| Abstract
| - Various 4-vinylimidazole derivatives have been prepared from the corresponding 4-iodoimidazoles orfrom urocanic acid. Several methods for the elaboration of these vinylimidazoles and their Diels−Alderreactions are reported. All of the vinylimidazoles prepared in the course of this study react withN-phenylmaleimide quite readily with mild thermal activation providing a single cycloadduct, in mostcases the initial, nonaromatic adduct. With more electron rich substrates, there is a tendency for theseinitial cycloadducts to undergo aromatization, ene reaction, and oxidation although this can be circumventedto a large extent by the choice of reaction conditions. Limited reactions were observed with otherdienophiles, providing the expected cycloadducts in most cases, although an abnormal adduct was obtainedin one case with dimethyl acetylene dicarboxylate. These substrates also participate in regioselectiveDiels−Alder reactions with monoactivated dienophiles, but require fairly forcing conditions, thus onlyproviding the aromatized cycloadducts in modest yields. An investigation of substituent effects at the2-position of the imidazole moiety was undertaken, in which electron-donating and weakly electron-withdrawing substituents are tolerated. In addition, several substrates with terminally substituted vinylmoieties have been investigated.
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