150723-29-8Relevant articles and documents
Kinetic and Mechanistic Studies of the Tandem Enediyne-Radical Cyclization
Grissom, Janet Wisniwski,Calkins, Trevor L.
, p. 5422 - 5427 (2007/10/02)
Enediynes 11 possesing a tethered olefin radical acceptor can participate in a tandem enediyne-radical cyclization to yield dihydrobenzindene derivatives 16.In the present study, the mechanism of this reaction was investigated utilizing kinetic studies to determine whether the mechanism was a radical chain, stepwise, or concerted process.Substrate concentration, 1,4-cyclohexadiene concentration, olefin geometry, and olefin electronics were varied.These experiments demonstrate that the reaction occurs under first-order kinetics over a wide variation in eithersubstrate or 1,4-CHD concentration.The reaction rate is also independent of olefin geometry and olefin electronics.The rate constants for the reactions were similar and ranged from 3.0E-4 s-1 to 6.0E-4 s-1.The data suggests that the tandem enediyne-radical cyclization proceeds through a distinct 1,4-diyl reactive intermediate such as 5 formed in the rate-determining enediyne cyclization step, followed by a radical cyclization to give 16.The tandem enediyne-radical cyclization mechanism is supported by trapping the intermediate biradical 18 in a tandem enediyne-6-exo-radical cyclization of 17 to give products 19a,b.
Aryl Radical Additions to Aldehydes and Oxime Ethers: The Tandem Enediyne-Radical Cyclization
Grissom, Janet Wisniewski,Klingberg, Detlef
, p. 6559 - 6564 (2007/10/02)
The previously unreported cyclization of aryl radicals onto aldehyde and oxime ether acceptors is described.The aryl radicals were generated from a cyclization of enediyne substrates.The aldehydes 6 and 9 and the oxime ethers 7 and 10 were heated to 190 deg C in chlorobenzene in the presence of 1,4-cyclohexadiene as a hydrogen atom source to yield the tandem enediyne-radical cyclization products 11a, 11b, 14, 21, and 22, and the simple enediyne cyclization products 12, 13, 15, 16, and 23.For the enediyne aldehyde substrates tandem enediyne-radical cyclization does not appear to be a synthetically useful process and a mixture of products was obtained.The aryl radicals generated in these enediyne cyclizatios subsequently undergo either a radical cyclization or other reactions such as hydrogen abstraction from 1,4-cyclohexadiene, decarbonylation, or intramolecular 1,5- and 1,6-hydrogen abstractinos.In contrast, the reactions with oxime ether precursors provide the tandem enediyne-radical cyclization products in good yield and provide a useful alternative to the tandem enediyne-6-exo-radical cyclization onto olefins.
