New synthesis of cis ‐3, cis ‐5‐ and trans ‐3, cis ‐5‐tetradecadienoic acids, pheromone constituents of attagenus elongatulus and A. megatoma

A new method for the synthesis of cis ‐3, cis ‐5‐ and trans ‐3, cis ‐5‐tetradecadienoic acids, pheromone constituents of the dermestid beetles Attagenus elongatulus and A. megatoma , was developed. The syntheses are based upon the formation of trans ‐2‐tetradecen‐5‐ynoic acid by reaction of 4‐bromo‐2‐butenoic acid with 1‐decynylmagnesium bromide. The enynoic acid undergoes alkali‐induced isomerization to yield a mixture of acids from which cis ‐3‐ and trans ‐3‐tetradecen‐5‐ynoic acids were separated in 31% and 34% yields, respectively. Methyl trans ‐2‐tetradecen‐5‐ynoate was similarly prepared and isomerized to furnish methyl cis ‐3‐tetradecen‐5‐ynoate in 8% yield. Reduction of the tetradecenynoic acids with dicyclohexylborane gave cis ‐3, cis ‐5‐and trans ‐3, cis ‐5‐tetradecadienoic acids in 4% and 39% yields, respectively. A better yield (49%) in the reduction of cis ‐3‐tetradecen‐5‐ynoic acid to cis ‐3, cis ‐5‐tetradecadienoic acid was obtained by hydrogenation over Lindlar's catalyst. Similarly, reduction of methyl cis ‐3‐tetradecen‐5‐ynoate with disiamylborane gave 22% methyl cis ‐3, cis ‐5‐tetradecadienoate.