A gold-catalyzed synthesis of fused carbocycles via a regioselective 6-endo dig process is reported. The selectivity can be modulated by the steric and electronic properties of gold(I) complexes. The ligands can influence the pathway selectivity for the first bond formation rather than through a common intermediate generated after an initial bond formation. This gold(I)-catalyzed transformation provides access to synthetically useful carbocyclic motifs that are found in numerous diterpenoid natural products.

A mild, efficient, and simple method for the synthesis of 3-ethoxycarbonylindoles has been developed. Addition of ethyl diazoacetate (EDA) to 2-aminobenzaldehydes cleanly affords the indole core. As opposed to other common approaches for the synthesis of indole, this method displays both excellent functional group tolerance and perfect regiochemical control. This allowed the synthesis of a variety of useful indole building blocks from 2-aminobenzaldehydes derived from readily available anthranilic acids.

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.

SummaryGold(I) complexes have emerged as powerful and useful catalysts for the formation of new C–C, C–O and C–N bonds. Taking advantage of the specificity of [IPrAuNCMe][SbF6] complexes to favor the 5-exo-dig cyclization over the 6-endo-dig pathway, we report a high yielding and efficient method to generate substituted polyaromatic heterocycles under remarkably mild reaction conditions.

A simple, mild, and efficient method to prepare 3‐ethoxycarbonylindoles is reported.