Copper-Catalyzed C–O Bond Formation: An Efficient One-Pot Highly Regioselective Synthesis of Furans from (2-Furyl)Carbene Complexes

Synthesis and structures of gold and copper carbene intermediates in catalytic amination of alkynes

Metal carbenes are often proposed as reactive intermediates in the late transition metal-catalysed transformations of alkynes. Owing to their high reactivity, however, isolation and structural characterization of metal carbene intermediates in these transformations has remained unknown. Herein, we report the isolation of two acyclic gold and copper carbene intermediates in either Au(I)- or Cu(I)-catalysed cyclization of N-alkynyl formamidines through five-exo-dig cyclization. X-ray diffraction, ¹³C NMR spectra data and computational analyses provide evidence for the formation of a gold carbene intermediate with a carbocation-like electronic character. Using the intrinsic bond orbital (IBO) approach, we also evaluate the π-stabilizing effects of organic substituents at the carbene carbon atom in the gold carbene intermediate. Another rare six-membered copper carbene complex is also obtained through 6-endo-dig cyclization. These metal carbenes have proven reactive toward oxidation. The metal-promoted cyclization of N-alkynyl formamidine provides a facile approach to synthesize metal carbene species.

Metal carbenes are typically highly reactive and unstable species, proposed as intermediates in numerous catalytic processes. Here the authors report the isolation and characterization of gold and copper carbene intermediates involved in catalytic cyclization reactions.

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.

Silver-catalyzed [3 + 2] domino reaction: an efficient strategy to synthesize imidazole-5-carbaldehydes

An unprecedented regioselective silver-catalyzed [3 + 2] domino reaction of amidines and ynals for the formation of C–N bonds has been developed.

Gold-catalyzed sequential annulations towards 3,4-fused bi/tri-cyclic furans involving a [3+2+2]-cycloaddition

A gold-catalyzed [3+2+2]-cycloaddition towards polysubstituted furan compounds has been realized.

A co-operative effect of visible light photo-catalysis and CoFe2O4 nanoparticles for green synthesis of furans in water

A novel approach to poly-functionalized furan synthesis is disclosed via oxidative decarboxylative [3+2] cycloaddition using co-operative catalysis by visible light and CoFe₂O₄ nanoparticles.

FeCl3/ZnI2-Catalyzed regioselective synthesis of angularly fused furans

The FeCl₃/ZnI₂-catalyzed synthesis of angularly fused furans by intermolecular coupling between enols and alkynes has been developed in ambient air.

Diastereoselective Synthesis of Cyclopenta[c]furans by a Catalytic Multicomponent Reaction

A diastereoselective three-component reaction between alkynyl enones, aldehydes and secondary amines is reported. With the aid of a benign indium catalyst, a range of highly substituted cyclopenta[c]furan derivatives can be obtained in a single-step procedure. The formation of the stereodefined heterocyclic motifs takes place via in situ generation of enamines followed by two sequential cyclization steps.

Hypoiodite-catalysed oxidative cyclisation of Michael adducts of chalcones with 1,3-dicarbonyl compounds: a facile and versatile approach to substituted furans and cyclopropanes

Hypoiodite catalysis for selective oxidative cyclization has been developed, yielding either furans or cyclopropanes with excellent diastereoselectivity.

Direct CuO nanoparticle-catalyzed synthesis of poly-substituted furans via oxidative C–H/C–H functionalization in aqueous medium

Here, we have reported CuO nanoparticles catalyzed synthesis of poly-functionalized furan derivatives via direct functionalization of α,β-unsaturated carbonyl compounds through conjugate addition initiated domino reactions in aqueous ethanol.

DFT study on the CuBr-catalyzed synthesis of highly substituted furans: effects of solvent DMF, substrate MeOH, trace H2O and the metallic valence state of Cu

Comparing the catalytic abilities of DMF, MeOH, and H₂O for intermolecular nucleophilic addition and H-transfer process.

A one pot, metal-free, three-component domino sequence for the synthesis of furans: an efficient C–O and C–N bond formation approach

A novel one pot, metal-free, three-component domino reaction for the formation of furan derivatives has been developed from 3-phenylpropiolaldehyde, 1,3-dicarbonyl compounds and aromatic amine or aliphatic acid.

Synthesis of multisubstituted furans via Cu(i)-catalyzed annulation of ketones with alkynoate under ligand- and additive-free conditions

A simple and efficient Cu(i)-catalyzed strategy for synthesis of mutisubstituted furans has been developed and this ligand- and additive-free annulation method is well suitable for both nonactivated arylmethyl ketones 1,3-dicarbonyl compounds.

Selectivity-switchable oxidation of tetraarylethylenes to fused polycyclic compounds

Selectivity-switchable oxidation of furan-containing tetraarylethylenes is reported.

Synthesis of Unsymmetrical Sulfides and Their Oxidation to Sulfones to Discover Potent Antileishmanial Agents

Unsymmetrical sulfides were first synthesized using combinations of a 1,3-dicarbonyl, an aromatic aldehyde and a thiol in the presence of 10 mol % ethanolic piperidine. These sulfides derivatives were subsequently converted into corresponding sulfones via oxidation in the presence of m-chloroperoxybenzoic acid (m-CPBA) at ice-bath to room temperature. The former reaction was achieved at room temperature through one-pot three-component. The later was obtained in good yields using mild reaction conditions with flexibility in choice from a range of substrates. The antimicrobial properties of the newly synthesized sulfone derivatives were investigated against the protozoan parasite, Leishmania donovani, a causative agent of visceral leishmaniasis (VL). Nine sulfone derivatives were found to be efficacious and exhibited significant antimicrobial activity. Further, these compounds were nontoxic on murine peritoneal macrophages thus eliminating potential cytoxicity in the host cells. These compounds may be indicated as potential leads in the treatment of visceral leishmaniasis.

Diversified Synthesis of Furans by Coupling between Enols/1,3-Dicarbonyl Compounds and Nitroolefins: Direct Access to Dioxa[5]helicenes

A versatile method for the diversified synthesis of furans and arenofurans has been developed that proceeds through K2CO3-promoted cyclization between enols/1,3-dicarbonyl compounds and nitroolefins at reflux in EtOH. This facile method has been successfully employed in the synthesis of benzotrifuran derivatives, which are useful hole-transporting materials. This procedure also provides direct access to dioxa[5]helicenes. This reaction offers a broad substrate scope, uses an inexpensive base and environmentally benign solvent, and is operationally simple.

Microwave-assisted C–N and C–S bond-forming reactions: an efficient three-component domino sequence for the synthesis of sulfoether-decorated imidazo[1,2-a]pyridines

Microwave-assisted three-component domino reaction for the synthesis of sulfoether-decorated imidazo[1,2-a]pyridines.

A [3 + 2]-annulation approach to tetrasubstituted furans from MBH-carbonates of acetylenic aldehydes via sequential substitution/cycloisomerization

A new organo base-mediated cascade reaction has been developed for the synthesis of uniquely substituted tetrasubstituted furans, 2-furan-3-yl acrylates, starting from MBH-carbonates of acetylenic aldehydes and keto-methylenes.

Pd-catalyzed cross-coupling of terminal alkynes with ene-yne-ketones: access to conjugated enynes via metal carbene migratory insertion

Pd-catalyzed oxidative cross-coupling of terminal alkynes with ene-yne-ketones has been developed, in which the ene-yne-ketones are served as carbene precursors and metal carbene migratory insertion process is the key step for C–C bond formation.