Cu(I)-Catalyzed Synthesis of Furan-Substituted Allenes by Use of Conjugated Ene-yne Ketones as Carbene Precursors

Lewis Acid-Catalyzed Synthesis of Polysubstituted Furans from Conjugated Ene-yne-ketones and 1,3,5-Triazinanes

An efficient and metal-free approach to the construction of diverse functionalized furan derivatives has been developed from ene-yne-ketones and 1,3,5-triazinanes. As an atom-economical and environment-friendly protocol, the new conditions are suitable for selective C-N and C-O bond formation of a wide range of polysubstituted furans in one pot.

Recent Advances in Catalytic Alkyne Transformation via Copper Carbene Intermediates

As one of the abundant and inexpensive metals on the earth, copper has demonstrated broad applications in synthetic chemistry and catalysis. Among these copper-catalyzed advances, copper carbenes are versatile and reactive intermediates that can mediate a variety of transformations, which have attracted much attention in the past decades. The present review summarizes two different reaction models that take place between a copper carbene intermediate and alkyne species, including the cross-coupling reaction of copper carbene intermediate with terminal alkyne, and the addition of copper carbene intermediate onto the C-C triple bond. This article will cover the profile from 2010 to 2021 by placing emphasis on the detailed catalytic models and highlighting the synthetic applications offered by these practical and mild methods.

Ready Access to Densely Substituted Furans Using Tsuji-Wacker-Type Cyclization

A competent method for the construction of highly substituted furans catalyzed by Pd(II) and Cu(II) chloride has been developed. The method provides easy access to di-, tri-, and tetrasubstituted furans from corresponding diols with relatively mild conditions in a unified strategy. The developed method has been successfully tested with more than 25 substrates, which resulted in furans of multiple substitution patterns with up to 84% isolated yields.

Zinc Iodide Catalyzed Synthesis of Trisubstituted Allenes from Terminal Alkynes and Ketones

A straightforward, user-friendly, efficient protocol for the one pot, ZnI₂-catalyzed allenylation of terminal alkynes with pyrrolidine and ketones, toward trisubstituted allenes, is described. Trisubstituted allenes can be obtained under either conventional heating or microwave irradiation conditions, which significantly reduces the reaction time. A sustainable, widely available, and low-cost metal salt catalyst is employed, and the reactions are carried out under solvent-free conditions. Among others, synthetically valuable allenes bearing functionalities such as amide, hydroxyl, or phthalimide can be efficiently prepared. Mechanistic experiments, including kinetic isotope effect measurements and density functional theory (DFT) calculations, suggest a rate-determining [1,5]-hydride transfer during the transformation of the intermediate propargylamine to the final allene.

Palladium-catalyzed cascade reactions of enynones and isocyanides: access towards functionalized ketenimine and its application

Palladium-catalyzed cascade reactions of enynones and isocyanides have been disclosed. This strategy allows for the synthesis of structurally unusual furan-incorporated ketenimines, which are stable and can undergo a formal [4+1] annulation with another isocyanide to yield indenone derivatives.

Synthesis of 2-alkenylfurans via a Ag(i)-catalyzed tandem cyclization/cross-coupling reaction of enynones with iodonium ylides

A silver(i)-catalyzed tandem cyclization/cross-coupling reaction of enynones with iodonium ylides to construct carbon-carbon double bonds has been developed. The strategy provides a novel method for the synthesis of 2-alkenylfurans. This is the first cross-coupling reaction between metal-carbene complexes and iodonium ylides.

Ag(I)-Catalyzed Tandem Reaction of Conjugated Ene-yne-ketones in the Presence of PhI(OAc)2 and Triethylamine: Synthesis of 2-Alkenylfurans

Silver-catalyzed tandem cyclization-elimination reactions of conjugated ene-yne-ketones in PhI(OAc)₂/triethylamine system lead to the formation of 2-alkenylfurans. 2-Furylsilver carbene and phenyliodonium ylide are proposed as the key intermediates in these transformations.

Synthesis of 2-acetyl trisubstituted furans via copper-mediated deacylation cleavage of unstrained C(sp3)–C(sp2) bonds

A copper-mediated tandem addition/cyclization/carbon–carbon cleavage reaction for the convenient synthesis of 2-acyl trisubstituted furans has been developed.

Palladium-catalyzed oxidative borylation of conjugated enynones through carbene migratory insertion: synthesis of furyl-substituted alkenylboronates

A new method for the synthesis of furyl-substituted alkenylboronates has been developed by palladium-catalyzed oxidative borylation reaction of conjugated enynones.

Copper-Catalyzed Regioselective and Stereoselective Coupling of Grignard Reagents with Pent-1-en-4-yn-3-yl Benzoates: A Shortcut to ( Z) -1,5-Disubstituted Pent-3-en-1-ynes from Accessible Starting Materials

Copper-catalyzed coupling of Grignard reagents with pent-1-en-4-yn-3-yl benzoates occurs regioselectively at the terminal alkenyl carbon rather than the alkynyl site, leading to the stereoselective formation of unexpected ( Z) -1,5-disubstituted pent-3-en-1-ynes without generation of the initially expected alkenyl allene products. By using easily accessible starting materials, this reaction can provide direct access to thermodynamically unfavorable Z-configured enynes, which widely exist in many bioactive natural products, such as the anti-inflammatory components in henna.

Copper-Catalyzed Cascade Aminoalkynylation-Oxidation of Propargylic Alcohols: Stereospecific Synthesis of ( Z)-2-Amino Conjugated Enynals/Enynones

Copper-catalyzed cascade aminoalkynylation-oxidation of propargylic alcohols has been realized, sterospecifically providing an array of ( Z)-2-amino conjugated enynals/enynones in good yields under mild conditions. This transformation involves a rare 1,3-alkynyl migration of propargylic alcohols and simultaneously forms C-C, C-N, and C═O bonds. Furthermore, ( Z)-2-amino conjugated enynals were applied to efficiently synthesize 3,5-disubstituted-1 H-pyrrole-2-carbaldehyde and conjugated enynol derivatives.

Palladium-catalyzed carbene/alkyne metathesis with enynones as carbene precursors: synthesis of fused polyheterocycles

An unprecedented palladium-catalyzed novel carbene/alkyne metathesis cascade reaction of alkyne-tethered enynones is described. This reaction affords fused polyheterocycles in moderate to good yields. The transformation begins with Pd-catalyzed 5-exo-dig cyclization of the enynone to form the donor/donor metal carbene, which then undergoes metathesis with the alkyne followed by electrophilic aromatic substitution.

Directing group assisted ZnI2-catalyzed cyclopropanation of indoles via 2-furylcarbenoids

An efficient method for the synthesis of cyclopropane-fused indolines via a Zn₂I catalyzed cyclopropanation of indoles and enynones was reported.

Access to sulfonylated furans or imidazo[1,2-a]pyridines via a metal-free three-component, domino reaction

An efficient three-component reaction for the synthesis of sulfonylated furans or imidazo[1,2-a]pyridines has been developed.

Transition-Metal-Catalyzed Cross-Couplings through Carbene Migratory Insertion

Transition-metal-catalyzed cross-coupling reactions have been well-established as indispensable tools in modern organic synthesis. One of the major research goals in cross-coupling area is expanding the scope of the coupling partners. In the past decade, diazo compounds (or their precursors N-tosylhydrazones) have emerged as nucleophilic cross-coupling partners in C-C single bond or C═C double bond formations in transition-metal-catalyzed reactions. This type of coupling reaction involves the following general steps. First, the organometallic species is generated by various processes, including oxidative addition, transmetalation, cyclization, C-C bond cleavage, and C-H bond activation. Subsequently, the organometallic species reacts with the diazo substrate to generate metal carbene intermediate, which undergoes rapid migratory insertion to form a C-C bond. The new organometallic species generated from migratory insertion may undergo various transformations. This type of carbene-based coupling has proven to be general: various transition metals including Pd, Cu, Rh, Ni, Co, and Ir are effective catalysts; the scope of the reaction has also been extended to substrates other than diazo compounds; and various cascade processes have also been devised based on the carbene migratory insertion. This review will summarize the achievements made in this field since 2001.

Facile synthesis of cyanofurans via Michael-addition/cyclization of ene–yne–ketones with trimethylsilyl cyanide

Carbene migratory insertion? No! Ene–yne–ketones were utilized as a Michael-addition acceptor to react with TMSCN, affording a series of cyanofurans.

The synthesis of cycloalka[b]furans via an Au(i)-catalyzed tandem reaction of 3-yne-1,2-diols

A rapid and convenient approach toward substituted cycloalka[b]furan compounds has been developed via an Au(i)-catalyzed cyclization/1,2-rearrangement/aromatization cascade.

Pd/Cu cooperative catalysis: an efficient synthesis of (3-isoindazolyl)allenes via cross-coupling of 2-alkynyl azobenzenes and terminal alkynes

We report a cooperative Pd/Cu-catalyzed synthesis of (3-isoindazolyl)allenes via cross-coupling of 2-alkynyl azobenzenes and terminal alkynes.

A highly efficient one-pot trifluoromethylation/cyclization reaction of electron-deficient 1,3-conjugated enynes: modular access to trifluoromethylated furans and 2,3-dihydrofurans

A highly efficient one-pot trifluoromethylation/cyclization reaction of conjugated enyne aldehydes and ketones was developed, which provides modular access to highly substituted trifluoromethylated furans and 2,3-dihydrofurans.

Direct access to 2-amino-5-azidomethylfurans through palladium-catalyzed azidative cycloisomerization of homoallenyl amides

A room temperature Pd-catalyzed azidative cycloisomerization of homoallenyl amides using TMSN₃ as the azidation reagent and PhI(O₂CCF₃)₂ as the oxidant is described, producing various 2-amino-5-azidomethylfurans in moderate to excellent yields.