Regiochemistry of mercury(II) oxide oxidation of unsymmetrical N,N-disubstituted hydroxylamines
作者:Sk.Asrof Ali、S.M. Azhar Hashmi、Mohammad N. Siddiqui、Mohammed I.M. Wazeer
DOI:10.1016/0040-4020(96)00904-0
日期:1996.11
Mercury(II) oxideoxidation of N,N-disubstituted hydroxylamines with the α and α′ carbon atoms containing one and two hydrogen atoms, respectively, gave aldonitrones in a highly regioselective manner. Removal of the α proton is involved in the rate determining step as shown by primary kinetic isotope effect.
Nitrones serve as starting materials for the synthesis of many heterocycles. Oxidation of secondary amines using hydrogen peroxide and the catalytic amount of methyltrioxorhenium in ionic liquids is a useful method for the preparation of nitrones. Ultrasonic irradiation and ionic liquids have a positive influence on the reaction. The nitrones required were isolated in good yields. Corresponding hydroxylamines
Nitrogen inversion and N–O bond rotation in some hydroxylamine and isoxazolidine derivatives
作者:Azfar Hassan、Mohamed I. M. Wazeer、Herman P. Perzanowski、Sk. Asrof Ali
DOI:10.1039/a604719j
日期:——
A series of trisubstituted hydroxylamine derivatives, both cyclic and
acyclic, has been prepared. The energy barriers in these hydroxylamines
are found to be dominated either by nitrogen inversion or NâO
bond rotation depending on the nature of the substituents attached to
the nitrogen. In several series of compounds, having
XC6H4CH2 substituents attached to
nitrogen, Hammett free energy correlations are obtained with positive
Ï values, indicating increased electron density at the
transition state for the inversion process. Isoxazolidines with C(5)
ethoxy substituents demonstrate a strong anomeric effect.
The present invention provides unimolecular metal complexes having increased activity in the copolymerization of carbon dioxide and epoxides. Also provided are methods of using such metal complexes in the synthesis of polymers. According to one aspect, the present invention provides metal complexes comprising an activating species with catalytic activity tethered to a ligand that is coordinated to the active metal center of the complex.
The present invention provides unimolecular metal complexes having increased activity in the copolymerization of carbon dioxide and epoxides. Also provided are methods of using such metal complexes in the synthesis of polymers. According to one aspect, the present invention provides metal complexes comprising an activating species with co-catalytic activity tethered to a multidentate ligand that is coordinated to the active metal center of the complex.