|
چکیده
|
Chiral bisoxazolines and oxazolines ligands are one of the most effective and popular classes of chiral ligands used for various metal-catalyzed asymmetric processes , such as allylic oxidation. The allylic oxidation of olefins using peresters in the presence of copper catalyst to give allylic esters is known as the Kharash-Sosnovsky reaction. This reaction has been the subject of great interest over the last decade and provides access to chiral allylic alcohols, which are key intermediates in natural product synthesis. Some sort of chiral biaryl bisoxazolineligands 1, 2 andnew class of various chiral monodentate oxazoline 3 and bisoxazoline ligands 4 were conveniently synthesized in high yields and enantiomeric excess. The obtained organic chiral ligands 3, 4 have been covalently grafted on ordered mesoporous silicas MCM-41, SBA-15 and the resulting inorganic-organic hybrid materials such a chiral heterogeneous catalysts 5 characterized by TGA, DTA, powder X-ray diffraction, BET, BJH, EDX,CHN analysis, SEM and FT-IR. The catalytic and induced asymmetric effects of the chiral copper (I) complexes of these homogeneous and heterogeneous catalysts on the asymmetric allylic oxidation of cycloolefins were investigated under different conditions. Reactions using the catalyst exhibited good enantioselectivities up to 95% and high yields up to 99%.
|