Synthesis of tsetse fly attractants from a cashew nut shell extract by isomerising metathesis

Starting from a purified cashew nut shell extract containing mostly anacardic acid derivatives, the tsetse fly attractants 3-ethyl- and 3-propylphenol were selectively synthesised. The mixture was first converted into 3-(non-8-enyl)phenol in 98% purity via ethenolysis and distillation with concomitant decarboxylation. The olefinic side chain was then shortened by isomerising cross-metathesis with short-chain olefins in the presence of a [Pd(μ-Br)(tBu3P)]2 isomerisation catalyst and a second-generation Hoveyda–Grubbs catalyst, and the synthesis was completed by a hydrogenation step.