Luiz Alte da Veiga

Cycloaddition reactions of 3-aryl-5-phenyl-5H, 7H-thiazolo[3,4-c]oxazol-4-ium-1-olates

Intermolecular 1,3-dipolar cycloaddition of (5R)- and (5S)-3,5-diphenyl-5H,7H-thiazolo[3,4-c]oxazol-4-ium-1-olates, (5R)- and (5S)-3-(p-methoxyphenyl)-5-phenyl-5H,7H-thiazolo-[3,4-c]oxazol-4-ium-1-olates with a range of dipolarophiles is described. New chiral 5-aryl-3-phenyl-1H,3H-pyrrolo[1,2-c]thiazoles with R and S configuration were obtained. The structure of methyl (3R)-3-phenyl-5-(p-methoxyphenyl)-1H,3H-pyrrolo[1,2-c]thiazole-6-carboxylate was determined by X-ray crystallography. The synthesis of 7,7a-dihydro-1H,3H-pyrrolo[1,2-c]thiazole-6,7-dicarboxylates was also achieved.

Strong hydrogen-bonded amino acid dimers in l-alanine alaninium nitrate

The title compound, C3H7NO2*C3H8NO2+*NO3-, contains L-alanine-alaninium dimers bonded via the carboxyl groups by a strong asymmetric hydrogen bond with an O...O distance of 2.4547 (19) A. The neutral alanine molecule exists as a zwitterion, where the carboxyl group is dissociated and the amino group is protonated. The alaninium cation has both groups in their acidic form. The alanine molecule and the alaninium cation differ only slightly in their conformation, having an N-C(alpha)-C=O torsion angle close to -25 degrees. The dimers and the nitrate anion are joined through a three-dimensional hydrogen-bond network, in which the full hydrogen-bonding capabilities of the amino groups of the two alanine moieties are realised.

Intermolecular Dipolar Cycloaddition Reactions of 5H,7H-Thiazolo[3,4-c]oxazol-4-ium-1-olates

Abstract (5R)-3-Methyl-5-phenyl-5H,7H-thiazolo[3,4-c]oxazol-4-ium-1-olate was generated in the presence of a range of dipolarophiles. The intermolecular 1,3-dipolar cycloaddition of this mesoionic species led to the synthesis of chiral 1H-pyrrolo[1,2-c]thiazole derivatives 7a, 7b, 8, 14, 18, 19 and 20. In the reaction with methyl and ethyl vinyl ketone, spiro compounds 9 and 15 were also obtained. The structure of compound 15 was determined by X-ray crystallography.

Crystal structure of hydrated diphenylguanidinium hexafluoroferrate (III)

Abstract The crystal structure of 3C13H14N3+FeF63−·3.5H2O was determined. Both phenyl rings of the diphenylguanidine cation are oriented syn to the central CNH2 group. The anions and cations are held together by a three-dimensional network of hydrogen bonds. In the synthesis of this compound, a second phase (iron trifluoride trihydrate) was formed and identified by powder diffraction data. Mossbauer results show two different iron environments compatible with the two phases reported.

(R,R)-N-phenyl-3,4-bis(diphenylphosphino)pyrrolidine: an N-aryl pyrrolidine ligand for enantioselective transfer hydrogenation

The N-aryl pyrrolidine diphosphine (R,R)-N-phenyl-3,4-bis(diphenylphosphino)pyrrolidine was obtained from natural tartaric acid. Contrary to our preliminary expectations, this new chiral ligand proved to be less selective than the corresponding N-benzyl pyrrolidine diphosphine. An attempted explanation of the observed behaviour based on the stereochemistry of the ligand as shown by X-ray crystallography is presented.

Structural and Magnetic Properties of [Mn3(C2H3O2)6(H2O)4]· 2(C2H5NO2)· 2(H2O)

Abstract Hexa-acetate-tetra-aqua-trimanganese diglycine dihydrated retains the two-dimensional character of commercial manganese diacetate tetrahydrate. The manganese atoms assemble in short centrosymetric chains that are further bridged through the carboxylic group of the acetate ions agglomerating the chains into a two-dimensional pattern. The layers are bonded through H-bonds involving the zwitterionic glycine and the solvate water molecules. Susceptibility measurements show a ferrimagnetic behaviour of the sample.