Palladium-catalyzed Hiyama cross-coupling reactions of aryl mesylates

Palladium-Catalyzed Hiyama-Type Coupling of Thianthrenium and Phenoxathiinium Salts

Here, we demonstrate palladium-catalyzed Hiyama-type cross-coupling reactions of aryl thianthrenium or phenoxathiinium salts. By employing stable and inexpensive organosilanes, the arylation, alkenylation, and alkynylation were realized in high efficiency using commercially available Pd(tBu3P)2 as the catalyst, thus providing a reliable method for preparation of biaryls, styrenes, and aryl acetylenes with a broad functional group tolerance under mild conditions. Given the accessibility of aryl thianthrenium or phenoxathiinium salts from simple arenes in a remarkable regioselective fashion, this protocol also provides an attractive approach for the late-stage modification of complex bioactive scaffolds.

Transition Metal Catalyzed Hiyama Cross-Coupling: Recent Methodology Developments and Synthetic Applications

Hiyama cross-coupling is a versatile reaction in synthetic organic chemistry for the construction of carbon-carbon bonds. It involves the coupling of organosilicons with organic halides using transition metal catalysts in good yields and high enantioselectivities. In recent years, hectic progress has been made by researchers toward the synthesis of diversified natural products and pharmaceutical drugs using the Hiyama coupling reaction. This review emphasizes the recent synthetic developments and applications of Hiyama cross-coupling.

trans-Dichlorobis(XPhos)palladium(II) Precatalyst for Suzuki-Miyaura Cross-Coupling Reactions of Aryl/Vinyl Sulfonates/Halides: Scope, Mechanistic Study, and Synthetic Applications

Suzuki-Miyaura cross-coupling reactions of aryl/vinyl sulfonates/halides with various boron species were performed using an easily available trans-dichlorobis(XPhos)palladium(II) precatalyst. Under microwave assistance, more than 30 coupling products were obtained with yields ranging from 23 to 99%, including the synthesis of two bioactive compounds, dubamine and tamoxifen. A mechanistic investigation of the Suzuki-Miyaura reaction was conducted notably by nuclear magnetic resonance (NMR) and high-resolution mass spectroscopy, revealing the nature of the active Pd⁰ species and of the reducing entity.

Photogenerated aryl mesylate and aryl diethyl phosphate radical cations: a time-resolved spectroscopy investigation

The photoinduced electron transfer reaction of selected aryl sulfonates and phosphates with K2S2O8 in a MeCN water (9 : 1) mixture has been investigated by LFP experiments.

Cross-coupling reactions towards the synthesis of natural products

Cross-coupling reactions are powerful synthetic tools for the formation of remarkable building blocks of many naturally occurring molecules, polymers and biologically active compounds. These reactions have brought potent transformations in chemical and pharmaceutical disciplines. In this review, we have focused on the use of cross-coupling reactions such as Suzuki, Negishi, Heck, Sonogashira and Stille in the total synthesis of some natural products of recent years (2016-2020). A short introduction of mentioned cross-coupling reactions along with highlighted aspects of natural products has been stated in separate sections. Additionally, few examples of natural products via incorporation of more than one type of cross-coupling reaction have also been added to demonstrate the importance of these reactions in organic synthesis.

Palladium-Catalyzed Cross-Couplings by C-O Bond Activation

Although palladium-catalyzed cross-coupling of aryl halides and reactive pseudohalides has revolutionized the way organic molecules are constructed today across various fields of chemistry, comparatively less progress has been made in the palladium-catalyzed cross-coupling of less reactive C-O electrophiles. This is despite the fact that the use of phenols and phenol derivatives as bench-stable cross-coupling partners has been well-recognized to bring about major advantages over aryl halides, such as (1) natural abundance of phenols, (2) avoidance of toxic halides, (3) orthogonal cross-coupling conditions, (4) prefunctionalization of phenolic substrates by electrophilic substitution or C-H functionalization, (5) ready availability of phenols from a different pool of precursors than aryl halides. In this review, we present an overview of recent advances made in the field of palladium-catalyzed cross-coupling of C-O electrophiles with a focus on (1) catalytic systems, (2) reaction type, and (3) class of C-O coupling partners. Although the field has been historically dominated by nickel catalysis, it is now evident that the use of more versatile, more functional group tolerant and highly active palladium catalysts supported by appropriately designed ancillary ligands enables the cross-coupling with improved substrate scope and generality, and likely represents a practical solution to the broadly applicable cross-coupling of various C-O bonds across diverse chemical disciplines. The review covers the period through June 2020.

Formation of XPhos-Ligated Palladium(0) Complexes and Reactivity in Oxidative Additions

Understanding the nature of the intermediate species operating within a palladium catalytic cycle is crucial for developing efficient cross-coupling reactions. Even though the XPhos/Pd(OAc)₂ catalytic system has found numerous applications, the nature of the active catalytic species remains elusive. A Pd⁰ complex ligated to XPhos has been detected and characterized in situ for the first time using cyclic voltammetry and NMR techniques. In the presence of XPhos, Pd(OAc)₂ initially associates with the ligand to form a complex in solution, which has been characterized as Pd^II (OAc)₂ (XPhos). This Pd^II center is then reduced to the Pd⁰ (XPhos)₂ species by an intramolecular process. This study also sheds light on the formation of Pd^I -Pd^I dimers. Finally, a kinetic study probes a dissociative mechanism for the oxidative addition with aryl halides involving Pd⁰ (XPhos) as the reactive species in equilibrium with the unreactive Pd⁰ (XPhos)₂ . Remarkably, the reportedly poorly reactive PhCl reacts at room temperature in the oxidative addition, which confirms the crucial role of the XPhos ligand in the activation of aryl chlorides.

Design, Synthesis, and Application of Polymer-Supported Silicon-Transfer Agents for Cross-Coupling Reactions with Organolithium Reagents

The initial design, synthesis, and validation of polymer-supported siloxane transfer agents have been achieved that permit the direct use of organolithium reagents in the palladium-catalyzed cross-coupling reactions. Through rational design, two generations of polymer support were developed that significantly simplify product purification and the transfer agent recycling.

Palladium-Catalyzed Suzuki-Miyaura Cross-Coupling of N-Mesylamides by N-C Cleavage: Electronic Effect of the Mesyl Group

A general Pd-catalyzed Suzuki-Miyaura cross-coupling of N-mesylamides with arylboronic acids by selective N-C cleavage has been developed. The presented results represent the first example of a transition-metal-catalyzed cross-coupling of amides activated by an atom-economic, cheap, and benign mesyl group. The reaction delivers arylated products featuring a range of useful functional groups by chemoselective cleavage of the amide N-C bond with high efficiency. Both the scope and the origin of high selectivity are discussed. A beneficial effect of the N-mesyl substituent on the bond activation in acyclic amides is presented.

Rhodium(iii)-catalyzed directed C–H benzylation and allylation of indoles with organosilicon reagents

Rhodium(iii)-catalyzed C2-benzylation and allylation of indoles with organosilicon reagents via chelation-assisted C–H activation has been developed.

A palladium-catalyzed coupling reaction of aryl nonaflates, sulfur dioxide, and hydrazines

A facile route to synthesise N-aminosulfonamides through a palladium-catalyzed coupling reaction of aryl nonaflates, sulfur dioxide, and hydrazines is reported. This transformation proceeds in the presence of Pd(OAc)₂/XantPhos, and TBAB in 1,4-dioxane at 80 °C, leading to the corresponding N-aminosulfonamides in moderate to good yields.

Palladium-Catalyzed Desilylative Acyloxylation of Silicon-Carbon Bonds on (Trimethylsilyl)arenes: Synthesis of Phenol Derivatives from Trimethylsilylarenes

A strategy for desilylative acetoxylation of (trimethylsilyl)arenes has been developed in which (trimethylsilyl)arenes are converted into acetoxyarenes. The direct acetoxylation is performed in the presence of 5 mol % of Pd(OAc)2 and PhI(OCOCF3)2 (1.5 equiv) in AcOH at 80 °C for 17 h. The acetoxyarenes are obtained in good to high yields (67-98%). The synthetic utility is demonstrated with a one-pot transformation of (trimethylsilyl)arenes to phenols by successive acetoxylation and hydrolysis. Furthermore, desilylative acyloxylation of 2-(trimethylsilyl)naphthalene using several carboxylic acids has been conducted.

Pd(II)-catalyzed ortho arylation of 2-arylbenzothiazoles with aryl iodides via benzothiazole-directed C-H activation

A novel and efficient method for the arylation of 2-arylbenzothiazoles is described via C-H activation. The desired C(Ar)-C(Ar) bond formation proceeded efficiently with good functional-group tolerance and high regioselectivity. Proposed mechanism for the arylation of 2-arylbenzothiazole is depicted.

Palladium-catalysed cross-coupling of organosilicon reagents

The palladium catalysed cross-coupling of organosilicon reagents with organo halides and pseudo-halides has developed over the past 30 years into an efficient and attractive carbon-carbon bond forming strategy. Extensive research within this field to expand and diversify on the scope of the organosilicon coupling reaction will continue to promote its use in the synthesis of biologically and pharmaceutically important organic molecules. The recent advances made within this area are explored in this critical review (199 references).

Palladium-catalyzed Hiyama cross-coupling of aryltrifluorosilanes with aryl and heteroaryl chlorides

An efficient, palladium-catalyzed Hiyama cross-coupling reaction of aryltrifluorosilanes with aryl chlorides has been developed. A wide variety of functionalized biaryl derivatives were isolated in good to excellent yields. The scope of this reaction has also been extended to heteroaryl chlorides, affording the corresponding heterobiaryl compounds in high yields.

Palladium-catalyzed cross-coupling reactions of aryl mesylates

Palladium-catalyzed cross-coupling reactions are state-of-the art methods for synthesis of many important compounds. The development of the use of the phenol-derived sulfonated hydroxyl group in the coupling reactions is highly attractive as the hydroxyl group is commonly present in organic compounds and they are versatile alternatives to aryl halides in cross-coupling reactions. In this tutorial review, we summarize the current development of palladium-catalyzed cross-coupling reactions of aryl mesylates.

Cross-Coupling Reactions of Alkenylsilanols with Fluoroalkylsulfonates: Development and Optimization of a Mild and Stereospecific Coupling Process

The development of an effective protocol for the palladium-catalyzed cross-coupling of (E)- and (Z)-alkenylsilanols with aryl triflates is described. A critical component in the optimization of this method was balancing the stability and reactivity of the triflates in the presence of a nucleophilic promoter. This report highlights that the use of a slightly soluble Brønsted base promoter that allows for a low, steady-state concentration of alkenyl(dimethyl)silanolate in solution, thus facilitating cross-coupling in preference to S-O bond cleavage of the triflate.

A general palladium catalyst system for Suzuki-Miyaura coupling of potassium aryltrifluoroborates and aryl mesylates

The first general examples of palladium-catalyzed Suzuki-type cross-coupling of aryl and heteroaryl mesylates with potassium aryl and heteroaryltrifluoroborates are presented. In addition to biaryl couplings, the cross-coupling reactions of aryl mesylates with alkyl and vinyltrifluoroborate salts have also been successfully accomplished.