Platinum coordinates to the oxygen atom of the hydroxyl group, thus liberating a proton. The proton attacks a carbon atom of the alpha triple bond and initiates a cationic cyclization reaction which annulates a five-membered all-carbon ring to the camphor skeleton. An additional sulfur-containing five-membered ring might be attached to the one containing the sulfonamide group, leading to a sulfur-stabilized carbocation. We have found such stabilized cations as intermediates in several other diyne cyclization reactions. In the case of the compound with phenyl instead of adamantyl groups, platinum then leaves the oxygen, leading to C-C bond cleavage and ring enlargement to an eight-membered ring, coupled with reduction of sulphur to the sulfinamide stage. However, with the adamantane groups, platinum induces a C-H bond activation of a methylene group of the adamantane moiety, followed by an additional C-C bond formation. The result is the annulation of a further five-membered ring to the polycyclic skeleton. Thus, a cascade of five steps is induced by the platinum catalyst. Semiempirical calculations (AM1, PM3) on the starting material and several conceivable products show that the ring closure of the diynes of the above type leads to a lower heat of formation, with a difference of at least 50 kcal/mol, which means that the formation of the final product is strongly favoured thermodynamically.