Hyperconjugative effect of C-Ge bonds: synthesis of multisubstituted alkenylgermanes via torquoselective olefination of acylgermanes with ynolates

The first highly Z-selective olefination of acylgermanes with ynolates affording multisubstituted alkenylgermanes was achieved. The torquoselectivity was ascribed to the hyperconjugative effect of C-Ge bonds in the transition state. The resulting (Z)-β-trialkylgermylacrylic acid has a hypervalent structure, which was converted into novel germalactones. A stereochemical complementary olefination via protonation of the β-lactone enolate, followed by decarboxylation, was also achieved.