Recyclable gold(I)-catalyzed heterocyclization of ynamides with benzyl or indolyl azides towards 2-aminoindoles or 3-amino-β-carbolines

A highly efficient heterogeneous gold(I)-catalyzed heterocyclization of ynamides with benzyl or indolyl azides has been achieved in 1,2-dichloroethane under mild conditions via a heterogenized α-imino gold carbene intermediate using 5 mol% of SBA-15-anchored strongly hindered NHC-gold(I) complex [IPr-SBA-15-AuNTf2] as the catalyst, delivering a wide range of valuable 2-aminoindoles or 3-amino-β-carbolines in mostly good to excellent yields with high regioselectivity. Furthermore, the new heterogenized NHC-gold(I) complex displays the same catalytic activity as IPrAuNTf2 and is facile to recover by centrifugation of the reaction mixture and can be reused at least seven times without any appreciable drop in its catalytic activity.

An MCM-41-immobilized dichloro(pyridine-2-carboxylato)gold(III) complex: an efficient and recyclable catalyst for the annulation of anthranils and ynamides

A new mesoporous MCM-41-immobilized dichloro(pyridine-2-carboxylato)gold(III) complex [MCM-41-PicAuCl₂] was synthesized via an addition reaction of a dichloro(3-hydroxypyridine-2-carboxylato)gold(III) complex to triethoxy(3-isocyanatopropyl)silane, followed by immobilization on MCM-41 and was characterized by different physico-chemical techniques. In the presence of 5 mol% of MCM-41-PicAuCl₂, the annulation reaction between anthranils and ynamides proceeded smoothly under mild conditions to afford diverse 6- or 5-formylindoles with high atom economy and good to excellent yields. This new heterogenized gold(III) complex can be easily recovered through a simple filtration process and recycled more than seven times without any apparent loss of its catalytic efficiency.

Regio- and Diastereoselective Construction of Functionalized Benzo[b]oxepines and Benzo[b]azepines via Recyclable Gold(I)-Catalyzed Cyclizations

The heterogeneous gold-catalyzed cyclization of (o-alkynyl)phenoxy- or N-(o-alkynylphenyl)tolylsulfonamidoacrylates with alcohols has been developed by using an MCM-41-anchored diphenylphosphine-Au(I) complex [MCM-41-Ph₂P-AuNTf₂] as the catalyst under mild reaction conditions, yielding diverse functionalized benzo[b]oxepines or benzo[b]azepines with good to high yields and excellent diastereoselectivity. This heterogenized gold(I) catalyst exhibits a comparable activity to homogeneous Ph₃PAuNTf₂ and can be facilely recovered by a simple filtration of the reaction solution and reused more than seven times with almost a consistent catalytic efficiency.

Recyclable Gold Catalyst for the Stereoselective Thioallylation of Alkynes

The heterogeneous gold(I)-catalyzed stereoselective thioallylation of electron-deficient alkynes with allyl sulfides has been achieved by using an MCM-41-immobilized sterically demanding NHC-gold(I) complex [MCM-41-IPrAuNTf₂] as the catalyst under mild conditions, delivering a wide variety of stereodefined tri- and tetrasubstituted functionalized vinyl sulfides in good to excellent yields. The new heterogeneous MCM-41-IPrAuNTf₂ catalyst exhibits an activity comparable to a homogeneous IPrAuNTf₂ complex and can be recovered via a simple filtration process and reused for at least seven consecutive cycles without any apparent loss of its catalytic activity and selectivity.

Silica-Supported Phosphine-Gold Complexes as an Efficient Catalytic System for a Dearomative Spirocyclization

The combination of metal catalyst and inorganic silica frameworks provides a greener approach to recyclable catalysis. In this study, three phosphine-gold chloride complexes have been successfully covalently grafted onto chiral silica nanohelices. The resulting 3D ensembles showed chiroptical properties that allowed the monitoring of the supported ligands. The heterogeneous gold chloride catalysts in cooperation with silver triflate exhibited high reactivity in various reactions, especially in the spirocyclization of aryl alkynoate esters, for which a catalytic loading of 0.05 mol % could be employed. The heterogeneous catalysts could be easily recovered and recycled seven or eight times without any loss of efficiency. By adding more silver triflate, 25 cycles with full conversion were achieved owing to a complex catalytic system based on silica and metallic species.

Recyclable heterogeneous gold(I)-catalyzed oxidative ring expansion of alkynyl quinols: a practical access to tropone and its analogues

The heterogeneous gold(i)-catalyzed oxidative ring expansion of alkynyl quinols has been achieved by using a benzyldiphenylphosphine-modified MCM-41-immobilized gold(i) complex [MCM-41-BnPh2P-AuNTf2] as the catalyst and 8-methylquinoline N-oxide as the oxidant under mild reaction conditions, yielding a variety of functionalized tropone derivatives in good to excellent yields. Extension of this methodology allows for facile construction of other seven- or six-membered ring systems including dibenzotropones, dibenzooxepines, phenanthrenes, and quinolin-2(1H)-ones. This new heterogeneous gold(i) complex can be readily recovered through a simple filtration process and recycled at least eight times without any apparent decrease in catalytic efficiency.

Highly para-selective C‒H alkylation of unactivated arenes with α-aryl-α-diazoesters catalyzed by gold(I) immobilized on MCM-41

The heterogeneous gold(I)-catalyzed highly para-selective C(sp2)–H bond alkylation of benzene derivatives with α-aryl-α-diazoesters possessing electron-withdrawing substituents on the aryl rings are achieved. The reactions proceed under mild conditions in good to excellent yields by using an MCM-41-anchored diphenylphosphine gold(I) complex [MCM-41-PPh2-AuOTf] as a recyclable catalyst.

Polymer-supported triphenylphosphine: application in organic synthesis and organometallic reactions

This comprehensive review highlights the diverse chemistry and applications of polymer-supported triphenylphosphine (PS-TPP) in organic synthesis since its inception. Specifically, the review describes applications of the preceding reagent in functional group interconversions, heterocycle synthesis, metal complexes and their application in synthesis, and total synthesis of natural products. Many examples are provided from the literature to show the scope and selectivity (regio, stereo, and chemo) in these transformations.

Highly efficient mesoporous polymer supported phosphine-gold(i) complex catalysts for amination of allylic alcohols and intramolecular cyclization reactions

A series of novel heterogeneous gold(i) catalysts were synthesized by immobilizing gold(i) complexes on ordered mesoporous polymer FDU-15 and characterized by XRD, N₂ adsorption–desorption, FT-IR, TEM, EDS, etc. The catalytic activities of these catalysts were evaluated by the amination reactions of allylic alcohols. Among the catalysts investigated, FDU-(p-CF₃Ph)₂PAuCl (3d) was identified as the most efficient catalyst. Compared to the homogeneous catalyst, the enhanced catalytic activity of the heterogeneous gold(i) catalyst is closely related to the mesoporous structure of FDU-15. The catalytic system was suitable for a broad range of substrates and can be easily recovered and recycled at least twelve times without significant loss of catalytic activity. In addition, the catalytic performance of 3d was further examined for intramolecular cyclization for the synthesis of heterocyclic compounds.

Preparation of highly ordered mesoporous polymer supported gold(i) catalyst as efficient and recyclable catalysts for construction of carbon–hetero bond.

Anchoring Triazole-Gold(I) Complex into Porous Organic Polymer To Boost the Stability and Reactivity of Gold(I) Catalyst

Stability and reactivity have been recognized as some critical issues for gold(I) catalysts. Such issues can be well-circumvented by anchoring the gold(I) complex onto the backbones of porous organic polymer (POP) followed by coordination with a triazole ligand as illustrated in the present work via a series of gold(I)-catalyzed reactions. In this strategy, 1,2,3-triazole was used as the special "X-factor" to avoid the formation of solid AgCl involved in typical gold-activation processes. The catalyst could be readily recycled without loss of reactivity. Moreover, compared with the PPh₃-modified polystyrene beads, the POP support was advantageous by providing high surface area, hierarchical porosity, and better stabilization of cations. In some cases, significantly improved reactivity was observed, even more so than using the homogeneous system, which further highlighted the great potential of this heterogeneous gold catalyst.

Highly efficient heterogeneous aerobic oxidative C–C coupling from Csp3–H bonds by a magnetic nanoparticle-immobilized bipy–gold(iii) catalyst

The cross-dehydrogenative coupling of tertiary amines with nitroalkanes and ketones has been achieved using a recyclable magnetic nanoparticle-immobilized bipy–gold(iii) catalyst.

Magnetic nanoparticle-supported phosphine gold(i) complex: a highly efficient and recyclable catalyst for the direct reductive amination of aldehydes and ketones

The direct reductive amination of aldehydes and ketones has been achieved with excellent yields using recyclable magnetic nanoparticle-supported gold(i) catalyst.

Leveraging the micellar effect: gold-catalyzed dehydrative cyclizations in water at room temperature

The first examples of gold-catalyzed cyclizations of diols and triols to the corresponding hetero- or spirocycles in an aqueous medium are presented. These reactions take place within nanomicelles, where the hydrophobic effect is operating, thereby driving the dehydrations, notwithstanding the surrounding water. By the addition of simple salts such as sodium chloride, reaction times and catalyst loadings can be significantly decreased.