21 июля, 2015 
Malyar Dicyclopentadiene is a feedstock for both the fragrance and polymer industries. It forms spontaneously from cyclopentadiene by a Diels — Alder reaction, and a retro-Diels-Alder reaction can be used to regenerate cyclopentadiene from it. A number of minor fragrance ingredients are produced by Diels-Alder reaction of the monomer with a variety of activated olefins in which the activating group X, is usually an aldehyde, ketone, ester or nitrile. However, the main fragrance uses stem from the dimer.
The two double bonds of dicyclopentadiene are very different in reactivity and, consequently, selective reactions are easy to achieve.
The bond in the bridged ring suffers a high degree of angle strain and readily undergoes any reaction that results in the two carbon atoms changing from sp2 to sp3 hybridization, since the latter have bond angles much closer to those required by the bridge structure. Thus, for example, carboxylic acids and alcohols will add to that bond under acid catalysis. The product is, of course, a mixture since the regiochemistry of the addition is unaffected by the position of the other double bond. The most important, by far, of the products shown in Scheme 4.67 is the product of addition of acetic acid, Jasmacyclene®. This material has a fruity, jasmine-like odour and its use by the fragrance industry runs into thousands of tonnes per annum. Apart from Florocyclene® and Gardocyclene®, the other products shown are all relatively low in tonnage. Dupical® and Scentenal® have fresh, floral, aldehydic odours, the others have varying proportions of floral and fruity notes.
CONCLUSIONS
The fragrance industry employs a very wide range of chemical processes and often has to deal with complex mixtures of structurally complex materials. The products must be produced at low cost and with minimal environmental impact. Minor components in mixtures may play disproportionately large parts in determining the odour of the whole, making quality control of processes a highly skilled occupation. The mechanism of perception of odorants is poorly understood in chemical terms. The continuously changing nature of the consumer goods’ market demands a continual supply of novel ingredients to meet the challenges of new products to be perfumed. Initial bioassay (smelling) can be performed by the chemist and, thus, feedback is instant; also there is no need for lengthy activity testing as in the pharmaceutical and agrochemical industries. Performance testing and scale-up are also faster than is the case with those industries. All of these factors combine to make fragrance chemistry an exciting and challenging environment where scientific, artistic and commercial skills must all be practised together at the highest level of each.
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