Preparation of vinylgermanes and a germole by the Pd-catalyzed reactions of Me(in3)GeCn with acetylenes

Abstract

The palladium-catalyzed reaction of trimethylgermyl cyanide (Me 3GeCN, 1) with terminal acetylenes is studied in detail with particular emphasis focused on functional group compatibility as well as the factor affecting stereoselectivity. The reaction of 1 with terminal aromatic acetylenes in the presence of PdCl 2 results in the highly regioselective addition of 1 to the carbon-carbon triple bonds, leading to β-cyano vinylgermanes in high yields. The stereoselectivity depends on the electronic nature of the substituents on the aromatic ring. Whereas the Z-stereoselectivity for arylacetylenes having a methoxy group at the o- or p-position is moderate (60–75%), extremely high Z-stereoselectivity(96%) is observed for the m-methoxyphenylacetylene. For all arylacetylenes with electron-withdrawing groups on the ring quite high selectivities (97%) are observed. The reaction of terminal aliphatic acetylenes too affords the adduct with high regio- and stereoselectivity. The reaction of 1 with 1,6-diynes results in unusual cyclization to give a germole as the main product.