Enantioselective inclusion of amide guests into a chiral N,N′-ditrityl amino amide host to compensate the loss of hydrogen bonds broken by installation of trityl groups

A new crystalline N,N′-ditrityl amino amide host included several amide guests in the host cavity to form inclusion crystals. Although the installation of trityl groups into (S)-2-aminopropanamide broke its inherent hydrogen bonds of amide groups, inclusion of guest amides compensated the loss of hydrogen bonds. X-ray crystallography showed that these inclusion cavities and host-guest interactions such as hydrogen bonds, van der Waals interaction, and CH⋯O interactions play important roles for highly enantioselective inclusion. The enantiomeric inclusion was 67% ee (S-form) for N-phenyl 2-methylbutanamide, 82% ee (S-form) for N-phenyl 2-chlorobutanamide, and 83% ee (S-form) for N-phenyl 2-bromobutanamide.