Studies on pyrazines. Part 32. Synthesis of trisubstituted and tetrasubstituted pyrazines as ant pheromones
The synthesis of trialkylpyrazines having methyl groups on C-2 and C-5 is described, which is completed by the cross-coupling reaction of 2-chloro-3,6-dimethylpyrazine with dialkylzinc in the presence of [1,3-bis(diphenylphosphino)propane] nickel(II) chloride. Similarly, 2,5-diisobutyl-, -diisopropyl- and -di-sec-butyl-3-methylpyrazines are prepared from the corresponding dialkyl chloropyrazines. The dimethyl products are acylated with an α-keto acid under the Minisci radical conditions providing 2-acyl-5-alkyl-3,6-dimethylpyrazines. Several compounds obtained in this study prove to be active as components of pheromones in ants.