Enantio‐ and Diastereoselective Suzuki–Miyaura Coupling with Racemic Bicycles

Herein, we describe a rhodium‐catalyzed enantio‐ and diastereoselective Suzuki–Miyaura cross‐coupling between racemic fused bicyclic allylic chlorides and boronic acids. The highly stereoselective transformation allows for the coupling of aryl, heteroaryl, and alkenyl boronic acids and gives access to functionalized bicyclic cyclopentenes, which can be converted into other five‐membered‐ring scaffolds with up to five contiguous stereocenters. Preliminary mechanistic studies suggest that these reactions occur with overall retention of the relative stereochemistry and are enantioconvergent for pseudo‐symmetric allylic chloride starting materials. In addition, a bicyclic allylic chloride starting material without pseudo‐symmetry undergoes a highly enantioselective regiodivergent reaction.     

Mechanism of Nickel‐Catalyzed Suzuki–Miyaura Coupling of Amides

The Ni‐catalyzed Suzuki–Miyaura coupling of N ‐tert‐butoxycarbonyl (N ‐Boc)‐protected amides provides a versatile strategy for the construction of C−C bonds. In this study, density functional theory (DFT) methods have been used to elucidate the mechanism of this reaction, with particular emphasis on the roles of N ‐Boc, K₃PO₄ and H₂O. Our results corroborated those of previous reports, indicating that the overall catalytic cycle consists of three steps, including oxidative addition, transmetalation, and reductive elimination. Three of the possible transmetalation mechanisms were examined to interpret the effects of K₃PO₄ and H₂O. According to the most feasible of these transmetalation mechanisms, K₃PO₄ (acting as a Lewis base) would initially interact with the Lewis acid PhBpin to give a K₃PO₄‐PhBpin complex, which would readily undergo a hydrogen transfer step with H₂O. The H transfer in the transmetalation step was determined to be the rate‐determining step. Notably, the theoretical results showed good agreement with the experimental data.     

Transmetalation in the Suzuki–Miyaura Coupling: The Fork in the Trail

The Suzuki–Miyaura coupling is one of the few transition‐metal‐catalyzed C? C bond‐forming reactions that have been used in applications ranging from discovery chemistry to manufacturing processes. Although coupling proceeds through the generic three‐stage ‘oxidative addition, transmetalation, reductive elimination’ sequence, there are a number of features that differentiate the Suzuki–Miyaura process from other transition‐metal‐catalyzed cross‐couplings. Most of these features are centered around, or are a consequence of, activation of the boron reagent for transmetalation through one or both of two distinct pathways. This review focuses on the evidence that has been presented for this ‘fork in the trail′, and the potential to apply such mechanistic insight to the design of reaction conditions.     

Heck and Suzuki–Miyaura couplings catalyzed by nanosized palladium in polyaniline

A novel route to prepare polyaniline (PANI)‐supported Pd(0) nanoparticles by a one‐pot chemical route is presented. Nanosized Pd(0) particles were first prepared by reduction of Pd(OAc)₂ using t‐BuONa activated sodium hydride in refluxing THF. A ligand exchange with aniline on t‐BuONa‐stabilized Pd(0) particles yielded aniline‐stabilized particles. Pd(0)/PANI nanocomposites were finally obtained by polymerizing aniline‐stabilized Pd(0) particles using ammonium persulfate. Nanocomposites were characterized by transmission electron microscopy, X‐ray diffraction and X‐ray photoelectron spectroscopy. Results show that this one‐pot experimental route is successful in producing hybrid materials constituted of Pd(0) nanoparticles stabilized by PANI due to the strong binding of PANI amine groups to Pd(0) particles. TEM images of the nanohybrids show that metal particles with diameters of ca. 4.9 nm are homogeneously dispersed in PANI. The preliminary results indicate that the Pd(0) particles supported on PANI behave as efficient heterogeneous catalysts in the Heck and Suzuki–Miyaura reactions of aryl iodides. Copyright © 2005 John Wiley & Sons, Ltd.     

Enabling Suzuki–Miyaura coupling of Lewis-basic arylboronic esters with a nonprecious metal catalyst

The high cost and negative environmental impact of precious metal catalysts has led to increased demand for nonprecious alternatives for widely practiced reactions such as the Suzuki–Miyaura coupling (SMC). Ni-catalyzed versions of this reaction have failed to achieve high reactivity with Lewis-basic arylboron nucleophiles, especially pinacolboron esters. We describe the development of (PPh₂Me)₂NiCl₂ as an inexpensive and air-stable precatalyst that addresses this challenge. Under activation by n-BuMgCl, this complex can catalyze the coupling of synthetically important heteroaryl pinacolborons with heteroaryl halides. Mildly basic conditions (aqueous K₃PO₄) allow the reaction to tolerate sensitive functional groups that were incompatible with other Ni-SMC methods. Experimental and computational studies suggest that catalyst inhibition by substitution of PPh₂Me from Ni(ii) intermediates by Lewis basic reactants and products is disfavored relative to more commonly employed ligands in the Ni-SMC, which allows it to operate efficiently in the presence of Lewis bases such as unhindered pyridines.

A simple inexpensive ligand enables the Ni-catalyzed Suzuki–Miyaura coupling of heterocyclic and Lewis-basic arylboronic esters under mild conditions.     

Microwave- and ultrasound-assisted Suzuki–Miyaura cross-coupling reactions catalyzed by Pd/PVP

Suzuki–Miyaura reactions using Pd/PVP as a catalyst source were carried out in water–ethanol solution. Under MW, sonication or thermal condition yields were very similar, from moderate to very good, in a variety of examples. However, TOFs were very different, 750/h under MW, 250/h under sonication, and 28/h under thermal conditions. Studies carried out under sonication showed that the whole system after product extraction can be re-used at least twice without any noticeable loss of yield.     

Oxygen‐Promoted Suzuki–Miyaura Reaction for Efficient Construction of Biaryls

As one of the most powerful and versatile methods for the construction of carbon–carbon bonds, the Suzuki–Miyaura cross‐coupling reaction has attracted great attention over the past three decades. In recent years, a huge amount of interest has been focused on the development of ligand‐free Suzuki–Miyaura reaction systems, which have the advantages of low cost, mild reaction conditions, and easy operation. So far, a number of ligand‐free Suzuki–Miyaura reaction systems have been developed by using simple palladium salts, nanopalladium, or supported palladium catalysts. In this account, we will review our recent research on the oxygen‐promoted ligand‐free Suzuki–Miyaura reaction. Interestingly, the oxygen‐promoting effect has been observed in different reaction media, including polyethylene glycol, organic/water mixed solvents and pure water. The oxygen‐promoted reaction systems demonstrate high efficiency for the construction of biaryls.

     

Facile Synthesis of Phenanthridinone Alkaloids via Suzuki–Miyaura Cross‐coupling

Phenanthridinone alkaloids crinasiadine 1 and N‐alkylcrinasiadines 6 , 7 , 8 , 9 , 10 have been synthesized based on palladium‐catalyzed tandem C–C and C–N bond formation starting from 2‐aminophenylboronic acid and 2‐bromobenzoate in short steps. Related alkaloids, 5,6‐dihydrobicolorine 2 , trisphaeridine 3 , and bicolorine 12 have also been synthesized.     

A novel P,O-type phosphorinane ligand for the Suzuki–Miyaura cross-coupling of aryl chlorides

The Pd-mediated Suzuki–Miyaura cross-coupling of substituted and unsubstituted aryl chlorides with phosphorinane ligands was investigated uncovering an interesting ligand effect. The scope of the most effective 4-hydroxyl-substituted phosphorinane ligand in Suzuki cross-coupling with challenging aryl chlorides is described.     

N‐heterocyclic carbene–palladium complexes for Suzuki–Miyaura coupling reaction with benzyl chloride and aromatic boronic acid leading to diarylmethanes

A family of N‐heterocyclic carbene–palladium(II)–N,N‐dimethylbenzylamine complexes ((NHC)LPdCl₂; L = N,N‐dimethylbenzylamine) were synthesized as well as characterized using single‐crystal X‐ray diffraction and spectroscopic data. These complexes exhibited higher catalytic activities for the Suzuki reaction of benzyl chlorides to afford diarylmethanes under milder conditions than other efficient (NHC)LPdCl₂ complexes. Using the optimum conditions, the expected coupling products were obtained in moderate to high yields. All reactions were carried out in air and all starting materials were used as supplied without purification.     

Suzuki–Miyaura Coupling of (Hetero)Aryl Sulfones: Complementary Reactivity Enables Iterative Polyaryl Synthesis

Ideal organic syntheses involve the rapid construction of C?C bonds, with minimal use of functional group interconversions. The Suzuki–Miyaura cross‐coupling (SMC) is a powerful way to form biaryl linkages, but the relatively similar reactivity of electrophilic partners makes iterative syntheses involving more than two sequential coupling events difficult to achieve without additional manipulations. Here we introduce (hetero)aryl sulfones as electrophilic coupling partners for the SMC reaction, which display an intermediate reactivity between those of typical aryl (pseudo)halides and nitroarenes. The new complementary reactivity allows for rapid sequential cross‐coupling of arenes bearing chloride, sulfone and nitro leaving groups, affording non‐symmetric ter‐ and quateraryls in only 2 or 3 steps, respectively. The SMC reactivity of (hetero)aryl sulfones is demonstrated in over 30 examples. Mechanistic experiments and DFT calculations are consistent with oxidative addition into the sulfone C?S bond as the turnover‐limiting step. The further development of electrophilic cross‐coupling partners with complementary reactivity may open new possibilities for divergent iterative synthesis starting from small pools of polyfunctionalized arenes.     

Stereodivergent Synthesis of Arylcyclopropylamines by Sequential CH Borylation and Suzuki–Miyaura Coupling

A step‐economical and stereodivergent synthesis of privileged 2‐arylcyclopropylamines (ACPAs) through a C(sp³)? H borylation and Suzuki–Miyaura coupling sequence has been developed. The iridium‐catalyzed C? H borylation of N‐cyclopropylpivalamide proceeds with cis selectivity. The subsequent B‐cyclopropyl Suzuki–Miyaura coupling catalyzed by [PdCl₂(dppf)]/Ag₂O proceeds with retention of configuration at the carbon center bearing the Bpin group, while epimerization at the nitrogen‐bound carbon atoms of both the starting materials and products is observed under the reaction conditions. This epimerization is, however, suppressed in the presence of O₂. The present new ACPA synthesis results in not only a significant reduction in the steps required for making ACPA derivatives, but also the ability to access either isomer (cis or trans) by simply changing the atmosphere (N₂ or O₂) in the coupling stage.     

Efficient Synthesis of Symmetrically and Unsymmetrically Substituted Hexaphenylbenzene Analogues by Suzuki–Miyaura Coupling Reactions

A series of symmetrically and unsymmetrically substituted hexaphenylbenzene (HPB) analogues were efficiently synthesized by using a sterically hindered Suzuki–Miyaura cross‐coupling reaction of arylboronic acids with 1,4‐diiodo‐2,3,5,6‐tetraarylbenzenes under our optimized reaction conditions. The 1,4‐diiodo‐2,3,5,6‐tetraarylbenzenes can be readily prepared by using a one‐pot Hart reaction. Oxidative cyclodehydrogenation of the dibromo derivative with FeCl₃ gave the corresponding hexabenzocoronene (HBC) derivative in good yield.     

Highly efficient polymer‐stabilized palladium heterogeneous catalyst: Synthesis,characterization and application for Suzuki–Miyaura and Mizoroki–Heck coupling reactions

A suitable approach to stabilize palladium nanoparticles (Pd NPs), with an average diameter of 3–4 nm, on magnetic polymer is described. A new magnetic polymer containing 4′‐(4‐hydroxyphenyl)‐2,2′:6′,2″‐terpyridine (HPTPy) ligand was prepared by the polymerization of itaconic acid (ITC) as a monomer and trimethylolpropane triacrylate (TMPTA) as a cross‐linker and fully characterized. Pd NPs embedded on the magnetic polymer were successfully applied in Suzuki–Miyaura and Mizoroki–Heck coupling reactions under low palladium loading conditions, and provided the corresponding products with excellent yields (up to 98%) and high catalytic activities (TOF up to 257 hr^?1). Also, the catalyst can be easily separated and reused for at least consecutive five times with a small drop in catalytic activity.     

Organotrifluoroborates and Monocoordinated Palladium Complexes as Catalysts—A Perfect Combination for Suzuki–Miyaura Coupling

Monocoordinated palladium catalysts derived from sterically hindered, electron‐rich phosphines or N‐heterocyclic carbenes have revolutionized the Suzuki–Miyaura coupling reaction. The emergence of organotrifluoroborates has provided important new perspectives for the organoboron component of these reactions. In combination, these two components prove to be extraordinarily powerful partners for cross‐coupling reactions.     

The Origin of Shape Sensitivity in Palladium‐Catalyzed Suzuki–Miyaura Cross Coupling Reactions

The shape sensitivity of Pd catalysts in Suzuki–Miyaura coupling reactions is studied using nanocrystals enclosed by well‐defined surface facets. The catalytic performance of Pd nanocrystals with cubic, cuboctahedral and octahedral morphologies are compared. Superior catalytic reactivity is observed for Pd NCs with {100} surface facets compared to {111} facets. The origin of the enhanced reactivity associated with a cubic morphology is related to the leaching susceptibility of the nanocrystals. Molecular oxygen plays a key role in facilitating the leaching of Pd atoms from the surface of the nanocrystals. The interaction of O₂ with Pd is itself facet‐dependent, which in turn gives rise to more efficient leaching from {100} facets, compared to {111} facets under the reaction conditions.