A Non-Diazo Approach to α-Oxo Gold Carbenes via Gold-Catalyzed Alkyne Oxidation
TL;DR: This Account shows that the unique access to the gold carbene species in homogeneous gold catalysis offers an opportunity to generate α-oxo gold carbenes if both nucleophile and electrophile are oxygen, which would enable readily available and safer alkynes to replace hazardous α-diazo carbonyl compounds as precursors in the realm of goldcarbene chemistry.
Abstract: For the past dozen years, homogeneous gold catalysis has evolved from a little known topic in organic synthesis to a fully blown research field of significant importance to synthetic practitioners, due to its novel reactivities and reaction modes. Cationic gold(I) complexes are powerful soft Lewis acids that can activate alkynes and allenes toward efficient attack by nucleophiles, leading to the generation of alkenyl gold intermediates. Some of the most versatile aspects of gold catalysis involve the generation of gold carbene intermediates, which occurs through the approach of an electrophile to the distal end of the alkenyl gold moiety, and their diverse transformations thereafter. On the other hand, α-oxo metal carbene/carbenoids are highly versatile intermediates in organic synthesis and can undergo various synthetically challenging yet highly valuable transformations such as C–H insertion, ylide formation, and cyclopropanation reactions. Metal-catalyzed dediazotizations of diazo carbonyl compounds ar...
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TL;DR: Gold(I) complexes selectively activate π-bonds of alkenes in complex molecular settings, which has been attributed to relativistic effects as discussed by the authors, and are the most effective catalysts for the electrophilic activation of alkynes under homogeneous conditions.
Abstract: 1.1. General Reactivity of Alkyne-Gold(I) Complexes
For centuries, gold had been considered a precious, purely decorative inert metal. It was not until 1986 that Ito and Hayashi described the first application of gold(I) in homogeneous catalysis.1 More than one decade later, the first examples of gold(I) activation of alkynes were reported by Teles2 and Tanaka,3 revealing the potential of gold(I) in organic synthesis. Now, gold(I) complexes are the most effective catalysts for the electrophilic activation of alkynes under homogeneous conditions, and a broad range of versatile synthetic tools have been developed for the construction of carbon–carbon or carbon–heteroatom bonds.
Gold(I) complexes selectively activate π-bonds of alkynes in complex molecular settings,4−10 which has been attributed to relativistic effects.11−13 In general, no other electrophilic late transition metal shows the breadth of synthetic applications of homogeneous gold(I) catalysts, although in occasions less Lewis acidic Pt(II) or Ag(I) complexes can be used as an alternative,9,10,14,15 particularly in the context of the activation of alkenes.16,17 Highly electrophilic Ga(III)18−22 and In(III)23,24 salts can also be used as catalysts, although often higher catalyst loadings are required.
In general, the nucleophilic Markovnikov attack to η2-[AuL]+-activated alkynes 1 forms trans-alkenyl-gold complexes 2 as intermediates (Scheme 1).4,5a,9,10,12,25−29 This activation mode also occurs in gold-catalyzed cycloisomerizations of 1,n-enynes and in hydroarylation reactions, in which the alkene or the arene act as the nucleophile.
Scheme 1
Anti-Nucleophilic Attack to η2-[AuL]+-Activated Alkynes
1,260 citations
TL;DR: The applications of gold catalysed reactions in total synthesis during the years since the last article are reviewed and literature analysis is conducted to evaluate the progress in this field.
Abstract: In this critical review the applications of gold catalysed reactions in total synthesis during the years since our last article are reviewed. At the end of this article a literature analysis is conducted to evaluate the progress in this field.
617 citations
TL;DR: This review summarizes recent advances in gold-catalyzed cyclopropanation divided by the type of carbenoid precursors.
Abstract: Homogeneous gold-catalyzed cyclopropanation has emerged as a powerful method in organic synthesis due to its rich chemistry and fascinating reactivity. This thriving strategy is remarkable for its mild conditions, good selectivity, and high efficiency, which provides complementarity and orthogonality to traditional metal-catalyzed cyclopropanation. This review summarizes recent advances in gold-catalyzed cyclopropanation divided by the type of carbenoid precursors. Besides the commonly used diazo compounds, current approaches enable readily available enynes, propargyl esters, cyclopropenes, cycloheptatrienes, alkynes, and sulfonium ylides as safer surrogates in the realm of gold carbenoid chemistry. Meanwhile, these reactions allow for the rapid building of molecular complexity including synthetically useful and intricate cyclic, heterocyclic, and polycyclic skeletons. The combination of the new reactivity of gold complexes with their capability to catalyze cyclopropanations may lead to myriad opportunities for the design of new reactions. Furthermore, the synthetic utilities of such superior methods have also been illustrated by the total syntheses of selected natural and biologically interesting products and the asymmetric formation of challenging target molecules.
375 citations
TL;DR: This review highlights the updated progress (2011-2015) in enantioselective gold catalysis and is classified according to the π-bonds activated by gold(i), in an order of alkynes, allenes and alkenes.
Abstract: Interest in homogeneous gold catalysis has undergone a marked increase. As strong yet air- and moisture-tolerant π-acids, cationic gold(I) complexes have been shown to catalyze diverse transformations of alkenes, alkynes and allenes, opening new opportunities for chemical synthesis. The development of efficient asymmetric variants is required in order to take full advantage of the preparative potential of these transformations. During the last few years, the chemical community has achieved tremendous success in the area. This review highlights the updated progress (2011–2015) in enantioselective gold catalysis. The discussion is classified according to the π-bonds activated by gold(I), in an order of alkynes, allenes and alkenes. Other gold activation modes, such as σ-Lewis acid catalyzed reactions and transformations of diazo compounds are also discussed.
363 citations
TL;DR: This critical review clearly indicates that silver catalysis provides a significant impetus to the rapid evolution of alkyne-based organic reactions, such as alkynylation, hydrofunctionalization, cycloaddition, cycloisomerization, and cascade reactions.
Abstract: Silver is a less expensive noble metal. Superior alkynophilicity due to π-coordination with the carbon-carbon triple bond makes silver salts ideal catalysts for alkyne-based organic reactions. This review highlights the progress in alkyne chemistry via silver catalysis primarily over the past five years (ca. 2010-2014). The discussion is developed in terms of the bond type formed with the acetylenic carbon (i.e., C-C, C-N, C-O, C-Halo, C-P and C-B). Compared with other coinage metals such as Au and Cu, silver catalysis is frequently observed to be unique. This critical review clearly indicates that silver catalysis provides a significant impetus to the rapid evolution of alkyne-based organic reactions, such as alkynylation, hydrofunctionalization, cycloaddition, cycloisomerization, and cascade reactions.
346 citations
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TL;DR: Important vinylgold intermediates, the transmetalation from gold to other transition metals, the development of new ligands for gold catalysis, and significant contributions from computational chemistry are other crucial points for the field highlighted here.
Abstract: Although homogeneous gold catalysis was known previously, an exponential growth was only induced 12 years ago. The key findings which induce that rise of the field are discussed. This includes early reactions of allenes and furanynes and intermediates of these conversions as well as hydroarylation reactions. Other substrate types addressed are alkynyl epoxides and N-propargyl carboxamides. Important vinylgold intermediates, the transmetalation from gold to other transition metals, the development of new ligands for gold catalysis, and significant contributions from computational chemistry are other crucial points for the field highlighted here.
2,792 citations
TL;DR: The ability of platinum and gold catalysts to effect powerful atom-economic transformations has led to a marked increase in their utilization and the application of platinum- and gold-catalyzed transformations in natural product synthesis is discussed.
Abstract: The ability of platinum and gold catalysts to effect powerful atom-economic transformations has led to a marked increase in their utilization. The quite remarkable correlation of their catalytic behavior with the available structural data, coordination chemistry, and organometallic reactivity patterns, including relativistic effects, allows the underlying principles of catalytic carbophilic activation by π acids to be formulated. The spectrum of reactivity extends beyond their utility as catalytic and benign alternatives to conventional stoichiometric π acids. The resulting reactivity profile allows this entire field of catalysis to be rationalized, and brings together the apparently disparate electrophilic metal carbene and nonclassical carbocation explanations. The advances in coupling, cycloisomerization, and structural reorganization—from the design of new transformations to the improvement to known reactions—are highlighted in this Review. The application of platinum- and gold-catalyzed transformations in natural product synthesis is also discussed.
1,938 citations
TL;DR: The proposed involvement of cyclopropyl metal carbenes of type 4 in the electrophilic activation of enynes by transition metals was first substantiated in reactions catalyzed by Pd(II), in which the initially formed cycloprostyl palladiumCarbenes undergo [4 + 2] cycloaddition with the double bond of the conjugate enyne.
Abstract: Gold salts and complexes have emerged in the past few years as the most powerful catalysts for electrophilic activation of alkynes toward a variety of nucleophiles under homogeneous conditions. In a simplified form, nucleophilic attack on the [AuL]-activated alkyne proceeds via π complexes 1 to give trans-alkenyl gold complexes of type 2 as intermediates (Scheme 1). This type of coordination is also a common theme in gold-catalyzed cycloisomerizations of enynes, in which the alkene function acts as the nucleophile. In the reaction of enynes with complexes of other transition metals, an Alder-ene cycloisomerization can take place by simultaneous coordination of the alkyne and the alkene to the metal followed by an oxidative cyclometalation. In contrast, this process does not occur for gold(I) since oxidative addition processes are not facile for this metal. 6 In addition, the [AuL] fragment, which is isolobal to H and HgL, adopts a linear coordination and binds to either the alkene or the alkyne. Thus, cycloisomerizations of enynes catalyzed by gold proceed by an initial coordination of the metal to the alkyne, and as illustrated in Scheme 2, the resulting complex 3 reacts with the alkene by either the 5-exo-dig or 6-endo-dig pathway to form the exoor endocyclopropyl gold carbene 4 or 5, respectively, as has been established with other electrophilic transition-metal complexes or halides MXn as catalysts. The proposed involvement of cyclopropyl metal carbenes of type 4 in the electrophilic activation of enynes by transition metals was first substantiated in reactions catalyzed by Pd(II), in which the initially formed cyclopropyl palladium carbenes undergo [4 + 2] cycloaddition with the double bond of the conjugate enyne. Strong evidence for the existence of cyclopropyl metal carbenes as intermediates was also obtained in the reaction of enynes bearing additional double bonds at the alkenyl chain with Ru(II) and Pt(II) catalysts. In these reactions, the cyclopropyl metal carbenes are trapped intramolecularly by the terminal alkene to give tetracycles containing two cyclopropanes. Gold(I) complexes usually surpass the reactivity shown by Pt(II) and other electrophilic metal salts and complexes for the activation of enynes. They are highly reactive yet uniquely selective Lewis acids that have a high affinity for π bonds. This high π-acidity is linked to relativistic effects, which reach a maximum in the periodic table with gold. However, on occasion, the stronger Lewis acidity of gold complexes can be detrimental in terms of selectivity and because of their low tolerance to certain functional groups. In these instances, the less-strongly Lewis acidic Pt(II) complexes could be the catalysts of choice. * To whom correspondence should be addressed. E-mail: aechavarren@ iciq.es. † Additional affiliation: Departamento de Quı́mica Orgánica, Universidad Autónoma de Madrid, Cantoblanco, 28049 Madrid, Spain. Scheme 1 Chem. Rev. 2008, 108, 3326–3350 3326
1,728 citations
Book•
19 Jan 1998
TL;DR: Synthesis of Alpha-Diazocarbonyl Compounds Catalysts for Metal Carbene Transformations Insertion Reactions Intermolecular Cyclopropanation and Related Addition Reactions Intramolecular cyclopropaneation and related addition Reactions Cycloaddition and Substitution Reactions with Aromatic and Heteroaromatic Compounds Generation and Reactions of Ylides from DBCs X-H InsertionReactions of DBC compounds (X = N,O,S,Se,P, Halogen) The
Abstract: Synthesis of Alpha-Diazocarbonyl Compounds Catalysts for Metal Carbene Transformations Insertion Reactions Intermolecular Cyclopropanation and Related Addition Reactions Intramolecular Cyclopropanation and Related Addition Reactions Cycloaddition and Substitution Reactions with Aromatic and Heteroaromatic Compounds Generation and Reactions of Ylides from Diazocarbonyl Compounds X-H Insertion Reactions of Diazocarbonyl Compounds (X = N,O,S,Se,P, Halogen) The Wolff Rearrangement and Related Reactions Reactions of Alpha-Diazocarbonyl Compounds with Aldehydes and Ketones Acid-Promoted Cyclization of Unsaturated and Aromatic Diazo Ketones Miscellaneous Diazocarbonyl Reactions Index
1,112 citations
TL;DR: Amino Acid Derivatives: Synthesis of R-Substituted Organometallic Reagents to N-tert-Butanesulfinyl Imines 3687 * E-mail: jellman@berkeley.edu.
Abstract: 10.2. Synthesis of Other -Amino Acid Derivatives 3676 10.2.1. Synthesis of -Amino Ketones 3676 10.2.2. Synthesis of -Amino Nitriles 3679 10.2.3. Synthesis of -Amino Phosphinates 3680 10.2.4. Synthesis of -Amino Sulfonates 3681 11. Synthesis of 1,2-Amino Alcohols 3681 11.1. 1,2-Addition to R-Alkoxy Imines 3681 11.2. 1,2-Addition of R-Substituted Organometallic Reagents to N-tert-Butanesulfinyl Imines 3687 * E-mail: jellman@berkeley.edu. † These authors contributed equally to this work. Chem. Rev. 2010, 110, 3600–3740 3600
890 citations