Cyclopinolenic acids: Synthesis, derivatives and thermal properties

The two isomeric cyclopinolenic acids (CP-1 and CP-2), components of distilled tall oil, have been synthesized by means of an intramolecular Diels-Alder reaction of isomers of 5,10,12-octadecatrienoic esters, themselves synthesized in a stereocontrolled manner. The 5 cis, 10 trans, 12 trans isomer cyclizes at 200°C to a 1:3 mixture of esters of CP-1 and CP-2. At 200°C, the 5 cis, 10 trans, 12c is isomer is unreactive, but at 240°C it gives the same CP-1 + CP-2 ester mixture, presumably by way of prior isomerization to the 5 cis, 10 trans, 12 trans isomer. A subambient thermal study of CP-1 and CP-2 and their derivatives shows that the compounds, excluding CP-1, lack crystalline structures or melting points, and display glass transitions only, below −80°C for esters and below −50°C for the carboxylic acids.