Sandalwood derivatives

In Chapter 6, we learnt that campholenic aldehyde is an important precursor for a family of synthetic sandalwood derivatives. Write a mechanism to account for the formation of campholenic aldehyde when oc-pinene oxide is treated with zinc bromide (Figure PI4). 

Many cyclic sesquiterpene alcohols are key odor components in essential oils, for example, cedrol in cedarwood oil, the vetiverols in vetiver oil, and the santalols in sandalwood oil. Since these alcohols have not yet been synthesized on an industrial scale, they are described under the oil in which they occur (Chapter 3). Some of their derivatives, however, are discussed in this section. 

Some alicyclic alcohols are important as synthetic sandalwood fragrances. A few alicyclic aldehydes are valuable perfume materials and are obtained by Diels Alder reactions using terpenes and acrolein. Esters derived from hydrogenated aromatic compounds, such as /cr/-butylcyclohexyl and decahydro-/3-naphthyl acetates, are also used in large amounts as fragrance materials. 

Kovatcheva, A., Buchbauer, G., Golbraikh, A., Wolschann, P. (2003) QSAR modeling of alpha-campholenic derivatives with sandalwood odor. T Chem Inf Comput Sci 43, 259-266. 

The odor of a freshly crushed mint leaf, like many plant odors, is due to the presence in the plant of volatile C10 and Ci5 compounds, which are called terpenes. Isolation of these substances from the various parts of plants, even from the wood in some cases, by steam distillation or ether extraction gives what are known as essential oils. These are widely used in perfumery, as food flavorings and medicines, and as solvents. Among the typical essential oils are those obtained from cloves, roses, lavender, citronella, eucalyptus, peppermint, camphor, sandalwood, cedar, and turpentine. Such substances are of interest to us here because, as was pointed out by Wallach in 1887 and reemphasized by Ruzicka in 1935, the components of the essential oils can be regarded as derived from isoprene ... 

The former are mostly derived from plants [vegetabty colours) and may be contained in woods (e.g., campeachy, Brazil wood, sandalwood, yellow wood, fustic), barks (quercitron), roots [madder, turmeric), leaves (indigo, woad), flowers [safflower), fruit (Persian berries) and lichens [archil). Far fewer are animal colours [cochineal, kermes). 

Kovatcheva A, Buchbauer G, Golbraikh A, Wolschann P. QSAR Modelling of a-campholenic derivatives with sandalwood odor. J. Ghent. Nf. Comput. Sci. 2003 43 259-266. 

Geraniol is the primordial monoterpene, and its simple derivatives and cyclization products occur in the oils of many plants, used as flavoring and aromatic agents (e.g., caraway, coriander, dill, eucalyptus, lavender, orange, peppermint, rose, and sandalwood), as well... 

Derivation Treatment of sandalwood oil or santalol with acetic anhydride. 

C12 hydrocarbon (271)135 by a similar route but this compound is not identical to a tricyclic hydrocarbon isolated from East Indian sandalwood oil and reported to have this structure. (+)-Copacamphor (272) and (+)-copaborneol (273) have been isolated from Espeltiopsis guacharaca.136 The interesting sinularene derivative (274) and the acetoxycyclosinularane (275) have been isolated from the marine source, Clavularia inflata.137 These compounds, together with an aromadendrane derivative (see p. 181) are the first sesquiterpenoids from Octocorallia of the order Stolonifera. 

Sandalwood oil is obtained by distillation of the parasitic tree Santa-lum album. The major components of the oil are the santalols (27, 28). Many syntheses of these and related chemicals have been reported but, elegant as they are, none compete economically with the oil itself. The synthetic sandalwood materials fall into two main classes, the so-called terpenophenols and the materials derived from campholenic aldehyde. 

Pale yellow somewhat viscid liquid characteristic sandalwood odor and taste. dg 0.965-0 980. aas —15 to —20 . njj 1.500-1 510. Very slightly sol in warer sol in 5 vols 70% alcohol. Keep well closed, cool and protected from light, Note West Indian sandalwood oil is derived from Amyris balsamifera and is not official. Its rotation is +24 to +29 . ll is less sol in 70% a]c than the East Indian, therap CAT Urinary anti-infective. 

The odours of sandalwood and cedarwood and their resistance to attack by fungi and insects have made them prized articles of commerce for both construction and decorative purposes for thousands of years. Similarly the oils derived from the woods have a long history of use in perfumery. 

The members of the second family of synthetic sandalwood materials are derived from campholenic aldehyde (6.72). This aldehyde is prepared by treatment of a-pinene oxide (6.71) with a Lewis acid, usually zinc chloride or bromide. a-Pinene oxide is, in turn, prepared from a-pinene... 

Aldol condensation between campholenic aldehyde (6.72) and an aldehyde or a ketone (6.73) produces an unsaturated derivative (6.74). It should be noted that this material contains an -double bond. The reason for this lies in the mechanism of the aldol condensation as described in Figure 6.4 and associated text. The carbonyl group of (6.74) can be reduced to the corresponding alcohol by, for example, a complex metal hydride such as lithium aluminium hydride or sodium boro-hydride. This produces the sandalwood material (6.75). Three typical examples are shown at the bottom of Figure 6.18. The first, (6.76), is known under various trade names such as Bangalol (Quest) and is... 

The two a-santalene derivatives (79) and (80) are constituents of the aerial parts of Ayapana amygdalina. (+)-Epi-c/5-/S-santalol (81) has been identified as a new minor component of East Indian sandalwood oil. Treatment of (+)-a-santalyl acetate (82) with hydrogen chloride followed by dehydrOchlorination with basic alumina produces a mixture of /3-santalyl acetate (83) and the acetate of (81). Last year Christenson and Willis reported the acid-catalysed rearrange-... 

The East Indian sandalwood oil probably represents one of the most precious perfumery natural raw materials because of the rarity of the natural plants from which it is extracted. As until recently [36] since no industrially viable process existed for production of (Z)-beta-santalol, the main olfactive constituent of Indian sandalwood (see Fig. 6), the focus was directed toward the search for cheaper synthetic analogs in order to also prevent resource depletion. Alpha-campholenic aldehyde derivatives are clearly affording the best, and most often used substitutes for such a natural resource [37]. 

Further relevant essential oil investigations have been performed the early works using FID, while the more recent ones using, preferably, a TOFMS as detector. Among the essential oils previously studied by means of GC x GC are peppermint [122] and Australian sandalwood [123], with the latter also analyzed through GC x GC-TOFMS in the same work. Essential oils derived from Thymbra spicata [124], Pistacia vera [125], hop [126], Teucrium chamaedrys [127], Rosa dama-scena [128], coriander [129], and Artemisia annua [130], as well as tobacco [131], have also been subjected to GC x GC-TOFMS analyses. The references cited herein represent only a fraction of the studies performed by means of GC x GC on essential oils. 

Of the other skeletal types shown in Fig. 8.1.10 bergamotane type (161) has not, apparently, yet been isolated from woody tissues. Santalane type is represented by sesquiterpenoids from Indian sandalwood oil, which is obtained by steam distillation of wood of Santalum album. Important constituents are a- and )ff-san-talene (182,183), and the derived allylic alcohols 184,185 which constitute almost 90% of the essential oil (71, 98, 238, 242). It may be noted that a-santalene was the first sesquiterpene for which the correct structure was proposed (344). 

This probably refers to the lake pigment made from sandalwood q.vI) however, reference to roots as the source also indicate that it may be from madder (. v.). Salter (1869) uses this term to refer to a pigment derived from a dye-wood (type not specified). The author describes the somewhat complex preparation as follows The powdered root exhausted by alcohol gives a solution to which lydrated oxide of lead is added in excess. The combination of colouring matter and lead oxide is then collected on a filter, washed with alcohol, dried, dissolved in acetic acid, and mixed with a quantity of water. The red being insoluble therein is precipitated, while the acetate of lead remains dissolved. After being washed, the colour is dried at a low temperature. Salter indicates that he is unaware of its use as a pigment in Britain. 

Sandalwood oil is obtained by distillation of the wood of the parasitic tree Santalum album. The isomeric alcohols a-santalol [115-71-9] (255) and (3-santalol [115-71-9] (256) account for 90% of the oil. Over-harvesting has taken the species to the brink of being endangered and supply is, consequently, now very short. Fortunately, the odor can be recreated using synthetic materials, such as the isobornylcyclohexanols (see under camphene in section Bicyclic Monoterpeniod Hydrocarbons) and the campholenic aldehyde derivatives described in Section 8.4.4. Details of sandalwood chemistry can be found in Chapter 6 of the book by Sell (323). 

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