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Chiral Trisimidazoline Catalyzed Bromolactonization
K. Murai, T. Matsushita, A. Nakamura, S. Fukushima, M. Shimura, H. Fujioka*
Osaka University, Japan
21 December 2010 (online)
The authors report an enantioselective bromolactonization of 5-substituted 5-hexenoic acids, catalyzed by the chiral C 3-symmetric trisimidazoline 1. By using 1,3-dibromo-5,5-dimethylhydantoin (DBDMH) as the Br+ source, a variety of 5-hexenoic acids, preferentially 5-aryl-substituted, were converted into the corresponding δ-lactones in high yields and enantioselectivities. The proposed mode of action involves the formation of a 1:3 complex of 1 and the substrate, at the same time embedding the substrate in a chiral environment and activating the carboxylic acid function. This proposal is supported by mechanistic studies and the utility of the products is underlined by derivatizations of the obtained bromolactones.