Spirosilanes Activate Gold(I)-Catalysts in Cycloisomerization and Intermolecular Reactions.

Gold-catalyzed reactions have established as a powerful tool in organic synthesis, offering efficient pathways to construct diverse molecular structures and notably scaffolds with high complexity. Most processes rely on the use of LAuCl precatalysts, which are generally activated, i.e., cationized, by silver salts. In this work, we explore the role of silicon-based Lewis acids based, such as spirosilane, derivatives as alternative activators in lieu of silver salts. It was found that Martin spirosilanes mediate the activation of gold precatalysts, facilitating diverse cyclization and cycloisomerization reactions as well as intermolecular reactions. NMR studies and computational investigations suggest that no real cationization, i.e., formation of an ionic pair, takes place, but rather activation through weak interaction between silicon and the chlorine atom of LAuCl. This preserves the Au─Cl bond and ultimately enables the LAuCl complex to be recovered. On the same line, the LAuCl-silane interaction has also proven to be beneficial for asymmetric catalysis. This work significantly contributes to the expansion of gold-catalyzed transformations by opening up the prospect of a more sustainable gold catalysis. It also opens perspectives on the use of silicon-based Lewis acids as versatile cooperative agents in organometallic chemistry.