A general approach to the synthesis of mono-olefinic insect sex pheromones of Z- or E-configuration.

Abstract

A series of insect sex pheromones and structurally related olefins have been synthesized with high stereoisomeric purity by two sequential cross-coupling reactions. Starting with (Z)- or (E)-1-bromo-2-phenylthioethene, (1) and (2), and Grignard reagents in the presence of nickel or palladium catalysts, two types of compounds have been prepared: (i) 1,2-dialkylethenes and (ii) alkenyl acetates. In the synthesis of the Z-isomers, the first step involves a cross-coupling reaction of compound (1) with the appropriate Grignard reagent in the presence of a catalytic amount of [PdCl₂(PPh₃)₂]. The second cross-coupling reaction is performed on the intermediate (Z)-phenylthioalkenes using a different Grignard reagent in the presence of [NiCl₂(dppe)](dppe = Ph₂PCH₂CH₂PPh₂) as a catalyst. In the synthesis of E-isomers both steps are cross-coupling reactions of Grignard reagents in the presence of [NiCl₂(dppe)] as a catalyst, the first step involving compound (2) and the second step involving the intermediate (E)-phenylthioalkenes obtained. The Grignard reagents used in the synthesis of the alkenyl acetates derive from protected ω-halohydrins.