Second example for the heterocomplexation of chiral diols and complete disproportionation of enantiomers for non-racemic 2,3-O-cyclohexylidene-1,1,4,4-tetraphenylthreitols

Inclusion complexation of a tricyclic dipeptide derived from (S)-proline toward several chiral diols was examined, and observed that inclusion complexation behavior depended strongly on the composition of diol. For 2,3-O-alkylidene-1,1,4,4-tetraphenylthreitols, the derivatives of cyclohexanone and acetone reacted with the dipeptide to generate a 1:2 inclusion complex; however, the former is achiroselective, affording the second heterocomplex known to date. Based on the heterocomplexation, complete disproportionation of enantiomers of non-racemic 2,3-O-cyclohexylidene-1,1,4,4-tetraphenylthreitol was successfully realized, leading to highly effective separation of the excess enantiomer from the racemate. On the other hand, inclusion complexation did not occur between the dipeptide and rac-pinanediol or (4R,5R)-4-diphenylhydroxymethyl-5-hydroxy-2,6,6-triphenyl-1,3,2-dioxaborolane.