(6′ RS ,8′ RS ,2 E )‐ und (6′ RS ,8′ SR ,2 E )‐3‐Methyl‐3‐(2y,2′,6′‐trimethyl‐7′‐oxabicyclo[4.3.0]non‐9′‐en‐8′‐yl)‐2‐propenal ([(5 RS ,8 RS )‐ und (5 RS ,8 SR )‐5,8‐Epoxy‐5,8‐dihydro‐ionyloinden]acetaldehyd): Synthese und Röntgenstrukturanalyse

Synthesis and X‐Ray Structure of (6′ RS ,8′ RS ,2 E )‐ and (6′ RS ,8′ SR ,2 E )‐3‐Methyl‐3‐(2′,2′,6′‐trimethyl‐7′‐oxabicyclo[4.3.0]non‐9′‐en‐8′‐yl)‐2‐propenal ([(5 RS ,8 RS )‐ and (5 RS ,8 SR )‐5,8‐Epoxy‐5,8‐dihydro‐ionylidene]acetaldehyde) To check our previous spectroscopic assignments of the structures of trans ‐ and cis ‐substituted furanoid end groups of carotenoid‐5,8‐epoxides, we now have synthesized the title compounds. An X‐ray structure determination of a single crystal of the trans ‐isomer (±)‐ ‐10A is in agreement with the 1 H‐NMR spectroscopic arguments: isomers with Δδ (HC(7), HC(8)) = 0.15–0.22 ppm and J > 1.4 for HC(7) belong to the cis ‐series; Δδ in trans ‐compounds is < 0.07 ppm, and HC(7) appears as a broad singulett.