Gold(I)-Catalyzed Cascade Cyclization Reactions of Allenynes for the Synthesis of Fused Cyclopropanes and Acenaphthenes

A gold-catalyzed reaction of phenylene-tethered allenynes with benzofurans gave 1-(naphth-1-yl)cyclopropa[b]benzofuran derivatives, whereas the reaction of 1-allenyl-2-ethynyl-3-methylbenzene derivatives in the absence of benzofurans gave acenaphthenes in good yields. These results can be rationalized by nucleophilic attack of the alkyne moiety on an activated allene to form a vinyl cation intermediate.