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Showing papers in "Journal of Organic Chemistry in 2002"


Journal ArticleDOI
TL;DR: A novel regiospecific copper(I)-catalyzed 1,3-dipolar cycloaddition of terminal alkynes to azides on solid-phase is reported, and the X-ray structure of 2-azido-2-methylpropanoic acid has been solved, to yield structural information on the 1, 3-dipoles entering the reaction.
Abstract: The cycloaddition of azides to alkynes is one of the most important synthetic routes to 1H-[1,2,3]-triazoles. Here a novel regiospecific copper(I)-catalyzed 1,3-dipolar cycloaddition of terminal alkynes to azides on solid-phase is reported. Primary, secondary, and tertiary alkyl azides, aryl azides, and an azido sugar were used successfully in the copper(I)-catalyzed cycloaddition producing diversely 1,4-substituted [1,2,3]-triazoles in peptide backbones or side chains. The reaction conditions were fully compatible with solid-phase peptide synthesis on polar supports. The copper(I) catalysis is mild and efficient (>95% conversion and purity in most cases) and furthermore, the X-ray structure of 2-azido-2-methylpropanoic acid has been solved, to yield structural information on the 1,3-dipoles entering the reaction. Novel Fmoc-protected amino azides derived from Fmoc-amino alcohols were prepared by the Mitsunobu reaction.

7,397 citations


Journal ArticleDOI
TL;DR: Pentaphenylferrocenyl di-tert-butylphosphine has been prepared in high yield from a two-step synthetic procedure, and the scope of various cross-coupling processes catalyzed by complexes bearing this ligand has been investigated.
Abstract: Pentaphenylferrocenyl di-tert-butylphosphine has been prepared in high yield from a two-step synthetic procedure, and the scope of various cross-coupling processes catalyzed by complexes bearing this ligand has been investigated. This ligand creates a remarkably general palladium catalyst for aryl halide amination and for Suzuki coupling. Turnovers of roughly 1000 were observed for aminations with unactivated aryl bromides or chlorides. In addition, complexes of this ligand catalyzed the formation of selected aryl ethers under mild conditions. The reactions encompassed electron-rich and electron-poor aryl bromides and chlorides. In the presence of catalysts containing this ligand, these aryl halides coupled with acyclic or cyclic secondary alkyl- and arylamines, with primary alkyl- and arylamines, and with aryl- and primary alkylboronic acids. These last couplings provide the first general procedure for reaction of terminal alkylboronic acids with aryl halides without toxic or expensive bases. The ligand ...

647 citations


Journal ArticleDOI
TL;DR: The various manifestations of aromaticity are related and aromaticity can be regarded statistically as a one-dimensional phenomenon, but when comparisons are restricted to some regions or groups of compounds, the quality of the correlations can deteriorate or even vanish.
Abstract: Statistical analyses of quantitative definitions of aromaticity, ASE (aromatic stabilization energies), RE (resonance energies), Λ (magnetic susceptibility exaltation), NICS, HOMA, I5, and AJ, evaluated for a set of 75 five-membered π-electron systems: aza and phospha derivatives of furan, thiophene, pyrrole, and phosphole (aromatic systems), and a set of 30 ring-monosubstituted compounds (aromatic, nonaromatic, and antiaromatic systems) revealed statistically significant correlations among the various aromaticity criteria, provided the whole set of compounds is involved. Hence, broadly considered, the various manifestations of aromaticity are related and aromaticity can be regarded statistically as a one-dimensional phenomenon. In contrast, when comparisons are restricted to some regions or groups of compounds, e.g., aromatic compounds with ASE > 5 kcal/mol or polyhetero-five-membered rings, the quality of the correlations can deteriorate or even vanish. In practical applications, energetic, geometric, ...

639 citations


Journal ArticleDOI
TL;DR: The reaction is inherently modular, allowing for substantial structural variations and for the incorporation of substituents at any site of the phenanthrene product except C-9, and is readily applied to the heterocyclic series as exemplified by the preparation of benzoindoles, naphthothiophenes as well as bridgehead nitrogen heterocycles.
Abstract: Readily available biphenyl derivatives containing an alkyne unit at one of their ortho positions are converted into substituted phenanthrenes upon exposure to catalytic amounts of either PtCl2, AuCl3, GaCl3, or InCl3 in toluene. This 6-endo-dig cyclization likely proceeds through initial π-coordination of the alkyne unit followed by interception of the resulting η2-metal complex by the adjacent arene ring. The reaction is inherently modular, allowing for substantial structural variations and for the incorporation of substituents at any site of the phenanthrene product except C-9. Moreover, the reaction is readily applied to the heterocyclic series as exemplified by the preparation of benzoindoles, naphthothiophenes as well as bridgehead nitrogen heterocycles.

310 citations


Journal ArticleDOI
TL;DR: Most alcohols are oxidized to ketones in high yield and selectivity within 1-2 h, and the catalytic system tolerates a wide range of O(2) concentrations without being deactivated.
Abstract: Efficient Ruthenium-Catalyzed Aerobic Oxidation of Alcohols Using a Biomimetic Coupled Catalytic System

259 citations


Journal ArticleDOI
TL;DR: It is shown that hexane and toluene together with solvents such as THF and dioxane can be heated way above their boiling point in sealed vessels using a small quantity of an ionic liquid, thereby allowing them to be used as media for microwave-assisted chemistry.
Abstract: The use of ionic liquids as aids for microwave heating of nonpolar solvents has been investigated. We show that hexane and toluene together with solvents such as THF and dioxane can be heated way above their boiling point in sealed vessels using a small quantity of an ionic liquid, thereby allowing them to be used as media for microwave-assisted chemistry. Using the appropriate ionic liquid, the heating can be performed with no contamination of the solvent. To show the applicability of the system, two test reactions have been successfully performed.

249 citations


Journal ArticleDOI
TL;DR: The carbonylation procedure reported herein, which relies on the in situ generation of carbon monoxide, serves as a convenient alternative to othercarbonylation methods and is particularly applicable to small-scale reactions where short reaction times are desired and the direct use of carbonmonoxide gas is impractical.
Abstract: Dimethylformamide (DMF) acts as an efficient source of carbon monoxide and dimethylamine in the palladium-catalyzed aminocarbonylation (Heck carbonylation) of p-tolyl bromide to provide the dimethylamide. Addition of amines to the reaction mixture in excess delivers the corresponding aryl amides in good yields. The amines employed, benzylamine, morpholine, and aniline, all constitute good reaction partners. The reaction proceeds smoothly with bromobenzene and more electron-rich aryl bromides, but electron-deficient aryl bromides fail to undergo aminocarbonylation. The reactions are conducted at 180-190 degrees C for 15-20 min with microwave heating in a reaction mixture containing imidazole and potassium tert-butoxide: the latter is required to promote decomposition of the DMF solvent at a suitable rate. The beneficial effects of controlled microwave irradiation as an energy source for the rapid heating of the carbonylation reaction mixture are demonstrated. The carbonylation procedure reported herein, which relies on the in situ generation of carbon monoxide, serves as a convenient alternative to other carbonylation methods and is particularly applicable to small-scale reactions where short reaction times are desired and the direct use of carbon monoxide gas is impractical.

240 citations


Journal ArticleDOI
TL;DR: 2,3-Disubstituted benzo[b]thiophenes have been prepared in excellent yields via coupling of terminal acetylenes with commercially available o-iodothioanisole in the presence of a palladium catalyst and subsequent electrophilic cyclization of the resulting o-(1-alkynyl)thioan isole derivatives.
Abstract: 2,3-Disubstituted benzo[b]thiophenes have been prepared in excellent yields via coupling of terminal acetylenes with commercially available o-iodothioanisole in the presence of a palladium catalyst and subsequent electrophilic cyclization of the resulting o-(1-alkynyl)thioanisole derivatives. I2, Br2, NBS, p-O2NC6H4SCl, and PhSeCl have been utilized as electrophiles. Aryl-, vinyl-, and alkyl-substituted terminal acetylenes undergo this coupling and cyclization to produce excellent yields of benzo[b]thiophenes. (Trimethylsilyl)acetylene also undergoes this coupling/cyclization process with I2, NBS, and the sulfur and selenium electrophiles to afford the corresponding 2-(trimethylsilyl)benzo[b]thiophenes. However, cyclization of the silyl-containing thioanisole using Br2 affords 2,3-dibromobenzo[b]thiophene.

237 citations


Journal ArticleDOI
TL;DR: The possibility to employ aryl-containing hydrosilanes in this reaction opens broad capabilities for the synthesis of alcohols via a trans- selective hydrosilylation/Tamao-Fleming oxidation sequence, complementary to the existing cis-selective hydroboration/oxidation protocol.
Abstract: A convenient and highly efficient method for the Lewis acid-catalyzed trans-selective hydrosilylation of alkenes has been developed. The mechanism of this novel protocol operates via direct additio...

235 citations


Journal ArticleDOI
TL;DR: 3-Pyridylboronic acid was prepared in high yield and bulk quantity from 3-bromopyridine via a protocol of lithium-halogen exchange and "in situ quench", and this technique was further studied and evaluated on other aryl halides in the preparation of aRYlboronic acids.
Abstract: 3-Pyridylboronic acid was prepared in high yield and bulk quantity from 3-bromopyridine via a protocol of lithium-halogen exchange and "in situ quench". This technique was further studied and evaluated on other aryl halides in the preparation of arylboronic acids.

228 citations


Journal ArticleDOI
TL;DR: With the optimized atom-efficient protocol, several polyfunctionalized alpha-silyloxy cyanohydrins were synthesized in good to excellent yields and a notable level of simple 1,3-diastereoselection was recorded in the case of 2-cyclohexen-1-one 2c.
Abstract: Low sensitivity toward traces of moisture and high tolerance of different functional groups make indium tribromide suitable for carrying out multistep synthetic sequences. In particular, we have realized a 1,4-conjugated addition of indoles/thiols to α,β-unsaturated ketones mediated by a catalytic amount (10 mol %) of InBr3 obtaining the desired β-substituted ketones in good yields. The Lewis acidity of indium salts was not affected by coordinating and acid nucleophiles; therefore, the subsequent catalytic 1,2-addition of Me3SiCN to carbonyl compounds can be performed in one pot. With the optimized atom-efficient protocol, several polyfunctionalized α-silyloxy cyanohydrins were synthesized in good to excellent yields (up to 97%) and a notable level of simple 1,3-diastereoselection (up to 84:16) was recorded in the case of 2-cyclohexen-1-one 2c.

Journal ArticleDOI
TL;DR: Pd/C was found to catalyze the Suzuki−Miyaura coupling reaction of halophenols in aqueous media, and the palladium catalyst was easily recovered and reused as mentioned in this paper.
Abstract: Pd/C was found to catalyze the Suzuki−Miyaura coupling reaction of halophenols in aqueous media. When halophenols were treated with ArB(OH)2 and a catalytic amount of 10% Pd/C (0.3 mol % Pd) in aqueous K2CO3 solution, the corresponding hydroxybiaryls were obtained in a high yield or quantitatively. The palladium catalyst was easily recovered and reused.

Journal ArticleDOI
TL;DR: The palladium-catalyzed, two-step, one-pot borylation/Suzuki coupling (BSC) reaction was developed to synthesize sterically hindered 2,2'-disubstituted biphenyl and phenyl-indole compounds in a short, simple, and efficient manner from two easily accessible aryl halides.
Abstract: The palladium-catalyzed, two-step, one-pot borylation/Suzuki coupling (BSC) reaction was developed to synthesize sterically hindered 2,2'-disubstituted biphenyl and phenyl-indole compounds in a short, simple, and efficient manner from two easily accessible aryl halides. High yields can be obtained by choosing properly both components according to their rough electronic properties. The illustration of the utility of this method was provided by the solution and solid-phase synthesis of seven- or eight-membered biphenyl lactams 5a-e, as well as paullone 3a. These compounds exhibit moderate albeit significant cytotoxicities and may serve as structural models for future medicinal chemistry developments.

Journal ArticleDOI
TL;DR: In this paper, a new catalytic enantioselective conjugate addition of nitroalkanes to acyclic α,β-unsaturated enones catalyzed by novel organic catalysts has been developed.
Abstract: A new catalytic enantioselective conjugate addition of nitroalkanes to acyclic α,β-unsaturated enones catalyzed by novel organic catalysts has been developed. A series of chiral amines has been tested as catalysts for the addition of 2-nitropropane to benzylideneacetone, and it is found that a novel imidazoline catalyst, prepared from phenylalanine, can catalyze a highly enantioselective 1,4-addition reaction. The reaction of various acyclic and cyclic nitroalkanes was found to proceed well with enantioselectivities up to 86% ee, and enantiopure products can be obtained by recrystallization. The potential of the reaction is documented by the reaction of a series of substituted α,β-unsaturated enones with different nitroalkanes. Furthermore, the synthetic applicability of the reaction is demonstrated by the formation of optically active functionalized pyrrolines and pyrrolidines by reductive amination of the products. On the basis of the absolute configuration of the conjugate addition products, the mechan...

Journal ArticleDOI
TL;DR: In this article, the tert-butylimines of o-(1-alkynyl)benzaldehydes and analogous pyridine carbaldehyde have been cyclized under very mild reaction conditions in the presence of I2, ICl, PhSeCl and p-O2NC6H4SCl to give the corresponding halogen-, selenium-, and sulfur-containing disubstituted isoquinolines and naphthyridines, respectively.
Abstract: The tert-butylimines of o-(1-alkynyl)benzaldehydes and analogous pyridinecarbaldehydes have been cyclized under very mild reaction conditions in the presence of I2, ICl, PhSeCl, PhSCl, and p-O2NC6H4SCl to give the corresponding halogen-, selenium-, and sulfur-containing disubstituted isoquinolines and naphthyridines, respectively. This methodology accommodates a variety of iminoalkynes and affords the anticipated heterocycles in moderate to excellent yields. Monosubstituted isoquinolines and naphthyridines have been synthesized by the metal-catalyzed ring closure of these same iminoalkynes. The silver-catalyzed ring closure is highly effective in cyclizing aryl-, alkenyl-, and alkyl-substituted iminoalkynes at 50 °C.

Journal ArticleDOI
TL;DR: A variety of ketoximes, easily prepared from the corresponding ketones, undergo the Beckmann rearrangement upon treatment with 2,4,6-trichloro[1,3,5]triazine in N,N-dimethylformamide at room temperature in excellent yields.
Abstract: A variety of ketoximes, easily prepared from the corresponding ketones, undergo the Beckmann rearrangement upon treatment with 2,4,6-trichloro[1,3,5]triazine in N,N-dimethylformamide at room temperature in excellent yields. This procedure can be applied to aldoximes for obtaining the corresponding nitriles.

Journal ArticleDOI
TL;DR: The catalytic enantioselective Henry reaction of α-keto esters with nitromethane has been developed in this article, where the reaction conditions have been optimized by the screening of different chiral Lewis acids, solvents, and bases, and it was found that the copper(II)−tert-butyl bisoxazoline complex in combination with triethylamine catalyzed a highly enanti-lective reaction giving optically active β-nitro-α-hydroxy esters in high yields and with excellent enantiomeric excess
Abstract: The catalytic enantioselective Henry reaction of α-keto esters with nitromethane has been developed. The reaction conditions have been optimized by the screening of different chiral Lewis acids, solvents, and bases, and it was found that the copper(II)−tert-butyl bisoxazoline complex in combination with triethylamine catalyzed a highly enantioselective reaction giving optically active β-nitro-α-hydroxy esters in high yields and with excellent enantiomeric excesses. The scope of the reaction is demonstrated by the reaction of a variety of different α-keto esters. The catalytic enantioselective Henry reaction of β,γ-unsaturated-α-keto esters proceeds as a 1,2-addition reaction exclusively, in contrast to the uncatalyzed reaction where both the 1,2- and 1,4-addition products are formed. It is demonstrated that the β-nitro-α-hydroxy esters can be converted into, e.g., Boc-protected β-amino-α-hydroxy esters in high yields and without loss of optical purity. The mechanism for the reaction is discussed, and it i...

Journal ArticleDOI
TL;DR: In this paper, two series of push-pull chromophores built around thiophene-based π-conjugating spacers rigidified either by covalent bonds or by noncovalent intramolecular interactions have been synthesized and characterized by UV−vis spectroscopy, electric field induced second harmonic generation (EFISH) and differential scanning calorimetry.
Abstract: Two series of push−pull chromophores built around thiophene-based π-conjugating spacers rigidified either by covalent bonds or by noncovalent intramolecular interactions have been synthesized and characterized by UV−vis spectroscopy, electric field induced second harmonic generation (EFISH) and differential scanning calorimetry. Comparison of the linear and second-order nonlinear optical properties of chromophores based on a covalently bridged dithienylethylene (DTE) spacer with those of their analogues based on open chain DTE shows that the rigidification of the spacer produces a considerable bathochromic shift of the absorption maximum together with a dramatic enhancement of the molecular quadratic hyperpolarizability (μβ) which reaches values among the highest reported so far. A second series of NLO-phores has been derived from a 2,2‘-bi(3,4-ethylenedioxythiophene) (BEDOT) π-conjugating spacer. As indicated by X-ray and UV−vis data, rigidification of the spacer originates in that case, from noncovalent...

Journal ArticleDOI
TL;DR: For the first time, the L-proline-catalyzed direct asymmetric self-aldolization of acetaldehyde is described affording (+)-(5S)-hydroxy-(2E)-hexenal 2 with ee's ranging from 57 to 90%.
Abstract: For the first time, the L-proline-catalyzed direct asymmetric self-aldolization of acetaldehyde is described affording (+)-(5S)-hydroxy-(2E)-hexenal 2 with ee's ranging from 57 to 90%. Further transformations of 2 into synthetically valuable building blocks are presented. A mechanism for the formation of 2 is proposed.

Journal ArticleDOI
TL;DR: The results demonstrated this methodology was highly chemoselective to favor mono-N-alkylation over dialkylation, offering wide applications in peptidomimetic syntheses.
Abstract: A novel method for the mono-N-alkylation of primary amines, diamines, and polyamines was developed using cesium bases in order to prepare secondary amines efficiently. A cesium base not only promoted alkylation of primary amines but also suppressed overalkylations of the produced secondary amines. Various amines, alkyl bromides, and alkyl sulfonates were examined, and the results demonstrated this methodology was highly chemoselective to favor mono-N-alkylation over dialkylation. In particular, use of either sterically demanding substrates or amino acid derivatives afforded the secondary amines exclusively, offering wide applications in peptidomimetic syntheses.

Journal ArticleDOI
TL;DR: X-ray crystal structures of pyrazinic acid 1 and isomeric methylpyrazine carboxylic acids 2-4 are analyzed to examine the occurrence of car boxylic acid-pyridine supramolecular synthon V in these heterocyclic acids.
Abstract: X-ray crystal structures of pyrazinic acid 1 and isomeric methylpyrazine carboxylic acids 2-4 are analyzed to examine the occurrence of carboxylic acid-pyridine supramolecular synthon V in these heterocyclic acids. Synthon V, assembled by (carboxyl)O-H...N(pyridine) and (pyridine)C-H...O(carbonyl) hydrogen bonds, controls self-assembly in the crystal structures of pyridine and pyrazine monocarboxylic acids. The recurrence of acid-pyridine heterodimer V compared to the more common acid-acid homodimer I in the crystal structures of pyridine and pyrazine monocarboxylic acids is explained by energy computations in the RHF 6-31G* basis set. Both the O-H.N and the C-H...O hydrogen bonds in synthon V result from activated acidic donor and basic acceptor atoms in 1-4. Pyrazine 2,3- and 2,5-dicarboxylic acids 10 and 11 crystallize as dihydrates with a (carboxyl)O-H...O(water) hydrogen bond in synthon VII, a recurring pattern in the diacid structures. In summary, the carboxylic acid group forms an O-H...N hydrogen bond in pyrazine monocarboxylic acids and an O-H...O hydrogen bond in pyrazine dicarboxylic acids. This structural analysis correlates molecular features with supramolecular synthons in pyridine and pyrazine carboxylic acids for future crystal engineering strategies.

Journal ArticleDOI
TL;DR: Oxime-derived chloro-bridged palladacycles 12 and 13 are efficient complexes for the Suzuki-Miyaura reactions of aryl-, allyl-, and benzyl halides with aryalboronic acids, showing good turnover numbers and turnover frequencies under aerobic conditions.
Abstract: Oxime-derived chloro-bridged palladacycles 12 and 13 are efficient complexes for the Suzuki−Miyaura reactions of aryl-, allyl-, and benzyl halides with arylboronic acids. The isolated catalysts are thermally stable, not sensitive to air or moisture, and easily accessible from inexpensive starting materials. The reaction can be performed under aerobic conditions with aryl bromides and chlorides, displaying turnover numbers (TON) of up to 5 × 105 and turnover frequencies (TOF) of up to 198 000 h-1 for aryl bromides. Aryl chlorides undergo the Suzuki reaction with arylboronic acids with TON of up to 4700 and TOF up to 4700 h-1. Even inexpensive and readily available benzyl and allyl chlorides undergo the coupling reaction with good turnover numbers. Complexes of 12 catalyze the syntheses of symmetrical biaryls in good yields via reductive coupling of iodoarenes in the presence of Hunig's base.

Journal ArticleDOI
TL;DR: The total synthesis of the isoquinoline natural product decumbenine B has been accomplished in seven steps and 20% overall yield by employing this palladium-catalyzed coupling and cyclization methodology.
Abstract: Monosubstituted isoquinolines and pyridines have been prepared in good to excellent yields via coupling of terminal acetylenes with the tert-butylimines of o-iodobenzaldehydes and 3-halo-2-alkenals in the presence of a palladium catalyst and subsequent copper-catalyzed cyclization of the intermediate iminoalkynes. In addition, isoquinoline heterocycles have been prepared in excellent yields via copper-catalyzed cyclization of iminoalkynes. The choice of cyclization conditions is dependent upon the nature of the terminal acetylene that is employed, as only aryl and alkenyl acetylenes cyclize under the palladium-catalyzed reaction conditions that have been developed. However, aryl-, vinylic-, and alkyl-substituted acetylenes undergo palladium-catalyzed coupling and subsequent copper-catalyzed cyclization in excellent yields. The total synthesis of the isoquinoline natural product decumbenine B has been accomplished in seven steps and 20% overall yield by employing this palladium-catalyzed coupling and cyclization methodology.

Journal ArticleDOI
TL;DR: Aigialomycins A-E (2-6), new 14-membered resorcylic macrolides, were isolated together with a known hypothemycin from the mangrove fungus, Aigialus parvus BCC 5311, and exhibited in vitro antimalarial activity.
Abstract: Aigialomycins A−E (2−6), new 14-membered resorcylic macrolides, were isolated together with a known hypothemycin (1) from the mangrove fungus, Aigialus parvus BCC 5311. Structures of these compounds, including absolute configuration, were elucidated by spectroscopic methods, chemical conversions, and X-ray crystallographic analysis. Hypothemycin and aigialomycin D (5) exhibited in vitro antimalarial activity with IC50 values of 2.2 and 6.6 μg/mL, respectively, while other analogues were inactive. Cytotoxicities of these compounds were also evaluated.

Journal ArticleDOI
TL;DR: Compared to palladium-catalyzed aminations, this procedure offers an alternative route to N-substituted anilines starting from readily available aryl chlorides.
Abstract: A general and simple nickel-catalyzed coupling of aryl chlorides and amines is reported. The scope and limitations of the coupling process using Ni(0), 1,3-bis(2,6-diisopropylphenyl)dihydroimidazol-2-ylidene, and NaO-t-Bu as base were investigated. Secondary cyclic and acyclic amines and anilines provided the arylamine coupling products in good to excellent yields. Compared to palladium-catalyzed aminations, this procedure offers an alternative route to N-substituted anilines starting from readily available aryl chlorides.

Journal ArticleDOI
TL;DR: Palladium-catalyzed reactions of aryl bromides and chlorides with two common stabilized carbanions-enolates of dialkyl malonates and alkyl cyanoesters-are reported, and the processes were shown to occur in a general fashion.
Abstract: Palladium-catalyzed reactions of aryl bromides and chlorides with two common stabilized carbanions-enolates of dialkyl malonates and alkyl cyanoesters-are reported. An exploration of the scope of these reactions was conducted, and the processes were shown to occur in a general fashion. Using P(t-Bu)(3) (1), the pentaphenylferrocenyl ligand (Ph(5)C(5))Fe(C(5)H(4))P(t-Bu)(2) (2), or the adamantyl ligand (1-Ad)P(t-Bu)(2) (3), reactions of electron-poor and electron-rich, sterically hindered and unhindered aryl bromides and chlorides were shown to react with diethyl malonate, di-tert-butyl malonate, diethyl fluoromalonate, ethyl cyanoacetate, and ethyl phenylcyanoacetate. Although alkyl malonates and ethyl alkylcyanoacetates did not react with aryl halides using these catalysts, the same products were formed conveniently in one pot from diethylmalonate by cross-coupling of an aryl halide in the presence of excess base and subsequent alkylation.

Journal ArticleDOI
TL;DR: The combination of P4S10 and hexamethyldisiloxane efficiently converts esters, lactones, amides, lactams, and ketones to their corresponding thiono derivatives and 3-oxoesters are converted to dithiolethiones by this reagent.
Abstract: The combination of P4S10 and hexamethyldisiloxane efficiently converts esters, lactones, amides, lactams, and ketones to their corresponding thiono derivatives. In the presence of elemental sulfur, 3-oxoesters are converted to dithiolethiones by this reagent. Yields are comparable to or superior to those obtained with Lawesson's reagent. The method has the advantage that reagent-derived byproducts may be removed by a simple hydrolytic workup or by filtration through silica gel, rather than by chromatography, as required for Lawesson's reagent.

Journal ArticleDOI
George Y. Li1
TL;DR: These anionic complexes are anticipated not only to accelerate the rate-determining oxidative addition of aryl chlorides but also to stabilize the palladium complexes in the catalytic cycle.
Abstract: Air-stable palladium complexes [(t-Bu)(2)P(OH)](2)PdCl(2), [(t-Bu)(2)P(OH)PdCl(2)](2), and [[(t-Bu)(2)PO...H...OP((t-Bu)(2)]PdCl](2) serve as efficient catalysts for a variety of cross-coupling reactions of vinyl and aryl chlorides with arylboronic acids, arylzinc reagents, and thiols to yield the corresponding styrene derivatives, biaryls, and thioethers. (31)P NMR and mechanistic studies argue that the phosphinous acid ligands in the complexes can be deprotonated in the presence of a base to yield an electron-rich anionic species, which is likely a catalyst intermediate, and dimeric [[(t-Bu)(2)PO...H...OP((t-Bu)(2)]PdCl](2) was isolated and cystallographically characterized. These anionic complexes are anticipated not only to accelerate the rate-determining oxidative addition of aryl chlorides but also to stabilize the palladium complexes in the catalytic cycle.

Journal ArticleDOI
TL;DR: The activation parameters DeltaH(), DeltaS(), and DeltaG() have been estimated for the reaction of chloride in each ionic liquid, and compared to a similar reaction in dichloromethane, where these parameters were found for reaction by both the free ion and the ion pair.
Abstract: In this work, the nucleophilicities of chloride, bromide, and iodide have been determined in the ionic liquids [bmim][N(Tf)2], [bm2im][N(Tf)2], and [bmpy][N(Tf)2] (where bmim = 1-butyl-3-methylimidazolium, bm2im = 1-butyl-2,3-dimethylimidazolium, bmpy = 1-butyl-1-methylpyrrolidinium, and N(Tf)2 = bis(trifluoromethylsulfonyl)imide). It was found that in the [bmim]+ ionic liquid, chloride was the least nucleophilic halide, but that changing the cation of the ionic liquid affected the relative nucleophilicities of the halides. The activation parameters ΔH⧧, ΔS⧧, and ΔG⧧ have been estimated for the reaction of chloride in each ionic liquid, and compared to a similar reaction in dichloromethane, where these parameters were found for reaction by both the free ion and the ion pair.

Journal ArticleDOI
TL;DR: The palladium-catalyzed cross-coupling reaction of potassium alkynyltrifluoroborates with aryl halides or triflates proceeds readily with moderate to excellent yields, which will provide an advantage in applications to combinatorial chemistry.
Abstract: The palladium-catalyzed cross-coupling reaction of potassium alkynyltrifluoroborates with aryl halides or triflates proceeds readily with moderate to excellent yields. The potassium alkynyltrifluoroborates are air- and moisture-stable crystalline solids that can be stored indefinitely, which will provide an advantage in applications to combinatorial chemistry. The alkynyl cross-coupling reaction can be effected using 9 mol % of PdCl2(dppf)·CH2Cl2 as catalyst in THF or THF−H2O in the presence of Cs2CO3 as the inorganic base. A variety of functional groups are tolerated in both partners.