The Acid-Catalyzed Cyclization of Acyclic Dienes

The acid-catalyzed cyclizations of trans,trans- and cis,cis-2,6-octadiene have been investigated utilizing deuterated acid to initiate cyclization. The stereochemistry of the products shows that the cyclization process is concerted with proton attack and follows the stereoelectronic predictions made for terpene biosynthesis. A small percentage of the time the acquisition of the nucleophile is clearly concerted with the preceding steps and leads, likewise, to the theoretically expected product.