Egidio Giorgio

Non-empirical assignment of the absolute configuration of (−)-naringenin, by coupling the exciton analysis of the circular dichroism spectrum and the ab initio calculation of the optical rotatory power

The non-empirical assignment of the absolute configuration of (-)-naringenin, the aglycone of (-)-naringin, a flavanone glycoside abundant in the albedo of immature grapefruits and showing several interesting biological properties, has been approached by two different methods: (a) the exciton analysis of the circular dichroism (CD) spectrum and (b) the ab initio calculation of the optical rotatory power. Both the methods indicate the configurational correlation (-)/(S), as empirically suggested by Gaffield. A comparison of advantages and limitations of the two methods of analysis is also presented.

1,1′-Binaphthylazepine-based ligands for asymmetric catalysis. Part 1: Preparation and characterization of some new aminoalcohols and diamines

Abstract Starting from ( S )-1,1′-binaphthol, a series of ten novel enantiopure 1,1′-binaphthylazepine-based aminoalcohols and diamines 1a – 1j were efficiently prepared and fully characterized. These derivatives, having either only an atropisomeric bridged-binaphthyl backbone or an additional stereogenic carbon center, can be interesting ligands for asymmetric catalysis.

Calculation of the gas phase specific rotation of (S)-propylene oxide at 355 nm

Abstract The experimental gas phase specific rotation of ( S )-propylene oxide at 355 nm is correctly predicted at the DFT/B3LYP level of theory only adopting fairly large basis sets, such as aug-cc-pVTZ and aug-cc-pVQZ, or, alternatively, the much smaller polarizability-consistent Sadlej basis set. Therefore, considering also the sensitivity to solvent effects, this small and rigid molecule, which has been considered an ideal test case for theoretical investigations, is, on the contrary, one of the most difficult cases to be treated.

1,1′-Binaphthylazepine-based ligands for asymmetric catalysis. Part 2: New aminoalcohols as chiral ligands in the enantioselective addition of ZnEt2 to aromatic aldehydes

Abstract The new enantiopure 1,2-aminoalcohols 1b – 1h having 1,1′-binaphthylazepine skeleton have been tested as catalytic precursors in the enantioselective addition of ZnEt 2 to benzaldehyde. The best results were seen with ligand 1d , which owes its chirality only to the atropisomerism of the binaphthyl nucleus and does not have any stereogenic carbon atom. In the presence of 1d benzaldehyde was quickly and cleanly transformed to ( S )-1-phenylpropanol in 99% yield and 87% e.e. The same ligand was also used in the asymmetric ZnEt 2 addition to other aryl aldehydes giving rise to ( S )-1-arylpropanols in almost quantitative yields and e.e.s up to 90%.

Absolute Configuration through the DFT Simulation of the Optical Rotation. Importance of the Correct Selection of the Input Geometry: A Caveat

In ab initio calculation of ORs of flexible molecules, the input geometries and conformer populations obtained at different levels of theory can yield opposite OR values. Therefore, when at the commonly used DFT/B3LYP/6-31G* level several conformers result, even showing the same sign of OR, additional geometry optimization at a higher level of theory will be absolutely required.

Rational design of chiral 1,1′-binaphthylazepine-based ligands for the enantioselective addition of ZnEt2 to aromatic aldehydes

Abstract By rational design, novel atropisomeric 1,1-binaphthylazepine-based 1,2-amino alcohols 1f and 1g have been prepared in enantiopure form and tested as catalytic precursors in the enantioselective addition of diethylzinc to aromatic aldehydes: the corresponding ( S )-1-arylpropanols have been obtained in quantitative yields and e.e.s up to 95%. A rationale explaining the stereochemical outcome of the reaction, as well as the influence of structural features of the ligands on the enantioselectivity of the addition, is also provided.

Circular dichroism spectra and absolute configuration of some aryl methyl sulfoxides

The absorption and circular dichroism (CD) spectra of three aryl sulfoxides, i.e. (-)-(S)-1-naphthyl methyl sulfoxide, (S)-1, (-)-(S)-1-(2-methyl)naphthyl methyl sulfoxide, (S)-2 and (-)-(S)-9-phenanthryl methyl sulfoxide, (S)-3, have been interpreted by means of the coupled oscillator model formulated by DeVoe. Theoretical spectra have been calculated starting from input geometries provided by molecular mechanics (MMX) calculations and by employing standard spectroscopic parameters to describe the allowed transitions of the aromatic and the sulfoxide chromophores. The satisfactory agreement between the predicted and experimental spectra allows us to confirm the configurational assignment of these compounds as (-)/(S). The analysis of CD spectra, affording the right assignment of the absolute configuration (AC) of the alkyl aryl sulfoxides, then offers a practical alternative to the more complex vibrational circular dichroism spectroscopy and ab initio optical rotation calculation techniques that have been used very recently to assign the AC of (-)-2 and (-)-3.