Abstract:
A series of chiral N-salicyl-β-amino alcohol was synthesized and evaluated as potential ligand for catalytic asymmetric Michael addition between dialkyl malonates and cyclohex-2-enone. Several reaction parameters have been optimized including solvent, temperature, ligand structure, type of metal co-catalyst, and metal-ligand ratio. The reaction in the presence of 10 % mol catalyst prepared from LiAlFL4 proceeded enantioselectively giving the Michael adduct in good yield and up to 88 % ee. Furthermore, it was revealed that steric effect of the alkyl substituent on the side chain of the N-salicyl-β-amino alcohol have a dramatic effect on the ee of the products. Electron donating substituents on the salicyl part of the ligand had no effect on the ee while electron withdrawing substituents decreased the ee. Bulky substituents on the salicyl group provide racemic product. The limitations of catalyst system depended on nucleophile and structure of substrate. No enantioselectivity was observed with acyclic enones and with other nuclephiles.