Regio- and Stereoselective Cyclization Reactions of Unsaturated Silyl Enol Ethers by Photoinduced Electron Transfer – Mechanistic Aspects and Synthetic Approach
作者:Sandra Hintz、Jochen Mattay、Rudi van Eldik、Wen-Fu Fu
various silyl enol ethers and silyloxy-2H-chromones bearing an olefinic or silylacetylenic side chain, The reactions result in regioselective ring closure with the formation of bi- to tetracyclic ring systems with a well-defined ring juncture, e.g. perhydrophenanthrenones 13 or benzo-annellated xanthenones 24. Our investigations have focussed on the optimization of this cyclization method with regard
PET-Oxidative cyclization of unsaturated silyl enol ethers. Regioselective control by solvent effects
作者:Sandra Hintz、Roland Fröhlich、Jochen Mattay
DOI:10.1016/0040-4039(96)01708-x
日期:1996.10
Monocyclic silyl enol ethers tethered to an olefinic or a silylacetylenic side chain are irradiated in the presence of the electrontransfer sensitizer 9,10-dicyanoanthracene (DCA). Cyclization of the initially formed silyloxy radical cations efficiently provides bicyclic and tricyclic ketones with definite stereochemistry. The regiochemistry of the cyclization step can be controlled by addition of
During the hydrogenation of the Δ3(3a)-4-hydrindenones or on Pd or Ni, we observe a shift of the double bond to Δ3a(7a)-4-hydrindenones and . The absolute configuration established for ketones and shows that the reaction is a suprafacial process. By deuteriation experiments, we observe that the reaction is irreversible and occurs with a molecular hydrogen exchange.