Photoinduced radical reactions of alpha-alkylated ethyl 2-oxo-1-cyclopentanecarboxylate derivatives: alpha-cleavage and cyclization to the skeleton of linear cyclohexano diquinanes

Tzvetkov NT, Waske PA, Neumann B, Stammler H-G, Mattay J. Photoinduced radical reactions of alpha-alkylated ethyl 2-oxo-1-cyclopentanecarboxylate derivatives: alpha-cleavage and cyclization to the skeleton of linear cyclohexano diquinanes. TETRAHEDRON LETTERS. 2008;49(10):1710-1713.The tricyclic core of linear cyclohexano diquinanes was synthesized using photoinduced electron transfer (PET) as a key step. The reaction proceeded in high regioselective manner via ketyl radical anions leading to distonic delta-keto radical anion as reactive intermediates. The irradiation was carried out at a wavelength of 254 nm with triethylamine (TEA) as a strong reducing reagent in acetonitrile. We also showed that the photolysis of the alpha-alkylated 2-oxocyclopentanecarboxylate derivatives does not lead to any cyclization products via a delta-hydrogen abstraction process. In this case alpha-C-C bond cleavage as a predominant process was observed. (c) 2007 Elsevier Ltd. All rights reserved