γ‐Unsaturated Aldehydes as Potential Lilial Replacers

Abstract

A series of Claisen rearrangements was undertaken in order to find a replacement for Lilial (=3-(4-(tert-butyl)phenyl)-2-methylpropanal), a high-tonnage perfumery ingredient with a lily-of-the-valley odour, which is a CMR2 material [1]. 5,7,7-Trimethyl-4-methyleneoctanal (10), the synthesis of which is described, became the main lead. It possesses an odour which is very close to that of Lilial but lacks its substantivity. Aldehydes with higher molecular weights than that of 10 were, therefore, synthesised in order to boost substantivity and to understand the structural requirements for a 'Lilial' odour. The aldehydes were obtained via Claisen rearrangements of 'exo-methylidene' vinyl ethers, allenyl vinyl ethers, or allenyl allyl ethers. Alternatively, coupling of terminal alkynes with allyl alcohols led to the desired aldehydes. Derivatives of 10 and their sila analogues were also synthesised. The olfactory properties of all synthesised molecules were evaluated for possible structure-odour relationships (SOR).

Total Synthesis of (−)‐Rotundone and (−)‐epi‐Rotundone from Monoterpene Precursors

“…For this purpose, ketone 15, prepared from raccitronellal as described, [31] was selectively oxidized with selenium dioxide, [32,33] and the resulting aldehyde/ketone mixture reduced with NaBH 4 to diol 16 (Scheme 8). Vinylation, [34] followed by Claisen rearrangement and Pd-catalyzed devinylation, [35] gave a diastereomeric mixture of hydroxy aldehyde, which was oxidized to keto aldehyde 17. Application of different methods described in the literature for the intramolecular aldolization of 1,5-dicarbonyl com- pounds (acid and base catalysis, proline) [36,37] gave only poor results if at all (see MeONa, HCl or proline in Table 1).…”

Lilial (butylphényl méthylpropional): Synthèse et Problématique Sanitaire

“…Il est peu coûteux et est utilisable à faible dose, ce qui peut expliquer l'engouement dont il a fait l'objet. On le considère comme un agent fixateur du fait de la ténacité de son odeur [5]. Le Lilial est constitué d'un mélange de deux énantiomères possédant sensiblement la même odeur.…”