Journal of Organic Chemistry p. 8139 - 8150 (1994)
Update date:2022-09-26
Topics: Radical reactions Steric hindrance Isomerization Substituent Effects π-Electron Density Halide Effects Geometric Isomerism Photodissociation
Krijnen, Erik S.
Zuilhof, Han
Lodder, Gerrit
The photochemical reactions in methanol of the vinylic halides 2-halo-1-phenyl-1,3-butadienes 1-3Z-X (β-halo-β-alkenylstyrenes) and 1-halo-1,2-diphenylethenes 4Z-X (α-halostilbenes), with X = Cl or Br, have been studied quantitatively.E/Z isomerization, dehydrohalogenation, nucleophilic substitution, a <1,3>-halogen shift, a <1,3>-hydrogen shift, and oxidation are observed as the primary reactions.No reductive dehalogenation products are formed.The efficiencies of product formation are dependent on the halogen used, the electron-donating capacity of the α-substituent, the ground state conformation of the starting material, and the wavelength of excitation.Apart from the photoinduced E/Z isomerization and the oxidation reaction typical for alkenes, product formation occurs exclusively via vinyl-cationic intermediates, which are formed upon photolytic cleavage of the carbon-halogen bond.These ionic species, or part of them, are present as vinyl cation/halide anion-pairs.
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Doi:10.1055/s-1994-25669
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