Manganese (III) based oxidative free-radical cyclizations. 2. Polycyclization reactions proceeding through tertiary cations.

✍ Scribed by Barry B. Snider; Raju Mohan; Steven A. Kates

• Book ID: 104233406
• Publisher: Elsevier Science
• Year: 1987
• Tongue: French
• Weight: 292 KB
• Volume: 28
• Category: Article
• ISSN: 0040-4039
• DOI: 10.1016/s0040-4039(01)81003-0

✦ Synopsis

Oxidative c Z clization of 5 with Mn(OAc) *2H 0 gives mainly the bit clic products 7 On the other and, These data sug est oxidative cyclization if lb and 17 gives mainly t e lactones 18 and Z 20.

to form 3, 4, 7, an % a.

that oxidation of a monocyclic radical to a cation precedes cyclization Oxidative free-radical cyclizations should vastly extend the synthetic utility of radical cyclizations' since the terminal radical will be trapped oxidatively rather than by reductive delivery of a hydrogen atom giving rise to a more highly functionalized and therefore synthetically useful adduct.

We3 and others&e5 have recently shown that the well-known oxidative addition of acetic acid to alkenes, using two equiv. of Mn(OAc),*ZHzO, to give rlactones,6s7 can be extended to oxidative free radical cyclization of unsaturated ,9-ketoacids, B-ketoesters and malonic acids. We found that oxidative cyclization of 1 (0.2 M) with Mn(OAc),*2HzO in acetic acid for 1 h at 15-20 "C gave 3 in 50% yield as a single stereoisomer. We report here further studies which indicate the scope and limitations of this reaction and help to define its mechanism. R Termination of a radical cyclization by addition to a benzene ring and oxidation to