Female moths of
Lyclene dharma dharma (Arctiidae, Lithosiinae) produce a novel sex pheromone composed of three methyl-branched ketones: 6-methyl-2-octadecanone (
I), 14-methyl-2-octadecanone (
II), and 6,14-dimethyl-2-octadecanone (
III). Their structures were confirmed by syntheses accomplished by a different route for each component. In order to obtain a sufficient amount of the synthetic pheromone, we developed new routes
via methyl-branched 1-alkenes: 6-methyl-1-octadecene (
1), 14-methyl-1-octadecene (
2), and 6,14-dimethyl-1-octadecene (
3). Compound
1 was synthesized by coupling between a C
10-chain bromide and a 3-methyl-branched C
8 unit (
A) prepared from 3-methyl-1,5-pentanediol,
2, by coupling between a C
11-chain bromide and a 3-methyl-branched C
7 unit (
B) prepared from 2-hexanone, and
3, by connecting
A and
B, using propargyl alcohol as a C
3 linchpin. The use of 3-chloro-1-propanol and
tert-butyl acetoacetate as the linchpin was also examined to connect the two synthetic blocks in the synthesis of
3. Components
I–
III were obtained by Wacker oxidation of the corresponding 1-alkenes
1–
3 in good yields.
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