Kinetics of the 1,5-dipolar cyclization of 2-Vinylpyridinium ylides to Indolizines. Determination of rate parameters by laser flash photolysis

✍ Scribed by Michael T. H. Liu; Yuri N. Romashin; Roland Bonneau

• Publisher: John Wiley and Sons
• Year: 1994
• Tongue: English
• Weight: 354 KB
• Volume: 26
• Category: Article
• ISSN: 0538-8066
• DOI: 10.1002/kin.550261205

✦ Synopsis

Nanosecond laser flash photolysis (A = 355 nm) of an aqueous solution of 3-chloro-3-p-chlorophenyldiazirine in isooctane produces a transient absorption at 310 nm due to the formation of the carbene. In the presence of 2-vinylpyridine, a second transient with a broad absorption band peaking at 520 nm grows in. This absorption is attributed to 2-vinylpyridinium ylide. The ylide decays with a lifetime equal to 33 p s at 25°C independent of the concentration of 2-vinylpyridine. As the ylide decays, there is a concomitant growth of an absorption at 330 nm, attributed to the formation of indolizine. The activation parameters for the 1,5-dipolar cyclization of the ylide to indolizine were determined; E, = 12.1 kcal mol-' and log A = 13.4.