Dianions and masked dianions represent important building blocks for the regioselective formation of carbon-carbon bonds. Cyclocondensation reactions of 1,3-bis(silyl enol ethers) with different mono(silyl enol ethers) provide an elegant approach for the synthesis of various complex carba-cycles from simple starting materials. A variety of functionalized and sterically encumbered triarylmethanes are prepared by combination of FeCl3-catalyzed benzylations of 1,3-diketones and formal [3+3] cyclocondensation reactions of mashed dianions. In this context, 4-methoxy-, 4-chloro and 4-fluoro-substituted triarylmethanes are prepared.
Furthermore, dianions were converted to pyranones by reaction with functionalized benzaldehydes. Various pyranones were synthesized containing 3-bromo-, 4-methyl-, 4-phenyl-, 4-methoxy- and 4-hydoxy-substituted phenyl groups.