Synthesis of Furans and 2,5-Dihydrofurans by Ag(I)-Catalyzed Isomerization of Allenones, Alkynyl Allylic Alcohols, and Allenylcarbinols

Direct access to furan and cyclopropane derivatives via palladium-catalyzed C-H activation/alkene insertion/annulation

A practical and effective palladium-catalyzed C-H activation/alkene insertion/annulation has been reported for the synthesis of furans and cyclopropanes from cyclic 1,3-diketones or 1,3-indandione and diverse alkenes, resulting in moderate to good yields. This protocol demonstrates excellent selectivity and is well-compatible with a wide range of alkene substrates, exhibiting exceptional regioselectivities, high efficiency, and good functional group tolerance.

Pentaleno[1,2-c]pyrroles: Tricyclic 5/5/5 Fused Rings

A novel method for the preparation of tetrahydropentaleno[1,2-c]pyrroles (8) is described via the reaction of anilines with 1-en-4-yn-3-ols in the presence of Lewis acid. Oxidation of 8 with Br₂ gave pentaleno[1,2-c]pyrroles (10), which is the first reported tricyclic 5/5/5 ring with a fully conjugated system. Structures of these obtained compounds were characterized by spectroscopic methods, and compounds 8a,b and 10c were further confirmed by X-ray crystallographic determination.

A silver-catalyzed domino inverse electron-demand oxo-Diels-Alder reaction of 3-cyclopropylideneprop-2-en-1-ones with 2,3-dioxopyrrolidines via cyclobutane-fused furan

A silver-catalyzed diastereoselective one-pot domino cyclization-migration/inverse electron-demand oxo-Diels-Alder reaction has been disclosed in this communication through the in situ generated cyclobutane-fused furan intermediate with 4-vinyl-2,3-dioxopyrrolidine for the construction of 2-oxopyrrolidine-fused tricyclic compounds in moderate to good yields with a broad substrate scope under mild conditions. This new synthetic protocol features good efficiency and atom- and step-economy. A plausible reaction mechanism has also been proposed on the basis of previous reports, NMR tracing and control experiments.

Bifunctional phosphine ligand-enabled gold-catalyzed direct cycloisomerization of alkynyl ketones to 2,5-disubstituted furans

An efficient synthesis of 2,5-disubstituted furans directly from alkynyl ketones has been developed via tandem gold(i)-catalyzed isomerization of alkynyl ketones to allenyl ketones and cycloisomerization. The key to the success of this chemistry is the use of a biphenyl-2-ylphosphine ligand featuring a critical remote tertiary amino group.

Facilitating Myers–Saito cyclization through acid-triggered tautomerization for the development of maleimide-based antitumor agents

Enyne-allene compounds undergo Myers–Saito cyclization at physiological temperature to generate diradical intermediates that are capable of inducing DNA damage and cell death.

Intermolecular Reductive Coupling Cyclisation of 1,1-Diaryl-2,2-Dicyanoethylenes with Aldehydes or Ketones to Synthesise Polysubstituted 2, 3-Dihydrofurans and Cyclopentenylamines Promoted by Samarium Metal in DMF

The intermolecular reductive coupling and cyclisation of 1,1-diaryl-2,2-dicyanoethylenes with carbonyl compounds promoted by metallic samarium in DMF afforded functionalised 2,3-dihydrofurans and cyclopentenylamines.

Ag–NHC anchored on silica: an efficient ultra-low loading catalyst for regioselective 1,2,3-triazole synthesis

A silica-supported silver complex, Ag–NHC@SiO₂, was prepared by an anchoring coordination technique, which was successfully employed for the click reaction under mild reaction conditions.

Transition-metal-free C–C σ-bond activation of α-aryl ketones and subsequent Zn-catalyzed intramolecular cyclization: synthesis of tetrasubstituted furans

Atom-economical synthesis of tetrasubstituted furans from α-aryl ketones and alkynones through base-promoted cleavage of unstrained C–C single bonds of ketones and subsequent Zn-catalyzed cyclization.

Palladium-Catalyzed C-S Bond Cleavage with Allenoates: Synthesis of Tetrasubstituted 2-Alkenylfuran Derivatives

Palladium-catalyzed C-S cleavage of tetrasubstituted internal alkene α-oxo ketene dithioacetals was realized with allenoates as the coupling partners, efficiently affording tetrasubstituted 2-alkenylfuran derivatives with excellent regioselectivity under mild conditions. Allenoates acted as C1 synthons in the desulfurative [4 + 1] annulation.

Silica-supported silver nanoparticles as an efficient catalyst for aromatic C-H alkylation and fluoroalkylation

The efficient catalysis of oxidative alkylation and fluoroalkylation of aromatic C-H bonds is of paramount importance in the pharmaceutical and agrochemical industries, and requires the development of convenient Ag0-based nano-architectures with high catalytic activity and recyclability. We prepared Ag-doped silica nanoparticles (Ag0/+@SiO2) with a specific nano-architecture, where ultra-small sized silver cores are immersed in silica spheres, 40 nm in size. The nano-architecture provides an efficient electrochemical oxidation of Ag+@SiO2 without any external oxidant. In turn, Ag+@SiO2 5 mol% results in 100% conversion of arenes into their alkylated and fluoroalkylated derivatives in a single step at room temperature under nanoheterogeneous electrochemical conditions. Negligible oxidative leaching of silver from Ag0/+@SiO2 is recorded during the catalytic coupling of arenes with acetic, difluoroacetic and trifluoroacetic acids, which enables the good recyclability of the catalytic function of the Ag0/+@SiO2 nanostructure. The catalyst can be easily separated from the reaction mixture and reused a minimum of five times upon electrochemical regeneration. The use of the developed Ag0@SiO2 nano-architecture as a heterogeneous catalyst facilitates aromatic C-H bond substitution by alkyl and fluoroalkyl groups, which are privileged structural motifs in pharmaceuticals and agrochemicals.

Silver & gold-catalyzed routes to furans and benzofurans

Silver and gold have become incredibly versatile and mild catalysts for numerous transformations, especially in heterocycle synthesis. For the most prominent of them, i.e. furans, silver and gold, with their unique reactivity and mildness, allow numerous possible routes to highly substituted and/or functionalized furans from a large variety of starting materials. Silver and gold catalysis provide thus the most flexible way to this important family of compounds. The present review describes these silver and gold-catalyzed routes, with some emphasis on mechanistic aspects, and proposes a comparison of both the silver and the gold-catalyzed syntheses of furans.

Synthesis of Multisubstituted Allenes, Furans, and Pyrroles via Tandem Palladium-Catalyzed Substitution and Cycloisomerization

A palladium-catalyzed propargyl substitution reaction of propargyl acetates with indium organothiolates is developed for the synthesis of multisubstituted allenyl sulfides. This procedure can be applied to the synthesis of multisubstituted furans and pyrroles via tandem palladium-catalyzed propargyl substitution and cycloisomerization reaction in one pot.

Controlled TfOH- or AuCl-catalyzed cycloisomerization and tandem hydrolytic defluorination of 1,2-allenyl perfluoroalkyl ketones

An efficient TfOH- or AuCl-catalyzed cycloisomerization reaction of easily availablen-perfluoroalkyl 1,2-allenyl ketones occurring smoothly to form 2-perfluoroalkyl furans or 2-furyl perfluoroalkyl ketones has been reported.

TfOH-catalyzed domino cycloisomerization/hydrolytic defluorination of 2,3-allenyl perfluoroalkyl ketones

A unique TfOH-catalyzed domino cycloisomerization/hydrolytic defluorination reaction of easily available n-perfluoroalkyl allenones in the presence of H2O providing furanyl perfluoroalkyl ketones has been developed. The (18)O-labelling experiments confirmed that the oxygen atom of the carbonyl group in the final products originates from water.

Bifunctionalized Allenes. Part XVI. Synthesis of 3-Phosphoryl-2,5-dihydrofurans by Coinage Metal-Catalyzed Cyclo-isomerization of Phosphorylated α-Hydroxyallenes

Phosphorylated α-hydroxyallenes 1 and 2 were smoothly converted into the corresponding 2,5-dihydrofurans 3 and 4 in an 5-endo-trig cycloisomerization reaction by using 5 mol % of coinage metal salts as catalyst. Experimental conditions such as the type of the solvent, the reaction temperature, the mol % and the type of the catalyst were optimized. This mild and efficient cyclization method can be applied to dimethyl 1-hydroxyalkyl-alka-1,2-dienephosphonates 1 and 2-diphenylphosphinoyl-2,3-dien-1-ols 2a–c and 3-diphenylphosphinoyl-3,4-dien-2-ols 2d,e, furnishing 3-phosphorylated 2,5-dihydrofurans 3 and 4 in very good yields.

A convenient base-mediated synthesis of 3-aryol-4-methyl (or benzyl)-2-methylthio furans from α-oxo ketene dithioacetals and propargyl alcohols via domino coupling/annulations

A convenient base-mediated synthesis of 3-aryol-4-methyl (or benzyl)-2-methylthio furans2has been developed through the domino coupling/annulations from α-oxo ketene dithioacetals1and propargyl alcohols.

Gold(I)-catalyzed formation of furans by a Claisen-type rearrangement of ynenyl allyl ethers

A series of ynenyl allyl ethers were rearranged into polysubstituted furans in the presence of a gold(I) catalyst. It is proposed that the transformation involves a Claisen-type rearrangement that allows the efficient creation of quaternary centers under mild experimental conditions.