Synthesis of C_2-Symmetric Bisamidines: A New Type of Chiral Metal-Free Lewis Acid Analogue Interacting with Carbonyl Groups

摘要

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.