Hydrophenoxylation of alkynes by gold catalysts: a mini review

CONTEXT

The field of chemistry has significantly evolved, with catalysis playing a crucial role in transforming chemical processes. From Valerius' use of sulfuric acid in the sixteenth century to modern advancements, catalysis has driven innovations across various industries. The introduction of gold as a catalyst marked a pivotal shift, expanding its applications beyond ornamentation to homogeneous catalysis. Gold's unique properties, such as its electrophilic nature and flexibility, have enabled its use in synthesizing complex molecules, including those in nanomedicine and sustainable chemical processes. The development of gold-based complexes, particularly in hydroalkoxylation and hydroamination reactions, showcases their efficiency in forming carbon-oxygen bonds under mild conditions. Recent studies on dual gold catalysis and heterobimetallic complexes further highlight gold's versatility in achieving high turnover rates and selectivity. This evolution underscores the potential of gold catalysis in advancing environmentally sustainable methodologies and enhancing the scope of modern synthetic chemistry. The debate about the nature of monogold and dual-gold catalysis is open.

METHODS

DFT calculations have played a key role in promoting the activation of alkynes, in particular the hydrophenoxylation of alkynes by metal-based catalysts. They not only help identify the most efficient and selective catalysts but also aid in screening for those capable of performing a dual metal catalytic mechanism. The most commonly used functionals are BP86 and B3LYP, with the SVP and 6-31G(d) basis sets employed for geometry optimizations, and M06 with TZVP or 6-311G(d,p) basis sets used for single-point energy calculations in a solvent. Grimme dispersion correction has been explicitly added either in the solvent single point energy calculations or in the gas phase geometry optimizations or in both. To point out that M06 implicitly includes part of this dispersion scheme.

Leveraging Metal and Ligand Reactive Sites for One Pot Reactions: Ligand-Centered Borenium Ions for Tandem Catalysis with Palladium

Tandem catalysts that perform two different organic transformations in a single pot are highly desirable because they enable rapid and efficient assembly of simple organic building blocks into more complex molecules. Many examples of tandem catalysis rely on metal-catalyzed reactions involving one or more metal complexes. Remarkably, despite surging interest in the development of chemically reactive (i. e., non-innocent) ligands, there are few examples of metal complexes that leverage ligand-centered reactivity to perform catalytic reactions in tandem with separate catalytic reactions at the metal. Here we report how multifunctional Pd complexes with triaminoborane-derived diphosphorus ligands, called TBDPhos, appear to facilitate borenium-catalyzed cycloaddition reactions at the ligand, and Pd-catalyzed Stille and Suzuki cross-coupling reactions at the metal. Both transformations can be accessed in one pot to afford rare examples of tandem catalysis using separate metal and ligand catalysis sites in a single complex.

Room temperature HFIP/Ag-promoted palladium-catalyzed C-H functionalization of benzothiazole with iodoarenes

A versatile synthetic protocol involving the room temperature direct arylation of benzothiazole with a wide variety of iodoarenes under Ag-promoted Pd-catalyzed conditions in HFIP as the reaction solvent has been presented. A sequential HFIP-promoted selective iodination of arenes followed by Pd-catalyzed direct arylation of benzothiazole has also been disclosed. The utility of the developed protocol has been demonstrated by the synthesis of anti-tumor agents, PMX-610 and CJM-126 (precursor).

Asymmetric Synthesis of Multi-Substituted Tetrahydrofurans via Palladium/Rhodium Synergistic Catalyzed [3+2] Decarboxylative Cycloaddition of Vinylethylene Carbonates

Unlike the comprehensive development of tandem multi-metallic catalysis, bimetallic synergistic catalysis has been challenging to achieve high stereoselectivity with the generation of multi-stereogenic centers. Herein, an efficient synergistic catalysis for the diastereo- and enantioselective synthesis of multi-substituted tetrahydrofuran derivatives has been developed. Under mild reaction conditions, a series of target molecules with three consecutive stereocenters were synthesized by a palladium(0)/rhodium(III) bimetal-catalyzed asymmetric decarboxylative [3+2]-cycloaddition of vinylethylene carbonates with α,β-unsaturated carbonyl compounds. The corresponding adducts were obtained with moderate to high yields (67 %∼98 %) and excellent stereoselectivities (>20 : 1 d.r., up to 99 % ee).

A comprehensive review of caged phosphines: synthesis, catalytic applications, and future perspectives

Caged phosphines are versatile ligands due to their rigid backbones, exhibiting a range of catalytic activities, as depicted through the given pictorial representation.

1,3,5-Triaza-7-phosphaadamantane (PTA) Derived Caged Phosphines for Palladium-Catalyzed Selective Functionalization of Nucleosides and Heteroarenes

Phosphines have, in combination with transition metals, played a pivotal role in the rapid development of efficient catalytic processes. Caged phosphines constitute a class of three-dimensional scaffolds providing unique control over steric and electronic properties. The versatility of the caged phosphine ligands has been demonstrated elegantly by the groups of Verkade, Gonzalvi as well as Stradiotto. Our research group has also been working extensively for the past several years in the development of 1,3,5-triaza-7-phosphaadamantane-based caged ligands and in this personal note we have summarized these applications pertaining to the modification of biologically useful nucleosides and heteroarenes.

Tandem Homometallic or Multimetallic Catalysis for Assembly of Base-Modified Nucleosides

Tandem catalysis has been at the forefront of synthesis in the past decade due to the reduction in the number of steps and purification needed for the synthesis of commercially relevant molecules. With the right combination of catalyst systems, which could be homometallic or multimetallic, one can construct complex structural motifs in a one-pot procedure without the requirement for the isolation of the intermediates, reducing both reagent waste and time. Over the years, application of tandem catalysis has certainly extended towards arene and heteroarene motifs; nucleoside modification using such a strategy has been rare. In this regard, we would like to report herein the development of numerous homometallic and multimetallic tandem catalytic protocols for the modification of nucleosides, providing efficient access to a diverse range of molecules with promising fluorescent properties, as well as pharmaceutically relevant antiviral drugs such as FV-100. © 2020 Wiley Periodicals LLC. Basic Protocol 1: Double tandem one-pot Sonogashira/cyclization of 5-IdU for the synthesis of FV-100 and analogs Basic Protocol 2: Double tandem one-pot Heck/Suzuki-Miyaura of 5-IdU for the synthesis of fluorescent nucleoside analogs Basic Protocol 3: Double tandem one-pot Suzuki-Miyaura cross-coupling of 5-IdU for the synthesis of fluorescent nucleoside analogs Basic Protocol 4: Double tandem one-pot amination/amidation for the synthesis of Sangivamycin precursor Basic Protocol 5: Triple tandem one-pot chemoselective etherification/Sonogashira coupling/cyclization for synthesis of BCNA analogs Basic Protocol 6: Triple tandem one-pot sequential Heck/borylation/Suzuki-Miyaura reaction.

Recent advances in metal catalyzed or mediated cyclization/functionalization of alkynes to construct isoxazoles

This review summarized the recent developments in metal catalyzed or mediated cyclization/functionalization of alkynes to construct isoxazoles.

Palladium-catalyzed enantioselective [5 + 4] annulation of ortho-quinone methides and vinylethylene carbonates

Highly enantioselective [5 + 4] annulations of ortho-quinone methides with vinylethylene carbonates are enabled by asymmetric palladium catalysis for the synthesis of chiral nine-membered benzo-heterocycles.