Synthesis and odor properties of carene and carane derivatives

In addition to α-pinene, (+)-car-3-ene 1 is the main component of turpentine obtained from the Pinus silvestris pine. Its content in Polish, German, and Russian turpentines is 15-41%. Until now, (+)-car-3-ene has been insufficiently used for the syntheses of odor compounds. Only two such compounds are manufactured on a commercial scale: 4-hydroxymethyl-2 -carene 2, having a flower odor with a fruit note, and its acetate with a herb-flower odor, the “turiol” and turiol acetate of Dragoco. The syntheses of several nitriles, derivatives of carene and carane, patented recently in Germany, also deserve attentions Interesting prospects are seen using (+)-car-3-ene for the synthesis of l-menthol by the series of reactions worked out by Sukh Dev and coworkers.

An extensive review of the possible uses of car-3-ene for the syntheses of odor compounds has recently been published by Verghese. The purpose of this report is to detail the syntheses of novel 4-substituted derivatives of carene and carane, and studies of their sensory (odorous) properties. The compounds were prepared from (+)-car-3-ene in a series of processes shown in figure 1.

In the first stage of the synthesis, (+)-car-3- ene 1 separated from Polish balsamic turpentine was changed, in the Prins reaction, to a mixture of acetates of 4-hydroxymethyl-2-carene 3 and 4-hydroxymethyl-3(10)-carene 4. Hydrolysis of this mixture resulted in a mixture of 4-hy - droxymethyl-2-carene 2 and 4-hydroxymethyl-3(10)-carene 5 in a ratio of 94:6. From alcohols 2 and 5, the respective alkoxynitriles 6 and 7 were prepared by reaction with acrylonitrile in an alkaline medium. On the other hand, by the oxidation of alcohols 2 and 5, an 83:17 mixture of 4-formyl-2-carene 8 and 4-formyl-3(10)-carene 9 was obtained. From the mixture of these aldehydes, their acetals with ethanediol-1,2 10 and 11 were prepared.

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