Spirocyclic germanes via transannular insertion reactions of vinyl germylenes into Si-Si bonds.

The reactions of two cyclic germylene phosphane adducts with monosubstituted acetylenes caused the formation of spirocyclic germanes, which is postulated to occur by double acetylene insertion into germylene attached bonds. Further insertion of the formed cyclic divinylgermylene into transannular Si-Si or Si-Ge bonds provides the spirocyclic germanes. Thermal treatment of two germacyclopropenes, formed by the reaction of the two cyclic germylene phosphane adducts with tolane, also produced spirocyclogermanes. The structures of the latter require, however, a more complicated mechanistic proposal.