Ruthenium-Promoted Ring-Closing Metathesis of Ene-Dienes. Competitive Intramolecular Regioselection as a Function of Chain Length

✍ Scribed by Kallol Basu; James C. Eppich; Leo A. Paquette

• Publisher: John Wiley and Sons
• Year: 2002
• Tongue: English
• Weight: 66 KB
• Volume: 344
• Category: Article
• ISSN: 1615-4150
• DOI: 10.1002/1615-4169(200208)344:6/7<615::aid-adsc615>3.0.co;2-o

✦ Synopsis

The course of ring-closing metathesis of a series of ene-dienes has been examined for its regioand stereoselectivity. Each example studied gave rise predominantly or exclusively to a cyclization product of a specific structural type. Each of the four possible mechanistic pathways are represented. Thus, 11a furnished the (Z)-monoene 12 in good yield without any evidence for formation of a 10-membered ring diene. For 11b, the kinetic preference lies very much in favor of producing the (E,Z)-diene 13. Systematic chain extension to the level of 11c is met with a return to preferred cycloalkene production, but now E-configured. As concerns 11d, the longest-chain homologue examined, ring-size effects are less distinctive and both monoene 15 and diene 16 are formed, the latter being favored by a factor of 4:1. These experimental results indicate that chain length significantly influences the regiochemical and stereochemical course of intramolecularly competitive metathesis reactions.