A-Atlantone

Formylation of Hmoneae. (-i-)-(4R)-Limonene (1) is formylated by the Vilsmeier reagent (2) stereoselectively to give mainly the (E)-of,)3-unsaturated aldehyde 3. The product was used tor the synthesis of (4R),(E)-a-atlantone (5), a sesquiterpene from Cedrus oils. 

Aryl fluorides, 149 Arylpenta-2,4-dienoates, 161 a-Arylpropionic acids, 314 Arylsulfonylalkynes, 7 Arylthallium bistrifluoroacetates, 462 a-Atlantone, 514 Atiolactic acid methyl ether, 290 Aucubin, 73... 

Motoyoshiya, J., Miyajima, M., Hirakawa, K., and Kakurai, T., Dimethyl (2-oxo-4-methyl-3-pente-nyljphosphonate as a precursor of a.a -dienones. Short syntheses of ( )-a-atlantone and ( )-flr-turmerone, J. Org. Chem., 50, 1326, 1985. 

The scheme used by the English terpene chemist R. C. Cookson,6 3 for the total synthesis of a-atlantone is shown in Figure 6.22. 

Synthesis of cn-Atlantone from d-Limonene. The total synthesis of a-atlantone from isoprene shown in Figure 6.22, gave positive proof of the structure as far as atom connectivity is concerned. However, what it did not achieve was to demonstrate the absolute stereochemistry of the product as the Diels-Alder reaction was not stereoselective. In order to establish the absolute stereochemistry, Cookson carried out a partial synthesis of a-atlantone from d-limonene.6 4 This is shown in Figure 6.24. 

Friedel-Crafts reaction between senecioyl chloride (6.96) and d-limonene (6.102) in the presence of stannic chloride at low temperature, gave a-atlantone in one step, along with the isomeric ketones... 

The relationship between the atlantones and deodarone is obvious. One can imagine the Michael addition of water to the two activated double bonds of a-atlantone (6.93) followed by dehydration of the resultant diol to produce the ether link of deodarone (6.95). Confirmation of the structure of deodarone relied on such interconversions. The first to show the relationship between the two ketones was the great Indian natural products chemist, Sukh Dev.6 5 He carried out a sequence similar to this hypothetical scheme. The hydroxide ion is a very poor nucleophile in Michael reactions and so Sukh Dev used the hydroperoxide anion... 

For example, cedarwood oils obtained from plants like Cedrus atlantica, Chamaecyparis funebris, or Juniperus mexicma, contain aromatic molecules, e.g., ( )-(+)-a-atlantone, a-thujone, or (+)-cedrol ... 

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