3‑Amino Oxindole Schiff Base Efficiently Paired with p‑Quinone Methide to Enable a New Diastereoselective and Enantioselective 1,6-Conjugated Addition in the Presence of a Cinchonidinium Phase Transfer Catalyst

Abstract

3‑Amino oxindole Schiff base has been used as an efficient substrate company with p‑quinone methides for a new highly diastereoselective and enantioselective 1,6-conjugate addition in the presence of a O-allyl-N-(9-anthracenylmethyl) cinchonidinium bromide phase transfer catalyst under mild reaction conditions. A broad series of chiral quaternary 3-amino oxindoles with 4-hydroxybenzyl scaffold were smoothly obtained in good to excellent yields with excellent diastereoselectivities (>20:1) and enantioselectivities (up to 99 % ee). A typical scale-up preparation and subsequent hydrolysis of a pyridine substrate was successfully performed and a potential valuable chiral amino-pyridine bifunctional chiral building block was obtained, which is structurally feasible as chiral ligand for asymmetric metallic catalysis.