Magnetic nanoparticle (MNP)-supported 9-amino(9-deoxy)epi-quinidine organocatalyst for the asymmetric α-amination of aldehydes

Abstract

Fe₃O₄ MNP-supported 9-amino(9-deoxy)epi-quinidine (Fe₃O₄/PVP@QDNH₂) with core–shell morphology and a high loading capacity of QDNH₂ (0.60 mmol g⁻¹) was prepared by an available one-pot method through the first homogeneous radical-mediated thiol–ene click reaction of QDNH₂ with 3-mercaptotrimethoxysilane (MPTMS) and then hydrolysis of –Si(OCH₃)₃ on the surface of Fe₃O₄/PVP MNPs, and exhibited the good isolated yields (75–89%), excellent diastereoselectivities (syn/anti = 95–98/2–5) and remarkable enantioselectivities (95–98% ee syn) in the α-amination of (2R,3S)-2-methyl-3-nitro-4-phenylbutyraldehyde and its derivatives with di-iso-propyl azodicarboxylate (DIAD). Fortunately, the good diastereoselectivity (syn/anti = 88/12) and excellent enantioselectivity (95% ee syn) in the fifth run could be achieved in 75% yield.