Lewis acid promoted aldol additions of α-thiosilylketeneacetals to α-alkoxy aldehydes: diastereoselective synthesis of -α-methylene-β-hydroxy-∂-alkoxy esters.

MgBr₂ mediated addition of Methyl α-methylthio propionate silylketene acetal to α and α,β-alkoxy aldehydes is highly 3,4 -selective (18:1). -α- methylene-β- hydroxy-∂-alkoxy esters (6) and (8) are synthesized.     

A 13C NMR study of β-carboline alkaloids

The ¹³C NMR spectra of β-carboline alkaloids were determined, and unambiguous assignments of the spectra were carried out from the long-range coupling constants.     

Synthesis of α-hydroxy-β-lactams

A convenient synthesis of α-hydroxy-β-lactams has been devised that involves the annelation of an inline with benzyloxyacetyl chloride and triethylamine and subsequent hydrogenolysis in the presence of palladium on carbon. In most cases a cis-β-lactam was obtained. A thioimidate can also be used as the imino component in the annelation reaction but the hydrogenolysis step fails. The annelation of the appropriate thiazoline to a 6-epi-penicillin derivative occurred much more readily with benzyloxyacetyl chloride than with azidoacetyl chloride.     

Stereochemical study of hindered α-glycols by 1H and 13C NMR spectroscopy

Sterically hindered α-glycols, obtained from electrochemical hydrodimerization of polycyclic ketones (indanone, tetralone, chromanone, flavanone, xanthone and fluorenone), were studied by ¹H and ¹³C NMR. Evidence of conformational hindrance was deduced from the ¹H spectra; meso or racemic configurations and the conformational stereochemistry of these molecules in solution were assigned.     

13C NMR of α-haloketones

The carbon chemical shifts of several series of α-haloketones have been measured. Whereas the carbon carrying the halogens shows a regular downfield shift with increasing electronegativity of the substituents, the adjacent carbonyl carbon is shifted upfield by chlorine, bromine and iodine, and is little affected by fluorine substitution. The conformational implications of these results are discussed.     

A revised assignment of the 13C NMR spectra of α- and β-pinenes

α-Pinene and β-pinene ¹³C enriched at the C-10 position were prepared by an unambiguous synthesis. ¹³C NMR spectral analysis provided evidence for a revised assignment for α-pinene at the C-9 and C-10 carbon atoms.     

Structural determination of ε‐lactams by 1H and 13C NMR

The thermodynamic products (ε‐lactams) of the degradation of ten different spirocyclic oxaziridines were analyzed by ¹H and ¹³C NMR spectroscopy. The preferred conformations were determined by examining the homonuclear spin–spin coupling constant and the chemical shift effects of the N‐substituent and the alkyl group of the aliphatic ring on ¹H and ¹³C NMR spectra. Copyright © 2009 John Wiley & Sons, Ltd.     

1H and 13C NMR study of the enol–enolic tautomerism of some cyclic β-ketoaldehydes

Aldehyde (δCH) and enolic (δOH) proton chemical shifts, the corresponding spin–spin coupling constants (JCH,OH) and the ¹³C chemical shifts (δC) have been measured for three cyclic β-ketoaldehydes as a function of temperature. A tautomeric equilibrium has been shown to exist between the aldo–enol ( A ) and hydroxymethylene ketone ( B ) forms. The chemical shifts δCH δOH and δC for the two pure tautomeric forms A and B have been calculated. The enthalpy changes ΔH in the tautomeric process A ? B and the percentages of the tautomeric forms have been determined.     

13C NMR study of the enol forms of β-diketones

Carbon-13 NMR spectra of a series of β-diketones in the enol form with various β-substituents have been studied. An additive influence of the β-substituents on the chemical shifts of the carbon atoms in the hydrogen bonded chelate ring has been found. It is shown that the α- and β-carbon chemical shifts can be calculated by means of a set of increments for arbitrary combinations of the X and Y substituents. Analysis of the experimental data enables the conclusions to be drawn that enol–enolic tautomerism with different populations of the forms (A) and (B) is absent in β-diketones and that the carbon chemical shift changes are caused by electron density redistribution in the hydrogen bonded chelate ring (C).     

Additive Pummerer reactions of vinylic sulfoxides. Synthesis of γ-hydroxy-α,β-unsaturated esters, α-hydroxyketones, and 2-phenylsulfenyl aldehydes and primary alcohols

Treatment of β-monosubstituted vinylic sulfoxides 1 with trifluoroacetic anhydride in dichloromethane gave excellent yields of 1,2-bis(trifluoroacetoxy)thioethers 6. Mildly basic methanolysis of 2-alkyl-substituted 6 gave α-hydroxyaldehydes 11 as monomer-dimer mixtures; similar treatment of the 2-aryl analogues afforded aryl (hydroxymethyl) ketones 12. Compounds 11 underwent Wittig reactions with methoxycarbonylmethylenetriphenylphosphorane to give high yields of γ-hydroxy-α,β-unsaturated esters 13, predominantly as the E-isomers. β-Monosubstituted vinylic sulfoxides 1 possessing a β-aryl group, and β-disubstituted vinylic sulfoxides 3 reacted with trifluoromethanesulfonic anhydride-sodium acetate in acetic anhydride to give 2-(phenylsulfenyl)acylals 14. These gave 2-phenylsulfenyl aldehydes 15 upon basic methanolysis, and the corresponding primary alcohols 16 on reduction with sodium borohydride. Reaction of both geometric isomers of enantiomerically pure vinylic sulfoxide 1o with TFAA gave racemic 6o as a mixture of diastereomers. Reaction of optically pure (E)- and (Z)-1p with trifluoromethanesulfonic anhydride-sodium acetate in acetic anhydride gave acylal 19 in 10.5 and 23% e.e., respectively.     

Some aspects of anisochronism of geminal methyl groups in quaternised α-dimethylamino esters (1H and 13C NMR)

The magnitude of chemical shift nonequivalence (Δδ) in compounds having the general formula R¹CH(COOR²)N⁺R³Me₂X^? is discussed from the viewpoint of selective shielding of one of the geminal groups by the ester group in the preferred rotamer. In addition, a novel example of the increase of Δδ with rise in temperature has been observed.     

A nuclear magnetic resonance (1H and 13C) and isotope ratio mass spectrometry (δ13C, δ2H and δ18O) study of Andalusian olive oils

We have determined δ¹³C, δ²H and δ¹⁸O isotopic abundances in Andalusian olive oils. In addition, the fatty acid composition and the distribution of isomers at positions 1,3 and 2 of glycerol were determined by ¹H and ¹³C nuclear magnetic resonance (NMR) spectroscopy, respectively. Isotopic results obtained for four series of oil samples extracted from olives harvested in the 2004/05 and 2005/06 seasons are discussed in terms of olive variety, ripeness, geographical origin, fatty acid composition and growing altitude. A distinction was also established between olives grown in irrigated and in dry land by studying selected samples of the previous series and others from the 2005/06, 2006/07, 2007/08 and 2008/09 seasons. The results showed that olive ripeness does not influence the abundance of any of the three isotopes studied. On the other hand, the olive variety influences the abundance of the oxygen and hydrogen isotopes, and also, less markedly, that of carbon. No clear‐cut effect of height or latitude on isotope values is observed, probably because the olive variety also changes with height and latitude, thus masking such influences. The oil samples from dryland‐grown olives had increased δ¹³C values relative to irrigation‐grown olives. In addition, no definite relationship appears to exist between isotope distribution and fatty acid composition. Finally, oil samples from olives harvested in the 2005/06 season in Italy could be distinguished from those from Spain in terms of their isotopic values (δ²H mainly). Copyright © 2010 John Wiley & Sons, Ltd.     

1H and 13C NMR study of 2‐hydroxyglutaric acid and its lactone

Determination of the level and absolute configuration of 2‐hydroxyglutaric acid in a patient's urine is a method of diagnosing two metabolic diseases. Such a determination can be done with the aid of NMR spectroscopic methods. In this paper the careful interpretation of ¹H and ¹³C NMR spectra of this metabolite and its lactone measured under conditions used in biomedical assays is reported. The ¹H chemical shifts and spin–spin coupling constants were derived using the total lineshape analysis method. Copyright © 2002 John Wiley & Sons, Ltd.     

13C NMR of camphene and α-pinene: Revised assignments

The ¹³NMR signals of camphene (1) and α-pinene (2) are reassigned unequivocally. J(CH) values of 1, 2, bornene, norbornene and norbornadiene are reported.     

1H and 13C NMR spectral assignments of 2′‐hydroxychalcones

Chalcones are of interest to medicinal chemists because their structures can be easily modified with various functional groups. The syntheses and biological activities of chalcones from natural sources are well known. In this study, 24 2′‐hydroxychalcones bearing methoxy substituents were synthesized, among which five are new. The NMR data for all synthesized chalcones are described for the first time. The complete assignments of the ¹H and ¹³C NMR data can be used for the identification of newly discovered and widely isolated, synthesized chalcones. Copyright © 2013 John Wiley & Sons, Ltd.     

A simple H NMR approach to the conformations of α,β-diarylacrylonitriles

Room temperature 60 MHz NMR data of α,β-diarylacrylonitriles were interpreted in a search for a method for routine stereochemical assignments and to establish the conformational preferences of the β-heterocyclic ring. The conformation of the α-phenyl group differs from that of diaryl ethylenes previously investigated. Solvent effect on the conformations is observed only for pyrrole derivatives.     

13C NMR of organosulfur compounds the 13C chemical shifts of monocyclic γ- and δ-sultones

The ¹³C NMR spectra of several monocyclic γ-sultones(1,2-oxathiolane 2,2-dioxides) and δ-sultones(1,2-oxathiane 2,2-dioxides) have been determined and are presented herein. The chemical shifts of the ring carbons of these compounds are compared in terms of conformational, electronic and anisotropic differences. Electric field effects may be responsible for the chemical shifts of the C-α carbon, but do not appear to be important for C-α. Anisotropic deshielding also appears to be important for the chemical shifts of C-α, but the effects on C-α appear to be small. Dipole changes at C-α and C-α, induced by back donation of electron density from the ring oxygen to sulfur, may explain the chemical shifts at C-α. Substituent effects are readily explained in terms of well-known effects. In general, the carbons closest to the sulfonate group are found to be the most affected, and the carbons of the δ-sultones proximate to the sulfonate group are found to be more deshielded than those of the γ-sultones.