Journal
SYNLETT
Volume 34, Issue 9, Pages 1063-1067Publisher
GEORG THIEME VERLAG KG
DOI: 10.1055/a-2004-3771
Keywords
catalysis; cyclization; electron transfer; iridium; photochemistry; radical reaction
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Under visible light irradiation, cyclic 2-alk-4enyl-substituted 1,3-diketones undergo an intramolecular endo-addition onto the double bond, resulting in spirocyclic products with yields ranging from 62 to 92%. The reaction can be promoted by both an organic photocatalyst (thioxanthone, 20 mol%) and an organometallic Ir-based photocatalyst (5 mol%). The addition of triisopropylthiophenol is necessary to obtain high yields.
When irradiated with visible light, various cyclic 2-alk-4enyl-substituted 1,3-diketones undergo an intramolecular endo-addi-tion (m = 1) onto the double bond resulting in spirocyclic products (11 examples, 62-92% yield). Both an organic (TXT: thioxanthone, 20 mol%) and an organometallic Ir-based photocatalyst (5 mol%) promote the reaction. Addition of triisopropylthiophenol is required to secure high yields. The spirocyclization of a 2-alk-5-enyl-substituted substrate (m = 2) delivers a mixture of the seven-membered endo- and the six membered exo-cyclization products.
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