The synthesis and conformational analysis of a new type of conformationally restricted alpha-amino acid analogue of the amino acid antibiotic furanomycin is presented. The restriction involves the cis-fused cyclobutane and tetrahydrofuran units, generating the unusual 2-oxabicyclo[3.2.0]heptane core, which is found in a great number of biologically active natural products. The ...

The parallel kinetic resolution of racemic 2-aryl-2-deuterio-propionic and butanoic acids using an equimolar combination of quasi-enantiomeric oxazolidin-2-ones is discussed. The levels of diastereoselectivity were high leading to enantiomerically pure D-labeled products in good yield.

A series of 12-phosphotungstic acid (PWA) supported on various porous carriers, such as silica, alumina, titania, clay, and carbon were prepared, and their catalytic performance evaluated in the synthesis of imidazoles in solvent-free condition. It was found that PWA supported on silica (PWA/SiO(2)) showed higher activity compared to other catalysts. ...

The one-pot Horner-Wadsworth-Emmons/oxa-Michael cascade followed by spiroketalisation affords the tetracyclic benzannulated spiroketal core of berkelic acid, an extremophile natural product with selective activity against ovarian cancer.

A mild and clean liquid nitration of benzene with 65% nitric acid as nitrating agent over silica supported ammonium salt of 12-molybdophosphoric acid catalysts has been investigated. These catalysts with different loadings were prepared by sol-gel method and characterized by X-ray diffraction (XRD) and FTIR spectra. The acidity of these ...

The chemical features, such as substrate stability, product distribution, and substrate generality, and the reaction mechanism of Br?nsted superacid-catalyzed cyclization reactions of aromatic ring-containing acetoacetates (beta-ketoesters) were examined in detail. While two types of carbonyl cyclization are possible, i.e., keto cyclization and ester cyclization, the former was found to take ...

The enantioselective conjugate addition of alkynyl nucleophiles has been a long-standing challenge in synthetic chemistry. This paper describes a highly practical asymmetric conjugate alkynylation of Meldrum's acid-derived acceptors using cinchonidine (<$100/kg) as the chiral mediator. The process provides practical access to chiral beta-alkynyl acids. Noteworthy attributes of the method are ...

Pd(II)-catalyzed enantioselective C-H olefination of diphenylacetic acid substrates has been achieved through the use of monoprotected chiral amino acid ligands. The absolute configuration of the resulting olefinated products is consistent with that of a proposed C-H insertion intermediate.

Periodic DFT calculations were performed on H-FER models having Si/Al ratios of 71 : 1, 35 : 1 and 8 : 1, in order to investigate the effect of aluminium content on the properties of the zeolite Br?nsted acid sites. Relative stability of these sites was found to be dependent ...

Selected Br?nsted acidic ionic liquids were tested as homogeneous catalysts for the dehydration of methanol to dimethyl ether. Ionic liquids incorporating an alkanesulfonic acid as a part of the cation, a complex acidic anion, [A(2)H](-), or both, proved to be good catalysts for this process, providing high conversions and selectivities. ...

We have successfully designed and synthesized core-shell multicomponent TiP nanospheres with a stable crystal core and orderly open nanopores, which have uniform distribution and good dispersion and offer great potential as a highly active Br?nsted acid catalyst.

Four novel derivatives of BINOL bearing S-tryptophan unit have been prepared and the structures of these compounds characterized by IR, MS, (1)H and (13)C NMR spectroscopy and elemental analysis. The enantioselective recognition of these receptors has been studied by fluorescence titration and (1)H NMR spectroscopy. The receptors exhibited different chiral ...

We describe our studies on the effect of various Lewis bases and Br?nsted acids as achiral additives on the stereoselectivity of some Rh(ii)-catalyzed cyclopropanations.

A variety of optically active 2-hydroxyalkanoates and the corresponding 2-acyloxyalkanoates are produced by the kinetic resolution of racemic 2-hydroxyalkanoates by using achiral 2,2-diarylacetic acid with hindered carboxylic anhydrides as the coupling reagents. The combined use of diphenylacetic acid, pivalic anhydride, and (+)-(R)-benzotetramisole ((R)-BTM) effectively produces (S)-2-hydroxyalkanoates and (R)-2-acyloxyalkanoates from the ...

Useful methods have been developed to construct ortho-arylated aryl aldoximes, aryl ketoximes, and fluorenones via Pd(II)-catalyzed direct C-H arylation by using arylboronic acids as arylating reagents based on the analysis of the pathways of direct functionalization of aryl aldoximes.

A first organocatalytic enantioselective route was developed for the conversion of readily prepared and air stable aliphatic hydrazones to synthetically valuable alpha-hydrazinonitriles. This BINOL-phosphate catalyzed Strecker-type reaction (see scheme, Ar = p-NO(2)-Ph) provides a new practical and direct route to alpha-hydrazino acids of synthetic and biological importance. The actually active ...

The title compound, C(8)H(6)O(6)·2H(2)O, was obtained by accident within a project on the synthesis of metal-organic coordination polymers by the reaction of LiOH with 2,5-dihy-droxy-terephthalic acid under solvothermal conditions. The asymmetric unit consists of half a 2,5-dihy-droxy-terephthalic acid mol-ecule located on a centre of inversion and one solvent water mol-ecule ...

β-Aryl-β-amino acids constitute very useful scaffolds able to lead, via various intra-molecular cyclisation reactions, to a great diversity of cyclic derivatives with numerous biological and therapeutic properties. The present article aims at reporting an exhaustive overview of these ring-closure sequences and their application in the medicinal chemistry field.

Sulfonated (SO(3)H-bearing) activated carbon (AC-SO(3)H) was synthesized by an aryl diazonium salt reduction process. The obtained material had a SO(3)H density of 0.64 mmol·g-1 and a specific surface area of 602 m2·g-1. The catalytic properties of AC-SO(3)H were compared with that of two commercial solid acid catalysts, Nafion NR50 and ...

The optical rotation of natural amino acids becomes more positive when the medium is changed from approximately neutral to strongly acidic (Clough-Lutz-Jirgensons (CLJ) effect). In this work, it is shown by time-dependent density functional computations that the effect can be generalized to other α-substituted chiral carboxylic acids. The physical origin ...

Algae are becoming a strategic source of fuels, food, feedstocks, and biologically active compounds. This potential has stimulated the development of innovative analytical methods focused on these microorganisms. Algal lipids are among the most promising potential products for fuels as well as for nutrition. The crucial parameter characterizing the algal ...

Palladium-catalyzed Suzuki cross-coupling of 2-aryl-4-chloro-3-iodoquinolines with excess arylboronic acids (2.5 equiv.) in the presence of tricyclohexylphosphine afforded the 2,3,4-triarylquinolines in one-pot operation. The incipient 2,3-diaryl-4-chloroquinolines were also prepared and transformed to the primary 4-amino-2,3-diarylquinolines and 2,3-diarylquinolin-4(1H)-ones.

Alpha,beta-Diamino acids have attracted considerable attention recently due to their growing importance in pharmaceutical and biochemical research. For example, this special class of alpha,beta-diamino acids has become the components of enzyme inhibitors, and has been incorporated into peptides which are used to modulate secondary and tertiary structural conformations. Although their ...

A mild, selective and efficient Nazarov cyclization of divinyl ketones catalyzed by phosphomolybdic acid (PMA) is described. The process demonstrates a broad substrate scope with functional group tolerance under short reaction times. PMA supported on silica gel is more efficient than the bulk catalyst and is recycled up to three ...

The resolution of chiral nitrones via derivatization of hydroxylamines was applied to MiPNO, a new, stable, easily prepared chiral cyclic nitrone. The application of MiPNO in totally regio- and diastereo-selective 1,3-dipolar cycloaddition reactions provides an expeditious enantioselective access to unusual gamma-hydroxy alpha-amino acids.

The complete conversion of racemic amino acid amides to optically active amino acid derivatives was accomplished via lipase/palladium-catalyzed dynamic kinetic resolution (DKR). In the DKR, a lipase catalyzes the selective acylation of L-substrate in the presence of acyl donor while unreacted D-substrate is isomerized by a Pd nanocatalyst to L-substrate. ...

Dipeptides obtained from l-proline and beta(3)-l-amino acids are reported to catalyze enantioselective direct aldol reaction in aqueous medium, leading to significant anti:syn diastereomeric ratios and enantiomeric excesses. The simple introduction of a polar substituent at the C-2 position of the beta(3)-l-amino acid was also found to enhance appreciably both diastereo- ...

The introduction of an o-carborane cage into the triarylborane significantly enhances the Lewis acidity of the boron atom leading to large increase in fluoride ion affinity.

Lewis acid promoted elimination of p-toluenesulfinc acid from sulfonyl indazoles and sulfonyl indoles generates the corresponding iminium ion that reacts with allyltin reagents, silyl enol ethers, silyl ketene acetals and electron-rich aromatics leading to functionalized indazole and indole derivatives.

A unified approach to the pyrrolidine triacid natural products isodomoic acids G and H has been developed. Total syntheses of both natural products were completed, and determination of the correct stereostructure of isodomoic acid G was established by comparing 5'-(R) and 5'-(S) isomers to a sample of authentic material. A ...

Thiosilane and a catalytic amount of a Br?nsted acid mediate the novel domino-type rearrangement reaction of the 4,4-disubstituted cyclohexadienones to produce the 3,4-disubstituted benzenethioethers; the key step is 1,2-addition of thiosilane to dienone.

The first Pd(II)-catalyzed P arylation has been performed by using palladium acetate, the rigid bidentate ligand dmphen (dmphen=2,9-dimethyl-1,10-phenanthroline), and without the addition of base or acid. Couplings of arylboronic acids or aryl trifluoroborates with H-phosphonate dialkyl esters were conducted in 30 min with controlled microwave (MW) heating under non-inert conditions. ...

Lewis acids catalyze the cyclization of methyl phenyldiazoacetates with an ortho-imino group, prepared from o-aminophenylacetic acid, to give 2,3-substituted indoles in quantitative yields.

The four aldopentoses ribose, arabinose, xylose, and lyxose were evaluated to test their suitability as linear linkers for the formation of intrinsically chiral covalent organic boronic ester networks. Based on X-ray crystal structures of the reaction products with phenylboronic acid, arabinose and xylose formed boronic acid diesters. Lyxose and ribose ...

Alpha-amino acid derivatives, particularly those of phenylglycine, can suffer significant racemization in Suzuki couplings. When arylpinacolboronate esters are used as coupling partners this unwanted side reaction can be suppressed by the use of Pd(OAc)(2) as Pd(0) source, in the presence of Buchwald's SPhos ligand. The syntheses of biaryl amino acids ...

Interactions between pyruvic acids and diphenylborinic acid form the basis of an efficient, direct, boron-catalyzed aldol reaction that takes place in water at room temperature with low catalyst loadings. Both boronic and borinic acids function as catalysts, with the latter demonstrating particularly high activity. A wide range of aldehydes, including ...

A highly torquoselective olefination of alkynoates to provide functionalized tetrasubstituted olefins, (E)-2-en-4-ynoic acids, is described. Addition of Br??nsted acids dramatically switched the mode of the Ag(I)-catalyzed cyclization of the resulting enyne carboxylic acids to give either tetronic acids or 2-pyrones.

A palladium catalyzed C-H activation of indoles and a silver catalyzed decarboxylative C-C activation of ortho substituted benzoic acids are synergistically combined to synthesize indoles arylated exclusively in the C-3 position. This novel decarboxylative C-H arylation methodology is compatible with electron-donating and -withdrawing substituents in both coupling partners.

Lewis acid complexation is generally required for chiral-auxiliary-controlled stereoselectivity, and chiral Lewis acid catalysis is frequently optimal for introducing asymmetry. In this work, we show that nitrile ylide cycloadditions to electron-poor acceptors attached to chiral auxiliaries proceed in high yield and stereoselectivity in the absence of Lewis acids. In contrast, ...

This manuscript details the development of a palladium-catalyzed hydroamination of vinyl ethers. It is proposed that palladium catalyzes the hydroamination via Bronsted base catalysis, where palladium is protonated by the relatively acidic sulfonamide to generate a palladium hydride as well as the active anionic sulfonamide nucleophile. Thus, this process is ...

The total syntheses of all stereoisomers of phenatic acid B and determination of their absolute configuration are described. The synthetic strategy is based on an efficient combination of the Sharpless asymmetric dihydroxylation, the Johnson-Claisen rearrangement, and hydroboration-oxidation. It involves 11-12 steps and overall yield of 5-8%.

The rearrangement of 2,5-bis(silylated)-N-Boc pyrroles in their 2,4-isomers is shown to proceed under mild acidic conditions. A reasonable mechanism, based on literature as well as experiments, is proposed to rationalize this transformation.

A systematic study outlining the enantioselective 1,4-addition of dialkylzinc reagents to 5-(1-arylalkylidene) and indenylidene Meldrum's acids is presented. Variation of the aryl and alkyl groups present on the alkylidene was thoroughly explored. The 1,4-addition displayed compatibility with a wide range of heteroaromatics and functional groups, and the arene pattern of ...

Conditions for the phosphoric acid-catalyzed highly enantioselective ring-opening of meso-aziridines with a series of functionalized aromatic thiol nucleophiles are described. The procedure utilizes commercially available aromatic thiols, a series of meso-aziridines, and a catalytic amount of VAPOL phosphoric acid to explore the substrate scope of this highly enantioselective reaction.

Generation of imino-quinone methide type intermediates from 2-aminothiazole-5-carbinols using alkylsulfonic acids in nitromethane followed by trapping with a wide range of nucleophiles effects C-C, C-O, C-N, C-S, and C-P bond formation.

Herein, we describe enantioselective addition of alkenyltin reagents possessing a reactive and sensitive allylic functionality not readily available to other classes of alkenyl metals. This method is enabled by the use of highly electrophilic alkylidene Meldrum's acids as acceptors and a cationic Rh(I)-diene complex as catalyst.

This letter describes two unprecedented one-pot high yielding synthetic approaches to imidazo[1,2-a]pyridine scaffolds from carbohydrates. The first approach involves microwave-assisted acid-catalyzed domino reactions of unprotected D-glucose/D-xylose with ammonium acetate and benzoin to afford polyhydroxy iminosugar-bearing tetrahydroimidazo[1,2-a]pyridines. In the second approach, polyhydroxy iminosugar-bearing tetrahydrobenzimidazo[1,2-a]pyridines were synthesized by using unprotected D-glucose/D-xylose and ...

A highly stereoselective synthesis of conformationally constrained cyclic gamma-amino acids has been devised. The key step involves an intramolecular cyclization of a nitronate onto a conjugated ester, promoted by a bifunctional thiourea catalyst. This methodology has been successfully applied to generate a variety of gamma-amino acids, including some containing three ...

A minor enantiomer recycling one-pot procedure employing two reinforcing chiral catalysts has been developed. Continuous regeneration of the achiral starting material is effected via selective enzyme-catalyzed hydrolysis of the minor product enantiomer from Lewis acid-Lewis base catalyzed addition of acyl cyanides to prochiral aldehydes in a two-phase solvent system. The ...

A three-step sequence to prepare polycyclic 2,5-dihydropyrroles from alpha-silyloxy ketones is presented. A Lewis acid-mediated ring fragmentation of cyclic gamma-silyloxy-beta-hydroxy-alpha-diazo esters provided tethered aldehyde ynoate intermediates which, when treated with amino acid silyl esters, underwent intramolecular azomethine ylide 1,3-dipolar cycloadditions. The 2,5-dihydropyrrole products were formed in good to excellent yield ...