Synthetic Studies of Amino Acid-type Natural Products Using a Functional Nitrone

Abstract

(5R)- [and (5S)]-5,6-Dihydro-5-phenyl-2H-1,4-oxazin-2-one N-oxides were designed and synthesized as chiral (E)-geometry-fixed α-alkoxycarbonylnitrones that exist as equilibrating mixture of (E)- and (Z)-isomers. The cyclic nitrone reacted with olefins under mild conditions to afford the main cycloadducts via the least sterically demanding exo modes. The nitrone also reacted with an allyl alcohol in the presence of magnesium bromide from the less hindered face via exo-mode to afford exclusively cycloadduct as a single stereoisomer. These reactions were applied to the syntheses of carbocyclic polyoxin C, anti-β-substituted aspartic acid, clavalanine, monatin, lycoperdic acid, neodysiherbaine A, and maremycins A and D₁.