Transition-metal-free Suzuki-type coupling reactions: scope and limitations of the methodology

The scope and limitations of the transition-metal-free Suzuki-type coupling of aryl halides and arylboronic acids to form biaryls are presented. Confirmation that the reaction is indeed metal-free is presented. The effects of changing base, solvent, reaction temperature, phase-transfer catalyst, and substrate are shown and the implications of these results discussed in terms of their impact on the synthetic versatility of the methodology. The main findings are that the reaction works well for aryl bromides, water is necessary as a solvent for the reaction, the optimum temperature for the reaction is 150 degrees C, the reaction is best performed by using microwave promotion with the exception of an electron-poor aryl bromide example where conventional heating may be used, only limited boronic acids can be used as coupling partners, sodium carbonate is the best base for the reaction, tetrabutylammonium bromide proves to be the best phase-transfer catalyst for the reaction, the reaction is limited to couplings between aryl halides and aryl boronic acids with sp(2)-sp(3) couplings proving ineffective, and NaBPh(4) can be used in the place of phenylboronic acid as a phenylating agent.     

Asymmetric Suzuki–Miyaura Cross‐Coupling for the Synthesis of Chiral Biaryl Compounds as Potential Monophosphine Ligands

Efficient asymmetric Suzuki–Miyaura coupling reactions have been employed for the first time to synthesize chiral biaryl compounds with phosphinate groups as chiral auxiliaries. A series of functionalized chiral biaryls are thereby synthesized in excellent yields and good diastereoselectivities (up to >95:5 d.r.) and axially chiral monophosphorus ligands are obtained through further functionalizations.     

Ligandless heterogeneous palladium: an efficient and recyclable catalyst for Suzuki‐type cross‐coupling reaction

A mild and efficient ligand‐free Suzuki‐type cross‐coupling reaction of benzoyl chlorides and arylboronic acids catalyzed by heterogeneous Pd/C was developed. Benzoyl chlorides undergo cross‐coupling with electronically diverse arylboronic acids to give biaryl ketones in excellent yield, under aqueous media and optimum temperature. The application of 3 mol% of 10 wt% Pd/C to the cross‐coupling delivers utmost efficiency, and could be reused up to many consecutive cycles without any loss in activity. This method proceeds under aqueous media and a recyclable catalytic system, offering an environmentally benign alternative to the existing protocols. Copyright © 2014 John Wiley & Sons, Ltd.     

A mild benzannulation through directed cycloaddition reactions

Simple as ABC: Alkynyl borane cycloadditions can be substrate-directed to assemble aromatic difluoroboranes within an extremely mild and efficient reaction manifold compared to that of traditional methods (see scheme). The aromatic boranes are readily transformed into a range of useful products.     

Novel substrates for palladium-catalyzed coupling reactions of arenes

Arenes and heteroarenes are ubiquitous substructures in biologically active agents and new materials. Thus, functionalization ("refinement") of simple arene precursors is still of major importance for preparative organic chemistry. During the last 20 years, especially transition-metal-catalyzed cross-coupling reactions of aryl halides and triflates have given arene chemistry new impetus. The first industrial applications were realized a few years ago. Quite recently, carbonic acid derivatives such as anhydrides and esters have added to the scope of substrates for these coupling reactions. Some recent developments in this area are presented in this Minireview.     

Microwave-promoted Palladium Catalyzed Suzuki Cross-coupling Reaction in Water

Suzuki coupling is probably the most versatile approach among the cross-coupling reactions and the reaction has long been the subject of intensive work in the area of transition-metal chemistry1. In recent years, various modifications involving the catalyst, solvents, bases, reaction conditions and synthetic technique have been developed 2. The Suzuki cross-coupling reaction in water is more safe, economical. It is an environmentally friendly alternative in organic synthesis. The use of w…     

Palladium-catalyzed cross-coupling reactions of silanolates: a paradigm shift in silicon-based cross-coupling reactions

This paper chronicles the conceptual development, proof of principle experiments, and recent advances in the palladium-catalyzed cross-coupling reactions of the conjugate bases of organosilanols. The discovery that led to the design and refinement of this process represents a classical illustration of how mechanistic studies can provide a fertile ground for the invention of new reactions. On the basis of a working hypothesis (which ultimately proved to be incorrect) and the desire to effect silicon-based cross-coupling without the agency of fluoride activation, a mild and practical palladium-catalyzed cross-coupling of alkenyl-, aryl-, and heteroaryl silanolates has been developed. The mechanistic underpinnings, methodological extensions, and the successful applications of this technology to the synthesis of complex molecules are described.     

N2,N2′‐disubstituted oxalic acid bishydrazides: novel ligands for copper‐catalyzed C?N coupling reactions in water

A series of N²,N²′‐disubstituted oxalic acid bishydrazides were synthesized. Some, for example, N²,N²′‐di‐1‐(4‐methoxyphenyl)‐ethanyloxylic‐(bishydrazide), are novel and effective ligands for copper‐catalyzed Ullmann‐type C N coupling reaction in water. A variety of amines could be effectively N‐arylated with aryl halides under both microwave irradiation and conventional heating (even at 30 °C) with good to excellent yields. Copyright © 2011 John Wiley & Sons, Ltd.     

Novel cyclodextrin‐modified h‐BN@Pd(II) nanomaterial: An efficient and recoverable catalyst for ligand‐free C‐C cross‐coupling reactions in water

An environmentally friendly palladium(II) catalyst supported on cyclodextrin‐modified h‐BN was successfully prepared. The catalyst was characterized by FT‐IR, SEM, TG, XRD and XPS, and the loading level of Pd in h‐BN@β‐CD@Pd(II) was measured to be 0.088 mmol g⁻¹ by ICP. It exhibits excellent catalytic activity for the Suzuki and Heck reactions in water, and can be easily separated and consecutively reused for at least nine times. In addition, a series of pharmacologically interesting products were successfully synthesized using this catalyst to demonstrate its potential applications in pharmaceutical industries. Above all, this work opens up an interesting and attractive avenue for the use of cyclodextrin‐functionalized h‐BN as an efficient support for hydrophilic heterogeneous catalysts.     

Suzuki cross‐coupling reactions of aryl chlorides using [Cl2Pd(COD)]/piperazine derivative under microwave conditions

A new strategy to significantly improve the efficiency of Suzuki reactions was achieved under microwave irradiation. [Cl₂Pd(COD)]/piperazine derivative 1 catalyzed aryl chlorides with phenylboronic acid in methanol (50%) affording excellent yields under aerobic conditions. Application of this strategy to the synthesis of liquid crystal material is also described. Copyright © 2011 John Wiley & Sons, Ltd.