181874-83-9Relevant academic research and scientific papers
Synthesis of cyclopropyl silyl ethers and their facile ring opening by photoinduced electron transfer as key step in radical/radical cationic cascade reactions
Waske, Prashant A.,Mattay, Jochen
, p. 10321 - 10330 (2005)
Various ring-fused cyclopropyl silyl ethers with an benzylic, olefinic or acetylenic side chain have been synthesized. Upon oxidative photoinduced electron transfer (PET) the cyclopropane ring opens and forms a reactive β-keto radical, which undergoes intramolecular cyclization. In some cases we observed only formation of ring opened non-cyclized products. With olefinic side chain 5-exo-trig mode of cyclization rather than 6-endo-trig mode of cyclization takes place whereas in case of acetylenic side chain we observed 6-endo cyclization.
Regio- and stereoselective cyclization reactions of unsaturated silyl enol ethers by photoinduced electron transfer - Mechanistic aspects and synthetic approach
Hintz, Sandra,Mattay, Jochen,Van Eldik, Rudi,Fu, Wen-Fu
, p. 1583 - 1596 (2007/10/03)
Oxidative photoinduced electron transfer (PET) reactions have been performed with various silyl enol ethers and silyloxy-2H-chromones bearing an olefmic 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 cychzation method with regard to irradiation time and product yield. The irradiation times could be reduced by using the cosensitized PET method. Modifying the substrate at the silyl group led to enhanced yields. In addition, we found that solvent and pressure dependences are important tools, allowing control of the regiochemistry. Both the synthesis of 6-endo products by radical cationic reaction pathways, as well as 5-exo ring closure by radical intermediates was achieved. Mechanistic details, including findings from deuterium labelling experiments, are discussed.
