Friedel-Crafts cycloisomerization

The putative metal cationic intermediates can be interconnected into a series of cationic processes such as Friedel-Crafts, pinacol, Nazarov, Prins-type reactions. In Scheme 7.28, the gold-catalyzed cycloisomerization of 1,6-enynes is followed by an intramolecular nucleophilic attack by the proximate carbonyl to generate the tetrahydro-pyranyl cation, which participate in a Prins-type reaction to produce tricyclic compounds resembling the core structures of several terpenoids [52]. 

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