Asymmetric Iodoamination of Chalcones and 4-Aryl-4-oxobutenoates Catalyzed by a Complex Based on Scandium(III) and a N,N′-Dioxide Ligand

摘要

Highly diastereo- and enantioselective iodoamination of chalcones, 4-aryl-4-oxobutenoates, and a trifluoro-substituted enone has been accomplished in the presence of a chiral N,N′-dioxide/[Sc(OTf)₃] complex (0.5–2 mol %), delivering the desired vicinal anti--iodo-β-amino carbonyl compounds regioselectively in high yields (up to 97 %) and with excellent diastereoselectivities (>99:1 d.r.) and enantioselectivities (up to 99 % ee). Enantiopure syn--iodo-β-amino products could also be obtained from the isomerization of particular iodo compounds. TsNHX species (X=Cl, Br, I), generated from the reactions between the halo sources and TsNH₂, were further confirmed as the active species in the haloamination reactions involved in the formation of the key halonium ion intermediates. A typical haloamination dependency was observed, with reactivity decreasing in the order NBS>NIS≫NCS.