New reactions and theory in organic photochemistry: The 1,3-vinyl migration and its relevance to exchange integral control.
The photochemistry of 1,1,4-triphenyl-1,4-pentadiene was investigated. Sensitized irradiation of this compound labeled at carbon 3 with (2)H led to a degenerate rearrangement wherein the diphenylvinyl moiety migrated 1,3, thus affording diene with (2)H substitution at carbon 5. In contrast, direct irradiation of the triphenyl pentadiene led to 1,3,3-triphenylbicyclo[2.1.0]pentane by a [2 + 2] cycloaddition. This multiplicity dependence of the photochemistry is understood on the basis of triplet reactants preferring a linearly conjugated diradical mechanism with a large exchange integral (K) and singlet reactants preferring an electrocyclic mechanism with a small exchange integral.
Zimmerman
H E
HE
Chemistry Department, University of Wisconsin, Madison, Wisconsin, 53706.
Penn
J H
JH
Johnson
M R
MR