Structure‐odor correlation, XXV. Synthesis and Olfactory Properties of the “Inverse” Megastigmatrienone and Its Analogs

Abstract

AbstractThe oxoisophorone monoacetal 2 is a convenient starting material for the synthesis of several megastigmatrienone analogs. Thus, the Wittig reaction of ketone 2, followed by deprotection, led to the dienones 7–10. The “inverse” megastigmatrienone 1 was synthesized from 2 via homologation (→11→12), Grignard reaction (→13) and hydrolysis. The mixture of the four stereoisomers of 1 is dominated by (E,E)‐1. In contrast, (Z,Z)‐1 was obtained as the main product when starting from 2 and proceeding via the reaction sequence →14 →15 →16 →17 and then (Z)‐selective Wittig reaction of aldehyde 17. Likewise, ketoaldehyde 17 is the starting material for the nor derivative 20. The odor evaluation of 1 showed that the typical strong and pleasant tobacco odor of megastigmatrienone D was by no means observed, neither in strength nor in quality. On the other hand, the four stereoisomers of 1 all exhibit a similar weak to moderate odor of floral, sweet, fresh and coumarin‐like tonalities.