Competing Mechanisms in Palladium-Catalyzed Alkoxycarbonylation of Styrene.

Palladium-catalyzed carbonylation is a versatile method for the synthesis of various aldehydes, esters, lactones, or lactams. Alkoxycarbonylation of alkenes with carbon monoxide and alcohol produces either saturated or unsaturated esters as a result of two distinct catalytic cycles. The existing literature presents an inconsistent account of the procedures favoring oxidative carbonylation products.

Using the Gut Microbiome to Assess Stocking Efforts of the Endangered Pallid Sturgeon, .

The endangered Pallid Sturgeon, , has been actively managed to prevent population declines, including stocking of hatchery-raised fish. The gut microbiome plays an innate role in an organism's absorption of nutrients by increasing nutrient availability and can provide new insights for Pallid Sturgeon management. In this study, the Pallid Sturgeon's microbiome is dominated by the phyla Proteobacteria, Firmicutes, Actinobacteria and Fusobacteria.

Non-enzymatic electrochemical determination of cholesterol in dairy products on boron-doped diamond electrode.

Determination of cholesterol in food matrices is essential for quality control concerning the health of consumers. Herein, a simple electrochemical approach for cholesterol quantitation in dairy products is evaluated. The newly developed differential pulse voltammetric method using acetonitrile-perchloric acid mixture as a supporting electrolyte is statistically compared to GC-MS and HPLC-UV.

Reductive Amination Revisited: Reduction of Aldimines with Trichlorosilane Catalyzed by Dimethylformamide─Functional Group Tolerance, Scope, and Limitations.

Aldimines, generated in situ from aliphatic, aromatic, and heteroaromatic aldehydes and aliphatic, aromatic, and heteroaromatic primary or secondary amines, can be reduced with trichlorosilane in the presence of dimethylformamide (DMF) as an organocatalyst (≤10 mol %) in toluene or CHCl at room temperature. The reduction tolerates ketone carbonyls, esters, amides, nitriles, sulfones, sulfonamides, NO, SF, and CF groups, boronic esters, azides, phosphine oxides, C═C and C≡C bonds, and ferrocenyl nucleus, but sulfoxides and -oxides are reduced. α,β-Unsaturated aldimines undergo 1,2-reduction only, leaving the C═C bond intact.

Reaction Outcome Critically Dependent on the Method of Workup: An Example from the Synthesis of 1-Isoquinolones.

A striking dependence on the method of workup has been found for annulation of benzonitriles ArC≡N to -methyl 2-toluamide (), facilitated by -BuLi (2 equiv): quenching the reaction by a slow addition water produced the expected 1-isoquinolones ; by contrast, slow pouring of the reaction mixture water afforded the cyclic aminals (retaining the NMe group of the original toluamide). The mechanism of the two processes is discussed in terms of the actual H concentration in the workup. Both and were then converted into the corresponding 1-chloroisoquinolines , coupling of which, mediated by (PhP)NiCl/Zn, afforded bis-isoquinolines .

Voltammetry of 7-dehydrocholesterol as a new and useful tool for Smith-Lemli-Opitz syndrome diagnosis.

7-Dehydrocholesterol is an essential biomarker of Smith-Lemli-Opitz syndrome, a congenital autosomal recessive disorder. This study shows for the first time that electrochemical oxidation of 7-dehydrocholesterol can be used for its voltammetric determination. Two classes of supporting electrolytes in acetonitrile and a mixture of acetonitrile-water were used: inorganic acids known to promote structural changes of steroids and indifferent electrolytes.

Habitat characterization and species distribution model of the only large-lake population of the endangered Silver Chub (, Kirtland 1844).

The endangered Silver Chub ( Kirtland 1844) is native to North America and primarily riverine, with the only known large-lake population in Lake Erie. Once a major component of the Lake Erie fish community, it declined and became nearly extirpated in the mid-1900s. Recent collections in western Lake Erie suggest that Silver Chub may be able to recover, but their habitat and distribution are poorly known.

A novel voltammetric approach to the detection of primary bile acids in serum samples.

An innovative voltammetric approach to the detection of cholic and chenodeoxycholic acids is presented. These two primary bile acids are important biomarkers of liver function in humans and are involved in many physiological processes in the human body. Herein we describe a way to reproducibly convert the hard-to-detect bile acid molecule into an easily detectable derivative in situ using 0.

A New Insight into the Stereoelectronic Control of the Pd -Catalyzed Allylic Substitution: Application for the Synthesis of Multisubstituted Pyran-2-ones via an Unusual 1,3-Transposition.

Pyran-2-ones 3 undergo a novel Pd -catalyzed 1,3-rearrangement to afford isomers 6. The reaction proceeds via an η -Pd complex, the pyramidalization of which (confirmed by quantum chemistry calculations) offers a favorable antiperiplanar alignment of the Pd-C and allylic C-O bonds (C), thus allowing the formation of an η -Pd intermediate. Subsequent rotation and rate-limiting recombination with the carboxylate arm then gives isomeric pyran-2-ones 6.

Cross-Aldol Reaction of Isatin with Acetone Catalyzed by Leucinol: A Mechanistic Investigation.

Comprehensive mechanistic studies on the enantioselective aldol reaction between isatin (1 a) and acetone, catalyzed by L-leucinol (3 a), unraveled that isatin, apart from being a substrate, also plays an active catalytic role. Conversion of the intermediate oxazolidine 4 into the reactive syn-enamine 6, catalyzed by isatin, was identified as the rate-determining step by both the calculations (ΔG(≠) =26.1 kcal mol(-1) for the analogous L-alaninol, 3 b) and the kinetic isotope effect (kH /kD =2.

The syn/anti-dichotomy in the palladium-catalyzed addition of nucleophiles to alkenes.

In this review the stereochemistry of palladium-catalyzed addition of nucleophiles to alkenes is discussed, and examples of these reactions in organic synthesis are given. Most of the reactions discussed involve oxygen and nitrogen nucleophiles; the Wacker oxidation of ethylene has been reviewed in detail. An anti-hydroxypalladation in the Wacker oxidation has strong support from both experimental and computational studies.

Palladium-catalyzed stereoselective intramolecular oxidative amidation of alkenes in the synthesis of 1,3- and 1,4-amino alcohols and 1,3-diamines.

An efficient and practical Pd-catalyzed intramolecular oxidative allylic amidation provides facile access to derivatives of 1,3- and 1,4-amino alcohols and 1,3-diamines. The method operates under mild reaction conditions (RT) with molecular oxygen (1 atm) as the sole reoxidant of Pd. Excellent diastereoselectivities were attained with substrates bearing a secondary stereogenic center.

Palladium-catalyzed alkoxycarbonylation of terminal alkenes to produce α,β-unsaturated esters: the key role of acetonitrile as a ligand.

A mild protocol has been developed for the Pd(II)-catalyzed alkoxycarbonylation of terminal olefins to produce α,β-unsaturated esters with a wide range of substrates. Key features are the use of MeCN as solvent (and/or ligand) to control the reactivity of the intermediate Pd complexes and the combination of CO with O2, which facilitates the Cu(II)-mediated reoxidation of the Pd(0) complex to Pd(II) and prevents double carbonylation.

Mechanistic dichotomy in the asymmetric allylation of aldehydes with allyltrichlorosilanes catalyzed by chiral pyridine N-oxides.

Detailed kinetic and computational investigation of the enantio- and diastereoselective allylation of aldehydes 1 with allyltrichlorosilanes 5, employing the pyridine N-oxides METHOX (9) and QUINOX (10) as chiral organocatalysts, indicate that the reaction can proceed through a dissociative (cationic) or associative (neutral) mechanism: METHOX apparently favors a pentacoordinate cationic transition state, while the less sterically demanding QUINOX is likely to operate via a hexacoordinate neutral complex. In both pathways, only one molecule of the catalyst is involved in the rate- and selectivity-determining step, which is supported by both experimental and computational data.

Genetic and morphometric differences demonstrate fine-scale population substructure of the yellow perch Perca flavescens: need for redefined management units.

Whole-body morphometrics and 15 nuclear DNA microsatellite loci were analysed for 158 Perca flavescens collected during the spawning season from four spawning locations in central Lake Erie, two along the northern shore and two along the southern shore, to evaluate fine-scale variation (spanning 17-94 km). Results showed significant morphological and genetic differences among P. flavescens from the four locations.

Catalyst development for organocatalytic hydrosilylation of aromatic ketones and ketimines.

A new family of Lewis basic 2-pyridyl oxazolines have been developed, which can act as efficient organocatalysts for the enantioselective reduction of prochiral aromatic ketones and ketimines with trichlorosilane, a readily available and inexpensive reagent. 1-Isoquinolyl oxazoline, derived from mandelic acid, was identified as the most efficient catalyst of the series, capable of delivering high enantioselectivities in the reduction of both ketones (up to 94% ee) and ketimines (up to 89% ee).

Stereoselective palladium-catalyzed functionalization of homoallylic alcohols: a convenient synthesis of di- and trisubstituted isoxazolidines and β-amino-δ-hydroxy esters.

Enantiopure, Boc-protected alkoxyamines 12 and 13, derived from the readily available homoallylic alcohols 4 via a reaction that involves either inversion or retention of configuration, undergo a diastereoselective Pd-catalyzed ring-closing carbonylative amidation to produce isoxazolidines 16/17 (≤50:1 diastereoisomer ratio (d.r.)) that can be readily converted into the N-Boc-protected esters of β-amino-δ-hydroxy acids and their γ-substituted homologues 37.

A modular approach to aryl-C-ribonucleosides via the allylic substitution and ring-closing metathesis sequence. a stereocontrolled synthesis of all four α-/β- and D-/L-C-nucleoside stereoisomers.

Iridium(I)-catalyzed allylation of the enantiopure monoprotected copper(I) alkoxide, generated from (S)-5a, with the enantiopure allylic carbonates (R)-9a,b has been developed as the key step in a new approach to C-nucleoside analogues. The anomeric center was thus constructed via a stereocontrolled formation of the C-O rather than C-C bond with retention of configuration. The resulting bisallyl ethers 15a,b (≥90% de and >99% ee) were converted into C-ribosides 29a,b via the Ru-catalyzed ring-closing metathesis, followed by a diastereoselective dihydroxylation catalyzed by OsO(4) or RuO(4) and deprotection.

Mapping lipid and detergent molecules at the surface of membrane proteins.

Electron-density maps for the crystal structures of membrane proteins often show features suggesting binding of lipids and/or detergent molecules on the hydrophobic surface, but usually it is difficult to identify the bound molecules. In our studies, heavy-atom-labelled phospholipids and detergents have been used to unequivocally identify these binding sites at the surfaces of test membrane proteins, the reaction centres from Rhodobacter sphaeroides and Blastochloris viridis. The generality of this method is discussed in the present article.

Enantioselective allylation of α,β-unsaturated aldehydes with allyltrichlorosilane catalyzed by METHOX.

α,β-Unsaturated aldehydes 6a-j undergo an enantioselective allylation with allylic trichlorosilanes 2a,b in the presence of METHOX (4) as a Lewis basic catalyst (≤10 mol %) to produce the homoallylic alcohols 7a-l at good to high enantioselectivity (83-96% ee). This study shows that the reactivity scope of METHOX can be extended from aromatic to nonaromatic aldehydes.

Dendron-anchored organocatalysts: the asymmetric reduction of imines with trichlorosilane, catalysed by an amino acid-derived formamide appended to a dendron.

Asymmetric reduction of ketimines with trichlorosilane can be catalysed by the Lewis-basic N-methylvaline-derived formamide anchored to a soluble dendron () with good enantioselectivity ( View Article and Find Full Text PDF

Weak intra- and intermolecular interactions in a binaphthol imine: an experimental charge-density study on (+/-)-8'-benzhydrylideneamino-1,1'-binaphthyl-2-ol.

The charge density in (+/-)-8'-benzhydrylideneamino-1,1'-binaphthyl-2-ol (1) has been studied experimentally using Mo Kalpha X-ray diffraction at 100 K, and by theory using density-functional thoery (DFT) calculations at the B3LYP/6-311++G** level. The nature of the weak intramolecular peri-C..

Desymmetrization of cyclic meso-epoxides with silicon tetrachloride catalyzed by PINDOX, a chiral bipyridine mono-N-oxide.

PINDOX 8 has been identified as a chiral organocatalyst for the enantioselective ring-opening of cyclic meso-epoxides with SiCl(4) to produce chlorohydrins in up to 90% ee. The catalyst is most effective with saturated cyclic substrates containing more than seven carbon units.

On the selective N-methylation of BOC-protected amino acids.

The selective N-methylation of BOC-protected valine 1a with MeI and NaH in THF (i.e., in the presence of a free carboxyl group) has been attributed to the protection of the carboxylate by chelation to Na(+).