Enantioselective protonation, until recently a largely overlooked reaction, has, in the last five years, developed into a field of intense research activity. The progress achieved parallels or complements that obtained in the understanding of enolate structures and reactivities. The conceptual simplicity and attractiveness of enantioselective protonation results from the fact that after reaction, the chiral proton donor is regenerated in its original protonated form by an extractive workup. Enantioselective protonation has been applied to the synthesis of amino acids, antiinflammatory agents (2-arylpropanoic acids), and fragrance compounds such as (S)-a-damascone, for which its industrial feasibility has been demonstrated.

Facing facts: Control of the configuration of the propargylic center in 1 is essential for the facial selectivity observed in the Pt‐, Au‐, or Cu‐catalyzed enyne cycloisomerization. This route has been used for the stereoselective synthesis of the naturally occurring sesquiterpene (−)‐cubebol (2).

Dedicated to Dr. Ferdinand Näf on the occasion of his 65th birthday Amphiphilic polystyrene-and polymethacrylate-based b-acyloxy ketones were investigated as potential delivery systems for the controlled release of damascones by retro-1,4-addition in applications of functional perfumery. A series of random copolymers being composed of the hydrophobic damascone-release unit and a second hydrophilic monomer were obtained by radical polymerization in organic solution by using 2,2'-azobis[2-methylpropanenitrile] (AIBN) as the radical source (Schemes 2 and 3). A first evaluation of the polymer conjugates in acidic or alkaline buffered aqueous solution, and in the presence of a surfactant, showed that polymethacrylates and polystyrenes having a carboxylic acid function as hydrophilic group are particularly interesting for the targeted applications ( Table 2). The release of d-damascone (1) from polymers with poly(methacrylic acid) and poly(vinylbenzoic acid) comonomers in different stoichiometric ratios was thus followed over several days at pH 4, 7, and 9 by comparison of fluorescence probing, solvent extraction, and particle-size measurements (Tables 3 and 4). In acidic media, the polymers were found to be stable, and almost no d-damascone (1) was released. In neutral or alkaline solution, where the carboxylic acid functions are deprotonated, the concentration of 1 increased over time. In the case of the polymethacrylates, the fluorescence probing experiments showed an increasing hydrophilicity of the polymer backbone with increasing fragrance release, whereas in the case of the polystyrene support, the hydrophilicity of the environment remained constant. These results suggest that the nature of the polymer backbone may have a stronger influence on the fragrance release than the ratio of hydrophilic and hydrophobic monomers in the polymer chain.1. Introduction. -The long-lastingness of fragrance perception is often directly associated with the efficiency of perfumed consumer products in body care or household applications. As a consequence of their high volatility, many attempts to control the evaporation of fragrances over time have been undertaken to increase their performance during and after application. As an alternative to encapsulation technologies (see, e.g., [1]), the development of chemical delivery systems for the controlled release of fragrances has become a more and more widely investigated area of research [2]. A series of precursor molecules, so called 'pro-fragrances', have been prepared, and a broad variety of reaction conditions, such as hydrolysis [3] [4] or the change of pH [5] [6], oxidation [7], the action of temperature, light [8] [9], enzymes or microorganisms [10] have been used to trigger the release of perfumery raw materials from their corresponding precursors.Recently, damascones (= 1-(2,6,6-trimethylcyclohexen-1-yl)but-2-en-1-ones) or damascenones (= 1-(2,6,6-trimethylcyclohexadien-1-yl)but-2-en-1-ones), the so-called rose ketones [11], were successfully released from different monomeri...

Die richtige Seitenwahl: Die Konfiguration des Propargyl‐Stereozentrums in 1 legt die Seitenselektivität bei der Pt‐, Au‐ oder Cu‐katalysierten Enin‐Cycloisomerisierung fest. Dieser Weg wurde bei der stereoselektiven Synthese des natürlichen Sesquiterpens (−)‐Cubebol (2) beschritten.

Scheme 3. Diastereoselective reductions of ketone 1. a) LiAlH 4 (1.15 equiv), THF, À70 8C to À50 8C; b) Red-Al ¾ (3.0 equiv), THF, À70 8C to room temperature; c) BH 3 ¥SMe 2 (0.71 equiv), THF, room temperature. NOE NOE NOE 3 J (H a /H b ) = 5.6 Hz 3 J (H a /H b ) = 0 Scheme 7. Structure determination of acetonides 16 and 17: a) 2-methoxypropene, cat. TFA, DMF, 25 8C, 3 h.