Highly asymmetric Henry reaction catalyzed by chiral copper(II) complexes

Two chiral pyridinylmethyl diphenylprolinolsilyl ether derivatives have been synthesized from N-alkylation of (S)-diphenylprolinolsilyl ether in a single step. They were successfully applied as ligands in the Cu(II)-catalyzed enantioselective Henry reaction between aldehydes and nitromethane in ethanol at room temperature. A variety of chiral Henry products β-nitroalcohols were obtained in good to high yields (up to 94%) with high to excellent enantioselectivities (up to 94% ee) under the optimized reaction conditions. The results indicate that the bulky substituent diphenylprolinolsilyl ether of ligand 2 plays an important role to induce the high stereoselectivity of the process.