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Keywords:

  • aggregation;
  • asymmetric catalysis;
  • chiral resolution;
  • molecular recognition;
  • self-assembly;
  • stacking interactions

Abstract

Solvent-dependent, self-discrimination of diamides is described. Mixing a solution of (R)-1 a and (S)-1 a, which are valine-derived, bis(2-hydroxyphenyl)diamide-bearing, multiple hydrogen-bonding modules, in dichloromethane immediately led to the formation of a thick suspension comprising a 1:1 heterochiral aggregate of 1 a. The solubility of heterochiral 1 a was substantially lower in halogenated solvents than in ethyl acetate. A perusal of racemic crystal structures obtained from chloroform and ethyl acetate revealed a significant difference in the crystal-packing pattern, which is likely to be the basis for the pronounced difference in solubility. Specific self-discrimination of 1 a in an ensemble of eight structurally related molecules showcased the specific aggregation through the hydrogen-bonding network of the bis(2-hydroxyphenyl)diamide framework. The low solubility of heterochiral 1 a in halogenated solvent was exploited to achieve high stereoselectivity in a catalytic asymmetric reaction by using a low enantiomeric excess sample of 1 a.