Synthesis Of Chiral Bis (Oxazolines) Lignads And Their Application In Asymmetric Cyclopropanation Reaction

The synthesis of chiral cyclopropanes remains a considerable challenge, especially due to the fact that cyclopropane rings are often found in a variety of natural products and biologically active compounds. Cyclopropanation by transition-metal-mediated carbene transfers from aliphatic diazo compounds to carbon-carbon double bonds is not only a major method, but also among the best developed and most general methods. In this dissertation, two kinds of bisoxazolines have been synthesized and applied to asymmetric cyclopropanation.In chapter 2, a series of chiral biferrocene-based bis(oxazolines) ligands, which have both central and planar chirality, were synthesized from carboxyferrocene and chiral amino alcohols as the starting materials. The complexes catalyzed the asymmetric cyclopropanation of styrene with diazoacetates gives moderate enantioselectivities. The ligand (3b), which have phenyl in the oxazoline ring and methyl on silicon, gives 44%ee for cis and 66% yield. Either electron withdrawing group or electron donor groups on the benzene ring will lead to a decline in enantioselectivity, while using ligand 3b in the asymmetric cyclopropanation of various alkenes with ethyl diazoacetates. The diastereoselectivity mainly depends on the hinderblock from diazo acetate.In chapter 3, bis(oxazolines) ligands 6a-6f were synthesized from 2,2-dimethyl-malonic acid and amino acids, through several reaction steps. Well levels of enantioselectivity have been achieved from cyclopropanation of styrene with diazoacetates. Particularly, ligand 6d afforded 85%ee for the tran5-isomer and 75%ee for the cis-isomer at room temperature. They are also outstanding, while applied to the asymmetry cyclopropanation reaction of isobutylene with ethyl diazoacetate (6d,85%ee; 6f,84%ee).