Synthesis of Racemic Stereoisomers

The direct synthesis of cis-permethric acid has attracted a lot of attention from several research groups. Starting from the technical 3,3-dimethylpentenoic ester 111 (Reaction scheme 122, preceding page), radical addition of thiophenol followed by a-chlorination of the sulfide 191 gives a protected aldehyde ester 792, which on decomposition and subsequent, alkoxy-treatment cyclizes to the dihydropyrone 193. Light-induced 

The very same pentenoic 111 acid may be equifunctionally activated by oxidation in a different way, when oxygen and acetic acid, catalyzed by palladium, are added to the olefinic bond, (Reaction scheme 124) forming an enolacetate precursor 197 [323, 328] for the acetal ester 198 as in the preceding reaction. 

---