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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 26, Number 8
BKCSDE 26(8)
August 20, 2005 

The Mechanisms for Thermal and Photochemical Isomerizations of N-Substituted 2-Halopyrroles: Syntheses of N-Substituted 3-Halopyrroles
Sung-Hyun Park, Hong-Joo Ha, Chultaek Lim, Dong-Kwon Lim, Kwang-Hee Lee, Yong-Tae Park*
N-Benzyl-2-halopyrrole, N-Benzyl-3-halopyrrole, Photochemical isomerization, Thermal isomerization, Pyrrole ring complex with bromonium ion
Halopyrroles, N-substituted 2-halopyrroles were prepared by halogenation of N-substituted pyrroles with NBS, NCS, or surfuryl chloride. N-Substituted 3-halopyrroles were synthesized by acid-catalyzed thermal and photochemical isomerization reactions of N-substituted 2-halopyrroles. Both the thermal and photochemical reactions were acid-catalyzed. For the acid-catalyzed isomerization, a mechanism of [1,3] bromine shift followed by deprotonation is operated. For the acid-catalyzed photoisomerization, an excited triplet state of 2- protonated N-benzyl-2-halopyrrole produces an intermediate N-substituted pyrrole complex with halonium ion which is equilibrated with N-substituted pyrrole plus halonium ion, and then the halonium ion newly adds to 3- position of N-substituted pyrrole followed by deprotonation to afford N-benzyl-3-halopyrrole.
1190 - 1196
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