Self-terminating radical oxygenations:: Probing of the scope of the concept by use of various organic O-centered radicals

Addition of various organic O-centered radicals XO. (i.e. (alkoxycarbonyl)oxyl radicals, ROC(O)O-., [(alkoxycarbonyl)acyl]oxyl radicals, ROC(O)C(O)O-., (carbamoyl)oxyl radicals, R2NC(O)O-., alkoxyl radicals, RO., and nitroxyl radicals, R2NO) to alkynes initiates an oxidative radical cyclization cascade, which is terminated by release of a C- or N-centered radical X-.. This finding clearly highlights the generality of the recently discovered concept of self-terminating radical oxygenations, through which Cequivalent toC triple bonds may be converted into carbonyl groups under very mild reaction conditions. (C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003.