RESUMO
Chiral binaphthyldiimine-Ni(II)-catalyzed asymmetric 1,3-dipolar cycloaddition reactions between acyclic carbonyl ylides generated from donor-acceptor oxiranes and aldehydes are reported. Both aromatic and aliphatic aldehydes could be used as dipolarophiles, providing cis-1,3-dioxolanes with high diastereo- and enantioselectivities. On the basis of mechanistic studies, a monomeric chiral Ni(II) complex was hypothesized to act as the active species for the cycloaddition. The high levels of asymmetric induction are satisfactorily explained by a concerted-asynchronous endo Si-face approach of the aldehyde.
RESUMO
The enantioselective oxidative ring-opening reaction of aziridines with α-nitroacetates has been developed. Good yields and enantioselectivity were observed for the reaction of various aziridines using a novel cinchona alkaloid amide/NiBr2 catalyst. Both enantiomers of products could be obtained by using pseudoenantiomeric chiral catalysts. This process offers an efficient route for the synthesis of α-aminoketones.