Cover Picture: Iron‐ and Bismuth‐Catalyzed Asymmetric Mukaiyama Aldol Reactions in Aqueous Media (Chem. Asian J. 12/2013)

Abstract

The Mukaiyama aldol reaction of a silyl enol ether with an aldehyde mediated by TiCl4 was first published in 1973. After that, tremendous efforts have been made to improve this potentially versatile protocol, leading to remarkable advances of this reaction. In their Full Paper on Shū Kobayashi et al. report on asymmetric Mukaiyama aldol reactions of silicon enolates with aldehydes catalyzed by chiral FeII and BiIII complexes. The reactions proceeded in the presence of water at 0 °C to afford the desired aldol products in high yields with high diastereo‐ and enantioselectivities. The assumed catalytic cycle and transition states indicated important roles of water in these efficient asymmetric Mukaiyama aldol reactions.

Mukaiyama Aldol Reactions in Aqueous Media

“…In 2012, a wider substrate scope with outstanding stereoselectivity was achieved in the presence of a chiral iron(II) complex comprising Fe(ClO 4 ) 2 and chiral 2,2′-bipyridine ligand 41 (Scheme 35 ). 122 , 123 Nevertheless, in this catalytic system, an excess amount of chiral ligand was required. Crystallographic investigations revealed that the central iron(II) ion is held in an almost square-planar fashion and the axial position of the pentagonal bipyramidal iron(II) complex is occupied by an additional water molecule.…”