Thapsic acid

The first syntheses [172] of macrocyclic scented compound were based on the Piria cyclisation (Raffaele Michele Rocco Piria (1814-1865), Italian chemist) of terminally functionalised aliphatic precursors. Thus, pyrolysis of the thorium salt of thapsic acid (Fig. 3.42) and purification via the semicarbazone gave exaltone in a yield of 5.5 % (Ruzicka cyclisation). The mechanism ofthis reactionhas not been finally established, although it is accepted that free radicals are involved in the cyclisation. [173] Oxidation using Caro s acid then gives exaltolide in 47 % yield. 

Thapsic acid (hexadecanedioic acid) may be isolated from the dried roots of Thapsia garganica, a Mediterranean, umbelliferous plant, which was known already In ancient times to be poisonous (due to thapsigargin and other components). In Arabian caravans it was called "deadly carrot," because camels would eat it and die quickly... 

Thapsic acid dioleyl ester in cycl exane. 

Fig. 76. Vapor pressure of solutions of thapsic acid dioleyl ester the curves obtained all lie below the straight line.

---