Aryl Radical Additions to Aldehydes and Oxime Ethers: The Tandem Enediyne-Radical Cyclization

Article abstract of DOI:10.1021/jo00076a011

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.