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In this paper we report on the asymmetric 1,3-dipolar cycloaddition reactions of nitrile oxides mediated by pybox/ytterbium triflates, -/magnesium bromide, and -/magnesium perchlorate. It was confirmed that the reactions proceed smoothly to give isoxazoline derivatives in high enantiomeric excesses with Mg2+ or Yb3+ complexes and acrylamide dipolarophiles bearing an oxazolidinone or imidazolidinone coordination auxiliary as well as a pybox ligand. In reactions with a dipolarophile bearing 4,4-dimethyloxazolidinone as the coordination auxiliary, an enantiomeric excess (59 % ee) of the corresponding cycloaddition product was achieved by using a slow addition technique to generate nitrile oxides in the presence of Yb(OTf)3/ph-pybox. The cycloaddition reaction of a dipolarophile with an unsubstituted oxazolidinone group in the presence of Yb(OTf)3/ph-pybox at a relatively high temperature (35 °C) produced a higher enantiomeric excess. A relatively low temperature (–78 °C) was required to obtain enantiomeric excesses such as 69 and 87 % ee in the reactions of a dipolarophile bearing an imidazolidinone group to afford cycloadducts in the presence of MgBr2/ip-pybox.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

Stable conformations of 12-crown-O 3 N and its Li complexes in aqueous solution were investigated. To calculate the free energy differences of conformers of 12-crown-O 3 N and its Li + complex, our procedure was to make useof two programs, CONFLEX and BOSS. The former generates conformers, and the latter calculates the differences in free energy of solvation between two conformers in aqueous solution. It was confirmed that the present procedure is applicable in solving the question of what is the most stable conformation of 12-crown-O 3 N in aqueous solution. Results of the calculations suggest that the order of stability for conformers in a vacuum is different from that in aqueous solution. It was also confirmed that the coordination geometry of solvent waters to Li + changes depending on the distance between the cation and the crown ring.

The hitherto unknown stereochemistry concerning the formation of 2,3-disubstituted cycloheptanones by the Michael addition reaction was studied. The Michael addition of thiophenol to 3-substituted 2-methylene-cycloheptanones in the presence of triethylamine in THF at ambient temperature produced 3-substituted 2-[(phenylthio)methyl]cycloheptanones with high cis selectivity (>96/4), which was unequivocally established by 1 H NMR and X-rays analyses

Reversal of enantioface selectivity was observed by merely switching the solvent from CH2Cl2 (enantiomer ratio of the adduct = 91:9) to THF (14:86) in the asymmetric Diels-Alder reaction catalyzed by the aluminum complex of a newly prepared chiral methol derivative. Negative nonlinear effect on the relationship between enantiomeric excesses of the reaction product and optical purities of the ligand was observed for the reaction in CH2Cl2 whilst linear relationship for that in THF.

Ab initio molecular orbital calculations at the MP4(SDTQ)/6-31G∗//RHF/6-31G∗ level of theory were used to obtain detailed insight into the reaction profile on the Mg controlled 1,3-cycloaddition of nitriles oxide with allylic alcohols. It was confirmed that the complex formation reduces the HOMO–LUMO energy gaps of the two reactants. The propensity correlates well to calculated activation energies of the cycloaddition. The syn-stereoselectivity depends on the steric repulsion between the vinyl fragment and the substituent at the α-position of the alcohol or alkoxide. THF or Et2O in the reaction mixture prevent the coordination of R1CNO from forming the Mg intermediate and result in deccelerating the cycloaddition. The results obtained in the present study well explain an important role of the Mg2+ ion in the 1,3-dipolar cycloadditions of nitrile oxides with allylic alcohols.

In the presence of magnesium perchlorate, 1,3-dipolar cycloaddition reactions of nitrile oxides to crotonamide bearing 4-benzyl-5,5-dimethyl-1,3-oxazolidin-2-one as the chiral auxiliary proceeded with a regio- and diastereo-selective manner to afford the corresponding chiral 2-isoxazoline. The mechanisms underlying the diastereoface selection in the cycloaddition reaction were investigated using the B3LYP/6-31G* level of theory.

The reaction of nitro olefins with thiolate anions followed by protonation at −78 o C gives anti-β-nitro sulfides. This procedure can be applied to the anti-selective preparation of β-nitro ethers and β-nitro selenides. The reaction of cyclic nitro olefins with aryl thiol gives cis-β-nitro sulfide in excellent selectivity. The conjugate addition of alkylaluminum reagents to phenylthio β-nitro olefins followed by protonation at −78 o C also results in selective formation of anti-β-nitro sulfides. Theoretical calculations show that the methylthio group on the β-position covers the one side of the nitronate plane effectively to give the anti isomer in a stereoselective way

The characteristics of Ca2+-binding sites and of the structural reorganization induced by Ca2+-binding in storage proteins and ion carriers are being studied as models for molecular mechanisms in Ca2+ channels and in Ca2+-dependent modulatory proteins. A first step in the study was the development of energy parameters for Ca2+ compatible with those in the CHARMM package of computer simulation software. Such parameters were obtained from an analytical fit to the potential surface for [(Ca)(OCH2)4]2+ calculated with an ab initio molecular orbital method. The resulting parametrization was tested for the hexapeptide cyclo-(Pro-Gly)3, and a 75 residue long calcium binding protein from bovine intestine (ICaBP). The geometrical parameters calculated for the hexapeptide and its 2:1 complex with Ca2+ were in good agreement with experimental data from crystallography and nmr. Similarly, the structure of ICaBP optimized with CHARMM using the new Ca2+ parameters showed good agreement with the x-ray structure both in the local structures of the calcium-binding sites and in the overall shape of the protein.

Asymptotic properties of the “attractive” vibronic coupling in a one-dimensional polymer are analyzed. The strength of the vibronic coupling grows linearly with the size of polymer, which may relate to the softening mechanism of Coulombic repulsive interaction between a Cooper pair of superconducting electrons.

The vinyl cation with a ethynyl fragment, C4H3+ is investigated with ab initio molecular orbital calculations. Two geometrical isomers of C4H3+, open chain and triangular geometries are calculated in order to ascertain the existence of the triangular isomer. The 4–31G* and MP3/6–31G*//4–31G* level calculations confirm that the latter is more stable than the former. However, the activation energy for intra-conversion is considered to be rather small. The calculated results are analyzed by comparing with experimental results. The relation between molecular vibration and reaction is analyzed by dynamic electron transfer.