Solvent‐Dependent Self‐Discrimination of Bis(2‐hydroxyphenyl)diamides |
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Authors: | Akinobu Matsuzawa Akihiro Nojiri Naoya Kumagai Masakatsu Shibasaki |
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Institution: | Graduate School of Pharmaceutical Sciences, The University of Tokyo, 7‐3‐1 Hongo, Bunkyo‐ku, Tokyo 113‐0033 (Japan), Fax: (+81)?3‐5684‐5206 |
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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 . |
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Keywords: | aggregation asymmetric catalysis chiral resolution molecular recognition self‐assembly stacking interactions |
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