Synthesis of (+)-(S)-isorobinal together with its antipod, a cyclic monoterpene functioning as the sex pheromone of Rhizoglyphus setosus and its distribution among Astigmata

Abstract

Both compounds, (+)-(S)- and (−)-(R)-4-isopropenyl-3-oxo-1-cyclohexene-1-carbaldehyde [(+)-(S)- and (−)-(R)-isorobinal, (S)- and (R)-1, [α]_D²⁸ +51° (c=1.0, CHCl₃) and [α]_D²⁵ −45° (c=1.3, CHCl₃), 95% ee and 88% ee], were synthesized in seven steps starting from (R)- and (S)-perillyl alcohol [(R)- and (S)-2] available commercially. Isorobinal (1) is distributed among seven species of Astigmata among 61 species examined. (S)-Isorobinal [(S)-1], known as the female sex pheromone of Rhizoglyphus setosus, was confirmed in two other Rhizoglyphus species, while its biological function remained obscure against each species. In the other four species, not only its configuration but also its function has not yet been determined.