Enantioselective conversion of linoleate hydroperoxide to an α, β‐epoxy alcohol by niobium ethoxide

Abstract

AbstractNiobium (V) ethoxide [Nb(OC2H5)5] catalyzed the rearrangement of methyl 13(S)‐hydroperoxy‐9(Z),11(E)‐octadecadienoate (Me‐HPODE) to epoxy hydroxy isomers. At low temperature (5°C) in aprotic solvent, Me‐HPODE was converted to the diastereomeric α, β‐epoxy alcohols, methyl 11(R,S),12(R,S)‐epoxy‐13(S)‐hydroxy‐9(Z)octadecenoate. These products are referred to as oxylipids and structurally resemble those obtained from the vanadium‐ and epoxygenase‐catalyzed rearrangement of Me‐HPODE but are distinct from products obtained from ferrous iron‐, hematin‐, and hemoglobin‐catalyzed rearrangements. Because the product of the niobium‐catalyzed rearrangement of Me‐HPODE was predominantly the erythro diastereomer, the rearrangement is distinguished from that produced by a titanium catalyst, in which the threo diastereomer [methyl 11(R), 12(R)‐epoxy‐13(S)‐hydroxy‐9(Z)‐octadecenoate] predominates, and from that produced by a vanadium catalyst, in which both diastereomers are produced in equal proportion. The synthesis of alcohol epoxide by Nb(OC2H5)5 was inhibited by traces of water, but inclusion of molecular sieves in the reaction medium did not improve yield, as the alcohol epoxide rearranged to ketonic materials.