An electron-deficient series of 1,2,4-triazines and quinazoline have been used for cross-dehydrogenative coupling with 1,3-dihydroxy and 1,3-dimethoxyxanthones to give stable nucleophilic addition products. The adducts and their subsequent oxidation products were obtained in good yields and the structures of the compounds were confirmed by 1H NMR spectroscopy. These results expand the scope of the methodology of nucleophilic substitution of hydrogen with the participation of xanthones with azines. Moreover, this methodology makes it possible to obtain new organic materials based on xanthones, which have a wide spectrum of biological activity.
The previous data obtained by 1H-NMR spectroscopy established the existence of an asymmetry of the bond between Pd and p-allylic groups, even in the p-allyl-Pd complexes dimers which are considered usually symmetric dimers. The asymmetry of the bond depends by the substitutes of the allylic group. Other analytical methods were investigated for additional proof of the obtained results. Thus, this paper discusses how this asymmetry would be reflected in the infrared spectra and in the reaction of the complexes with carbon monoxide.
Background::
Chiral β-hydroxy esters and α-substituted β-hydroxy esters represent versatile building blocks for
pheromones, β-lactam antibiotics and 1,2- or 1,3-aminoalcohols.
Objective::
Synthesis of versatile α-substituted β-keto esters and their diastereoselective reduction to the corresponding
syn- or anti-α-substituted β-hydroxy esters. Assignment of the relative configuration by NMR-spectroscopy after a CURTIUS
rearrangement of α-substituted β-keto esters to 4-substituted 5-methyloxazolidin-2-ones.
Method::
Diastereoselective reduction was achieved by using different LEWIS acids (zinc, titanium and cerium) in combination
with complex borohydrides as reducing agents. Assignment of the relative configuration was verified by 1H-NMR
spectroscopy after CURTIUS-rearrangement of α-substituted β-hydroxy esters to 4-substituted 5-methyloxazolidin-2-ones.
Results::
For the syn-selective reduction, titanium tetrachloride (TiCl4) in combination with a pyridine-borane complex (py
BH3) led to diastereoselectivities up to 99% dr. High anti-selective reduction was achieved by using cerium trichloride
(CeCl3) and steric hindered reducing agents such as lithium triethylborohydride (LiEt3BH). After CURTIUS-rearrangement
of each α-substituted β-hydroxy ester to the corresponding 4-substituted 5-methyloxazolidin-2-one, the relative configuration
was confirmed by 1H NMR-spectroscopy.
Conclusion::
We have expanded the procedure of LEWIS acid-mediated diastereoselective reduction to bulky α-substituents
such as the isopropyl group and the electron withdrawing phenyl ring.
Conformational properties of ribonucleoside 5'-O-phosphonylmethyl derivatives have been determined by 1H NMR spectroscopy and compared with those of natural nucleosides and 5'-nucleotides.
IDENTIFICAÇÃO DE PRODUTOS DA OXIDAÇÃO DE ÓLEOS COMESTÍVEIS ATRAVÉS DA ESPECTROSCOPIA DE RMN DE 1H / IDENTIFICATION OF OXIDATION PRODUCTS IN EDIBLE OIL BY MEANS OF 1H NMR SPECTROSCOPY
