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Studies related to the insect control potential of thujone derivatives

University of British Columbia

Treatment of cedar leaf oil with aqueous potassium permanganate resulted in the oxidative ring opening of thujone (VI), the major component of the leaf oil, to yield the crystalline α-thujaketonic acid (VII). This material because of its availability and interesting structure represented an attractive starting material for the synthesis of some novel analogs of possible insect controlling agents. Therefore, to achieve this goal the functionalization of the ketonic carbonyl of α-thujaketonic acid was studied. Treatment of the sodium salt of α-thujaketonic acid in dimethyl sulfoxide with the phosphorane produced from either methyltriphenylphosphoniurn bromide or isopropyl-triphenylphosphoniurn iodide yielded the methylene and isopropylidene derivatives of α-thujaketonic acid (XIII, XIV). These two compounds represented two novel analogs of chrysanthemic acid, a naturally occurring material of which numerous derivatives are known which possess insecticidal activity. With the establishment of the conditions for the Wittig reaction of α-thujaketonic acid with a phosphonium salt, two routes for the synthesis of phosphonium salts which when coupled to α- or β-thujaketonic acid (XI, XII) would lead to insect hormone analogs, were studied. Thus, Horner reaction of 2-butanone with trimethylphos- phonoacetate resulted in the preparation of cis and trans methyl 3-methyl-2-pentenoates (XX, XXI), which were separated by means of spinning band distillation. In the first sequence studied the separate isomers were elaborated via standard means to yield the cis and trans 7-methyl-6-nonene-3-ols (XXVI and XXXII) which possessed the desired carbon skeleton. However, upon conversion of the trans secondary alcohol (XXXII) to the iodide (XXXIII), and treatment of this iodide with triphenylphosphine, none of the desired trans 7-methyl-6-nonene-3-triphenyl-phosphonium iodide (XIX) was isolated. Therefore, the study of an alternate route for the synthesis of the desired cis and trans 7-methyl-6-nonene-3-triphenylphosphonium iodides (XVIII and XIX) was undertaken. Elaboration of cis methyl 3-methyl-2-pentenoate to cis 5-methyl-4-heptenetriphenylphosphonium iodide (XLVI) was achieved by standard means. Treatment of this phosphonium salt with n-butyllithium and ethyl iodide then yielded the desired cis 7-methyl-6-nonene-3-triphenylphosphonium iodide (XVIII).

Text

2010-01-27

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http://hdl.handle.net/2429/19182

Chemistry

University of British Columbia

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