New Syntheses of the Bark Beetle Pheromones 2-Methyl-6-methylene-7-octen-4-ol (Ipsenol) and 2-Methyl-6-methylene-2,7-octadien-4-ol (Ipsdienol).

Abstract
3-Methylene-4-pentenal was prepared by a thermal sigmatropic rearrangement of 2,3-butadienyl vinyl ether. Treatment of 3-methylene-4-pentenal with isobutylmagnesium bromide provided 2-methyl-6-methylene-7-octen-4-ol (ipsenol) while with isobutenylmagnesium bromide 2-methyl-6-methylene-2,7-octadien-4-ol (ipsdienol) was obtained. Use of (+)-(2S,3S)-N,N,N'',N''-tetramethyl-2,3-dimethoxybutan-1,4-diamine as chelating agent in the latter reactions produced optically active ipsenol and ipsdienol in low optical yields. The synthesis of 2-methyl-6-methylene-(3E)-7-octadien-2-ol is described; acid-catalyzed rearrangement of the latter gave only a small amount of ipsdienol. [Ipsenol and Ipsdienol were pheromones of Ips spp.].