Highly Stereoselective Samarium(II) Iodide-Mediated Aldol Reactions of Acylaziridines with Aldehydes

Abstract

Abstract The samarium(II) iodide-mediated stereoselective aldol reactions of acylaziridines with aldehydes are described. β-Amino–β′-hydroxy ketones were synthesized in high yields by the aldol reaction of aldehydes with samarium enolates generated by aziridine-fragmentation of aziridinyl ketones with two moles of samarium(II) iodide. By the choice of an appropriate nitrogen protecting group, depending on the substituent at C-3 position of aziridinyl ketone, anti,anti-β-amino–β′-hydroxy ketones were diastereoselectively obtained among the four possible diastereomers. Further, enantiomerically pure anti,anti-β-amino–β′-hydroxy ketones were successfully obtained by this aldol reaction when chiral aziridinyl ketones were used. In addition, δ-amino–β′-hydroxy–β,γ-unsaturated esters were also synthesized in high yields by the aldol reaction of aldehydes with samarium enolates generated by aziridine-fragmentation and olefin-migration of γ,δ-aziridinyl–α,β-unsaturated esters using two moles of samarium(II) iodide. This aldol reaction proceeded with complete α-regioselectivity and formed (E)-olefin selectively. By introducing chiral oxazolidin-2-one auxiliary to γ,δ-aziridinyl–α,β-unsaturated carbonyl system, this reaction was extended successfully to the asymmetric reaction and enantiomerically pure syn-δ-amino–β′-hydroxy-β,γ-unsaturated esters were obtained in high yields.