New compounds with small rings in essential oils

Despite the continuing discovery of new synthetic fragrance raw materials, essential oils still remain the other half of the foundation of perfumery. Consequently, the analysis of essential oils is still very much of interest, as is illustrated by the excellent series of articles by Lawrence in this journal. We now wish to report a number of products containing small (three-, four-, and five-membered) rings, most of which are found for the first time in essential oils. These products were isolated by chemical group separation, liquid and gas chromatography, whereupon the structures were determined by mass, infrared and NMR spectroscopy. All structures were confirmed by synthesis. The essential oils used were obtained from regular commercial sources.

Cyclopropane derivatives

Two homologous acetates were found in abrette seed oil, which were identified as 1-(2- acetoxyethyl)-2-hexylcyclopropane (I) and 1-(4-acetoxybutyl)-2-hexylcyclopropane (II) (see Table I).

Although three-member ring compounds with a terpenoid skeleton (e.g., chrysanthemum acid, thujane and carane derivatives) are not uncommon in essential oils, only a few cyclopropane derivatives with straight chain substituents were found. One example is cascarillic acid (III), a constituent of cascarilla oil, another, 2-pentylcyclopropane carboxylic acid (IV), which we recently reported to occur in patchouli oil. Longer chain cyclopropane carboxylic acids are found in bacteria as a part of phospholipid molecules or as triglycerides. The biosynthesis of these compounds involves the methylation of unsaturated fatty acids by S-adenosyl-Lmethionine, and probably the ambrette acetates are formed by a similar pathway.

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