Testing Differently Substituted Quinoxaline-2,3-Dithiolate Ligands in Z-Stereoretentive Olefin Metathesis Leading to Pheromone of Rice Yellow Stem Borer (Scirpophaga incertulas)

Abstract

Stereoselective olefin metathesis offers access to geometrically well-defined C–C double bonds and is considered a promising new method for transforming plant oils to valuable chemicals. A set of Z-stereoretentive catalysts bearing quinoxaline-2,3-dithiolate ligands functionalized with halogens, electron-withdrawing (EWG), electron-donating (EDG), and π-altered were obtained and characterized. New catalysts were tested in a model Z-stereoselective cross-metathesis (CM) and in the synthesis of a pheromone of rice yellow stem borer (Scirpophaga incertulas). Although none of the new catalysts surpassed the parent catalyst Ru5a—featuring non-substituted quinoxaline-2,3-dithiolate ligand—the ester-substituted complex Ru5h offered a similarly high level of Z-selectivity (>95:5) and productivity, whereas the carboxylic ester function can open perspectives for future immobilization or polar-tagging.

Practical Applications: Decreasing availability of fossil organic feedstock and current policies of the European Union drive scientists to look for alternative sustainable sources of fine chemicals. In this context, Z-stereoselective olefin metathesis offers preferential access to geometrically well-defined C–C double bonds and is considered a new promising method for transforming plant oils to valuable chemicals. One of them is sex pheromones of various insects—biodegradable and non-toxic chemical substances—used in small amounts to lure insects into pheromone traps. In the present work, a female sex pheromone of rice yellow stem borer (Scirpophaga incertulas) was obtained in high yield and selectivity, showing a possible application of the newly obtained Z-stereoretentive catalysts in the field of modern and environmentally conscious farming.