Gold Catalysis: Anellated Heterocycles and Dependency of the Reaction Pathway on the Tether Length

A series of furan-yne substrates with an arylalkynylamide substructure were prepared and subjected to catalytic amounts of phosphanegold(I) complexes. With two carbon atoms in the tether between the arylalkynylamide and the furan subunits, the formation of benzoanellated heterocycles was observed, a number of interesting heterocyclic framworks could be accessed in this way. With three carbon atoms in the tether, the outcome was quite different, cyclopentadiene derivatives anellated to tetrahydropyridine rings were isolated. The two different pathways suggested are supported by calculations regarding the selectivity-determining step.