Irina P. Smoliakova

Direct ortho -palladation of 2-phenyl-2-oxazoline: Crystal structure of Cl2Pd(OCH2CH2NCPh)2 and Cl(PPh3)Pd(OCH2CH2NCC6H4)

Direct ortho -palladation of sterically non-hindered 2-phenyl-2-oxazoline ( 1 ) using Pd(OAc) 2 and AcONa in AcOH provided di-μ-acetatobis-[2-(2-oxazolinyl)phenyl,1-C,3-N]dipalladium(II) ( 3a ) in a yield of 63%. Dimeric complex 3a was converted into the corresponding μ-chloro analog ( 3b ) by the reaction with LiCl in acetone in quantitative yield. Compound 3b was also obtained in 90% yield by the ligand exchange reaction of oxazoline ( 1 ) with dimeric ortho -palladated complex of N , N -dimethylbenzylamine in a AcOH–CHCl 3 mixture at 50°C. The same reaction at room temperature provided the coordination complex dichlorobis-(2-phenyl-2-oxazoline)palladium(II) ( 2 ); the use of toluene in this reaction (50°C) led to the formation of chloro[ N , N -dimethylbenzylamino]-(2-phenyl-2-oxazoline)palladium(II) ( 5 ). Dimer 3b reacted with 2,4-pentadionate and PPh 3 to yield the corresponding mononuclear derivatives 6 and 7 , respectively. The structures of coordination complex 2 and phosphane adduct 7 were confirmed by X-ray diffraction analysis. Compound 2 has a centrosymmetric structure with strictly planar coordination environment of the palladium center and a close above-plane approach of the ortho -CH bond to the metal center. In adduct 7 , both the palladium coordination sphere and palladacycle are nearly planar.

Homochiral cyclopalladated complexes of (S)-4-tert-butyl-2-phenyl-2-oxazoline. X-ray study of (S,S)-di-μ-chlorobis-{2-[2-(4-tert-butyl)oxazolinyl]phenyl-C,N}dipalladium(II)

Abstract Due to steric promotion of CH bond activation, the direct ortho-palladation of (S)-4-tert-butyl-2-phenyl-2-oxazoline using Pd(OAc)2 in AcOH provided (S,S)-di-μ-acetatobis-[2-(2-(4-tert-butyl)oxazolinyl)phenyl-C,N]dipalladium(II) (2) in an excellent yield. This complex was converted into its corresponding μ-chloro analog (3) using LiCl in acetone. Dimer 3 reacted with PPh3 to furnish the phosphane mononuclear derivative 4. The structure of the dimer complex 3 was confirmed by X-ray diffraction analysis.

Extractable Organic Carbon and its Differentiation by Polarity in Diesel Exhaust, Wood Smoke, and Urban Particulate Matter

In order to determine whether characterization of organic carbon (OC) in particulate matter (PM) is limited due to the extraction or analysis, we have evaluated the OC extractability from three model PM matrices (wood smoke, diesel exhaust, and urban PM). We have compared hot pressurized water (HPW) fractionation and sequential organic solvent Soxhlet extraction. The evaluation of extraction efficiency was based on three methods: thermal optical transmittance (TOT), reflectance, and total organic carbon analyses. For all three PM samples, comparable OC yields were obtained with both extraction methods accounting for ∼ 45–60% of the total OC found in PM (based on TOT). These recoveries also suggest that a significant portion of OC in all PM materials remains unextractable. Further investigation of OC distribution in different polarity fractions using spectrometric techniques (including gas chromatography with mass spectrometry, carbon 1s near-edge X-ray absorption fine structure, and proton nuclear magnetic resonance spectroscopies) revealed that sequential extraction may be useful approach to differentiate the constituents attributed to primary emission sources and to secondary aerosol formation, respectively. In contrast to the common expectation that polarity of constituents corresponds to the polarity of the extracting solvent, distribution of OC species (among the different polarity fractions) also depended on their availability (i.e., analyte-matrix interactions). It appears that secondary OC species (e.g., diacids) are not deeply embedded into the matrix, and thus were recovered in the solvent of a corresponding polarity. By contrast, primary OC constituents are strongly bound to the matrix and thus required harsh conditions to be recovered.

Structural Characterization of α,β-Unsaturated Aldehydes by GC/MS is Dependent upon Ionization Method

Abstractα,β-unsaturated aldehydes are toxic products of lipid peroxidation. Detection and characterization of these aldehydes is important in many human disease states as well as in the food industry. Our study shows that electron ionization-mass spectrometry (EI-MS) and positive-ion chemical ionization-mass spectrometry (PICI-MS), but not electron capture negative ionization-mass spectrometry (ECNI-MS), can be used to detect the C4-hydroxylation state of α,β-unsaturated aldehydes derivatized with pentafluorobenzyl hydroxylamine alone. EI-MS and PICI-MS spectra of 4-hydroxy-2-alkenals contained a fragment with m/z 252, whereas spectra of 2-alkenals contained a fragment with m/z 250. These fragments are consistent with fragmentation between C3 and C4 with transfer of two hydrogens from C4 and the C4 hydroxyl group in the case of 4-hydroxy-2-alkenals. In addition, EI-MS and PICI-MS were able to distinguish 4-hydroxy-2-alkenals and 2-alkenals from 4-keto-2-alkenals and 4-hydroxyalkanals. On the other hand, ECNI-MS provided complex spectra regarding C4-hydroxylation state. Furthermore, the syn- and anti-configurations of PFB-oximes had different resultant spectra using ECNI-MS, but not with EI-MS or PICI-MS. These data indicate that EI-MS and PICI-MS are more amenable for structural analysis of α,β-unsaturated aldehydes than ECNI-MS.

Reaction of vinyl ethers with ArSCl adducts of d-glucal

Abstract Lewis acid mediated reactions of vinyl ethers with ArSCl adducts of benzyl protected D-glucal followed by quenching of the five-membered sulfonium salt intermediates with external nucleophiles, H2O, MeOH, and n-Bu4NBH4, lead to a highly stereoselective formation of β-C-glucopyranosides with different functional groups in the lateral chain.

One-pot synthesis of C-glycosylic compounds (C-glycosides) from d-glucal, p-tolylsulfenyl chloride and aromatic/heteroaromatic compounds in the presence of Lewis acids

In the presence of Zn(CN)(2), benzylated 2-thio-2-S-(p-tolyl)pyranosyl chlorides (2) generated in situ from tri-O-benzyl-D-glucal and p-TolSCl, smoothly react with thiophene, 2-methylthiophene, furan, 2-methylfuran, and N-methylpyrrole to give heteroaryl 2-thio-2-S-(p-tolyl)-C-beta-D-glucopyranosylic compounds (C-glycosides) in good yields. Upon treatment with SnCl(4), the reaction of chlorides 2 with thiophene or 1,4-dimethoxybenzene provides the corresponding benzylated C-beta-D-glucofuranosylic derivatives. Under the same conditions, the use of 2-methylthiophene, furan, 2-methylfuran, or N-methylpyrrole yields (2S,3R,4R,5S)-1,3,4-tribenzyloxy-6,6-diheteroaryl-5-(p-tolylthio)-2-hexanoles. Treatment of 2 and mesitylene with AgBF(4) yielded 1,6-anhydro-3,4-di-O-benzyl-2-thio-2-S-(p-tolyl)-beta-D-glucose.

Stereoselective synthesis of β-C-d-glucopyranosides using the reaction of TMSCN and Grignard reagents with cyclic five-membered sulfonium salt intermediates

Abstract In the presence of a Lewis acid, ArSCl adducts of tri- O -benzyl- d -glucal react with vinyl ethers to form cyclic five-membered sulfonium salt intermediates. The latter are capable of reacting with TMSCN and Grignard reagents furnishing exclusively 2- S -(aryl)-2-thio-β- C - d -glucopyranosides. The one-pot reaction also proceeds with high stereoselectivity of C–C bond formation in the lateral chain providing exclusively or predominantly C -glycosides with ( S )-configuration of the chiral center in the lateral chain.

The Use of tert-Butyl Vinyl Ether in Stepwise Electrophilic Addition Reactions

Abstract tert-Butyl vinyl ether (1) reacts with p-TolSCl to give 2-tert-butoxy-2-chloroethyl p-tolyl sulfide (2). In the presence of SnCl4, 2 reacts with silyl enol ethers, allyltrimethylsilane, and vinyl ethers to form a C-C bond. In the case of vinyl ethers, the reaction proceeds through the formation of the 5-membered sulfonium salt intermediate which in turn can react with H2O, TMSCN, allyltrimethylsilane, and Grignard reagents.

Stereoselective synthesis of C-[2-S-(p-tolyl)-2-thio-β-d-galactopyranosyl] compounds using the reaction of TolSCl adducts of d-galactal with C-nucleophiles

Pyranosyl chlorides prepared in situ from tri-O-benzyl-D-galactal and TolSCl react with silyl enol ethers, allyltrimethylsilane, and vinyl ethers to give a mixture of beta-C-galacto and alpha-C-talopyranosides in a ratio of 19:1.

Tandem sequence of ArSCl initiated AdE reactions resulting in formation of two C–C bonds

A one-pot procedure for the sequence of reactions between arylsulfanyl chloride, vinyl ether-I, vinyl ether-II and organomagnesium reagents has been developed for assembling polyfunctional compounds from simple precursors. 2,3-Dihydropyran and various vinyl ethers have been used as VE-I and/or VE-II. The dependence of the stereochemical course of the carbon–carbon bond formation step upon the Lewis acid has been studied. In the case of the sequence p-toiylsulfanyl chloride, 2,3-dihydropyran, 1-methoxy-2-methylpropene and Grignard reagent the reaction initiated with TiCl4 takes place with a very high diastereoselectivity ( > 95%).