Novel Sesquiterpene Skeletons by Multiple Wagner-Meerwein Rearrangements of a Longipinane-1,9-diol Derivative.

The tricyclic sesquiterpene (1,3,4,5,7,8,9,10,11)-7,8-diangeloyloxylongipinan-1,9-diol, or rasteviol (), underwent multiple Wagner-Meerwein molecular rearrangements and several hydride shifts when treated with EtO-BF to generate the six new compounds (1,3,4,5,7,8,9,10,11)-7,8-diangeloyloxy-1,9-epoxyjiquilpane (), (1,3,4,5,7,8,9,11)-8-angeloyloxy-1,7-epoxyzamor-10(14)-ene (), (2,3,4,5,6,7,8,9,10)-7,8-diangeloyloxy-6,9-epoxyjanitziane (), (4,5,7,8,9,10,11)-7,8-diangeloyloxy-9-hydroxyjiquilp-3(15)-ene (), (2,3,5,7,8,10,11)-7,8-diangeloyloxyiratzian-9-one (), and (2,3,5,10,11)-8-angeloyloxyiratzi-7-en-9-one (), of which , , , and possess new hydrocarbon skeletons. Their structures were determined by 1D and 2D NMR in combination with single-crystal X-ray diffraction analyses of derivatives , , , and , which allowed confirmation of their absolute configurations by means of the Flack and Hooft parameters. In addition, some reaction mechanism information was gained from deuterium labeling experiments.

Gas-Phase Acidities and Basicities of Alanines and N-Benzylalanines by the Extended Kinetic Method.

This paper reports an experimental determination of the gas-phase acidities and basicities of N-benzylalanines, in both their α and β forms, by means of the extended kinetic method (EKM). The experimental gas-phase acidity of β-alanine was also determined. Standard ab initio molecular orbital calculations at the G3 level were performed for alanines, and at the G3(MP2)//B3LYP level for N-benzylalanines.

Experimental and computational thermochemical study of N-benzylalanines.

Calorimetric measurements are expected to provide useful data regarding the relative stability of α- versus β-amino acid isomers, which, in turn, may help us to understand why nature chose α- instead of β-amino acids for the formation of the biomolecules that are essential constituents of life on earth. The present study is a combination of the experimental determination of the enthalpy of formation of N-benzyl-β-alanine, and high-level ab initio calculations of its molecular structure. The experimentally determined standard molar enthalpy of formation of N-benzyl-β-alanine in gaseous phase at T = 298.

Experimental and computational thermochemical study of α-alanine (DL) and β-alanine.

This paper reports an experimental and theoretical study of the gas phase standard (p° = 0.1 MPa) molar enthalpies of formation, at T = 298.15 K, of α-alanine (DL) and β-alanine.

Preparation of chiral derivatives of beta-Ala containing the alpha-phenylethyl group: useful starting materials for the asymmetric synthesis of beta-amino acids.

The use of microwave (MW) irradiation for the condensation reaction between acetophenone and alpha-phenylethylamine to prepare (R,R)-bis[alpha-phenylethyl]amine results in significantly reduced reaction times relative to the use of conventional heating. In this protocol, a secondary amine, (R,R)-bis(alpha-phenylethyl)amine is treated with acryloyl chloride to afford conjugated amide N,N-bis[(R)-alpha-phenylethyl]prop-2-enamide, (R,R)-3. 1,4-Addition of alpha-phenylethylamine to unsaturated (R,R)-3 affords propanamide N,N-Bis[(R)-alpha-phenylethyl]-3-N-[(S)-alpha-phenylethyl]amino-propanamide, (R,R,S)-4, which can be alkylated with high diastereoselectivity to give derivative N,N-Bis[(R)-alpha-phenylethyl]-3-N'-[(S)-alpha-phenylethyl]amino-propanamide, (R,R,S,S)-5.

Calorimetric and computational study of 1,3- and 1,4-oxathiane sulfones.

The enthalpies of formation in the condensed and gas states, DeltafH degrees m(cd) and DeltafH degrees m(g), of 1,3- and 1,4-oxathiane sulfones were derived from their respective enthalpies of combustion in oxygen, measured by a rotating bomb calorimeter and the variation of vapor pressures with temperatures determined by the Knudsen effusion technique. Standard ab initio molecular orbital calculations at the G2(MP2) and G3 levels were performed, and a theoretical study on molecular and electronic structure of the compounds has been carried out. Calculated DeltafH degrees m(g) values at the G3 level using atomization reactions agree well with the experimental ones.

Calorimetric and computational study of 1,4-dithiacyclohexane 1,1-dioxide (1,4-dithiane sulfone).

This work reports the enthalpies of formation in the condensed and gas state of 1,4-dithiacyclohexane 1,1-dioxide (1,4-dithiane sulfone, 5), derived from the enthalpy of combustion in oxygen, measured by a rotating bomb calorimeter and the variation of vapor pressures with temperatures determined by the Knudsen effusion technique. The theoretically estimated enthalpy of formation was calculated from high-level ab initio molecular orbital calculations at the G2(MP2) level. The theoretical calculations appear to be in very good agreement with experiment.

Thermochemistry of 1,3-dithiacyclohexane 1-oxide (1,3-dithiane sulfoxide): calorimetric and computational study.

The enthalpies of combustion and sublimation of 1,3-dithiacyclohexane 1-oxide (1,3-dithiane sulfoxide, 2) were measured by a rotating-bomb combustion calorimeter and the Knudsen effusion technique, and the gas-phase enthalpy of formation was determined, DeltafH degrees m(g) = -98.0 +/- 1.9 kJ mol(-1).

Calorimetric and computational study of 1,3-dithiacyclohexane 1,1-dioxide (1,3-dithiane sulfone).

The enthalpies of combustion and sublimation of 1,3-dithiacyclohexane 1,1-dioxide (1,3-dithiane sulfone) were measured by a rotating-bomb combustion calorimeter and the Knudsen effusion technique, and the gas-phase enthalpy of formation was determined, Delta(f)H(m)*(g) = -326.3 +/- 2.0 kJ mol(-1).

Calorimetric and computational study of thiacyclohexane 1-oxide and thiacyclohexane 1,1-dioxide (thiane sulfoxide and thiane sulfone). Enthalpies of formation and the energy of the S=O bond.

A rotating-bomb combustion calorimeter specifically designed for the study of sulfur-containing compounds [J. Chem. Thermodyn.