ABSTRACT
Using our tridentate NHC-amidate-alkoxide Pd(II) complex, we developed a catalytic method for oxidative C-C bond cleavage of glycerol. The glycerol was degraded exclusively to formic acid and CO2. Two possible degradation pathways were proposed through 13C labeled studies.
ABSTRACT
Oxidation of various carbohydrates to ammonium formate was investigated in the presence of hydrogen peroxide and ammonium hydroxide. Most of the examined carbohydrates except nonreducing sugars were efficiently converted into ammonium formate under environment friendly and mild conditions in aqueous media.
ABSTRACT
A palladium-catalyzed diacetoxylation of alkenes in the presence of peracetic acid and acetic anhydride was developed to produce diacetates efficiently and diastereoselectively. Due to its mild conditions, this method was suitable for a broad range of substrates encompassing conjugated and nonconjugated olefins.
Subject(s)
Acetic Anhydrides/chemistry , Alkenes/chemistry , Palladium/chemistry , Peracetic Acid/chemistry , Catalysis , Combinatorial Chemistry Techniques , Molecular Structure , StereoisomerismABSTRACT
Chiral dimeric tridentate NHC-amidate-alkoxide palladium(II) complexes, 3a and 3b, effected oxidative boron Heck-type reactions of aryl boronic acids with both acyclic and cyclic alkenes at room temperature to afford the corresponding coupling products with high enantioselectivities. The high degree of enantioselection, far superior to existing methods, stems from differences in the nonbonding interactions in the proposed transition states, due to the influence from bulky substituents of the alkene substrates and the "counter axial groups" of the palladium(II) catalysts.
Subject(s)
Alkenes/chemistry , Boron/chemistry , Boronic Acids/chemistry , Organometallic Compounds/chemistry , Oxides/chemistry , Palladium/chemistry , Catalysis , Cyclization , Kinetics , Ligands , Molecular Structure , Oxidation-Reduction , Stereoisomerism , Structure-Activity Relationship , TemperatureABSTRACT
A simple and efficient one-pot, three-component method has been developed for the synthesis of alpha-aminonitriles. This Strecker reaction is applicable for aldehydes and ketones with aliphatic or aromatic amines and trimethylsilyl cyanide in the presence of a palladium Lewis acid catalyst in dichloromethane solvent at room temperature.
Subject(s)
Aldehydes/chemistry , Amides/chemistry , Heterocyclic Compounds/chemical synthesis , Ketones/chemistry , Methane/analogs & derivatives , Palladium/chemistry , Catalysis , Heterocyclic Compounds/chemistry , Methane/chemistry , Molecular StructureABSTRACT
While developing novel catalysts for carbon-carbon or carbon-heteroatom coupling (N, O, or F), we were able to introduce tridentate NHC-amidate-alkoxide palladium(II) complexes. In aqueous solution, these NHC-Pd(II) complexes showed high ability for C-H activation of various hydrocarbons (cyclohexane, cyclopentane, dimethyl ether, THF, acetone, and toluene) under mild conditions.
ABSTRACT
The enyne, ubiquitous in natural products, can be a challenge to generate since these moieties require many synthetic transformations to assemble them. We developed a simpler protocol to construct enynes while we found that this oxidative reaction was tolerant in substrate scope. In addition, the utility of this reaction was demonstrated through the attempt in synthesizing antifungal agent Lamisi.
ABSTRACT
Reported herein is a new approach to prepare biaryl derivatives via a tandem Pd catalyzed boron-Heck and Suzuki reaction. This one-pot tandem process avoided purification or addition of extra catalyst between steps. The resulting biaryl compounds can be prepared with substrate variability in good to moderate yields.
ABSTRACT
Reported herein is a novel approach to the total syntheses of (-)-alpha-kainic acid and (+)-alpha-allokainic acid, where the stereochemistries on C(2), C(3), and C(4) of the pyrrolidine core were introduced efficiently and selectively. A regio- and stereoselective C-H insertion reaction was utilized to prepare the gamma-lactam as an intermediate. A Michael-type cyclization of phenylsulfone with a conjugated acetylenic ketone was developed to prepare the tricyclic ketone as a key intermediate for (-)-alpha-kainic acid. Subsequently, a stereoselective dephenylsulfonylation was carried out successfully to secure the cis relationship at C(3) and C(4) centers. An unprecedented acetylation on the phenylsulfone, followed by a stereoselective dephenylsulfonylation, secured the trans relationship at C(3) and C(4) centers in (+)-alpha-allokainic acid.
Subject(s)
Kainic Acid/analogs & derivatives , Kainic Acid/chemical synthesis , Cyclization , Kainic Acid/chemistry , Molecular Conformation , StereoisomerismABSTRACT
Herein, we report an asymmetric intermolecular Heck-type reaction of acyclic alkenes by using a palladium-pyridinyl oxazoline diacetate complex under oxidative palladium(II) catalysis conditions. A premade palladium-ligand complex afforded higher enantioselectivities than a corresponding premixed palladium-ligand system, while offering enhanced asymmetric induction when compared to known intermolecular Heck-type protocols.
Subject(s)
Alkenes/chemistry , Palladium/chemistry , Alkenes/chemical synthesis , Catalysis , Crystallography, X-Ray , Cyclization , Ligands , Models, Molecular , Molecular Structure , Oxidation-Reduction , StereoisomerismABSTRACT
We report herein the development of a general and mild protocol of oxygen-promoted Pd(II) catalysis resulting in the selective cross-couplings of alkenyl- and arylboron compounds with various olefins. Unlike most cross-coupling reactions, this new methodology works well even in the absence of bases, consequently averting undesired homo-couplings. Nitrogen-based ligands including dimethyl-phenanathroline enhance reactivities and offer a highly efficient and stereoselective methodology to overcome challenging substrate limitations. For instance, oxidative palladium(II) catalysis is effective with highly substituted alkenes and cyclic alkenes, which are known to be incompatible with other known catalytic conditions. Most examined reactions progressed smoothly to completion at low temperatures and in short times. These interesting results provide mechanistic insights and utilities for a new paradigm of palladium catalytic cycles without bases.
Subject(s)
Carbon/chemistry , Cross-Linking Reagents/chemistry , Nitrogen/chemistry , Palladium/chemistry , Alkenes/chemistry , Boron/chemistry , Boronic Acids/chemistry , Catalysis , Cyclohexanones/chemistry , Esterification , Ligands , Molecular Structure , Oxidation-Reduction , Solvents , TemperatureABSTRACT
[reaction: see text] Oxygen-promoted Pd(II) catalysis facilitated the synthesis of conjugated dienes by cross-coupling of alkenylboronic compounds and various olefins including highly substituted alkenes and cyclohexenone. Under mild conditions, these versatile reactions were efficient and highly stereoselective.
Subject(s)
Alkenes/chemistry , Boron Compounds/chemistry , Oxygen/chemistry , Palladium/chemistry , Catalysis , Cations, Divalent , Cross-Linking Reagents/chemistry , Cyclohexanones/chemistry , Molecular Structure , Oxidation-Reduction , StereoisomerismABSTRACT
Sol-gel capillary microextraction (CME) is a new direction in the solventless sample preparation for the preconcentration of trace analytes, and presents significant interest in environmental, pharmaceutical, petrochemical, biomedical, agricultural, food, flavor, and a host of other important areas. It utilizes advanced material properties of organic-inorganic hybrid sol-gel polymers to perform efficient extraction and preconcentration of target compounds from a wide variety of matrices. In the present work, a novel benzyl-terminated dendron-based sol-gel coating was developed for CME. A detailed investigation was conducted to evaluate the performance of the newly developed sol-gel dendrimer coatings to perform solventless extraction of a wide range of polar and nonpolar analytes. The characteristic branched architecture of dendrons makes them structurally superior extraction media compared with their traditional linear polymeric counterparts. Sol-gel chemistry was used to chemically immobilize dendritic macromolecules on fused silica capillary inner surface. Due to the strong chemical bonding with the capillary inner walls, sol-gel dendron coatings showed excellent thermal and solvent stability in capillary microextraction in hyphenation with chromatographic analysis. Efficient extraction of a wide range of analytes from their aqueous solutions was accomplished using sol-gel dendron coated fused silica capillaries. Low parts per trillion level detection limits were achieved in CME-GC for both polar and nonpolar analytes including polyaromatic hydrocarbons (PAHs), aldehydes, ketones, phenols, and alcohols.
Subject(s)
Chromatography, Gel/methods , Gels , Microscopy, Electron, Scanning , Sensitivity and SpecificityABSTRACT
The polymers containing ribose rings: poly(5'-acrylamido-5'-deoxy-1',2'-O-isopropylidene-alpha-D-ribose) (11), poly(5'-acrylamido-5'-deoxy-alpha-D-ribose) (12) and poly(5'-acrylamido-5'-deoxy-1'-O-methyl-D-ribose) (13) were prepared as enzyme mimics. Polymers 12 and 13 with free vic-cis-diol groups catalyzed the hydrolysis of phosphodiester (ethyl p-nitrophenyl phosphate and N-methylpyridinium 4-tert-butylcatechol cyclic phosphate) and phosphomonoester substrates with a rate acceleration of 10 approximately equal to 10(3) compared with the uncatalyzed reaction. They also catalyzed the reverse reactions, i.e., the esterification of phosphomonoester to phosphodiester and the phosphorylation of alcohols with phosphate ions. The catalytic activity was attributable to the vic-cis-diols of riboses on polymer chains, which formed hydrogen bonds with two phosphoryl oxygen atoms of phosphates so as to activate the phosphorus atoms to be attacked by nucleophiles. The catalytic activity was negligible for polymer 11 where vic-cis-diol groups were blocked with isopropylidene groups. The catalytic activity was attributable to the vic-cis-diols of riboses on polymer chains, which formed hydrogen bonds with two phosphoryl oxygen atoms of phosphates so as to activate the phosphorus atoms to be attacked by nucleophiles.
Subject(s)
Organophosphates/metabolism , Polymers/metabolism , Ribose/chemistry , Catalysis/drug effects , Enzyme Inhibitors/pharmacology , Hydrolysis/drug effects , Kinetics , Magnetic Resonance Spectroscopy , Models, Chemical , Molecular Structure , Organophosphates/chemistry , Organophosphorus Compounds/chemistry , Organophosphorus Compounds/metabolism , Phosphates/pharmacology , Phosphorylation/drug effects , Polymers/chemical synthesis , Polymers/chemistry , Potassium Compounds/pharmacology , Ribose/chemical synthesis , Sodium Acetate/pharmacology , Substrate Specificity , Time FactorsABSTRACT
Routes for the syntheses of isomeric, zwitterionic, bisterpyridine-Ru(II)-based macromolecules are described. Access to these novel architectures is facilitated by the construction of terpyridine-modified, 1-->3 C-branched, ester-terminated building blocks. Constitutional isomers result from the interchangable placement of methyl and tert-butyl ester groups on both the branched framework near the Ru(II) centers and the termini of the branched construct. Water solubility is imparted to each isomer through selective transformation of the tert-butyl esters to their corresponding carboxylates. Along with the standard characterization techniques, electrochemical and spectroscopic data also support the structural formation.
ABSTRACT
The first examples of metallodendritic spiranes have been obtained via incorporation of single terpyridine units within each dendritic quadrant.
