Gold(I)-catalyzed formation of bridged and fused carbocycles

For many years, despite a rich coordination chemistry, gold (Au) was judged as being catalytically inactive for the formation of carbon-carbon bonds. In mid-1970, few reports demonstrated that Au salts could be very useful reagents to catalyze organic transformations. In recent years, homogeneous catalysis by Au has received considerable attention by the scientific community. It was shown that Au(I) or (III) catalysts are specific and more reactive than most of the other soft Lewis acids such as Hg(II), Cu(II), Pt(II), and Pd(II). Taking advantage of the affinity of cationic phosphine Au complexes to triple bonds, we conceived a Au(I)-catalyzed 6-endo-dig cyclization of cyclic enol ether to prepare bridged and fused bicyclic ketone. Keeping in mind that 5-exo-dig cyclizations can be a competitive process, we surveyed various Au(I) complexes.