AbstractDie Alkohole (III) bzw. (IV), die als Gemisch bei der Kondensation des Cyclohexenons (I) mit dem Crotylzinkbromid (II) erhalten werden, werden mit CrO3 zu dem Aromastoff Megastigmadien (V) bzw. dem Z‐Isomeren (VI) oxidiert; Photoisomerisierung von (VI) gibt (V).

Megastigma‐5,8‐dien‐4‐one, an aroma constituent of the yellow passion fruit and Virginia tobaccoPreparative gas chromatography allowed isolation of megastigma‐5, 8 (E)‐dien‐4‐one (3) from small subfractions of both yellow passion fruit and Virginia tobacco condensates. Along with 3, the Z‐isomer 4 occurs in the aroma of the yellow passion fruit. Both these novel flavor compounds were synthesized by a two‐step, non‐biomimetic route starting from 2, 6, 6‐trimethylcyclohex‐2‐en‐1‐one. The E‐isomer 3 was also formed by acid‐catalyzed dehydration/rearrangements of ionol‐ and damascol monoepoxides 5, 6, 7, 8 and hydroxy‐ionols and ‐damascol 9, 10 and 11. Such a biomimetic conversion indirectly supports the assumption that 3 and 4 might originate from the oxidative degradation of carotenoid precursors possibly related to canthaxanthine.