Chapter 25, Problem 20P

Pyrethrins are a group of naturally occurring insecticidal substances found in the flowers of various plants of the chrysanthemum family. The following is the structure of a typical pyrethrin, cinerin I (exclusive of stereochemistry):

(a) Locate any isoprene units present in cinerin I.

(b) Hydrolysis of cinerin I gives an optically active carboxylic acid, $(+)\text{-chrysanthemic acid}$. Ozonolysis of $(+)\text{-chrysanthemic acid}$, followed by oxidation, gives acetone and an optically active dicarboxylic acid, $(-)\text{-caronic acid }\left({\text{C}}_{\text{7}}{\text{H}}_{\text{10}}{\text{O}}_{\text{4}}\right)$. What is the structure of $(-)\text{-caronic acid }$? Are the two carboxyl groups cis or trans to each other? What does this information tell you about the structure of $(+)\text{-chrysanthemic acid}$?