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Regio‐ and Stereoselective Cyclization Reactions of Unsaturated Silyl Enol Ethers by Photoinduced Electron Transfer – Mechanistic Aspects and Synthetic Approach
Author(s) -
Hintz Sandra,
Mattay Jochen,
van Eldik Rudi,
Fu WenFu
Publication year - 1998
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/(sici)1099-0690(199808)1998:8<1583::aid-ejoc1583>3.0.co;2-r
Subject(s) - chemistry , regioselectivity , silylation , enol , photoinduced electron transfer , stereoselectivity , ring (chemistry) , radical cyclization , photochemistry , yield (engineering) , electron transfer , stereochemistry , organic chemistry , catalysis , materials science , metallurgy
Oxidative photoinduced electron transfer (PET) reactions have been performed with various silyl enol ethers and silyloxy‐2 H ‐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 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.