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Naturally occurring γ-butyrolactones and their synthetic analogues display a wide range of bioactivities. Here, the multicomponent reaction of dimethyl 2-benzyl-3-methylenesuccinate with bromobenzene and benzaldehyde catalyzed by cobalt (II) bromide afforded a maculalactone derivative with three stereogenic centers. This reaction presented moderate diastereoselectivity and yielded different proportions of all the four possible diastereoisomers. The anti:anti (majority), anti:syn, syn:anti, and syn:syn diastereoisomers were isolated and characterized by 1D and 2D NMR experiments. Because the stereochemical assignment of all the diastereoisomers by Nuclear Overhauser Effect Difference (NOEDiff) experiments was not definitive, the 1H and 13C NMR chemical shifts were predicted by theoretical calculations with the density functional theory at the B3LYP/6-31G(d) level. The relative configurations of all the four diastereoisomers were assigned by using the CP3 parameter to compare the experimental and the calculated data and by determining the CP3 probability, which provided high level of confidence.

The possibility of determining enantiomeric excess (ee) in chiral compounds by nuclear magnetic resonance (NMR) was discovered half a century ago and remains an important strategy nowadays. One way to determine ee in chiral compounds is to obtain diastereoisomers by using chiral derivatization agents (CDAs). CDAs bearing an aldehyde function have helped to discriminate primary chiral amines through a reaction that promptly yields imines. To the best of our knowledge, acyclic terpenes displaying an aldehyde function like S-citronellal have not been used in this context yet. In this study, we obtained excellent accuracy when we quantified aliphatic and aromatic amines by 1H and 13C NMR using S-citronellal as CDA. This analytical method proved to be fast and useful to quantify primary chiral amines.

This Letter describes the use of NbCl5 as the Lewis acid in Friedel–Crafts reactions, in which a bifunctional electrophile reacts inter- and intramolecularly with an aromatic ring to produce a number of indanones in a single step, maintaining mild conditions and good yields.

We describe here the dynamic 1 H NMR studies of dimethyl 2-(triphenylphosphoranylidene) succinate ( 1 ). Phosphorane 1 has a bond presenting slow (in the 1 H NMR time scale) rotation which results in spectra of two isomers at the same time. From the spectral data were calculated the rate constant and thermodynamic parameters for the rotational process.

The direct E/Z configuration assignment of tri- and tetra-substituted stilbenes (and other analogous olefins) when only one of the isomers is available is a quite challenging task. Sometimes, a chemical transformation or some other tedious method is necessary for determination of the double bond substitution pattern. In this paper, we relied on theoretical calculation of chemical shifts as a complementary tool for 1H NMR determination of the configuration of an α-phenylcinnamic acid prepared as a unique isomer by the Perkin reaction.

The keto–enol tautomerization for 4,4-dimethyl-cyclohexane-1,3-dione ( 1 ) and for 4-methyl-cyclohexane-1,3-dione ( 2 ) was investigated. We observed that one of the possible keto-enolic forms for each compound is more stable than the other and thus was preferentially formed in the keto–enol tautomerism. This study was supported through NMR analysis, geometry optimization calculations and NBO analysis for keto-enolic forms ( 3 and 4 ) and ( 5a , b and 6a , b) .

In this paper we present a complete 1H and 13C NMR spectral analysis of three lignan lactones (methylpluviatolide, dimethylmatairesinol and hinokinin) by the use of techniques such as COSY, HMQC, HMBC and J-resolved. Complete assignment and all homonuclear hydrogen coupling constant measurements were performed, providing enough data also to the confirmation of the relative stereochemistry.

Theoretical methods were used for the correct structure assignments of the natural products jungianol and mutisianthol. A three stage protocol for the calculation was used: a conformational search using molecular mechanics (MM3), a DFT (B3LYP) structure optimization and ab initio (HF/GIAO) or DFT (B3LYP/GIAO) calculation of magnetic properties.

A detailed NMR analysis with total assignment of 1 H and 13 C NMR data for the endo and the exo adducts, obtained by Diels–Alder reaction between 2-cyclohexenone and cyclopentadiene, is described. The unequivocal assignment of the endo and exo structures was performed by 1 H and 13 C NMR. These assignments were supported by theoretical chemical shift calculations at GIAO/HF level using 6-311+g(2d,p) from optimized structures at the B3LYP/6-31g(d) level.

GIAO and CSGT models at Hartree–Fock and DFT/B3LYP levels of theory using different basis sets were employed for calculations of 1 H and 13 C NMR chemical shifts for para -X-substituted (X = H, CH 3 O and NO 2 ) aromatic carbonyl compounds. For these compounds the best choice to evaluate theoretical chemical shifts is B3LYP/cc-pVDZ using CSGT model.

2012Non-substituted B-ring flavonoids and anindole alkaloid from Piper aleyreanum(Piperaceae) BIOCHEMICAL SYSTEMATICS AND ECOLOGY, OXFORD, v. 45, n. 1, Special Issue, supl. 1, Part1, pp. 206-208, DEC, 2012http://www.producao.usp.br/handle/BDPI/37434 Downloaded from: Biblioteca Digital da Producao Intelectual - BDPI, Universidade de Sao Paulo

The long-range ( 4 J HH ) coupling constants of 28 compounds, cyclopentane and cyclohexane derivatives, have been analyzed by means of principal component analysis (PCA). The corresponding dihedral angles ( θ 1 and θ 2 ) and cos 2 θ 1 cos 2 θ 2 , besides the ‘ W ’ constants, were utilized as variables in multivariable data analysis. Dihedral (torsion) angles were calculated utilizing three different methods: PC Model, CS Mopac Pro and gaussian98 , to improve data reliability. The measured 4 J HH showed a clear tendency of increasing with the variations in torsion angles from approximately 90–180°, as expected. PCA allowed discrimination of the behaviour of various compounds. It was noted that the compounds analyzed exhibit strong clustering due to structural similarities. Particularly interesting results were obtained in the PCA of gaussian98 data, where seven different clusters of compounds were found.

The conformational preferences of p-menthan-3,9-diols in both aqueous and chloroform solutions have been investigated by molecular dynamics simulations. The effects of changing the stereochemistry at the C3 atom on the dynamics of these compounds have been studied by considering the two epimers. The results reveal a strong dependence of conformation on both the stereochemistry and the environment. In some cases the formation of an intramolecular hydrogen bond stabilises unusual conformations for the cyclohexane ring.

The core structure of the natural sesquiterpene lactones furanoheliangolides, an 11-oxabicyclo[6.2.1]undecane system, was synthesized through a pathway involving two Diels–Alder reactions.

A rationalization is suggested which can help organic chemists in realizing analyses of the relative stereochemistry of substituted cyclopentanes by proton NMR, through the coupling constants between vicinal hydrogens. Some useful generalizations, derived from the dihedral angles found for cyclopentane through a molecular mechanics program, are given.

A synthesis of a functionalized bicyclo[6.2.1]undecane, N -(7-hydroxymethyl-bicyclo[6.2.1]undeca-3,5,9-trien-2-yl)-4-methyl-benzenesulfonamide, is described. Starting with a [6+4] cycloaddition between cyclopentadiene and cycloheptatrienone, the final product was prepared in five steps with an overall 37% yield. The remarkable resistance to hydrolysis of an intermediate lactam was overcome by tosylating the amide and reducing with LiAlH 4 .

A method for the preparation of 3-substituted furans starting with the addition of bis(phenylthio)methyllithium to an ester, followed by a sequence consisting of a Wittig reaction, a DIBAL-H reduction and an iodine-mediated cyclization is described.