Asymmetrische Katalyse durch Vitamin B₁₂: Isomerisierung achiraler 1,4-Epiperoxide zu optisch aktiven 4-Hydroxycycloalk-2-en-1-onen

Abstract

Achiral cyclic 1,4-epiperoxides undergo fast isomerization to optically active 4-hydroxycycloalk-2-en-1-ones in presence of catalytic amounts of cob(II)alamin (B_12r). Light-induced oxygenation of cyclic conjugated dienes in MeOH to 1,4-epiperoxides followed by isomerization with 0,5 mol-% B₁₂ and 5 mol-% vitamin C in the same solvent allows the conversion of cyclohexa-1,3-diene to (S)-4-hydroxycyclohex-2-en-1-one (yield 50%,ee 17%) and of cyclopentadiene to (S)-4-hydroxycyclopent-2-en-1-one (yield 70%, ee = 17.5%) in one pot.