The Synthesis Of Axially Chiral Imidazoline Ligands With Binaphthyl Backbone And Their Application In The Cyclopropanation Reaction

This thesis discusses the synthesis and characterization of axially chiral bi(imidazoline) ligands with binaphthyl backbone and their application in the asymmetric cyclopropanation reaction. The main research contents are as follows:1. Synthesis of1-bromo-2-naphthoic acid51-bromo-2-naphthoic acid5was obtained through bromination, hydrolysis, oxidation from2-methylnaphthalene1as the starting material(Scheme1).2. Synthesis of naphthyl imidazoline ligands7a-cNaphthyl imidazoline7a-c were prepared froml-bromo-2-naphthoic acid5.The new compounds7a-c were characterized by IR,1H NMR,13C NMR, MS (Scheme2). 3. Synthesis of axially chiral compounds (aS,S,S)-8a-cThe axially chiral imidazoline ligands with binaphthyl backbone8a-c were obtained from a mixture of naphthyl imidazoline7a-c and freshly activated copper in dry pyridine which were heated at reflux under argon atmosphere for12h. In this reaction, it produced excess aS diastereomer, after isolated from column chromatography, single diastereomers (aS,S,S)-8a-c were obtained (Scheme3). The new compounds (aS,S,S)-8a-c were characterized by IR,1H NMR,13C NMR, MS, HQMS. The molecular structure and absolute configuration of ligands (aS,S,S)-8a-b were confirmed by X-ray single crystal diffraction.4. The axially chiral bi(imidazoline) ligands (aS,S,S)-8a-c applied in the asymmetric cyclopropanation reaction.The newly synthesized axially chiral bi(imidazoline) ligands with binaphthyl backbone (aS,S,S)-8a-c were employed to the asymmetric cyclopropanation. After screening of the ligands, the dosage of ligands, solvents and temperature,(aS,S,S)-8b was found to have a ideal catalyst result (Scheme4). Under optimized condition, using5.0mol%CuOTf(C6H6)o.5/5.5mol%(aS,S,S)-8b in CH2Cl2, heating to reflux for34h, the cyclopropanation yield was47%, with trans/cis=80/20(trans ee=75%, cis ee=66%). After expanding the substrate, we found the cyclopropanation products had moderate diastereomer selectivity and stereoselectivity.