Heterocomplexation of a Chiral Dipeptide and Quantitative Enantiomeric Enrichment of Nonracemic 1,1′-Bi-2-naphthol

Heterocomplexation of a chiral host to a racemic guest has been discovered. A cyclic dipeptide generated from (S)-proline alkyl ester undergoes an achiroselective complexation to both the enantiomers of racemic BINOL in benzene to yield a crystalline heterocomplex bearing the solvent molecules. However, complexation crystallization does not occur between the diptide and either enantiomer of BINOL under similar conditions. The difference in complexation behavior has been successfully applied in the enantiomeric enrichment of nonracemic BINOLs, and almost quantitative separation of the excess enantiomer from racemic BINOL was achieved.