One-pot synthesis of 1,4-diarylsubstituted 1,3-diynes from the sequential coupling reactions of aryl iodides and propiolic acid

1,4-Disubstituted 1,3-dialkynes were obtained from the one-pot palladium/copper-catalyzed coupling reactions of aryl iodide and propiolic acid. The optimized catalytic system consisted of 5.0 mol % Pd(PPh₃)₂Cl₂, 10 mol % dppb, 10 mol % CuI, 2.4 equiv of DBU, and 1.2 equiv of K₂CO₃. The coupling reaction was carried out at 30 °C for 6 h and subsequently at 80 °C for 3 h.     

Fast racemization and dynamic kinetic resolution of primary benzyl amines

We prepared a Pd nanocatalyst (average diameter of Pd nanoparticles = 1.73 nm) displaying a remarkable activity for the racemization and dynamic kinetic resolution (DKR) of 1-methylbenzylamine. It was eight times more active than the previous best. The DKR of 1-methylbenzylamine with the Pd nanocatalyst (2 mol %) in the presence of a thermostable lipase (Novozym 435) was complete in 6 h at 70 °C. The DKRs of other benzyl amines also proceeded to completion in 6 h under similar conditions except the amount of Pd nanocatalyst.     

Reusable Pd nanoparticles immobilized on functional ionic liquid co-polymerized with styrene for Suzuki reactions in water-ethanol solution

Co-polymer of 3-(2,3-dihydroxypropyl)-1-vinylimidazolium chloride and styrene was synthesized and used as a support of Pd nanoparticles. The Pd@poly-Sty-co-diOH-Cl catalyst can efficiently catalyze Suzuki reactions for a wide range of aryl iodides and bromides with 0.05 mol % Pd at 70 °C in water-ethanol solution under air, and the catalyst can be recycled and reused for several times without significant loss of activity.     

Palladium(II)-catalyzed 1,4-addition of arylboronic acids to β-arylenals for enantioselective syntheses of 3,3-diarylalkanals: a short synthesis of (+)-(R)-CDP 840

1,4-Addition of arylboronic acid to trans-β-arylenals proceeded smoothly in acetone-water (10/1) at 10-25 °C in the presence of [Pd(S,S-chiraphos)(PhCN)₂](SbF₆)₂ (0.5 mol %), AgX (X = BF₄, SbF₆, 10 mol %) and aqueous 42% HBF₄ to afford optically active 3,3-diarylalkanals with high enantioselectivities in a range of 86-97% ee. The protocol provided a method for short-step synthesis of optically active (+)-(R)-CDP 840.     

Direct synthesis of primary arylamines via C-N cross-coupling of aryl bromides and triflates with amides

Aryl halides and triflates are coupled with primary amides to give the corresponding arylamines in the presence of a palladium catalyst, a suitable ligand, and a base. The catalyst system performs well for a large number of different substrates at 100-150 °C without solvent, and with low catalyst levels (0.12 mol % Pd). Nicotinamide might be useful as a nitrogen source in the Pd-catalyzed amination reaction.     

Palladium catalyzed alkynylation of aryl halides (Sonogashira reaction) in water

The palladium catalyzed alkynylation of aryl halides (Sonogashira reaction) has been achieved in pure water without any additives or phase transfer catalysts. The reaction, which requires only 0.5 mol % of Pd(PPh₃)₄ catalyst, is remarkably fast (30 min at 70 °C) producing high yields of the aryl alkyne products.     

Preparation of N-arylpiperazines and other N-aryl compounds from aryl bromides as scaffolds of bioactive compounds

Aryl bromides are coupled with N-compounds to give the corresponding arylamines in the presence of a palladium catalyst, a suitable ligand, and a weak base. The catalysts perform well for a large number of different starting material combinations at 100-150 °C with drops of toluene or without solvent, and with low catalyst levels (0.12 mol % Pd). The low catalyst amount makes the process environment friendly.     

Tandem catalysis in ionic liquids: a recyclable catalytic synthesis of benzofuran derivatives

A convenient, recyclable catalytic synthesis of benzofuran-2-acetic esters 2 by sequential Pd(0)-catalyzed deallylation—Pd(II)-catalyzed carbonylative heterocyclization of 1-(2-allyloxyphenyl)-2-yn-1-ols 1 in ionic liquids is presented. Reactions were typically carried out in BmimBF₄ as the solvent at 100 °C and under 30 atm of CO, in the presence of catalytic amounts (1 mol %) of PdI₂ in conjunction with KI (1 equiv), PPh₃ (4 mol %), MeOH (28 equiv), and H₂O (2 equiv). The solvent-catalyst system could be recycled several times without appreciable loss of catalytic activity.     

Palladium-catalyzed cross-coupling reaction of alkynylzincs with benzylic electrophiles

The reaction of alkynylzinc bromides with benzyl bromides or chlorides in the presence of a catalytic amount of Pd(DPEphos)Cl₂ in THF at 23 °C cleanly produces the corresponding benzylated alkynes in 73-97% yields. With 10⁻³ mol % of Pd(DPEphos)Cl₂, the maximum turnover number of 7.1 × 10⁴ has been observed for the formation of PhCCCH₂Ph.     

Hiyama reaction of aryl bromides with arylsiloxanes catalyzed by a reusable palladium(II)/cationic bipyridyl system in water

A Pd(NH₃)₂Cl₂/cationic bipyridyl catalytic system catalyzed the cross-coupling reaction of aryl bromides with arylsiloxanes in water under aerobic conditions in the presence of NaOH to afford biaryls in good to high yields. The reaction was performed at 120 °C and the loading amount of catalyst can be as low as 0.001 mol %. After extraction, the residual aqueous phase can be reused several times with only a slight decrease in activity.     

Enthalpies of mixing of liquid alloys in the In-Pd-Sn system and the limiting binary systems

The partial and integral enthalpies of mixing of molten binary In-Pd (up to about 29 at.% Pd), In-Sn (entire compositional range) and Pd-Sn (up to about 53 at.% Pd) alloys were determined at 900 °C. A Calvet-type microcalorimeter was used for the measurements employing a drop calorimetric technique. Additionally, five sections in the ternary In-Pd-Sn system (compositions up to about 40 at.% Pd) were investigated at 900 °C. The ternary interaction parameters were fitted using the Redlich-Kister-Muggiano model for substitutional solutions. The isoenthalpy curves for In-Pd-Sn at 900 °C were constructed for the integral molar enthalpy of mixing. Furthermore, the experimental results in the ternary system were compared with calculated values obtained by employing different binary extrapolation models.     

Pd-catalyzed enantioselective synthesis of quaternary α-amino acid derivatives using a phenylalanine-derived P-chirogenic diaminophosphine oxide

A Pd-catalyzed enantioselective synthesis of quaternary α-amino acid derivatives using a phenylalanine-derived P-chirogenic diaminophosphine oxide is described. Asymmetric allylic substitution using acyclic β-keto esters with a nitrogen functional group at the α-carbon as prochiral nucleophiles proceeded in the presence of 5 mol % of Pd catalyst, 10 mol % of chiral diaminophosphine oxide 1j, BSA, and appropriate additives, affording the corresponding quaternary α-amino acid derivatives in excellent yield and in up to 92% ee.     

Palladium-catalyzed cross-coupling of trimethoxysilylbenzene with aryl bromides and chlorides using phosphite ligands

Phosphites were employed as ligands in palladium-catalyzed Hiyama coupling reactions. The optimized reaction conditions were equimolar amounts (5 mol % each) of Pd(acac)₂ and phosphite 1 in p-xylene at 80 °C with TBAF as an additive. This catalyst system exhibited high activities in the reactions with trimethoxysilylbenzene and aryl bromides that have electron-donating or electron-withdrawing groups. In the case of aryl chlorides, substrates possessing electron-withdrawing groups gave the coupled products in high yields.     

Development and application of a capillary electrophoresis based method for the assessment of monosaccharide in soil using acid hydrolysis

An efficient methodology for the determination of carbohydrate content in soils, employing acid hydrolysis and subsequent capillary electrophoresis analysis (CE), is here described. Polysaccharides present in soil samples were hydrolyzed, at 100 °C during 4 h, to their monosaccharide form, by addition of 2 mol dm⁻³ trifluoroacetic acid (TFA) directly to soil. The resulting monosaccharides were then quantitatively derivatized with 4-aminobenzoic acid ethyl ester, via reductive amination with sodium cyanoborohydride, and separated by CE, coupled to an UV-vis diode array set at 300 nm. Separation electrolyte consisted of 5.0 × 10⁻² mol dm⁻³ sodium tetraborate buffer (pH 10.2) and 6 × 10⁻³ mol dm⁻³ sodium dodecylsulphate. A 78 cm long capillary with an internal and external diameter of 75 and 375 μm, respectively, was used and separation performed at 16 °C, with an applied voltage of 30 kV. Quantification was undertaken using ribose as the internal standard. As an application example, carbohydrate composition (w/w) of a farmyard manure fertilized soil was found to vary between 0.0045 ± 0.0003% (glucose) and 0.0267 ± 0.0002% (arabinose) of the total soil content. Xylose, rhamnose, mannose, fucose and galactose content were also studied in the present work.     

Highly-efficient and recyclable nanosized MCM-41 anchored palladium bipyridyl complex-catalyzed coupling of acyl chlorides and terminal alkynes for the formation of ynones

A highly-efficient and practical method for the formation of ynones from a variety of acyl chlorides and terminal alkynes catalyzed by a nanosized MCM-41 anchored palladium bipyridyl complex is described herein. Aroyl, heteroaroyl, and alkyl acyl chlorides were easily coupled with terminal alkynes, giving good to high isolated yields in the presence of a very low catalyst loading (0.002-0.1 mol % Pd) in Et₃N or diisopropylethylamine at 50 °C. Furthermore, the reaction scale was up to 150 mmol for a single batch reaction, providing the potential for practically synthetic application. After centrifugation, the supported catalyst was able to be recycled and reused several times with only a slight decrease in activity.     

Sensitive determination of pipecolic acid in serum by high-performance liquid chromatography using 4-(5,6-dimethoxy-2-phthalimidinyl)-2-methoxyphenylsulfonyl chloride as a fluorescent labelling reagent

A simple and highly sensitive high-performance liquid chromatography (HPLC) for the determination of pipecolic acid (PA) in serum was developed. Pipecolic acid and nipecotic acid (internal standard (IS)) were derivatised with 4-(5,6-dimethoxy-2-phthalimidinyl)-2-methoxyphenylsulfonyl chloride (DMS-Cl) to produce fluorescent sulfonamides. The labelling reaction was carried out at 70 °C for 15 min at pH 9.0. The fluorescent derivatives were separated on a reversed-phase column (45 °C) with a stepwise elution using methanol/acetonitrile/10 mmol l⁻¹ acetic acid (42:5:53) and methanol at a flow rate of 1.0 ml/min and detected at excitation and emission wavelengths of 316 and 403 nm, respectively. The labelling yield was 100.8%. The detection limit of pipecolic acid was 4 fmol at signal-to-noise ratio of 3. The within-day and day-to-day relative standard deviations were 3.3-8.1 and 1.4-6.4%, respectively. The concentration of pipecolic acid in normal human serum was 1.09±0.37 μmol l⁻¹.     

An efficient protocol for copper-free palladium-catalyzed Sonogashira cross-coupling in aqueous media at low temperatures

A thorough study on copper-free Sonogashira cross-couplings in water was carried out using the palladacycle, [{Pd(μ-Cl){κ²-P,C-P(ⁱPr)₂(OC₆H₃-2-Ph)}}₂] as pre-catalyst with different bases and palladium concentrations. The highly active pre-catalyst imparts good to near quantitative yields using a concentration of 0.25 mol % at 40 °C. This broadly applicable protocol exhibits high tolerance of functional groups and substitution patterns.     

A one-pot synthesis of 2,3-dihydro-1H-pyrrolo[3,2-c]quinolines

A one-pot synthesis of the 2,3-dihydro-1H-pyrrolo[3,2-c]quinoline core from substituted 2-iodoanilines and 2,3-dihydro-1H-pyrrole was achieved using 10 mol % Pd(PPh₃)₄, and K₂CO₃ in 1,4-dioxane at 170 °C for 1 h in a microwave oven. This reaction can be carried out on a gram scale. The proposed mechanism involves a Heck-coupling reaction followed by intra-molecular Schiff base formation and double bond migration.     

Dynamic kinetic resolution of hemiaminals using a novel DMAP catalyst

We describe the first catalytic dynamic kinetic resolution of hemiaminals mediated by an organocatalyst. A 0.1-1 mol % catalyst loading is effective for the dynamic kinetic resolution of hemiaminals to produce esters up to 88% ee in high yields. A 10 mol % catalyst loading resulted in a decreased selectivity, whereas the selectivity increased at 50 °C. The absolute configuration is assigned on the basis of the empirical Cotton effect rule.     

Catalytic cyanosilylation of ketones using organic catalyst 1,1,3,3-tetramethylguanidine

1,1,3,3-Tetramethylguanidine acts as a highly effective catalyst for cyanosilylation of various ketones and aldehydes to the corresponding cyanohydrin trimethylsilyl ethers in up to 99% yield. The reaction proceeds smoothly with 0.1 mol % catalyst loading at 25 °C under solvent-free conditions.