All of the stereoisomers of 10,14-dimethyloctadec-1-ene (1), (Lyonetia prunifoliella), were synthesized by starting from the enantiomers of citronellol (4) and methyl 3-hydroxy-2-5,9-dimethyloctadecane (2) and 5,9-dimethylheptadecane (3), the sex pheromone components of the apple leafminer methylpropanoate (11).
The apple leafminer (Lyonetia prunifoliella) is a pest in apple orchards in eastern North America. In 1997 Gries et al. identified three methyl-branched hydrocarbons, 10,14dimethyloctadec-1-ene (1, Scheme 1), 5,9-dimethyloctadecane (2) and 5,9-dimethylheptadecane (3) as its synergistic female-produced pheromone components. [1] Structural assignment of 1, 2 and 3 was carried out by comparing natural products with the corresponding synthetic hydrocarbons obtained as stereoisomeric mixtures. In field trapping experiments, 1, 2 and 3 singly were unattractive to males, but as ternary mixture attracted numerous male moths. The importance of 1 in the pheromone communication of L. prunifoliella was revealed by the fact that no attraction of males to the pheromone lure was observed without 1. [1] Each of the hydrocarbons 1, 2 and 3 has two stereogenic centers, and therefore possesses four stereoisomers. The enantiomeric composition of the naturally occurring 1, 2 and 3 is not determined yet, but may be clarified by testing the pheromone activity of every stereoisomer of 1, 2 and 3. In Scheme 1. Sex pheromone components of Lyonetia prunifoliella and order to achieve this aim, we decided to synthesize all the their retrosynthetic analysis stereoisomers of 1, 2 and 3 according to the plan shown in Scheme 1. The carbon skeleton of 1 can be constructed by connecting the chiral and non-racemic building blocks A was converted into (S)-5a in 86% yield as reported by Mori and B, which in turn are to be derived from C and D. Both and Kato. [3] The corresponding tosylate (S)-5b was treated the enantiomers of methyl 3-hydroxy-2-methylpropanoate with 5-hexenylmagnesium bromide in the presence of (C) as well as those of citronellol (D) are commercially Li 2 CuBr 2 β’SMe 2 β’SPh [4] to give a 7:3 mixture of the desired available, and previously employed by us for the synthesis (S)-6 and the by-product (S)-7, which presumably was genof the stereoisomers of 3,13-dimethylheptadecane, the pheerated by a cyclization process such as conversion of E into romone of the western false hemlock looper. [2] The stereo-F. This type of cyclization had been recorded in the cases isomers of 1 can be converted into the stereoisomers of 2 of the Grignard reaction in general [5] and in the case of 5and 3.
hexenylmagnesium chloride in particular. [6] The mixture of Scheme 2 summarizes the preparation of the building the acetates (S)-6 and (S)-7 was then hydrolyzed with poblocks 10 (Ο B) and 13b (Ο A). (S)-Citronellol (4, 97% e.e.) tassium hydroxide to give a mixture of the alcohols (S)-8 and (S)-9, which was separated by chromatography on silica gel impregnated with silver nitrate to give the pure alcohol