The Synthesis of C2-symmetric Chiral S, S-bis (Bidentate Oxazoline Benzamide-Cu (II) Complexes) and Their Applications in Oxidation of Allylic C–H Bonds of Cyclic Olefins

During the last decades, the role of chirality transformation in chiral oxazoline ligands have been confirmed in numerous transition-metal-catalyzed asymmetric transformations. Although chiral bisoxazolines ligands can be extensively used in catalytic asymmetric synthesis, chiral mono oxazoline versions have rarely presented comparable impacts [1-4]. Asymmetric allylic C–H bonds oxidation of olefins to chiral allylic esters and chiral allylic alcohols is considered one of the most important reactions in organic chemistry, in which, unlike hydroxylation and epoxidation, a second functional group is formed while the double bond remains unchanged[5,6]. In this work, a new type of chiral bidentate oxazoline benzamide ligands was conveniently synthesized from inexpensive and commercially available materials in high yields and enantiomeric excesses. The corresponding chiral copper complexes with this class of ligands [C2 symmetric S, S-bis(bidentate oxazoline benzamide-Cu(II) complex] were synthesized accordingly. The utilization of these chiral complexes in the enantioselective esterification of allylic C–H bonds of cyclic olefins with tert-butyl-4-nitrobenzoperoxoate resulted in the highest activities, yields (up to 95%) and enantioselectivities (up to 94%) in the presence of HZSM-5 zeolite[5,6].