Of rose oxide

This reaction was used for a convenient synthesis of Rose oxide (equation 11)... 

In sensitized or photocatalyzed reactions, conditions of total or constant absorbance can easily be controlled by the concentration of the sensitizer or photocatalyst added. In addition, experience has shown that the concept of spatial separation between the light source and the reaction mixture is in general not required. Dragoco uses immersion-type annular reactor geometries [2, 3, 69, 70] for the production of ( —)-rose oxide by rose bengal sensitized oxidation of (— )-citronellol (Eqs. 45-48, Figure 23). 

Figure 23. Synthesis of (—)-rose oxide by sensitized oxidation of (-)-citronellol [2, 3,81].

Scheme 77 Photooxygenation of (-)-p-citronellol (279) conducted in a glass microreactor and the subsequent use of hydroperoxide 278 in the synthesis of (-)-rose oxide (200).

Photo-oxidation of citronellol in polystyrene beads [120]. A sample of 3.0 g of polystyrene beads (commercial, cross-polymerized with 1% of divinylbenzene) was treated with a solution of 2 mg of tetraphenylporphyrin and 780 mg (5 mmol) of citronellol in 20 mL of ethyl acetate in a petri-dish (30 cm diameter). After 2h in a ventilated hood, the solvent has evaporated and the petri-dish was covered with a glass plate and irradiated for 5 h with a 150 W halogen lamp. The solid support was then washed with 3 x 20 mL of ethanol, the combined ethanol fractions were rota-evaporated and 900 mg of the hydroperoxide mixture (96%) was isolated as a slightly yellow oil. The hydroperoxides were quantitatively reduced to the corresponding allylic alcohols by treatment with sodium sulfite. One of these products is used in the industrial synthesis of rose oxide. 

Calandre was created in 1968 to reflect the metallic theme used at that time by Paco Rabanne in his fashion designs. Although it follows the same general pattern as Madame Rochas, both the rose and muguet notes show interesting developments. The use of rose oxide and diphenyl oxide in combination with geranium, nerol, and geranyl acetate as part of the rose complex provides much of the "metallic" character. 

Anselmi et al. (02JCS(P2)1525), very recently published the conformational analysis and dynamics of cA/ rafts-4-methylcyclohexyl tetrahydro-pyranyl ethers (cf. Scheme 12) and compared their structures with the floral odors of the compounds. The cis isomer 40(cis), endowed with a main white flower note, has an bent, oval molecular shape. The trans derivatives 40(trans) and 41, exhibit different odors, possess an extended structure of cylindrical molecular shape. Brenna et al. (02CJC714) reexamined the configuration/conformation of rose oxide analogues. However, the conformational analysis provided poorer results than published previously (78JPC303) without even citing the previous paper. 

Such allyloxylation reactions allow, for example, the formation of ( )-rose oxide from citronellol [161]. The synthesis of butenolides can be efficiently performed starting from )6-unsaturated acids [172] ... 

Certainly economical considerations are an important starting point for the development of a successful aroma chemical. The sensorial profile, impact and the absence of off notes is often underestimated. It is part of the knowledge and the professional skills of a flavourist to understand the relevance of effects like aging, isomerisation and oxidation. Over the years numerous strategies for the synthesis of fairly simple aroma chemicals, like straight-chain esters, and of complex structures, like the different isomers of rose oxide (2S, 4R rose oxide and 2R, 4R rose oxide), have been developed. 

Nearly all the synthetic work in this group concerns the preparation of rose oxide, a review of which has appeared in Polish. 

In a third synthesis of rose oxide (909) from the lactone 919, addition of propynyllithium, followed by borohydride reduction, gave the diol 920, to which the additional methyl group was added with lithium dimethyl cuprate. Hydrolysis and treatment with silver nitrate yielded the rose oxides (909). This same paper describes a related synthesis of the naturally occurring 2,2,6-trimethyl-6-vinylpyran (921) (Vol. 2, p. 167). 

Yamamoto and Nakamura have reported a synthesis of rose oxide from the dimer 922 of isoprene. Prins reaction (formaldehyde) yielded the dihydropyran 923, which underwent specific ozonolysis and hydrogenation to the known (and naturally occurring) ketone 924. Conversion of the latter to rose oxide (909) is well known (Vol. 2, p. 168, Ref. 586). 

Monnerie, N., Ortner, J., Economic Evaluation of the Industrial Photosynthesis of Rose Oxide via Lamp or Solar Operated Photooxidation of Citronellol, J. Solar Energy Eng. 2001, 123, 171 174. 

A variant of the ring-closure reactions for the synthesis of rose oxide (299) has been described by Eschinazi. It consists of oxidising the double bond of citronellyl acetate (296) with performic acid, then thermolysing the fully acetylated compound (297) to yield the diene acetate (298), the corresponding alcohol of... 

Other methods for the production of rose oxide consist of halogenation-dehalogena-tion reactions of citronellol [183b]-[183d]. 

The occurrence and syntheses of rose oxides, dihydrorose oxides, rosefuran, and nerol oxides, together with related compounds, have been reviewed. The structure of a cyclic monoterpenoid ether from Artemisia tridentata, which is related to the santolinyl monoterpenoids, has been confirmed (c/. Vol, 7, p. 20) as (227) and renamed artemiseole (c/. Vol. 8, p. 58 for an incorrect structural deduction).Interestingly, another new component of A. tridentata, the (3S)-diastereoisomer of (74), with formic acid yields (227) in contrast to (74) which yields the acyclic aldehyde (228). ° It is possible that some of the 31% of unidentified components in the essential oil of A. annua may correspond to these new compounds.The quinone (229) has been isolated from Lithospermum erythrofhizon, and further details on the presence of aeginetolide in Aeginetia indica have been published. 

Matsuda, H. Yamamoto, T. Kanisawa, T. Synthesis and Odor Properties of Optical Isomers of Rose oxide and Dihydrorose oxide, in The 13th International Congress of Flavours, Fragrances and Essential Oils. 1995. Istanbul, Turkey, pp 85-91. 

Two further syntheses of rose oxide (415) are described. The first is a modification of the route from citronellol (416), anodic oxidation of which (in acetonitrile with tetraethylammonium tosylate as supporting electrolyte) leads to a 71 29 mixture of ns tra s-(415). The other route is of the dihydropyran type ... 

In this chapter, we first describe the peculiar electronic structure of 2 and its impact on its chemical reactivity that is opposite from that of ordinary oxygen 02-Then, we compare the respective advantages and limitations of photochemical and chemical methods to generate 2 in a context of industrial development. In particular, we detail the criteria for choosing a reaction medium compatible with both the organic substrate and water-soluble chemical sources of 02- Finally, the main reactions of 2 in organic chemistry are listed and illustrated with two industrially relevant examples recently developed in the fields of perfumery (synthesis of rose oxide) and pharmacy (synthesis of artemisinin). 

Scheme 22.7 Synthesis of rose oxide from p-citroneiioi.

We thank all the coworkers of (former) DSM Fine Chemicals Austria who were involved in the R D and the production of rose oxide via DSO, in particular, Walther Jary and Peter Pochlauer. 

Synthesis of rose oxide (5) by photooxygenation of citronellal as the first step Rose Bengal is used as a photosensitizer Ohioff et al. (1961)... 

Reduction of (R)-(+)-citronellal by lithiumaluminumhydride yields (R)-(+)-citro-nellol which undergoes a photo ene reaction to the hydroperoxide in the presenee of the xanthene dye rose Bengal as a photosensitizer of singlet-oxygen. Sodium sulfite reduces hydroperoxide to the diol which is, when catalyzed by acids, dehydrated to the ir s-isomer of rose oxide... 

A practical example of the use of singlet oxygen is provided by the synthesis of rose oxide (131) from /3-citronellol (129, equation 12.84). The sensitizer was rose bengal, a dye that can be used for singlet oxygen reactions induced by sunlight. The product of the ene reaction was reduced with Na2S03 to a diol (130), which then underwent spontaneous cyclization to 131 in a cold, acidic solution. ... 

The s)mthesis of rose oxide discussed on page 852 involves the singlet oxidation of citroneUol to form 2,6-dimethyl-3-octene-2,8-diol (130). Another diol is also formed, with a percent )deld about half that of 130. What is the other product, and what is the mechanism of its formation ... 

Meyer et al. examined the formation of rose oxide by the oxidation ofdtronellol with singlet oxygen in a temperature-resistant glass (Borofloat) microreactor [9]. A 10 mL P-citronellol-ethanol solution with Ru(T>py)3Cl2 is circulated through the microchannel reactor (hold-up volume 0.27 mL). Products are identified by H PLC analysis. After an irradiation time of 40 min, space-time yields of 0.8 mmol L min are obtained. In a comparable batch process, space-time yields are 10 times lower. 

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