Abstract
Reported is the highly diastereo- and enantioselective one-pot Michael-aldol reaction of α,β-unsaturated aldehydes 1 with imidazoles 2 to give fused heterocycles 3. The reaction is proposed to proceed first via an intermolecular Michael addition, followed by an intramolecular aldol reaction. Both steps are mediated by the same organocatalyst. Aromatic α,β-unsaturated aldehydes participate efficiently in the reaction, regardless of electronic character and substitution pattern. Aliphatic aldehydes gave inferior results (65-67% yield). High yields of products were also obtained irrespective of substitution on the imidazole fragment. Excellent diastereo- and enantioselectivities were observed in all cases, and the absolute configuration of one example was proved by X-ray crystallographic analysis. A mechanism is proposed without evidence.
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