Cyclization after Enediyne Construction

A second, less used, strategy encompasses the Lewis acid catalyzed intramolecular reaction of a silyl enol ether with a propargyl cation. The latter can be conveniently generated by a cobalt complexed propargyl ether. This complexation strongly helps the carbocation formation. By using cobalt complexation, intramolecular aldol type reactions (for R = OR ) have been accomplished.  

For the construction of the required acyclic enediyne, the method of choice is the Sonogashira coupling of terminal alkynes with Z dichloroethylene. The complete stereoselectivity for the Z double bond and the mild 

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