Oronzo Sciacovelli

Synthesis of dehydrophenylalanine derivatives by palladium catalyzed arylation of 2-acetamidoacrylic acid

Arylation of 2-acetamidoacrylic acid using Pd(OAc)2/PPh3 or PdCl2 (PPh3)2 as catalytic systems leads to α-acetamidocinnamic acids of Z configuration.

On the structure of intermediate adducts arising from dithionite reduction of pyridinium salts: a novel class of derivatives of the parent sulfinic acid

Abstract 13C and 17O NMR spectroscopy show that adducts arising from dithionite reduction of 3- or 3,5-cyano- or carbamoyl-substituted pyridinium salts to the corresponding 1,4-dihydropyridines, are S-anions of esters of the simplest parent sulfinic acid. A pathway for formation of the 1,4-dihydropyridines, involving an intramolecular hydride transfer, is suggested.

17O NMR of organic peroxides: chromium(VI) and molybdenum(VI) oxide diperoxide as compared to simple organic peroxides

Abstract High resolution 17O NMR spectra of 17O-labeled t-BuOOH, t-BuOOBu-t, (HMPA)MoO(O2)2 and (L)CrO(O2)2 (with L = HMPA, Py) have been measured. Significant differences were found in the peroxide bond resonances of the chromium with respect to the molybdenum peroxo complex, in that chromium(VI)oxide diperoxide showed two distinct 17O resonance signals, suggesting non-equivalence of the oxygen atoms in the O-O bond; this feature was not present in the spectra of (HMPA)MoO(O2)2. For both peroxometal complexes, no 17O NMR evidence could be found for significant exchange between oxo and peroxo oxygens.

A novel stereoselective route to cis-olefins via addition of vinyl cuprates to αβ-unsaturated sulphones and subsequent desulphonylation

Dialkenylcuprates, generated by addition of dialkylcuprates to acetylene, react with αβ-unsaturated sulphones to give cis-γδ-unsaturated sulphones which can be easily desulphonylated with retention of the double-bond configuration.

1H-1H Inter-ring coupling constants in isoquinoline and quinazoline. Their relationship with corresponding 19F-19F couplings in perfluoro derivatives

Abstract Complete spectral analysis of 1 H NMR spectra of isoquinoline and quinazoline is performed. Signs of inter-ring coupling constants ( J HH ir ) are determined by INDOR experiments. The mechanisms of transmission of J HH ir are discussed. A linear correlation exists between the majority of J HH ir of quinoline, isoquinoline, and quinazoline and J HH ir of their perfluoroderivatives; exceptions are rationalized. The linear relationship with the near-zero value of intercept J HH ir = 0.02 4 + 0.04 0 J HH ir strongly suggests that J HH ir originate, almost quantitatively, from the Fermi contact term and are transmitted via the π-electron system, except for the peri J HH ir . A computation of the proportionality between J HH ir and J HH ir in quinoline using the Pople and Santry expression for the contribution of π electrons to interring coupling constants gives results which are in satisfactory agreement with those observed experimentally.

PCILO calculation on the ansa conformation of hexahydrorifamycin S

Abstract PCILO calculation on the conformation of the 16, 17, 18, 19, 28, 29 hexahydrorifamycin S points to an ansa chain conformation of the C(12)–C(28) fragment from the alternatives given by a previous 1H NMR spectroscopic study. The energetically favoured conformation of the C(19)–N fragment has also been determined.

Methyl substituent effects on 1H1H intraring coupling constants in some dimethylnaphthalenes

Abstract Iterative analysis of 1 H NMR spectra of 1,4- ( I ), 1,3- ( II ), and 2,3-dimethylnaphthalene ( III ) has been performed. Spectral analysis and the INDOR technique have indicated a positive value (∼ +0.7 Hz) for the para coupling 5 J 58 , which has been previously reported to assume negative values in compounds I and II . The interring substituent effects of methyl groups on coupling constants have been estimated. A negligible effect has been found when the methyl group is in position 2 or position 3. This observation has made estimation of the effect of the methyl group in position 1 possible from the coupling-constant values in II . Substitution in position 1 causes an increase in 3 J 78 (+0.22 Hz), and a small decrease in 3 J 56 (−0.12 Hz), leaving 3 J 67 , 4 J 57 , and 5 J 58 practically unchanged.

Application of MNDO Approximation to the Calculation of Nuclear Spin-Spin Coupling Constants. I. Substituent Effect on1H-13C Coupling Constants Methane Derivatives

Theoretical calculations performed using the coupled Hartree–Fock perturbation theory (CHFPT) show that the MNDO approximation is superior to INDO and MINDO3 in computing nuclear spin coupling constants between directly bonded carbon and hydrogen in polysubstituted methanes, HCXYZ. The CHFPT–MNDO program is parametrized for the atoms of the second and third rows of the Periodic Table. Substituent effects on JHC are well reproduced except for the chlorine atom, whose effect is systematically underestimated (ca. 9 Hz).

A conformational study of the 3-p-tolylsulphonylbutan-2-ol and 1,2-diphenyl-2-p-tolylsulphonylethanol diastereoisomeric pairs

Solvent and temperature effects upon the conformation of erythro- and threo-3-p-tolylsulphonylbutan-2-ol (I) and (III), and of erythro- and threo-1,2-diphenyl-2-p-tolylsulphonylethanol (II) and (IV) have been studied by i.r. and 1H n.m.r. spectroscopic techniques. All compounds form an intramolecular hydrogen bond in chloroform and carbon tetrachloride solutions, whereas in dimethyl sulphoxide, pyridine, and acetone hydrogen bond formation with the solvent occurs. Steric requirements control the conformational preference of (II) and (IV) in all solvents. The conformation of (I) and (III) in polar solvents may be determined primarily by a gauche attractive interaction between oxygen and sulphur atoms. In low polarity solvents the conformations which facilitate intra-molecular hydrogen bonding are preferred.