Gold-Catalyzed Tandem Oxidative Coupling Reaction between β-Ketoallenes and Electron-Rich Arenes to 2-Furylmethylarenes

A tandem oxidative coupling reaction of β-ketoallenes and arenes was developed, which leads to the formation of 2-furylmethylarenes using AuCl₃ and phenyliodine diacetate. The Au^III salt catalyzed the cyclization of β-ketoallenes to form a 2-furylmethyl gold intermediate, and the subsequent C-H functionalization of arenes proceeded smoothly. During the oxidative coupling, nucleophilic additions occurred at the center and terminal carbon atoms of the allene moiety to form C-O and C-C bonds.

Synthetic Studies toward (±)-Furanocembranoid 1: Construction of the Acyclic Carbon Framework

Herein, we report the synthesis of the entire acyclic carbon framework toward (±)-furanocembranoid 1 via the longest linear sequence of 12 steps from commercially available linalool and diethyl 2-isopropylmalonate. Key to the success of this synthetic approach is a silver-catalyzed enyne-annulation reaction for the formation of 2,4-disubstituted furan motif of unique furanocembranoid 1, isolated from Croton oblongifolius. Construction of macrocycle has also been explored using the ring-closing metathesis reaction.

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.

Gold-catalyzed ring enlargement and cycloisomerization of alkynylamide tethered alkylidenecyclopropanes

A gold(i)-catalyzed ring enlargement and cycloisomerization of alkynylamide tethered alkylidenecyclopropanes has been developed, providing facile access to functionalized polycyclic and spiropolycyclic products based on the use of gold(i) catalysts.

Gold-catalyzed ring-expansion through acyl migration to afford furan-fused polycyclic compounds

A gold-catalyzed ring-expansion reaction of alkynones to access furan-fused polycyclic compounds is reported.

Epoxy and aziridinyl enolsilanes in diastereoselective inter- and intramolecular Friedel–Crafts alkylations

Diastereoselective Friedel–Crafts reactions of optically pure epoxy enolsilanes afford enantiomerically-enriched β-hydroxy-α-arylketones. Aziridinyl enolsilanes react in an analogous manner.

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.

Rhodium-catalyzed synthesis of multi-substituted furans from N-sulfonyl-1,2,3-triazoles bearing a tethered carbonyl group

The efficient synthesis of highly functionalized furan derivatives from 1-sulfonyl-1,2,3-triazoles with a pendent carbonyl group is reported. The process involves an intramolecular trapping of α-imino carbene and subsequent aromatization.

Ligand design in gold catalysis and chemistry of gold-oxonium intermediates

Gold catalysis is considered one of the most important breakthroughs in organic synthesis during the last decade. Many gold-catalyzed reactions suffer from high catalyst loading, which is a serious limitation on the application of gold catalysis in larger scale synthesis. Because ligands play a major role in the tuning of reactivity of transition metal catalysts, there has been an increased effort on rationally understanding ligand effects in gold catalysis and using a rational ligand design to achieve higher efficiency. In the first part of this chapter, selected examples of ligand design in gold catalysis are discussed. In the second part, the chemistry of gold-oxonium intermediate is examined. An oxonium intermediate is generated when a oxygen nucleophile (ketone, aldehyde, or ether) attacks a cationic gold-activated multiple bond. This oxonium intermediate, being a highly energetic species, has the potential to undergo further transformations such as electron transfer/rearrangement/protodeauration to form diverse products.

Gold(I)-catalyzed formation of furans from γ-acyloxyalkynyl ketones

Various γ-acyloxyalkynyl ketones were efficiently converted into highly substituted furans with 2.5 mol % of triflimide (triphenylphosphine)gold(I) as a catalyst in dichloroethane at 70 °C.

Strained small rings in gold-catalyzed rapid chemical transformations

Gold-catalyzed reactions, which have been widely explored over the past several years, are powerful tools in organic synthesis to access complex molecular frameworks, and some corresponding excellent reviews have been reported. However, little attention has been paid to summarize the reactions of strained small-ring-containing molecules catalyzed by gold. This critical review mainly puts its emphasis on the recent progress in the field of gold-catalyzed transformations of cyclopropyl-, cyclopropenyl-, epoxy- and aziridinyl-containing molecules. The rapid construction of interesting building blocks in organic synthesis from strained small rings catalyzed by gold has been summarized in this review (106 references).

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.

1,3-Difurfurylbenzimidazolium chloride monohydrate

The title compound, C(17)H(15)N(2)O(2) (+)·Cl(-)·H(2)O, was synthesized from benzimidazole and furfryl chloride in dimethyl-formamide. The cationic benzimidazolium ring is connected to two furan rings via methyl-ene bridges. The furan rings make dihedral angle of 79.09 (18)° with respect to each other, and make dihedral angles of 73.92 (12) and 72.58 (13)° with respect to the benzimidazole ring. O-H⋯Cl, C-H⋯O and C-H⋯Cl hydrogen bonds and C-H⋯π inter-actions contribute to the stabilization of the crystal structure. Furthermore, there is a π-π inter-action between adjacent five- and six-membered rings of the benzimidazole groups [centroid-centroid distance = 3.5305 (8) Å].