cis-4-tert-butyl-2-methyl-1,3-diphenyl-1,3-butadiene. Finally, the carbalumination of teri-butyl(phenyl)acetylene by triphenylaluminum occurred regiospecifically to form 3,3-diniethyl-l,1-diphenyl-1-butene. The regiochemistry of the hydralumination observed here is shown to be consistent with a polar view, but that of the carbaluminations is seen to require a steric explanation. The nature of suitable activated complexes and the possible role of π-complex intermediates in the reductive oligomerization of alkynes are briefly considered.
This account summarizes recent developments in the use of cheap, benign, and non-toxic iron salts as precatalysts for various cross coupling reactions. Although not yet nearly as mature as their palladium- or nickel -catalyzed counterparts, these transformations provide efficient and scalable solutions for many types of C-C-bond formations. Selected applications to the total synthesis of bioactive natural products illustrate the present state of the art.
The reaction between trialkylaluminium compounds and aliphatic alk-1-ynes in the presence of catalytic amounts of iron trichloride has been studied under various experimental conditions. The reaction affords a complex mixture of products, the main components being essentially 2-alkylalk-1-enes and trialkylbuta-1,3-dienes; linear oligomers and cyclo-trimers are also recovered under suitable experimental conditions. The use of (S)-3-methylpent-1-yne gives rise to optically active products in high optical yields. The mechanism of the reaction is discussed and tentatively interpreted in terms of alkyliron intermediates.
Bromomagnesium diphenylcuprate and iodomagnesium dimethylcuprate have been prepared, and their thermal stability and some of their reactions investigated. In diethyl ether, 50% of the BrMgPh2Cu decomposes in 12h at room temperature and 50% of the IMgMe2Cu decomposes at 0°C in 14 but the cuprates are more stable in THF at or below 0°C. They react with acid chlorides to give 16–76% yields of the corresponding ketones. With bromine and iodine, BrMgPh2Cu gives bromobenzene and iodobenzene in 56 and 48% yield, respectively. Oxidation of BrMgPh2Cu with nitrobenzene or copper(II) chloride gives, respectively, 61 and 34% of biphenyl. Reaction of BrMgPh2Cu with acetic or benzoic anhydride yields 46–55% of the corresponding ketone and 34–37% of the corresponding carboxylic acids.
In the presence of dichlorobis(triphenylphosphine) nickel, acetylenic compounds undergo stereospecific or stereoselective syn addition of non recuding Grignard reagent. With reducing Grignard reagents, addition and reduction reactions are observed. These reactions yield vinylic organomagnesium compounds. A catalytic process is proposed to explain the experimental results.RésuméEn présence de dichlorobis(triphénylphosphine) nickel, les organomagnésiens non réducteurs s'additionnent aux acétyléniques suivant des réactions de syn addition le plus souvent stéréospécifiques. Avec les organomagnésiens réducteurs, il y a compétition entre des réactions d'addition et de réduction. Ces réactions conduisent à la formation d'organomagnésiens vinyliques. Un processus catalytique est proposé pour rendre compte des résultats expérimentaux.
Nonstabilized Fe(II) alkyls (RFeCl, R2Fe, R2FeM, R4FeM2; R = Me, n-Bu, M = Li, MgBr) are readily accessible in solution (THF, Et2O, CH2Cl2) by reaction of MeLi, MeMgBr, n-BuLi or n-BuMgBr, respectively, with FeCl2 at -78 to -50°C. The needed FeCl2 can be made by in-situ-reduction with RLi or RMgBr. For checking the transmetallation process the “β-bromostyrene-ketone test” is especially favorable in case of the methyl derivatives. The prepared Fe compounds are alkylating reagents of high selectivity.
Polysubstituted vinyl sulfones were prepared stereoselectively by the carbomagnesiation of acetylenic sulfones in the presence of Cu(I). Bisubstituted vinyl sulfones were obtained by the carbomagnesiation of acetylenic sulfones followed by hydrolysis. Trisubstituted vinyl sulfones were obtained by the carbomagnesiation of acetylenic sulfones followed by reacting with other electrophiles.
A new highlight in the repertoire of carbometalation reactions is the highly stereo- and regioselective nickel-catalyzed carbozincation of internal alkynes. This is exemplified by a short and effective synthesis of the anti-breast-cancer drug (Z)-tamoxifen. This reaction also allows the stereoselective synthesis of various tri- and tetrasubstituted olefins in good yield.
The Pd-catalyzed cross coupling reactions between sp2-C halides and terminal acetylenes have been independently reported by Heck, Cassar and us in 1975. The former two methods have been developed as an extension of the Heck reaction to an acetylenic CH-bond. Ours has been discovered on the base of combination of Pd-catalyzed cross-coupling of sp2-C halides with terminal acetylenes and Cu-catalyzed alkynylation of metal complexes developed by us in the course of systematic studies on transition metal acetylide chemistry. The coupling reactions have been used extensively as a reliable method for the synthesis of eneyne-based acetylenic materials. Some recent advances of the coupling are also described.
Treatment of homopropargylic alcohol derivatives or phenylacetylene compounds with phenylmagnesium bromide in the presence of a catalytic amount of manganese(II) chloride afforded phenylated products in good yields with high regio-and stereoselectivities.
The reactions of 30 carboxylatopentaamminecobalt(III) complexes (containing a variety of straight-chain, branched-chain, and aromatic ligands) with Cr2+ have been studied. A number of the acyclic ligands have alkylmercapto substituants, whereas most of the aromatic ligands are nitro derivatives. The specific rates for reduction of the acyclic derivatives have been found to be much more sensitive to steric crowding than are benzoato derivatives; α substitution is particularly effective in retarding reduction, the triethylacetato complex (VII, k = 0.00241. mole-1 sec-1) being more resistant to reduction than any other carboxylato complex reported. The α-NH3+ substituent, as found in the complexes of the amino acids at low pH values, is also strongly rate retarding. The moderate increases in reduction rates observed when α,β unsaturation is introduced into acyclic ligands also appears to be steric, rather than electronic, in origin, and no special effects are noted on incorporating a second double bond in conjugation with the first (XVII). Conjugative enhancement of reduction, sometimes attributed to remote attack, is, as in earlier studies, confined to complexes derived from readily reducible ligands. Rate enhancement (from five- to fiftyfold) resulting from substitution of a sulfur atom α or β to the coordinated carboxyl appears to be general. Reductions of the nitro derivatives, which involve changes not only at coordinated cobalt, but also at the NO2 groups, are complex and have not been separated into clean-cut kinetic steps. The very fast reduction of the nitro group of the o-nitrobenzoato complex is accompanied by some "leak through" of reducing capacity, resulting in a much more rapid reduction of Co(III) than would result from preliminary reduction of NO2 to an amino group. With the p-nitro complex in 1.2 M HClO4, release of Co(II) is delayed until 1.5-2.0 equiv of Cr2+ have been added (but, nevertheless, represents a very rapid reduction), whereas with the m-nitro isomer, 4 equiv of Cr2+ must be added before Co2+ appears. Leak through during the fast stages in these reactions is taken as a strong indication of reduction of coordinated Co(III) via remote attack at the nitro group or at a group derived from it by reduction. The nitro group (in the ortho sequence) and the nitroso group (in the para sequence) appear to be the principal "bridging" substituents. In addition, the reduction of the 3-nitro-4-methylbenzoato complex appears to involve a small degree of "meta-oriented remote attack" at the nitroso stage. The striking spectral changes occurring during the early stages of these reductions are considered. Evidence is cited (in the p-nitro reduction) for an intensely colored Cr(III)-bound nitro radical cation lying apart from the principal reduction sequence and also for a nitroso radical cation; both of these are observed in 1.2 M acid, but are destroyed in 0.024 M acid.
In order to study the possible importance of pπ-pπ effects in organoaluminum chemistry, a study of the synthesis and properties of vinylaluminum compounds has been undertaken. Aryl-substituted vinylaluminum systems have been prepared by the addition of triphenylaluminum, in turn, to diphenylacetylene, methylphenyl-acetylene, and 1,3,3,3-tetraphenylpropyne. Examination of the hydrolysis products has permitted considerable insight into the electronic and steric factors involved in such additions. Parallel efforts to add the Al-H bond of diphenylaluminum hydride to alkynes were frustrated by the inability to prepare pure diphenylaluminum hydride from lithium hydride and diphenylaluminum chloride. The foregoing cis-β-phenylvinylaluminum compounds were found to undergo a novel metalative cyclization with the formation of the aluminole ring system. The preparation, isolation, and chemical structure proof were carried through in considerable detail for 1,2,3-triphenylbenzaluminole and 5-phenyldibenzaluminole. The mechanistic kinship between the addition of aluminum aryls to alkynes and the metalative formation of aluminoles is assessed in terms of reaction conditions and electronic factors. The import of these results to further synthetic and theoretical studies is emphasized.
Introduction of an azido substituent at the α position of benzyl ethers can be achieved by treating them with IN3 in refluxing acetonitrile. Some of the products obtained after 20 min–5 h are given.
Alex Fallis was born in Toronto and received his BSc Hon. (1963), MA (1964), and PhD (1967) degrees from the University of Toronto with Professor Peter Yates. After an NRC Postdoctoral Fellowship at Oxford University with Professor E. R. H. Jones he joined the Department of Chemistry at Memorial University of Newfoundland in 1969. In 1988 he was appointed Professor in the Department of Chemistry at the University of Ottawa and was Director of the Ottawa-Carleton Chemistry Institute from 1990–1993. In 1996 he was awarded the Basic Science Research Award of the Ottawa Life Sciences Council, for 1997–2000 he received the Saunders-Matthey Foundation award for Breast Cancer Research, and was the recipient of the Alfred Bader Award of the Canadian Society for Chemistry for 1998.
The principal topics in cocatalytic chemistry are discussed. The topics discussed include: types and intrinsic structural features of commonly-used activators; activation processes embodied in the various chemical reactions between the precatalyst and cocatalyst; catalyst-cocatalyst structure-activity relationships as revealed by the nature of cation-anion interactions in both the solid state and in solution; thermodynamics of catalyst activation; kinetics of ion pair dissociation/reorganization processes; and how these interactions are intimately connected with polymerization activity and stereospecificity. Common deactivation processes and the forces stabilizing highly electrophilic cationic metal complexes in solution are also discussed.
One-pot co-catalyst systems are covered in this tutorial review. It is divided into three sections according to the reaction types: i) one catalyst performs a desired reaction as the second catalyst restores the first catalytic species back into its original state for the next catalytic cycles, ii) two catalysts carry out sequential organic transformations, in which the first step is carried out by one catalyst to afford certain intermediates being to be subjected to the second catalyst for the next step, and iii) cooperative catalytic actions on both substrates by suitable catalysts proceed in a substrate-selective manner followed by the subsequent coupling of the two activated adducts providing the desired products.
A concise total synthesis of the cytotoxic marine natural product amphidinolide X (1) is described. A key step of the highly convergent route to this structurally rather unusual macrodiolide derivative consists of a newly developed, highly syn selective formation of allenol 6 by an iron-catalyzed ring opening reaction of the enantioenriched propargyl epoxide 5 (derived from a Sharpless epoxidation) with a Grignard reagent. Allenol 6 was then cyclized with the aid of Ag(I) to give dihydrofuran 7 containing the (R)-configured quarternary sp3 chiral center at C19 of the target. The anti-configured chiral centers at C10 and C11 were formed by the palladium-catalyzed, Et2Zn-promoted addition of propargyl mesylate 12 to the functionalized aldehyde 11. The key fragment coupling at the C13-C14 bond was achieved by the "9-MeO-9-BBN" variant of the alkyl-Suzuki reaction. Finally, the 16-membered macrodiolide ring was formed by a Yamaguchi esterification/lactonization strategy.
The applications of iron catalysts in organic synthesis are compiled. Whereas for decades only a few iron-catalyzed C-C bond formation reactions have been developed, the field now comprises many major accomplishments, and efficient processes for addition, cross-coupling, and cycloadditions reactions have emerged over the last ten years. Significant progress has also been made in enantioselective transformations as exemplified by the achievements in Diels-Alder reactions, 1,3-dipolar cycloadditions and sulfoxidations.
For a recent review on carbometalation of heteroatom-containing alkynes and alkenes, see: Fallis, A
- P G Forgione
(2) For a recent review on carbometalation of heteroatom-containing alkynes and alkenes, see: Fallis, A. G.; Forgione, P. Tetrahedron 2001, 57, 5899- 5913
Unfunctionalized alkynes used for the arylmetalation are all aryl-substituted acetylenes. For examples, see: (a)
- J J Eisch
- W C Kaska
- J J Eisch
Unfunctionalized alkynes used for the arylmetalation are all aryl-substituted acetylenes. For examples, see: (a) Eisch, J. J.; Kaska, W. C. J. Am. Chem. Soc. 1966, 88, 2976-2983. (b) Eisch, J. J.;
ComprehensiVe Organic Synthesis
- P Knochel
Knochel, P. In ComprehensiVe Organic Synthesis; Trost, B. M., Fleming, I., Semmelhack, M. F., Eds.; Pergamon Press: New York, 1991; Vol. 4, Chapter 4.4; pp 865-911.