The Claisen Transposition in the Preparation of New Odorant Substances

In course of the search for new odorant substances, our laboratory has applied different reactions on different substances in order to evaluate the resulting products.

One of these reactions was the allylic transposition of the allylic enol ethers. This reaction is well known in the literature and many references to it are already in existence (see References 1 to 12).

Although the way in which the allylic enol ether is produced is not completely understood, many authors are in agreement on the reaction mechanism described in Scheme 1. In this scheme the step (a) consists in the formation of the dimethyl acetal of a symmetrical or assymmetrical ketone (I). After that, in steps (b) and (c), an allyl methyl acetal (III) is formed, which, owing to another loss of a methanol molecule, leads to the formation of an allyl enol ether (IV). The final step (d) is a transposition in which 6 atoms are involved and which forms a γ,δ-unsaturated ketone (V).

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