Electronic and Conformational Effects in the Photochemistry of .alpha.-Alkenyl-Substituted Vinyl Halides
The photochemical reactions in methanol of the vinylic halides 2-halo-1-phenyl-1,3-butadienes 1-3Z-X (beta-halo-beta-alkenylstyrenes) and 1-halo-1,2-diphenylethenes 4Z-X (alpha-halostilbenes), with X = Cl or Br, have been studied quantitatively. E/Z isomerization, dehydrohalogenation, nucleophilic s...
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Published in | Journal of organic chemistry Vol. 59; no. 26; pp. 8139 - 8150 |
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Main Authors | , , |
Format | Journal Article |
Language | English |
Published |
WASHINGTON
American Chemical Society
01.12.1994
Amer Chemical Soc |
Subjects | |
Online Access | Get full text |
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Summary: | The photochemical reactions in methanol of the vinylic halides 2-halo-1-phenyl-1,3-butadienes 1-3Z-X (beta-halo-beta-alkenylstyrenes) and 1-halo-1,2-diphenylethenes 4Z-X (alpha-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 a-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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Bibliography: | ark:/67375/TPS-F362KVW3-J istex:70290DC43C8B476274AA4F8B4A51DCBCB5C04F05 |
ISSN: | 0022-3263 1520-6904 |
DOI: | 10.1021/jo00105a035 |