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

Nanosecond laser flash photolysis (lambda = 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 mu s at 25 degrees C independent of the concentration of 2-vinylpyridine. As the ylide decays, there isa 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(alpha) = 12.1 kcal mol(-1) and log A = 13.4. (C) 1994 John Wiley & Sons, Inc.PT: J; CR: BONNEAU R, 1989, J CHEM SOC P1, P1547 BONNEAU R, 1994, J CHEM SOC CHEM COMM, P509 DIX EJ, 1993, J AM CHEM SOC, V115, P10424 FLITSCH W, 1984, COMPREHENSIVE HETERO, V4, P443 GRAHAM WH, 1965, J AM CHEM SOC, V87, P4396 KATRITZKY AR, 1990, ADV HETEROCYCLIC CHE, V47, P216 LIU MTH, IN PRESS J PHOTO CHE LIU MTH, 1994, RES CHEM INTERMEDIAT, V20, P195 MODARELLI DA, 1992, J AM CHEM SOC, V114, P7304 UCHIDA T, 1976, SYNTHESIS-STUTTGART, P209; NR: 10; TC: 13; J9: INT J CHEM KINET; PG: 6; GA: PR800Source type: Electronic(1