Radical cyclization of O-trityl oximino esters: a ring closure that preserves the oxime function Derrick L. J. Clive* and Rajendra Subedi Chemistry Department, University of Alberta, Edmonton, Alberta, Canada T6G 2G2. E-mail: derrick.clive@ualberta.ca Received (in Corvallis, OR, USA) 4th November 1999, Accepted 16th December 1999 O-Trityl oximino esters 1 undergo stannane-induced radical cyclization to regenerate an oxime function, affording oximino lactones 4; these can be converted into enamides (e.g. 11b), and such a transformation was used to make the natural product 14c. We report radical ring closures of the type summarized in Scheme 1 (X = homolyzable group). 1,2 The special feature of such reactions is that the sp 2 status of the acceptor carbon is preserved—a result that is different from the one seen in the classical cyclization of hexenyl radicals or the radical cycliza- tion of O-alkyl oxime ethers. 3–5 Regeneration of the oxime function after the radical closure must involve 6 tautomerization of an intermediate nitroso compound, as shown in Scheme 1, 3 ? 4.† The starting oximino esters (cf. 1) are prepared using the crystalline reagent 5 (mp 165–166 °C), which is easily made (76%) by stirring equimolar amounts of O-trityl hydroxylamine and glyoxylic acid monohydrate in THF for 4 h. Evaporation of Table 1 Esterification of various alcohols and subsequent radical cyclizations a Scheme 1 This journal is © The Royal Society of Chemistry 2000 Chem. Commun., 2000, 237–238 237