Investigation of catalytic activity and catalytic mechanism of chiral amino diol tridentate ligands in the asymmetric addition of aldehydes in the present of methyllithium reagent

Several highly modular chiral amino diol tridentate ligands were found to be effective for the asymmetric alkylation reaction of aromatic aldehydes in the presence of methyllithium reagent, providing up to 96% ee values and up to 94% yields under relatively mild conditions. The investigation of the catalytic activity of these ligands shows a correlation of enantioselectivities of ligands with steric properties of substituent N-alkyl and nucleophilic Li-alkyl. With the addition of Ti(O-i-Pr)4 to the ligand 3c, the 1H NMR spectrum reveals a hexa-coordinate Ti transition state complex with only one Ti metal center generated in solution.