Effects of Structural Modifications on the Odour of Jasmone Analogues

Jasmone (1) and methyl jasmonate (2) are well known and organoleptically important constituents of the essential oil, concrete and absolute of jasmin (Jasminium grandiflorum), Because of the commercial value of the jasmin oils and extracts, a great deal of research has been carried out on these two materials and the chemical literature abounds with their syntheses. Inevitably, synthetic chemists have turned their attention not only to the naturally occurring substances themselves, but also to analogues and in particular those which are easier to prepare or which might be expected to possess some practical advantage over the natural prototypes. Thus such materials as dihydrojasmone (3), 2-heptylcyclopentanone (4) and methyl dihydrojasmonate (5) have become important perfumery chemicals.

In order to direct such research, perfumery chemists have endeavored to identify any structure/odour correlations which exist in this group of compounds. In the 1930s Werner observed that 5- and 6-membered cyclic ketones bearing an alkyl group in the position alpha to the carbonyl possessed useful jasmin odours but only if they contained between 9 and 15 carbon atoms in total, being the optimum. He also noted that those ketones with a straight chain substituent had a more agreeable bouquet than the branched chain isomers. On considering the structures of a wide range of jasmin chemicals, both cyclic and open chain, Boelens concluded that all jasmine chemicals possess a molecular structure having a strongly polar group, a weakly polar group and a alkyl chain arranged around a central carbon atom as shown in figure 1. He added that the alkyl chain should be unbranched and unsubstituted since branching or substitution causes an increase in the fruity nuances at the expense of the jasmin character of the material.

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