Asymmetric Rhodium-Catalyzed Hydrogenation Meets Gold-Catalyzed Cyclization: Enantioselective Synthesis of 8-Hydroxytetrahydroisoquinolines

An Intramolecular Reaction between Pyrroles and Alkynes Leads to Pyrrole Dearomatization under Cooperative Actions of a Gold Catalyst and Isoxazole Cocatalysts

The gold-catalyzed one-pot synthesis of 3H-benzo[e]isoindoles (3) from a mixture of isoxazole (2) and diynamides (1) is described. This tandem catalysis involves two separate steps: (i) initial synthesis of 2-(3-pyrrolyl)-1-alkynylbenzenes and (ii) a novel alkyne/pyrrole coupling reaction through pyrrole dearomatization. Our control experiments reveal the cooperative action of the gold catalyst and isoxazole cocatalyst to enable the novel alkyne/pyrrole coupling leading to a 1,2-acyl shift.

Ag-Catalyzed Multicomponent Synthesis of Heterocyclic Compounds: A Review

The investigation of the procedures for the multi-component synthesis of heterocycles has attracted the interest of organic and medicinal chemists. The use of heterogeneous catalysts, especially transition metal catalysts in organic synthesis, can provide a new, improved alternative to traditional methods in modern synthetic chemistry. The main focus is on the utilization of silver as a catalyst for the multi-component synthesis of heterocyclic compounds. The present review describes some important reported studies for the period of 2010 to 2020. Conclusion: The present review addresses some of the important reported studies on multi-component synthesis of heterocycles in the period of 2010-2020. These approaches were performed under classical and nonclassical conditions, using Ag salts, Ag NPs, Ag on the support, Ag as co-catalysts with other transition metals, ionic liquids, acidic or basic materials. Most of the reported reactions were performed under solvent-free conditions or in green solvents and the utilized catalysts were mostly recyclable. The main aim of the present review is to provide the organic chemists with the most appropriate procedures in the multi-component synthesis of desired heterocycles using silver catalysts.

Gold-Catalyzed Spirocyclization of Furan-ynones and Unexpected Skeleton Rearrangement of the Resulting Spirohydrofurans

A gold-catalyzed cyclization of aniline-tethered furan-ynones has been developed. The reaction proceeds via trapping of the resulting stabilized cationic intermediate with an amide group leading to polycycles featured with a spiro-cyclohexadienone-hydrofuran framework with high efficiency. The resulting N-alkyl products undergo photorearrangements to afford the ring-enlarged benzo[b]azepine derivatives or iron-promoted novel rearrangement to diketone-containing spirocycles involving multiple C-X bond cleavages and formations.

Divergent gold-catalysed reactions of cyclopropenylmethyl sulfonamides with tethered heteroaromatics

Cyclopropenylmethyl sulfonamides with tethered heteroaromatics have been demonstrated to undergo divergent gold-catalysed cyclisation reactions. A formal dearomative (4+3) cycloaddition takes place with furan-tethered substrates, yielding densely functionalised 5,7-fused heterocycles related to the bioactive curcusone natural products. Indole-tethered substrates display divergent reactivity giving biologically important tetrahydro-β-carbolines via a Friedel-Crafts mechanism.

Total Synthesis of Endolides A and B

The total synthesis of endolides A and B has been achieved in a concise, highly stereoselective fashion (12 steps, 16.2% and 16.0% overall yields, respectively). Key features of the route include a modified Negishi coupling between 3-bromofuran and an organozinc reagent derived from an iodoalanine derivative for the synthesis of 3-(3-furyl)-alanine derivative, and a judicious choice of reaction conditions to surmount the conformational constraints placed by converting a linear peptide into the corresponding macrocycle.

Selective hydrogenation of unsaturated aldehydes over Pt nanoparticles promoted by the cooperation of steric and electronic effects

The selective hydrogenation of α,β-unsaturated aldehydes to unsaturated alcohols can reach high selectivity and activity at room temperature using Pt nanoparticles immobilized on a non-porous Al₂O₃ support stabilized by aspartic acid.

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.

Diastereodivergent organocatalysis for the asymmetric synthesis of chiral annulated furans

Disclosed herein is a stereoselective method for the synthesis of 2,3-furan fused carbocycles bearing adjacent quaternary and tertiary carbon stereocenters. The chemistry is based on an asymmetric addition of β-ketoesters to 2-(1-alkynyl)-2-alkene-1-ones catalysed by natural cinchona alkaloids followed by a silver-catalysed intramolecular cycloisomerisation. By exploiting the distinct catalysis modes of quinine, which can act either as a general base or, upon opportune modifications, as a phase transfer catalyst, a complete switch of the enforced sense of diastereoinduction is achieved. The stereodivergent systems enable access to the full matrix of all possible stereoisomeric products.

A gold-catalyzed 1,2-acyloxy migration/intramolecular cyclopropanation/ring enlargement cascade: syntheses of medium-sized heterocycles

A gold catalyzed 1,2-acyloxy migration/intramolecular cyclopropanation/ring enlargement cascade of furan substrates provides a new highly efficient procedure for the formation of ten and eleven-membered ring compounds. A new transformation type of intermolecular furan compound catalyzed by a gold catalyst was reported.

Intriguing mechanistic labyrinths in gold(I) catalysis

Many mechanistically intriguing reactions have been developed in the last decade using gold(I) as catalyst. Here we review the main mechanistic proposals in gold-catalysed activation of alkynes and allenes, in which this metal plays a central role by stabilising a variety of complex cationic intermediates.

Gold Catalysis: Biarylphosphine Ligands as Key for the Synthesis of Dihydroisocoumarins

A gold-catalyzed phenol synthesis was successfully used in the synthesis of dihydroisocoumarins for the first time. A large number of gold(i) complexes were prepared and tested; only complexes based on the biarylphosphine motif were successful.

Intermolecular reactions of gold(i)-carbenes with furans by related mechanisms

The intermolecular gold(i)-catalyzed reactions of propargyl carboxylates, 1,6-enynes, or 7-substituted 1,3,5-cycloheptatrienes with furans afford cyclopentenones, polyenes or polycyclic compounds by related mechanisms initiated by the electrophilic addition of gold(i) carbenes to furans followed by ring-opening.