Gold Catalyzed Cyclopropanation/[5+3] Cycloaddition of 1,4,9-and 1,4,10-Allenenynes to Bicyclo[3.3.1]nonane Derivatives

A synthetic method to prepare cycloalkyl- and (hetero)aryl-fused bicyclo[3.3.1]nonane derivatives from gold(I)-catalyzed cyclopropanation/[5+3] cycloaddition of 1,4,9- and 1,4,10-allenenynes is described. The suggested double cycloisomerization mechanism delineates the first example of a stepwise [5+3] cycloaddition pathway in gold catalysis, a mode of reactivity that is also sparse in organic chemistry. Experimental and Density Functional Theory (DFT) computational studies based on a proposed gold carbenoid species provides insight into this unique selectivity that leads to the assembly of the architecturally challenging bridged carbocyclic motif.