Metal Ion-Mediated Diastereoface-Selective Nitrone Cycloadditions. Reaction Mechanism for the Reversal of Regioselectivity Observed in the Magnesium and Zinc Ion-Mediated Nitrone Cycloadditions of Allylic Alcohols

Article abstract of DOI:10.1016/0040-4039(95)00911-U

Magnesium and zinc ion-mediated cycloaddition reactions of a carbonyl-conjugated nitrone, (Z)-N-(benzoylmethylene)aniline N-oxide to the allylic alcohols bearing a chirality at α-position give isoxazolidine-5-alcohol and isoxazolidine-4-alcohol derivatives, respectively, both in highly lk-1,2-inductive manners. α,α-Disubstitution of allylic alcohol dipolarophiles virtually inhibits the zinc ion-catalyzed reaction paths, and use of a coordinating solvent in the magnesium ion-catalyzed reactions leads to the reversal of regioselectivity.Reaction mechanism for the metal ion-catalyzed competitive cycloadditions is proposed. - Keywords: nitrone cycloaddition; allylic alcohol; diastereofacial selectivity; rate acceleration; regiocontrol