Novel ligand-free, cobalt-catalyzed [2+2+2] cycloadditions: Syntheses of 1,4-disilatetralines and 1,3-disilaindanes

A new and simple catalytic system for efficient [2+2+2] alkyne cycloadditions was discovered. Cobalt(II) iodide in acetonitrile, in the presence of zinc powder, can catalyze arene synthesis at room temperature, and a 2.5% catalyst load gives almost complete consumption of the starting materials within ca. five minutes. Sterically hindered diynes can be efficiently coupled with terminal and internal monoynes. A large excess of monoyne is not required. Relatively small amounts of byproducts make the isolation of the target compound straightforward. This method allows efficient one-step syntheses of 1,4-disilatetralines and 1,3-disilaindanes, which are hardly available using other methods.