Search

A simple and efficient Mn-catalyzed acylation of amines is achieved using both acyl and alkoxy functions of unactivated esters with the liberation of molecular hydrogen as a sole byproduct. The present protocol provides an atom-economical and sustainable route for the synthesis of amides from esters by employing an earth-abundant manganese salt and inexpensive phosphine-free tridentate ligand. [ABSTRACT FROM AUTHOR]

We performed in situ observations of the crystallization and melting behaviors of palm mid fraction (PMF) on sorbitan ester (SE) crystals comprising different fatty acid moieties (sorbitan tripalmitate (STP), sorbitan tristearate (STS), or sorbitan tribehenate (STB)) to reveal the epitaxial relationship between fat crystals and emulsifier crystals. The effects of SEs on the thermal behavior and polymorphism of PMF were investigated by differential scanning calorimetry and synchrotron radiation X-ray diffraction. These measurements showed that the addition of STP and STS greatly increased the crystallization temperature of PMF, which was caused by the crystallized SEs that were nucleated prior to PMF. Microscopic observations demonstrated that PMF crystals were oriented in the same direction as crystals of STP and STS because the chain lengths of the fatty acid moieties were similar to those of PMF. In contrast, when STB was used as a substrate, PMF crystals were not oriented in the same direction as STB crystals because there is a large difference between the chain lengths of STB and PMF. These results revealed that crystal growth of PMF on STP and STS crystals occurs via epitaxial growth, whereas PMF crystallization on STB crystals occurs via general heterogeneous nucleation. [ABSTRACT FROM AUTHOR]

New pincer ruthenium complexes bearing a monodentate N-heterocyclic carbene ligand were synthesized and demonstrated as powerful hydrogenation catalysts. With an atmospheric pressure of hydrogen gas, aromatic, heteroaromatic, and aliphatic esters as well as lactones were converted into the corresponding alcohols at 50 °C. This reaction protocol offers reliable access to alcohols using an easy operational setup. [ABSTRACT FROM AUTHOR]

A method for chemoselective carbonyl ylide formation utilizing the Rh(II) catalyzed decomposition of electronically differentiated diazo malonates is disclosed. Treatment of ethyl, trifluoro ethyl diazo malonate with a Rh(II) catalyst selectively forms a carbonyl ylide from the relatively electron rich ethyl ester. This carbonyl ylide can be trapped by various alkynes giving highly functionalized oxabicyclic compounds in a chemo-, regio-, and diastereoselective fashion. [ABSTRACT FROM AUTHOR]

A highly enantioselective Friedel-Crafts alkylation of pyrrole to β,-unsaturated a-ketoesters was developed by virtue of a chiral copper complex, affording the alkylated derivatives of pyrrole with good yields and excellent enantioselectivities. Moreover, merging copper catalysis with gold catalysis realized a one-pot construction of the seven-membered ring to give annulated pyrroles with moderate to good yields and high enantiomeric excesses. [ABSTRACT FROM AUTHOR]

The ability to control chemical functionality is an exciting feature of modern polymer science that enables precise design of drug delivery systems. Ring-opening polymerization of functional monomers has emerged as a versatile method to prepare clinically translatable degradable polyesters.1 A variety of functional groups have been introduced into lactones; however, the direct polymerization of tertiary amine functionalized cyclic esters has remained elusive. We report a strategy that enabled the rapid synthesis of >130 lipocationic polyesters directly from functional monomers without protecting groups. These polymers are highly effective for siRNA delivery at low doses in vitro and in vivo. [ABSTRACT FROM AUTHOR]

A sequential procedure for the synthesis of 2,5-disubstituted thiazoles from terminal alkynes, sulfonyl azides, and thionoesters is reported. A copper(I)-catalyzed 1,3-dipolar cycloaddition of terminal alkynes with sulfonyl azides affords 1-sulfonyl-1,2,3-triazoles, which then react with thionoesters in the presence of a rhodium(II) catalyst. The resulting 3-sulfonyl-4-thiazolines subsequently aromatize into the corresponding 2,5-disubstituted thiazoles by elimination of the sulfonyl group. [ABSTRACT FROM AUTHOR]

Highly practical synthetic methods were developed for the C- and N-selective Grignard addition reactions of N-4-MeOC6H4-protected a-aldimino esters in the presence or absence of zinc(II) chloride. Diastereoselective C-alkyl addition, tandem C-alkyl addition-N-alkylation, and some transformations to synthetically useful optically active azacycles were demonstrated. [ABSTRACT FROM AUTHOR]

Cell-permeating esters of 2-ketoglutarate (2-KG) have been synthesized through a convergent sequence from two modules in two and three steps, respectively. This route provides access to a full series of mono- and disubstituted 2-KG esters, enabling us to define the effect of regioisomeric masking on metabolite release and antihypoxic activity in cell-based assays. In addition to providing insight into the biological activity of cell permeable 2-KG esters, the straightforward and modular nature of this synthetic route may prove useful for the development of next-generation 2-KG analogues for diagnostic and therapeutic applications. [ABSTRACT FROM AUTHOR]

Unexpectedly high rates of reaction between alkyllithium reagents and amides, compared to esters and ketones, were observed by Rapid Inject NMR and competition experiments. Spectroscopic investigations with 4-fluorophenyllithium (ArLi, mixture of monomer and dimer in THF) and a benzoate ester identified two reactive intermediates, a homodimer of the tetrahedral intermediate, stable below -100 °C, and a mixed dimer with ArLi. Direct formation of dimers suggested that the ArLi dimer may be the reactive aggregate rather than the usually more reactive monomer. In contrast, RINMR experiments with ketones demonstrated that the ArLi monomer was the reactive species. [ABSTRACT FROM AUTHOR]

Multicomponent self-assembly of Re2(CO)10, diaryl dichalcogenide ligands (REER), andphenyl-1,3,5-tris(isonicotinate)(ptin) under solvothermal conditions has resulted in the formationof chalcogen-bridged trigonal metallaprisms of the general formula[{(CO)3Re(μ-ER)2Re(CO)3}3(μ3-ptin)2] (1–5), wherein E = S, Se and R = phenyl, p-tolyl,benzyl. Oxidative addition of diaryl disulfide/diaryl diselenide toRe2(CO)10with the ester-functionalized tritopiclinker ptin has yielded trigonal metallaprisms 1–5under facile reaction conditions. The metallaprisms 1–5have been characterized using elementalanalysis and IR, UV–vis, and NMR spectroscopic techniques.Single-crystal X-ray structures have been obtained for 3and 4. The structural features and chirality of metallaprisms 3and 4in the solid state have been highlighted. [ABSTRACT FROM AUTHOR]

Copper(I)-catalyzed conjugate additionsof silyl boronic estersto α,β-unsaturated aldehydes, ketones, and esters aresynthetically well-established reactions. For the first time centralreactive intermediates as well as the boron enolates as the primaryreaction products are isolated and employed in order to deduce catalyticcycles on an experimental basis. Employing an NHC CuIcomplexas a model catalyst, it is possible to perform efficient catalytictransformations as well as to isolate and characterize the formedcopper enolate complexes as the key intermediates. It is shown thatfor this catalytic system the nature of this enolateO- or C-enolateis crucial for thecatalytic process. For α,β-unsaturated aldehydes and ketonesthe O-enolate is formed predominantly, while forα,β-unsaturated esters the C-enolateis the major product. Catalytic turnover is only facile for copper O-enolates, as they react efficiently with the silyl boronicester under (re)formation of the catalytically active Cu–Sispecies and a thermodynamically favored boric acid ester. Thus, theformation of copper C-enolates is inhibiting thecatalytic process, and effective turnover is possible only after solvolysisby an alcohol additive. The individual catalytic processes were retracedby performing stepwise stoichiometric reactions monitored by in situNMR spectroscopy. [ABSTRACT FROM AUTHOR]

Decreases of up to 50% in the moistureuptake of polycyanuratenetworks based on 2,2-bis(4-cyanatophenyl)propane (BADCy) and 1,1-bis(4-cyanatophenyl)ethane(LECy) were observed when analogous networks containing a single methylgroup ortho- to each aryl–cyanurate linkagewere prepared by reduction and acid-catalyzed coupling of salicylicacid followed by treatment with cyanogen bromide and subsequent cyclotrimerization.The differences in water uptake were observed despite similar decreasesin packing fraction as conversion proceeded in all networks studied.Conversely, the presence or absence of methyl groups at arylene bridges,remote from the cyanurate oxygen, had no influence on water uptake.Vitrification during cure had little effect on either free volumedevelopment or moisture uptake. These results confirm that sterichindrance from ortho-methyl groups inhibits absorptionof water presumably by decreasing the thermodynamic favorability ofsterically permitted interaction with the cyanurate oxygen. A furtherexamination of the effect of two different catalysts, 2 parts perhundred of a 30:1 by weight mixture of nonylphenol and copper(II)acetylacetonate and 500 ppm of dibutyltin dilaurate (DBTDL), comparedto analogous uncatalyzed networks, showed that hydrolytic stabilitywas dramatically affected by catalyst choice, while thermochemicalstability was also impacted. These results provide important insightsinto the mechanisms that determine structure–property relationshipsin polycyanurate networks. [ABSTRACT FROM AUTHOR]

The N-heterocyclic carbene and hydroxamic acid cocatalyzed kinetic resolution of cyclic amines generates enantioenriched amines and amides with selectivity factors up to 127. In this report, a quantum mechanical study of the reaction mechanism indicates that the selectivity-determining aminolysis step occurs via a novel concerted pathway in which the hydroxamic c acid plays a key role in directing proton transfer from the incoming amine. This modality was found to be general in amide bond formation from a number of activated esters including those generated from HOBt and HOAt, reagents that are broadly used in peptide coupling. For the kinetic resolution, the proposed model accurately predicts the faster reacting enantiomer. A breakdown of the steric and electronic control elements shows that a gearing effect in the transition state is responsible for the observed selectivity. [ABSTRACT FROM AUTHOR]

Recent developments in ambient mass spectrometry (AMS), such as atmospheric solids analysis probe (ASAP) mass spectrometry, open a whole new range of possibilities to screen for drug preparations. In this study, the potential of ASAP for the rapid identification and quantification of anabolic steroid esters has been evaluated. These compounds are known to be used both in human and in food producing animals to enhance performances and to improve the rate of growth, respectively. Using a triple quadrupole (QqQ) MS instrument, mechanism of ionization and fragmentation in both positive and negative mode were studied for a range of 21 selected steroid esters (based on testosterone, estradiol, nandrolone, and boldenone) which highlighted common neutral mass loss of 96.1, thus allowing rapid screening in minutes to reveal steroid ester presence with minimal sample preparation. Ester identification is further achieved through an efficient 2 min workflow on a QqQMS instrument. Moreover, the use of isotope labeled internal standards permitted the quantification of the corresponding steroid esters in selected reaction monitoring (SRM) mode, for the first time in ASAP. This approach was successfully applied for characterization of oily commercial preparations. These results open new perspectives in hormone (and drug) rapid analysis by ASAP-MS in the near future. [ABSTRACT FROM AUTHOR]

A C60Prato derivativewith bis-tBu ester was prepared as a stableand convenient scaffold forthe development of fullerene derivatives such as water-soluble C60–PEG conjugates, fulleropeptides viasolid phase synthesis, and bis-functionalized C60. [ABSTRACT FROM AUTHOR]

Thealkylation of (Z)-3-aryl-2-fluoroallyl acetatewith the malonate anion by the [Pd(C3H5)(cod)]BF4/2,2′-bpy catalyst proceeds through the carbon–fluorinebond cleavage, and 2 equiv of the malonate nucleophile was introducedto the allyl substrate. [ABSTRACT FROM AUTHOR]