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

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 (0.52 mol%), delivering the desired vicinal anti-alpha-iodo-beta-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-alpha-iodo-beta-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.