Ketones from carotenoid degradation

The ionones and damascones are derived in nature from the degradation of carotenoids. Similarly, the related irones are formed by degradation of other higher terpenes. The ionones are synthesized from citral by aldol condensation with a ketone to form what are known as v /-ionones, which are then cyclized using an acid catalyst, as shown in Scheme 4.39. Some specific syntheses are shown later in Scheme 4.42, along with the syntheses of vitamin A and carotene. The ionones possess odours which are reminiscent of violet, sometimes also with woody notes. 

Although the three C-10 aroma components (276) to (278) are monoterpenoids from a formal point of view, they should probably be considered as degradation products of corresponding carotenoid compounds. At any rate, this assumption was made for the formation of safranal (277) (527), the main component of saffron oil (72, 727). The ketone (278) has only been detected in Burley tobacco (777, 502). P-Cyclocitral (276) and safranal (277) were also shown to be present in tea (491). 

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