Studies On Asymmetric Cyanation Of Carbonyl Compounds Catalyzed By A Novel C₂-Symmetric Chiral N,N'-Dioxide Titanium Complexes

Cyanohydrins are versatile intermediates in the context of organic synthesis, especially, in asymmetric synthesis. The addition of TMSCN and EtOCOCN to carbonyl compounds is the most direct, efficient, and prevailing strategy. In this dissertation, the efforts were focused on asymmetric cyanation of carbonyl compounds. A series of useful and creative results have been obtained.A novel C2-symmetric chiral N,N'-dioxide of twenty-four ligands were synthesized, as well as five achiral N-oxides, one chiral octa-hydro-biisoquinoline and two proline-based ligands. The chiral N,N'-dioxide titanium complexes were prepared in situ and successfully applied in asymmetric cyanosilylation of ketones.The electronic and spatial effects of the substitutes on chiral N,N'-dioxide ligands impacting on the enantioselectivity and reactivity of this reaction were systematically studied. The results revealed that 57h-Ti(OiPr)4 showed an excellent chiral induction in presence of achiral N-oxide 64i in this reaction. We investigated several factors in detail that affected the enatioselectivity, such as the structure of the ligands (steric and electric effects), central metal, molar ratio of chiral ligands toTi(OiPr)4, solvent, concentration of substrates, different amount of catalyst, reaction temperature and so on. Under the optimized conditions, most of the aromatic,α,β-unsaturated, heterocyclic, aliphatic and steric hindrance ketones could be converted into the corresponding cyanohydrin trimethylsilyl ethers in 62-92% yields...