Conical intersection control of heterocyclic photochemical bond scission.
The photochemistry of the heterocycle 5,6-dihydro-1-methyl-5,5-diphenylpyridin-2(1H)-one (compound 1 in the text) leads to two competitive reactions (the reactions are depicted in the Introduction to the article). These arise from fission of bond a, between the nitrogen (N-6) and C-1, and bond b, between C-4, with the two phenyl substituents, and C-5, adjacent to the nitrogen. Scission of bond a alone leads to a zwitterionic intermediate which can be trapped by nucleophiles, while cleavage of bonds a and b together affords two fragments--a ketene and an imine. The ketene could be intercepted with nucleophiles and the imine trimerized. Computation reveals little weakening of bonds a and b. But as stretching begins, conical intersections are encountered, leading to ground-state products.
Zimmerman
Howard E
HE
Department of Chemistry, University of Wisconsin-Madison, Madison, WI 53706, USA. zimmerman@chem.wisc.edu
Mitkin
Oleg D
OD