Asymmetric Alkylation of Activated Imines with Titanium-TADDOLate Lewis Acid Catalysts
Sean H. Majer, Vassar College ’15 and Prof. Joseph M. Tanski
Titanium-TADDOLate catalysts for asymmetric alkylation of activated imines to yield tertiary chiral alkyl substituents on amines are introduced, outlining their structures and reactivity. We discuss the significance of chiral substituents on amines in organic synthesis, emphasizing their importance in biochemical systems. Multiple oximes were synthesized and converted to activated diphenylphosphinoyl imine substrates for alkylation. The activating groups are placed on these imines in an attempt to pull electron density away form the pro-chiral carbon center and promote alkylation. Molecular structures were obtained for these activated imines by single-crystal X-ray diffraction. We found that the methyl substituted imine was actually an oxime ester, containing an extra oxygen atom between nitrogen and phosphorus. This compound, compared to the diphenylphosphinoyl imine, has an additional axis of rotation about the phosphorus oxygen bond, perhaps making it more suitable for coordination to the titanium Lewis acid catalytic center that mediates the alkylation. Lastly, we explain preliminary results of alkylation of the oxime ester.