ABSTRACT
The unexpected formation of previously nondescribed (semi)conjugated ethyl trienoate revealed its powerful aroma of fresh pineapple. Thus, we have designed, prepared and evaluated a set of its carbonyl analogues as mixtures of (E/Z)-isomers. Although their synthesis from natural ocimene led to target compounds in low yields, optimized preparation from geranyl acetate furnished an aldehyde as high-yielding common intermediate on multigram scale. A series of its Wittig olefinations provided corresponding (E,E)-configured carbonyl dienes. Final acid-catalyzed elimination of allylic acetates provided the desired “pineapple” target in moderate yield. Sensory analysis revealed that only the parent compound possesses the typical pineapple aroma. Although analogous tBu- and/or Bn-esters feature an additional green note, the most similar Me-ester differs by its fresh woody aroma analogously to methyl ketone.
GRAPHICAL ABSTRACT
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Acknowledgments
We thank Dr. Oľga Vyviurská for analytical measurements. We are grateful to Prof. František Považanec and Dr. Pavol Jakubec for proof-reading and valuable suggestions. Dedicated to the memory of Kristína Csatayová.