A novel non-C2-symmetric bis-benzimidazolium salt derived from (±)-valinol has been prepared by a simple and straightforward process in good yield. The structure of bis-benzimidazolium salt provided a bulky steric group on the ethylene bridge; which facilitates the catalytic efficacy in the C(sp2)–C(sp2) formation. Its catalytic activity in Suzuki–Miyaura cross-coupling reaction of unactivated aryl chlorides has been found to have high efficacy in 1 mol% Pd loading. This protocol demonstrated the potential on the synthesis of sterically hindered biaryls. 相似文献
A nickel/dppf catalyst system was found to successfully achieve the Suzuki–Miyaura cross-coupling reactions of 3- and 4-chloropyridine and of 6-chloroquinoline but not of 2-chloropyridine or of other α-halo-N-heterocycles. Further investigations revealed that chloropyridines undergo rapid oxidative addition to [Ni(COD)(dppf)] but that α-halo-N-heterocycles lead to the formation of stable dimeric nickel species that are catalytically inactive in Suzuki–Miyaura cross-coupling reactions. However, the corresponding Kumada–Tamao–Corriu reactions all proceed readily, which is attributed to more rapid transmetalation of Grignard reagents.Nickel complexes with a dppf ligand can form inactive dinickel(ii) complexes during Suzuki–Miyaura cross-coupling reactions. However, these complexes can react with Grignard reagents in Kumada–Tamao–Corriu cross-coupling reactions.相似文献
A library of 32 members of 3,4-dihydro-3-oxo-2H-1,4-benzoxazines has been synthesized from two substituted 2-aminophenols via microwave-assisted one-pot regioselective annulation of 2-bromoalkanoates and subsequent Suzuki–Miyaura cross-coupling of the chloro-substituted scaffolds. The latter transformation was carried out using our Aphos–Pd(OAc)2 catalyst and the coupling of the aryl chlorides with arylboronic acids proceeded under mild reaction conditions at 60–80 °C in THF–H2O (10:1) in the presence of K3PO4·3H2O as the base to furnish the corresponding biaryl products in 80–98% yields. 相似文献
The excellent functional group tolerance of the Suzuki–Miyaura cross-coupling reactions has been decisive for their success in the pharmaceutical industry. Highly diversified (hetero)aromatic scaffolds can be effectively coupled in the final step(s) of a convergent synthetic route. In contrast, electrophilic Pd catalysts for non-directed C–H activation are particularly sensitive to inhibition by coordinating groups in pharmaceutical precursors. While C–H arylation enables the direct conversion of (hetero)aromatics without preinstalled functional or directing groups, its functional group tolerance should be increased to be viable in late-stage cross-couplings. In this work, we report on a dual ligand approach that combines a strongly coordinating phosphine ligand with a chelating 2-hydroxypyridine for the highly robust C–H coupling of bicyclic N-heteroaromatics with aryl bromide scaffolds. The catalyst speciation was studied via in situ XAS measurements, confirming the coordination of both ligands under the reaction conditions. The C–H activation catalyst was shown to be tolerant to a wide range of pharmaceutically relevant scaffolds, including examples of late-stage functionalization of known drug molecules.Ligand combination of a 2-pyridone with traditional phosphines enables superior functional group tolerance in the C–H (hetero)arylation of pharmaceutically relevant N-heterocyclic scaffolds.相似文献
Sulfuric chloride is used as the source of the –SO2– group in a palladium-catalyzed three-component synthesis of sulfonamides. Suzuki–Miyaura coupling between the in situ generated sulfamoyl chlorides and boronic acids gives rise to diverse sulfonamides in moderate to high yields with excellent reaction selectivity. Although this transformation is not workable for primary amines or anilines, the results show high functional group tolerance. With the solving of the desulfonylation problem and utilization of cheap and easily accessible sulfuric chloride as the source of sulfur dioxide, redox-neutral three-component synthesis of sulfonamides is first achieved.Sulfuric chloride is used as the source of the –SO2– group in a palladium-catalyzed three-component synthesis of sulfonamides.Since its development in the 1970s,1 Suzuki–Miyaura coupling has become a widely used synthetic step in diverse areas. With two of the most widely sourced materials, organoborons and alkyl/aryl halides, a number of C–C coupling reactions are established and the Suzuki–Miyaura reaction has successfully acted as the key step in the synthesis of medicines and agrochemicals.2In addition to the well-known aryl halides and esters, various other substrates such as acid chlorides,3 anhydrides,4 diazonium salts5 and sulfonyl chlorides6 were also reported for the coupling in the past decades. As far as acid chlorides are concerned, carbamoyl chlorides were successfully transformed to the corresponding benzamides in the early years of the 21st century.7 However, the use of sulfamoyl chlorides as coupling partners is challenging due to the strong electron-withdrawing properties of the sulfonyl group, which cause the tendency of desulfonylation to form tertiary amines.Synthesis of sulfonyl-containing compounds, especially sulfones and sulfonamides, via the insertion of sulfur dioxide has been extensively studied during the last decade.8 A series of sulfur-containing surrogates have been developed as the source of the –SO2– group. Willis and co-workers first reported the use of DABCO·(SO2)2, a bench-stable solid adduct of DABCO and gaseous SO2 discovered by Santos and Mello,9a as the source of sulfur dioxide in the synthesis of sulfonylhydrazines.9b Soon after, alkali metal metabisulfites were found to provide sulfur dioxide for the formation of sulfonyl compounds.10 In the recent developments in this field, DABCO·(SO2)2 and metabisulfites have become the most popular SO2 surrogates for the insertion of sulfur dioxide.8 However, the practical applications of sulfur dioxide insertion reactions are limited by atom-efficiency problems and the unique properties of reactants. For instance, the three-component synthesis of aryl sulfonylhydrazines using aryl halides, SO2 surrogates and hydrazines by a SO2-doped Buchward–Hartwig reaction was realized in the earliest developments in this field.10 However, similar transformations from aryl halides and amines to the corresponding sulfonamides still remain unresolved (Scheme 1a).11,12Open in a separate windowScheme 1Synthetic approaches to sulfonamides.In order to provide a simple and efficient method for the three-component synthesis of aryl sulfonamides without the pre-synthesis of sulfonyl chlorides, many scientists have made various attempts. Interestingly, the use of arylboronic acids instead of aryl halides provided an alternative route. An oxidative reaction between boronic acids, DABCO·(SO2)2 and amines for the preparation of aryl sulfonamides at high temperature was realized,12 while reductive couplings of boronic acids, SO2 surrogates and nitroarenes were also reported (Scheme 1b).13 However, due to the reversed electronic properties of boronic acids from halides, additional additives and restrictions had to be considered. Extra oxidants and harsh conditions were usually used, and some of the transformations required “oxidative” substrates, such as nitroarenes and chloroamines.14Early in 2020, a reductive hydrosulfonamination of alkenes by sulfamoyl chlorides was reported,15 which gave us the inspiration to use in situ generated sulfamoyl chlorides as the electrophile for the synthesis of aryl sulfonamides by Suzuki–Miyaura coupling. In this way, sulfamoyl chlorides could be formed by nucleophilic substitution of an amine to sulfuric chloride, and the S(vi) central atom introduced into the reaction could reverse the electronic properties of the amine, which would eliminate the addition of oxidants (Scheme 1c). With the utilization of boronic acids as the coupling partner, a palladium-catalyzed Suzuki–Miyaura coupling could provide the sulfonamide products. Compared with traditional attempts, reversing the electronic properties of an amine from nucleophilic to electrophilic could reverse the whole reaction process, and two-step synthesis starting from the amine side could bypass the existing difficulty of S–N bond forming reductive elimination.12 Instead, a C–S bond formation could be the key for success (Scheme 2). In this proposed route, the presence of a base would be essential to remove the acid generated in situ during the reaction process. Additionally, we expected that the addition of a ligand would improve the oxidative addition of Pd(0) to sulfamoyl chloride, thus leading to the desired sulfonamide product.Open in a separate windowScheme 2Comparison between the traditional route and designed work.As designed based on our assumption, we used a commercialized sulfamoyl chloride intermediate A, which would be generated from morpholine 1a and SO2Cl2, to start our early investigations. The results showed that the direct Suzuki–Miyaura coupling of sulfamoyl chloride intermediate A and 2-naphthaleneboronic acid 2a mostly led to the generation of byproduct 3a′ with traditional phosphine ligands added to the reaction, and the desired product 3a was obtained in poor yields (Table 1, entries 1 and 2). It is known that an electron-rich ligand would enhance the oxidative addition of Pd(0) to the electrophile, and the bulky factor would facilitate the reductive elimination process. As expected, the yield of product 3a was increased significantly when electron-rich and bulky tris-(2,6-dimethoxyphenyl)phosphine was used as the ligand (Table 1, entry 3). Moreover, the reaction could proceed more efficiently by using a mixture of THF and MeCN as the co-solvent (Table 1, entry 4).Early investigations using morpholine-4-sulfonyl chloride A as the starting material
Entry
Solvent
Ligand
Yielda (%)
1
1,4-Dioxane
PtBu3·HBF4
14
2
THF
PtBu3·HBF4
23
3
THF
PAr3·Ar = 2,6-di-OMe–C6H3
57
4
THF/MeCN
PAr3·Ar = 2,6-di-OMe–C6H3
72
Open in a separate windowa1H NMR yield obtained using 1,3,5-trimethoxybenzene as the internal standard.With that brief conclusion in hand, we then shifted our focus to the in situ generation of sulfamoyl chloride intermediate A in the reaction process, and a number of attempts were made with morpholine 1a and SO2Cl2 (for details, see the ESI†). After careful measurement of product 3a and desulfonylated byproduct 3a′ generated during the transformation, the selective formation of compound 3a was realized and “standard conditions” were identified. By using PdCl2(PhCN)2 as the catalyst and Na2HPO4 as the base, the desired product 3a was isolated in 71% yield, giving the least amount of desulfonylated product 3a′ (Table 2, entry 1). The control experiment showed that 3a or 3a′ was not detected in the absence of the palladium catalyst (Table 2, entry 2). It was also observed that compound 3a′ could not be generated when SO2Cl2 was omitted (Table 2, entry 3), indicating that the byproduct wasn''t produced by the direct coupling of boronic acid and amine. Other changes to the catalyst, ligand, base or solvent all resulted in lower yields of compound 3a or higher yields of desulfonylated product 3a′ (Table 2, entries 4–7).Effects of variation of reaction parametersa
Entry
Variation from “standard conditions”
Yield of 3a′b (%)
Yield of 3ab (%)
1
None
5
80 (69)
2
No PdCl2(PhCN)2
n.d.
n.d.
3
No SO2Cl2
n.d.
n.d.
4
Pd(OAc)2 instead of PdCl2(PhCN)2
13
80
5
PPh3 instead of PAr3
15
68
6
K2CO3 instead of Na2HPO4
43
23
7
MeCN instead of THF/MeCN
16
63
Open in a separate windowaStandard conditions: morpholine 1a (0.2 mmol, 1.0 equiv.), SO2Cl2 (0.5 mmol, 2.5 equiv.), Et3N (0.53 mmol, 2.65 equiv.), 2-naphthaleneboronic acid 2a (0.4 mmol, 2.0 equiv.), Na2HPO4 (0.6 mmol, 3.0 equiv.), PdCl2(PhCN)2 (10 mol%), tris-(2,6-dimethoxyphenyl)phosphine (20 mol%), THF (1.0 mL)/MeCN (1.5 mL), 70 °C, 16 h. See the ESI for the detailed procedure.b1H NMR yield obtained using 1,3,5-trimethoxybenzene as the internal standard. The isolated yield of entry 1 is shown in parentheses.With the “standard conditions” in hand, various secondary amines 1 and arylboronic acids 2 were subjected to the reaction for the exploration of substrate adaptability (Scheme 3). To our delight, most of the reactions proceeded smoothly, giving rise to the desired product 3 in moderate to high yields. Considering the scope of boronic acids, a number of para-, meta- and ortho-(3t) substituted boronic acids showed good reactivities. However, lower yields were observed for some substrates with electron-withdrawing substituents, providing more desulfonylated byproducts due to the electron-deficiency of the palladium intermediate. Aryl boronic acids with acid-sensitive Boc-substituted amine, oxidation-sensitive phenol, sulfide and vinyl substitution were all tolerated. It is noteworthy that bromo- and acetoxy-substrates could also be efficiently converted to the corresponding products 3f and 3r, showing quite high selectivity during the reaction process. A series of heteroaromatic products were afforded successfully as well, and compounds with indole, indazole, dibenzothiophene and pyridine were all compatible (3aa–3af).Open in a separate windowScheme 3Synthesis of sulfonamides via a palladium-catalyzed Suzuki–Miyaura coupling. Isolated yields.Subsequently, with respect to amines, 4-phenylboronic acid and 4-(methylthio)phenylboronic acid were selected as coupling partners based on their electronic properties and cost. Saturated cyclic products 3ah–3an were obtained in moderate yields, among which an α-amino acid derivative showed high reactivity, giving rise to product 3aj in 71% yield. Methylallylamine was transformed to the corresponding product 3ao smoothly, and thiomorpholine 1,1-dioxide was also tolerated under the conditions (3ap). Various sensitive groups including acetyl, Boc, Cbz and cyclopropylcarbonyl (3aq–3at) on amines remained intact during the transformation. However, the amine scope was limited, since the transformation failed to provide the corresponding products when primary amines or anilines were used as the substrates. We assumed that during the reaction process for the oxidative addition of the sulfamoyl chloride intermediate to the palladium catalyst, Pd–SO2–NHR would be formed when a primary amine was used. Thus, β-hydride elimination would occur instead of the desired process.Furthermore, the practicality of this method was also verified by gram-scale synthesis and late-stage functionalization (Scheme 4). The reaction worked smoothly on the 4.0 mmol scale, and reducing the loading amount of the palladium catalyst to 1 mol% showed no obvious impact on the transformation. With a boronic acid synthesized from estrone and desloratadine, an antihistamine drug used as the substrate, the target products 4a and 4b were achieved in moderate to good yields, showing potential possibilities for synthetic applications.Open in a separate windowScheme 4Gram-scale synthesis and late-stage functionalization.In conclusion, a redox-neutral three-component synthesis of sulfonamides is established through a palladium-catalyzed Suzuki–Miyaura coupling of sulfuric chloride, secondary amines and arylboronic acids. Sulfuric chloride is used as the source of sulfur dioxide, and the S(vi) linchpin makes the transformation possible without the assistance of oxidants. Although this transformation is not workable for primary amines or anilines, the results show high functional group tolerance and good selectivity. A clear reaction process is described, in which the in situ generated sulfamoyl chloride undergoes a palladium-catalyzed Suzuki–Miyaura reaction with boronic acids, giving rise to the corresponding sulfonamide products. Additionally, the desulfonylation problem is surmounted during the reaction process. With a boronic acid synthesized from estrone and an antihistamine drug, desloratadine, used as the substrate, the target products are achieved in moderate to good yields, showing potential possibilities for synthetic applications in organic chemistry and medicinal chemistry. 相似文献
Using biomass-derived solvents in various organic reactions is challenging for the fine chemicals industry. We herein report a Pd/C catalyzed Suzuki–Miyaura reaction in water extract of suaeda salsa (WES) without using external phosphine ligand, base, and organic solvent. The cross-coupling reactions were carried out in a basic WES medium with a broad substrate scope and wide functional group tolerance. Furthermore, the high purity of solid biaryl products can be obtained by column chromatography or filtration. 相似文献
Pd-catalyzed Suzuki–Miyaura cross-coupling is one of the most straightforward and versatile methods for the construction of functionalized arenes and heteroarenes but site-selective cross-coupling of polyhalogenated (hetero)arenes containing identical halogen substituents remains a challenging problem. Herein, we report a new candidate for heterocyclic Suzuki–Miyaura coupling reaction. This candidate has been applied in organometallic systems by combining classical aryl boronic acid reagents with non-classical heteroarenes. Experimental and computational studies of the mechanism of the reactions were performed, with an emphasis on the identity of the reactive species in the oxidative addition step and the nature of the precise site selectivity. The influence of both the aromaticity of the metalla-aromatic substrates and the steric and electronic properties of the halogenated sites are studied in detail.We describe unique polyhalogenated heteroarene candidates for site-selective cross-coupling, which shows high catalytic performances in the functionalization of polycyclic metalla-aromatics with excellent photophysical properties.相似文献
Forging carbon–carbon (C–C) linkage in DNA-encoded combinatorial library synthesis represents a fundamental task for drug discovery, especially with broad substrate scope and exquisite functional group tolerance. Here we reported the palladium-catalyzed Suzuki–Miyaura, Heck and Hiyama type cross-coupling via DNA-conjugated aryl diazonium intermediates for DNA-encoded chemical library (DEL) synthesis. Starting from commodity arylamines, this synthetic route facilely delivers vast chemical diversity at a mild temperature and pH, thus circumventing damage to fragile functional groups. Given its orthogonality with traditional aryl halide-based cross-coupling, the aryl diazonium-centered strategy expands the compatible synthesis of complex C–C bond-connected scaffolds. In addition, DNA-tethered pharmaceutical compounds (e.g., HDAC inhibitor) are constructed without decomposition of susceptible bioactive warheads (e.g., hydroxamic acid), emphasizing the superiority of the aryl diazonium-based approach. Together with the convenient transformation into an aryl azide photo-crosslinker, aryl diazonium''s DNA-compatible diversification synergistically demonstrated its competence to create medicinally relevant combinatorial libraries and investigate protein–ligand interactions in pharmaceutical research.Taking advantage of aryl diazonium intermediates, this work reported a DNA-compatible C–C bond formation strategy, achieving broad substrate scope, exquisite functional group tolerance, and orthogonality to aryl halide-based coupling reactions.相似文献
A ruthenium-catalyzed ortho C–H arylation process is described using visible light. Using the readily available catalyst [RuCl2(p-cymene)]2, visible light irradiation was found to enable arylation of 2-aryl-pyridines at room temperature for a range of aryl bromides and iodides.A ruthenium-catalyzed ortho C–H arylation process is described using visible light.相似文献
Pd(MeCN)2Cl2/PCy3 was found to be an efficient catalytic system for the Suzuki–Miyaura cross‐couplings of aryl chlorides with arylboronic acids under solvent‐free conditions. Furthermore, the presence of the conventional solvents had deleterious effect on the reaction. In the presence of Pd(MeCN)2Cl2, PCy3, and TBAF (tetra‐n‐butylammonium fluoride), a number of aryl chlorides including heteroaryl chlorides were coupled with arylboronic acids or heteroarylboronic acids smoothly to afford the corresponding products in moderate to excellent yields. 相似文献
A dinickel(0)–N2 complex, stabilized with a rigid acridane-based PNP pincer ligand, was studied for its ability to activate C(sp2)–H and C(sp2)–O bonds. Stabilized by a Ni–μ–N2–Na+ interaction, it activates C–H bonds of unfunctionalized arenes, affording nickel–aryl and nickel–hydride products. Concomitantly, two sodium cations get reduced to Na(0), which was identified and quantified by several methods. Our experimental results, including product analysis and kinetic measurements, strongly suggest that this C(sp2)–H activation does not follow the typical oxidative addition mechanism occurring at a low-valent single metal centre. Instead, via a bimolecular pathway, two powerfully reducing nickel ions cooperatively activate an arene C–H bond and concomitantly reduce two Lewis acidic alkali metals under ambient conditions. As a novel synthetic protocol, nickel(ii)–aryl species were directly synthesized from nickel(ii) precursors in benzene or toluene with excess Na under ambient conditions. Furthermore, when the dinickel(0)–N2 complex is accessed via reduction of the nickel(ii)–phenyl species, the resulting phenyl anion deprotonates a C–H bond of glyme or 15-crown-5 leading to C–O bond cleavage, which produces vinyl ether. The dinickel(0)–N2 species then cleaves the C(sp2)–O bond of vinyl ether to produce a nickel(ii)–vinyl complex. These results may provide a new strategy for the activation of C–H and C–O bonds mediated by a low valent nickel ion supported by a structurally rigidified ligand scaffold.A structurally rigidified nickel(0) complex was found to be capable of cleaving both C(sp2)–H and C(sp2)–O bonds.相似文献
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.相似文献
A general and highly efficient trifluoromethylated-N-heterocyclic carbene (NHC)-based catalyst for the palladium-catalyzed Suzuki–Miyaura reaction was reported. In the presence of the catalyst, reactions of non-activated aryl chlorides and triflates with aryl boronic acids occurred at room temperature with good to excellent yields (63–98%). In addition, catalysts generated from a combination of Pd(OAc)2/imidazolium salt 6a is not only effective for the coupling of heteroaryl boronic acid with aryl halides and heteroaryl halides, but also efficient for coupling of other heteroaryl halides and heteroaryl boronic acids. Finally, the catalyst is highly effective for Suzuki–Miyaura reaction of aryl bromides and chlorides with 0.01–0.1 mol % loading if the temperature was raised at refluxed THF/H2O. 相似文献
The cover picture shows the structure of a Pd(II)‐enaminone complex which is prepared from Pd(OAc)2 and NH2‐featured enaminone, as well as its application in catalyzing the Suzuki‐Miyaura cross coupling reaction. As unprecedented Pd(II)‐organic species, it has been broadly used to catalyze the Suzuki‐Miyaura reaction of aryl bromides/chlorides and exhibited evidently superior catalytic activity over those commercially available Pd‐catalysts. Alongside the efficient and broad catalysis in Suzuki‐Miyaura reaction in clean aqueous medium, simply modifying reaction conditions and the enaminone structure in the Pd(II)‐enaminone complex, the homo‐coupling of aryl boronic acids can also be efficiently executed. The results disclose the application promise of enaminones in new frontiers of organometallics and catalysis. More details are discussed in the article by Wan et al. on page on page 254—258.
We report here cobalt–N-heterocyclic carbene catalytic systems for the intramolecular decarbonylative coupling through the chelation-assisted C–C bond cleavage of acylindoles and diarylketones. The reaction tolerates a wide range of functional groups such as alkyl, aryl, and heteroaryl groups, giving the decarbonylative products in moderate to excellent yields. This transformation involves the cleavage of two C–C bonds and formation of a new C–C bond without the use of noble metals, thus reinforcing the potential application of decarbonylation as an effective tool for C–C bond formation.A method for cobalt–N-heterocyclic carbene catalytic systems for the intramolecular decarbonylative coupling of ketones was achieved.相似文献
There is a widespread perception that the high level of endo selectivity witnessed in many Diels–Alder reactions is an intrinsic feature of the transformation. In contrast to expectations based upon this existing belief, the first experimental Diels–Alder reactions of a novel, deuterium-labeled 1,3-butadiene with commonly used mono-substituted alkenic dienophiles (acrolein, methyl vinyl ketone, acrylic acid, methyl acrylate, acrylamide and acrylonitrile) reveal kinetic endo : exo ratios close to 1 : 1. Maleonitrile, butenolide, α-methylene γ-butyrolactone, and N-methylmaleimide behave differently, as does methyl vinyl ketone under Lewis acid catalysis. CBS-QB3 calculations incorporating solvent and temperature parameters give endo : exo product ratios that are in near quantitative agreement with these and earlier experimental findings. This work challenges the preconception of innate endo-selectivity by providing the first experimental evidence that the simplest Diels–Alder reactions are not endo-selective. Trends in behaviour are traced to steric and electronic effects in Diels–Alder transition structures, giving new insights into these fundamental processes.Cycloadditions of deuterium-labeled 1,3-butadiene with monosubstituted alkenic dienophiles challenge the widespread assumption of endo-selectivity in prototypical Diels–Alder reactions.相似文献
Treatment of the imines a–c with palladium(II) acetate in acetic acid yielded the μ-acetate dinuclear complexes 1a–c, which readily reacted with sodium chloride or bromide to provide μ-halide analogues. The reaction of the latter with nitrogen, phosphorus and oxygen donor nucleophiles yielded new imine palladacycles following the cleavage of the Pd2X2 unit. The complexes were fully characterized by microanalysis, 1H, 13C and 31P NMR spectroscopies, as appropriate. The compounds were applied as catalysts in the Suzuki–Miyaura coupling reaction in aqueous and semi-aqueous media. 相似文献
The first examples of a highly efficient and enantioselective carbene-mediated insertion reaction, from a sulfur ylide, are described. By way of a catalytic asymmetric insertion reaction into N–H bonds from carbonyl sulfoxonium ylides and anilines, using a copper-bifunctional squaramide cooperative catalysis approach, thirty-seven α-arylglycine esters were synthesized in enantiomeric ratios up to 92 : 8 (99 : 1 after a single recrystallization) and reaction yields ranging between 49–96%. Furthermore, the protocol benefits from quick reaction times and is conducted in a straightforward manner.The first examples of a highly efficient and enantioselective carbene-mediated insertion reaction, from a sulfur ylide, are described.相似文献