Cu-catalyzed regio- and stereoselective sulfonylation of multi-substituted allenes

Regio- and stereoselective sulfonylation of allenes under Cu catalysis is described. Allenyl sp carbons exclusively react with TsCN to give the corresponding alkenyl sulfones. The reaction is initiated by addition of tosyl radical to form benzyl radical intermediates, which determines the reaction pathway. The structure of the products is highly dependent on the substituents on allenes.     

Pd-CNT-catalyzed ligandless and additive-free heterogeneous Suzuki-Miyaura cross-coupling of arylbromides

Pd-CNT efficiently catalyzed Suzuki-Miyaura coupling of arylbromides under ligandless and additive-free conditions in aqueous media. For hydrophilic substrates, the reaction could be carried out in neat water.     

Use of a bulky phosphine of weak σ-donicity with palladium as a versatile and highly-active catalytic system: allylation and arylation coupling reactions at 10-10 mol% catalyst loadings of ferrocenyl bis(difurylphosphine)/Pd

Carbon-carbon(sp²-sp² and sp¹-sp²) and carbon-nitrogen (nucleophilic allylation) coupling processes are promoted by a catalytic system containing [PdCl(η³-C₃H₅)]₂ with the new ferrocenyl bis(difurylphosphine) 1,1′-bis[di(5-methyl-2-furyl)phosphino]ferrocene, Fc[P(Fu^Me)₂]₂. Starting from aryl bromides or allylic acetates this versatile catalyst system may be used at low palladium loadings (10⁻¹-10⁻⁴ mol%) in some Heck, Suzuki, Sonogashira and allylic amination reactions to give cross-coupled products in excellent yield. Remarkably high activity is obtained in allylic substitution reactions, providing a significant impetus for the development of bulky phosphines possessing weak σ-donicity for this particular reaction.     

Cu-catalyzed decarboxylative iodination of aryl carboxylic acids with NaI: A practical entry to aryl iodides under aerobic conditions

A simple and practical Cu-catalyzed decarboxylative iodination has been well established under aerobic condition, which provides a useful method to synthesize aryl iodides in moderate to good yields with the use of (hetero)aryl carboxylic acids and NaI as starting materials. Thiabendazole has been prepared via a three-step procedure to show synthetic practicability of the protocol.     

Stille cross-coupling of activated alkyltin reagents under "ligandless" conditions

Monoalkyltins activated by a fluoride source are shown to be as reactive as their vinyl or aryl homologues in the Stille coupling reaction, thus providing an easy entry into the pallado-catalyzed formation of Csp3-Csp2 bonds. In addition to this uncommon reactivity, this methodology holds several advantages such as (i) a quantitative preparation of stable and easy to handle alkyltin reagents 2, (ii) a simplified coupling procedure without any phosphine added ligand under neutral conditions, and (iii) a facile purification step of the organic products from the inorganic nontoxic tin byproducts.     

An improved protocol for ligandless Suzuki-Miyaura coupling in water

Using a reverse order of addition of reagents, PdCl₂ and Pd(OAc)₂ are efficient catalysts for the Suzuki-Miyaura reactions in water. The ligandless and mild conditions, the high stability of the catalytic system, short reaction time and good to excellent yields are important features of this protocol.     

Atom-efficient Pd-catalyzed cross-couplings of chloroarenes with triarylbismuth reagents

Various Pd-catalyzed protocols have been developed for the atom-efficient cross-coupling of chloroarenes with triarylbismuth reagents. Using the developed protocols, an efficient synthesis of unsymmetrical biaryls in good to excellent yields was achieved by employing electron-deficient chloroarenes and a range of triarylbismuth reagents.     

Substituted 1-(isoxazol-3-yl)methyl-1H-1,2,3-triazoles: Synthesis,palladium(II) complexes,and high-turnover catalysis in aqueous media

New substituted 3-((1H-1,2,3-triazol-1-yl)methyl)-5-arylisoxazoles (aryl?=?Ph, p-Tol) and 2-(5-phenylisoxazol-3-yl)-5-(2-(1-((5-(p-tolyl)isoxazol-3-yl)methyl)-1H-1,2,3-triazol-4-yl)ethyl)-1,3,4-oxadiazole were synthesized by means of click-chemistry procedures. The obtained compounds were used as ligands in preparation of palladium(II) complexes, and the latter proved to be high-turnover-number catalysts for CC cross-coupling reactions under Green Chemistry conditions. One of the ligands was structurally characterized by single crystal X-ray diffraction, and the structure of complexes was determined by ¹H, ¹³C, ¹⁵N NMR spectroscopy and quantum-chemical modeling.     

Unexpected formation of porphyrinic enyne under Sonogashira conditions

Reaction of 5-iodo-10,15,20-tris(3,5-di-tert-butylphenyl)porphyrin with excess trimethylsilylacetylene under Sonogashira conditions gives an unexpected porphyrinic enyne suitable for further transformations. The NMR spectrum and structural analysis of the porphyrin enynes show that the substituent on the acetylene group is positioned above the porphyrin ring. This structural characteristic makes the microenvironment of the porphyrin center in a controllable fashion.     

Palladium-catalyzed aryl-amidation. Synthesis of non-racemic N-aryl lactams

The Buchwald/Hartwig aryl amination method was used to construct a series of chiral, non-racemic N-aryl pyrrolidinones from a common pyrrolidinone precursor and the corresponding aryl bromide. The stereochemical integrity of the N-aryl lactam after cross-coupling was proven by synthesis of the racemic compounds and comparison by ¹H NMR spectroscopy using Pirkle's chiral solvating agent.     

Reactions of vinyltributylgermanes and aryl halides under Heck conditions

We describe the palladium-mediated reaction of vinyltributylgermanes with aryl halides under Heck conditions. Depending on their degree of substitution, (E)-vinyltributylgermanes preferentially afford either the cine or Z-alkenyl coupled products in moderate yields. Substituents at the allylic position, especially oxygen, impact regio- and stereoselectivity.     

A new class of readily available and conformationally rigid phosphino-oxazoline ligands for asymmetric catalysis

A new class of conformationally rigid phosphino-oxazoline ligands 3 were synthesized via an efficient ortho-substitution of phenyl glycinol as the key step. Divergent synthetic routes for easy ligand modulation, as well as a procedure suitable for scale-up synthesis, were established. The catalytic potential of ligands 3 has been demonstrated in the highly enantioselective Ir-catalyzed hydrogenation of alkenes and Pd-catalyzed allylic substitution and intermolecular Heck reactions.     

Formation and propagation of well-defined Pd nanoparticles (PdNPs) during C–H bond functionalization of heteroarenes: are nanoparticles a moribund form of Pd or an active catalytic species?

Examination of a series of C–H bond functionalization reactions of heteroarenes (e.g., indole, benzoxazole, benzthiazole, benzimidazole and purine derivatives) mediated by Pd(OAc)₂, a commonly used C–H bond functionalization catalyst, reveals that well-defined Pd nanoparticles (PdNPs) are rapidly formed under working catalyst conditions. The PdNPs can be characterized ex situ after entrapment in a polymer matrix (polyvinylpyrrolidinone, PVP). Independently synthesized Pd(PVP)NPs are catalytically competent species, exhibiting catalyst activity commensurate with Pd(OAc)₂ in several C–H bond functionalization reactions. Across a range of reactions, Pd concentration is a common variable, which can be linked to the propagation of PdNPs under working catalytic conditions using polar solvents like DMF, DMSO and acetic acid.     

Synthesis of 2,3-disubstituted pyrazines and quinoxalines by Heck cross-coupling reactions of 2,3-dichloropyrazine and 2,3-dichloroquinoxaline. Influence of the temperature on the product distribution

Heck cross-coupling reactions of 2,3-dichloropyrazine provide a convenient approach to 2,3-dialkenyl-, 2-alkenyl-3-alkyl-, and 2,3-dialkylpyrazines depending on the reaction conditions.     

Cross-couplings of alkyl electrophiles under "ligandless" conditions: Negishi reactions of organozirconium reagents

This report establishes that simple, "ligandless" palladium complexes can catalyze the first zirconium-Negishi reactions of alkyl electrophiles. In view of the attractiveness of ligandless catalysts (cost, simplicity, and ease of purification), these observations add a significant and intriguing new dimension to the development of effective palladium-based processes for coupling alkyl electrophiles.     

Simple and efficient copper-catalyzed S-arylation of diaryl disulfides with triarylbismuthanes under aerobic conditions

Novel and simple copper-catalyzed C(aryl)-S bond formation of diaryl disulfides with bismuth reagents is described. Reactions of diaryl disulfides with triarylbismuthanes in the presence of CuOAc (10 mol %) and 1,10-phenanthroline (10 mol %) under aerobic conditions led to the formation of unsymmetrical diaryl sulfides in satisfactory yields. The reaction is atom-economic and all three aryl groups of the triarylbismuthanes and both sulfanyl groups of the diaryl disulfides could be transferred to the coupling products.     

Highly practical boronic acid surrogates for the Suzuki-Miyaura cross-coupling

Boronic acids and esters are well known substrates for the Suzuki-Miyaura cross-coupling. Yet their isolation can sometimes be tedious. We report here that the use of aryl dioxazaborocanes afford a simple isolation procedure while keeping a high efficiency in the cross-coupling process.     

Palladium-catalysed α-arylation of esters and amides under microwave conditions

A rapid and convenient approach for the α-arylation of esters and amides using Reformatsky reagents under a microwave accelerated reaction protocol has been established.     

Asymmetric organocatalysis of epoxidation by iminium salts under non-aqueous conditions

Three iminium salts have been tested as catalysts for the asymmetric epoxidation of simple alkenes under non-aqueous conditions in various solvents, at varying temperatures, employing tetraphenylphosphonium monoperoxybisulfate (TPPP) as the stoichiometric oxidant. Enantiomeric excesses of up to 89% have been observed.     

Direct palladium-catalyzed C-3 arylation of free (NH)-indoles with aryl bromides under ligandless conditions

A new method for the efficient, practical, and highly regioselective direct palladium-catalyzed C-3 arylation of free (NH)-indole and its electron-rich 1-unsubstituted derivatives under ligandless conditions is described. The reactions, which are run outside a glovebox without purification of solvent and reagents, involve treatment of free (NH)-indoles with activated, unactivated, and deactivated aryl bromides in refluxing toluene in the presence of K2CO3 as the base and a catalyst system consisting of a combination of Pd(OAc)2 and benzyl(tributyl)ammonium chloride. The experimental results are consistent with a catalytic cycle based on an electrophilic palladation pathway at the 3-position of 1-indolyl potassium salts.