Metal mediated carbometallation of alkynes and alkenes containing adjacent heteroatoms

Palladium-catalyzed hydroarylation of 1,3-diynes with arylboronic acids

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 PCy3 as the ligand, affording functionalized enynes in good to excellent yields. Its efficiency is demonstrated by its good functional group tolerance 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.

Uncatalyzed Carbometallation Involving Group 13 Elements: Carboboration and Carboalumination of Alkenes and Alkynes

Carbometallation of alkenes and alkynes are powerful carbon-carbon bond-forming reactions. The use of compounds containing bonds between carbon and group 13 elements, particularly boron and aluminum, are particularly attractive because of the versatility of subsequent transformations. Uncatalyzed carboboration and carboalumination represent less common classes of reactions. This Short Review discusses uncatalyzed carboboration and carboalumination reactions of alkenes and alkynes, including the reaction design and mechanism.

Palladium-Catalyzed Cross-Coupling Reactions of Borylated Alkenes for the Stereoselective Synthesis of Tetrasubstituted Double Bond

The stereoselective formation of tetrasubstituted alkenes remains one of the key goals of modern organic synthesis. In addition to other methods, the stereoselective synthesis of tetrasubstituted alkenes can be achieved by means of cross-coupling reactions of electrophilic and nucleophilic alkene templates. The use of electrophilic templates for the stereoselective synthesis of tetrasubstituted alkenes has previously been described. Therefore, the present review summarizes the procedures available for the stereoselective preparation of tetrasubstituted alkenes using stable and isolable nucleophilic templates.

Directed Regioselective Carbometallation of 1,2-Dialkyl-Substituted Cyclopropenes

A regio- and diastereoselective copper-catalyzed carbomagnesiation of 1,2-dialkylated cyclopropenes is reported. The regioselectivity is controlled by a subtle tethered Lewis basic moiety. The chelating moieties allow the differentiation between two electronically tantamount organometallic intermediates. Further functionalization grants access to polysubstituted stereodefined cyclopropanes bearing up to five alkyl groups.

Reductive Ni-catalysis for stereoselective carboarylation of terminal aryl alkynes

Stereoselective dicarbofunctionalization of terminal aryl alkynes has been achieved through reductive Ni-catalysis. The exclusive regioselective and anti-addition selective alkylarylation of terminal alkynes is accomplished using alkyl iodide and aryl iodide as electrophilic coupling partners in the presence of NiBr₂ as the catalyst and Mn as an inexpensive reductant.

1,2-Carbopentafluorophenylation of Alkynes: The Metallomimetic Pull-Push Reactivity of Tris(pentafluorophenyl)borane

We report the novel single-step 1,2-dicarbofunctionalization of an arylacetylene with an allylsilane and tris(pentafluorophenyl)borane [B(C₆ F₅ )₃ ] involving C-C bond formation with C-H bond scission at the β-position to the silicon atom of an allylsilane and B→C migration of a C₆ F₅ group. The 1,2-carbopentafluorophenylation occurs smoothly without the requirement for a catalyst or heating. Mechanistic studies suggest that the metallomimetic "pull-push" reactivity of B(C₆ F₅ )₃ imparts consecutive electrophilic and nucleophilic characteristics to the benzylic carbon of the arylacetylene. Subsequent photochemical 6π-electrocyclization affords tetrafluoronaphthalenes, which are important in the pharmaceutical and materials sciences. Owing to the unique reactivity of B(C₆ F₅ )₃ , the 1,2-carbopentafluorophenylation using 2-substituted furan proceeded with ring opening, and the reaction using silyl enolates formed a C-C bond with C-O bond scission at the silyloxy-substituted carbon.

Catalytic asymmetric Nakamura reaction by gold(I)/chiral N,N'-dioxide-indium(III) or nickel(II) synergistic catalysis

Intermolecular addition of enols and enolates to unactivated alkynes was proved to be a simple and powerful method for carbon-carbon bond formation. Up to date, a catalytic asymmetric version of alkyne with 1,3-dicarbonyl compound has not been realized. Herein, we achieve the catalytic asymmetric intermolecular addition of 1,3-dicarbonyl compounds to unactivated 1-alkynes attributing to the synergistic activation of chiral N,N′-dioxide-indium(III) or nickel(II) Lewis acid and achiral gold(I) π-acid. A range of β-ketoamides, β-ketoesters and 1,3-diketones transform to the corresponding products with a tetra-substituted chiral center in good yields with good e.r. values. Besides, a possible catalytic cycle and a transition state model are proposed to illustrate the reaction process and the origin of chiral induction based on the experimental investigations.

Although enols and enolates addition to unactivated alkynes is used for carbon-carbon bond modification a catalytic asymmetric alkyne with 1,3-dicarbonyl compound has been elusive. Here, the authors achieve this using the synergistic activation of chiral N,N′-dioxide-indium(III) or nickel(II) Lewis acid and achiral gold(I) π-acid.”

Ni-Catalyzed electrophile driven regioselective arylative cyclization of ortho-functional diaryl acetylenes for the synthesis of pyridine and indene derivatives

A regioselective arylative cyclization of ortho functional diaryl acetylenes for the synthesis of selectively substituted diaryl pyridine and indene derivatives is accomplished through an electrophile driven alkyne polarization.

Iron catalyzed stereoselective alkene synthesis: a sustainable pathway

Replacing expensive or toxic transition metals with iron has become an important trend. This article summarises the recent progresses of a wide range of Fe-catalyzed reactions for accessing various stereodefined alkenes.

syn-Selective alkylarylation of terminal alkynes via the combination of photoredox and nickel catalysis

Substituted alkenes are pivotal structural motifs found in pharmaceuticals and agrochemicals. Although numerous methods have been developed to construct substituted alkenes, a generally efficient, mild, catalytic platform for the conversion of alkynes to this highly functionalized scaffold via successive C–C bond forming steps remains in high demand. Here we describe an intermolecular, regio- and syn-stereoselective alkylarylation of terminal alkynes with tertiary alkyl oxalates via photoredox-Ni dual catalysis. This catalytic protocol, synergistically combining Ir/Ni-catalyzed alkyne difunctionalization with photoinduced alkene isomerization, affords trisubstituted alkenes with excellent efficiency and syn-stereoselectivity. The mild conditions tolerate many functional groups, allowing for a broad scope with respect to terminal alkynes, aryl bromides, and alkyl oxalates.

Converting alkynes into alkenes with high stereoselectivity via two consecutive C-C bond forming steps is a desirable process, yet very challenging. Here, the authors describe a dual photoredox-nickel catalytic system for the regio- and syn-selective alkylarylation of terminal alkynes with alkyl oxalates and aryl bromides.

Regio- and Stereoselective Allylindation of Alkynes Using InBr₃ and Allylic Silanes: Synthesis, Characterization, and Application of 1,4-Dienylindiums toward Skipped Dienes

Regioselective anti-allylindation of alkynes was achieved using InBr₃ and allylic silanes. Various types of alkynes and allylic silanes were applicable to the present allylindation. This sequential process used the generated 1,4-dienylindiums to establish novel synthetic methods for skipped dienes. The 1,4-dienylindiums were characterized by spectral analysis and treated with I₂ to stereoselectively give 1-iodo-1,4-dienes. The Pd-catalyzed cross coupling of 1,4-dienylindium with iodobenzene successfully proceeded in a one-pot manner to afford the corresponding 1-aryl-1,4-diene.

Zirconocene catalyzed diastereoselective carbometalation of cyclobutenes

The regio- and diastereoselective zirconocene-catalyzed carbomagnesiation of cyclobutenes is herein reported to afford configurationally stable cyclobutylmagnesium species that could subsequently react with a large variety of electrophiles to give polysubstituted cyclobutane species as a single diastereoisomer.

Regioselective access of alkylidendibenzo[c,f]oxocine framework via cyclocarbopalladation/cross-coupling cascade reactions and reductive Heck strategy

Palladium-catalyzed dual strategies of cascade cyclocarbopalladation/cross-coupling of alkynes and a reductive Heck reaction have been developed to construct dibenzo[c,f]oxocine frameworks with tri- and tetra-substituted exo-cyclic alkenes with high stereo- and regio-control.

Copper-catalyzed silylation reactions of propargyl epoxides: easy access to 2,3-allenols and stereodefined alkenes

Efficient silylation reactions of propargyl epoxides catalyzed by copper catalysts have been developed.

Copper mediated carbometalation reactions

Since the first discovery of carbocupration of alkynes in the 1970s a tremendous amount of research has been carried out in this field. The exceptionally high selectivities obtained attribute to the great synthetic value of carbocupration reactions. This tutorial review will present the most important features of carbocupration of alkynes and highlight the most relevant reviews. Then a comprehensive review of copper mediated carbometalation of cyclopropenes will follow. The latter method has received much attention over the last decade as it allows the highly selective construction of poly-substituted cyclopropanes which can be transformed into acyclic derivatives bearing one or multiple tertiary or quaternary carbon stereocenters.

Enantioselective Nickel-Catalyzed anti-Carbometallative Cyclizations of Alkynyl Electrophiles Enabled by Reversible Alkenylnickel E/Z Isomerization

Nickel-catalyzed additions of arylboronic acids to alkynes, followed by enantioselective cyclizations of the alkenylnickel species onto tethered ketones or enones, are reported. These reactions are reliant upon the formal anti-carbonickelation of the alkyne, which is postulated to occur by the reversible E/Z isomerization of an alkenylnickel species.

Enantiospecific Alkynylation of Alkylboronic Esters

Enantioenriched secondary and tertiary alkyl pinacolboronic esters undergo enantiospecific deborylative alkynylation through a Zweifel-type alkenylation followed by a 1,2-elimination reaction. The process involves use of α-lithio vinyl bromide or vinyl carbamate species, for which application to Zweifel-type reactions has not previously been explored. The resulting functionalized 1,1-disubstituted alkenes undergo facile base-mediated elimination to generate terminal alkyne products in high yield and excellent levels of enantiospecificity over a wide range of pinacolboronic ester substrates. Furthermore, along with terminal alkynes, internal and silyl-protected alkynes can be formed by simply introducing a suitable carbon- or silicon-based electrophile after the base-mediated 1,2-elimination reaction.

Palladium(ii)-catalyzed hydroxy-involved enolate-type efficient C–C functionalization of hydroxynaphthoquinones at room temperature

A simple, mild, efficient and scalable strategy has been developed for synthesizing hydroxynaphthoquinones via a Pd-catalyzed hydroxy-involved enolate-type reaction.

Cobalt catalysis involving π components in organic synthesis

Over the last three decades, transition-metal-catalyzed organic transformations have been shown to be extremely important in organic synthesis. However, most of the successful reactions are associated with noble metals, which are generally toxic, expensive, and less abundant. Therefore, we have focused on catalysis using the abundant first-row transition metals, specifically cobalt. In this Account, we demonstrate the potential of cobalt catalysis in organic synthesis as revealed by our research. We have developed many useful catalytic systems using cobalt complexes. Overall, they can be classified into several broad types of reactions, specifically [2 + 2 + 2] and [2 + 2] cycloadditions; enyne reductive coupling; reductive [3 + 2] cycloaddition of alkynes/allenes with enones; reductive coupling of alkyl iodides with alkenes; addition of organoboronic acids to alkynes, alkenes, or aldehydes; carbocyclization of o-iodoaryl ketones/aldehydes with alkynes/electron-deficient alkenes; coupling of thiols with aryl and alkyl halides; enyne coupling; and C-H bond activation. Reactions relying on π components, specifically cycloaddition, reductive coupling, and enyne coupling, mostly afford products with excellent stereo- and regioselectivity and superior atom economy. We believe that these cobalt-catalyzed π-component coupling reactions proceed through five-membered cobaltacyclic intermediates formed by the oxidative cyclometalation of two coordinated π bonds of the substrates to the low-valent cobalt species. The high regio- and stereoselectivity of these reactions are achieved as a result of the electronic and steric effects of the π components. Mostly, electron-withdrawing groups and bulkier groups attached to the π bonds prefer to be placed near the cobalt center of the cobaltacycle. Most of these transformations proceed through low-valent cobalt complexes, which are conveniently generated in situ from air-stable Co(II) salts by Zn- or Mn-mediated reduction. Overall, we have shown these reactions to be excellent substitutes for less desirable noble-metal systems. Recent successes in cobalt-catalyzed C-H activation have especially advanced the applicability of cobalt in this field. In addition to the more common low-valent-cobalt-catalyzed C-H activation reactions, an in situ-formed cobalt(III) five-membered complex with a 1,6-enyne effectively couples with aromatic ketones and esters through ortho C-H activation, opening a new window in this research area. Interestingly, this reaction proceeds under milder reaction conditions with broad substrate scope. Furthermore, many of the reactions we have developed are highly enantioselective, including enantioselective reductive coupling of enones and alkynes, addition of organoboronic acids to aldehydes, and the cyclization of 2-iodobenzoates with aldehydes. Overall, this Account demonstrates the versatility and utility of cobalt catalysis in organic synthesis.

Recent advances in the ruthenium-catalyzed hydroarylation of alkynes with aromatics: synthesis of trisubstituted alkenes

The hydroarylation of alkynes with amide, azole, carbamate, phosphine oxide, amine, acetyl, sulfoxide and sulphur substituted aromatics in the presence of a ruthenium catalyst via chelation-assisted C–H bond activation is discussed.

Ruthenium-catalyzed highly regio- and stereoselective hydroarylation of aromatic sulfoxides with alkynes via C–H bond activation

A ruthenium-catalyzed hydroarylation of aromatic sulfoxides with alkynes in the presence of AgSbF₆ and pivalic acid yielding trisubstituted alkenes is described.

Discovering complexes containing a metal–metal quintuple bond: from theory to practice

Recent advances in quintuple bonding are highlighted based on theoretical predictions and experimental achievements.