Gold-Catalyzed Assembly of Heterobicyclic Systems

We have described an efficient gold-catalyzed double cyclization of 1,5-enynes to afford a range of heterobicyclic compounds, including oxabicylclo[3.2.1]octenes, azabicyclo[3.2.1]octenes, oxaspiro[5.4]decene, azaspiro[5.4]decene, oxaspiro[5.5]undecene, oxabicyclo[4.3.0]nonene, azabicyclo[4.3.0]nonene, and oxabicyclo[4.4.0]decene. The mechanism of this reaction is proposed to involve a chemoselective gold-based alkyne activation, carbocyclization, intramolecular nucleophilic addition, followed by protodemetalation. The most notable aspect of this process is the efficient and diastereospecific interception of the reactive intermediate of the initial 6-endo-dig (or 5-endo-dig) cyclization with either oxygen- or nitrogen-based nucleophiles.