Laser flash photolysis studies of nitrogen ylides generated by the reaction of arylchlorocarbenes with substituted vinylpyridines and 1-azabuta-1, 3-dienes

摘要

Laser Flash Photolysis of arylchlorodiazirines in isooctane/CH_2Cl_2 in the presence of substituted vinylpyridines yields substituted vinylpyridinium ylide (#lambda#=540 nm). As the ylide decays a concomitant growth causes an absorption at 330 nm, attributed to the formation of substituted indolizine. The reaction experiences the intramolecular 1, 5-cyclization of the ylide intermediate. The kinetic parameters for the ylide formation and the 1,5-cyclization have been obtained. The activation energy for the latter process is reduced by 3-4 kcal mol~(-1) when the vinylpyridine has a phenyl ring as a substituent in #beta#-position of the ethylenic group. Laser Flash Photolysis of phenylchlorodiazirine in isooctane in the presence of 1-azabuta-1, 3-diene yields azomethine ylide (#lambda#=550 nm) as an intermediate. The kinetic parameters for the ylide formations and further intramolecular 1, 5-cyclization to pyrrole have been determined. The results resemble those obtained for the 1, 5-cyclization of vinylpyridinium ylide.