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Synthesis and Odor Characteristics of New Gem-Dimethylcyclohexane Derivatives

Contact Author Stanislaw Lochynski, Czeslaw Wawrzenczyk, and Miroslaw Walkowicz, Jozef Gora
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Searching for cyclic analogs of the insect juvenile hormones, we synthesized a series of new compounds containing the cyclogeraniolene system. This system can be considered as a cyclic form of acyclic terpenes, such as dihydrocitronellol, dihydrogeraniol, and menthocitronellol. The isoprenoid chain in these compounds is rolled to form the cyclohexane ring by connection of the carbon atoms C-7 and C-10. As compared with the classical cyclic systems of the cyclogeraniol type, the compounds obtained by us contain the gem-dimethyl groups in the 3-position in relation to a chain with the functional group.

A series of our compounds exhibited interesting odor propeties, which was not a surprise because many other odoriferous compounds from the gem-dimethylcyclohexane derivatives group are known.

Materials and Methods

The starting materials for synthesis of these compounds were the easily available terpenic component, (+)-3-carene and commercial dimedone. The key compound for synthesis of final products with the (Z)-menthocitronellyl skeleton, ester 11A, was obtained by the multistep synthesis from 1, presented in figure 2. In the first step of the synthesis, 1 was converted into keto aldehyde 2 by ozonolysis in the usual manner. Product 2 was transformed by modified intramolecular condensation in 1-acetyl-3,3-dimethyl-1,4-cyclohexadiene which formed saturated ketone 4C after hydrogenation over Pd/C. Monocyclic ketone 3 was selectively reduced with zinc dust in 25% aqueous KOH to give 1-acetyl-5,5-dimethyl-3-cyclohexene which was then degraded to 5,5-dimethyl-3-cyclohexenoic acid, a yield of about 70%, by the reaction with sodium hypobromide. Acid 5 was then reduced with lithium aluminium hydride (LAH) to alcohol 6 which was converted into 5,5-dimethyl-3-3cyclohexenyl/acetonitrile via tosylate 7 and bromide 8 (overall yield ca. 90%). Hydrolysis of nitrile 9 afforded acid 10 with ten carbon atoms which was esterified with ethanol to ethyl 5,5-dimethyl-3-cyclohexenyl/ acetate.

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