Total synthesis of a trichlorocamphene and a tetrachlorodihydrocamphene, and structural feature leading to chlorinated bornanes, camphenes, and dihydrocamphenes

The study of the total synthesis of toxaphene was the topic of the present investigation. Dichloromethyl groups should be introduced as carboxylic functions and later be converted. Strategy for the formation of the bornane backbone was the Diels-Alder addition of cyclopentadiene and anhydrous methylmaleic acid followed by Wagner-Meerwein rearrangement. However, the rearrangement failed, but chlorination of the double bond of the cycloadduct with MnCl2/acetic chloride, reduction of the carboxylic groups with LiAlH4 to the diol, subsequent esterification with p-tosyl chloride, and finally substitution of the tosylates by chloride using LiCl led to 5-exo,6-exo,8,10-tetrachlorodihydrocamphene and 5-exo,6-exo,8-trichlorocamphene. The mechanistic study revealed pathways for the formation of polychlorinated camphenes and dihydrocamphenes whose presence in toxaphene has been reported before but not mechanistically explained.