Mechanism of Stereoselectivity of MichaelAddition Catalyzed by Chiral Rare-Earth Metal / N ,N’- Dioxide Complex: A Theoretical Study

Abstract

Asymmetric Michael addition was achieved by using the rare earth catalystincluding the chiral N ,N ’-dioxidederivative ligand. The enantioselectivity of this catalytic reaction could beswitched by changing the rare earth from Scandium to Yttrium. To understand themechanism of the stereoselectivity, we applied an automated reaction pathsearch method, called the artificial force induced reaction (AFIR) method, andexplored various reaction pathways giving major and minor products. It wasfound that the reaction started from the coordination of one of the reactants, pyrazolonederivative, to Scandium. In this coordination structure, the reactive carbon inthe pyrazolone moiety was not covered by the chiral ligand, and the approachdirection of the other reactant, α , β -unsaturated carbonylcompound, was not restricted. Thus, the stereoselectivity could be controlledby the stability of the transition states of the following reaction step, suchas C-C bond formation or proton transfer. In this presentation, we will reportthe details about the structures of transition states and discuss about theorigin of stereoselectivity.