Synthesis of C2-Symmetric Bisamidines: A New Type of Chiral Metal-Free Lewis Acid Analogue Interacting with Carbonyl Groups
The Journal of Organic Chemistry2007Vol. 72(15), pp. 5618–5624
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Abstract
The chiral bisamidine 5 has been prepared in just two steps from malonodinitrile. In the monocationic form this compound adopts a planar conformation with an almost convergent orientation of two N-H groups. Ketones, aldehydes, and nitro compounds are assumed to bind to this strongly polar cleft via hydrogen bonds, resulting in a Lewis-acid-like activation of the carbonyl groups. A broad scope of reactions (Diels-Alder, hetero-Diels-Alder, Friedel-Crafts) can be catalyzed. The observed accelerations surpass the rate effects of neutral hydrogen-bond donors such as thioureas or TADDOLs.
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