A new example of a racemate showing unusual enantiomeric resolution phenomenon, in which simple recrystallization of the racemate leads to remarkable enantiomeric enrichment of either enantiomer up to 100% ee in the mother liquor, has been found. This compound is
. By repeating recrystallization of (±)-SN and the resulting deposited crystals successively and collecting the resulting enantiomerically enriched mother liquors with the same chirality sense, highly efficient enantiomeric resolution of the racemate into its separate enantiomers has been accomplished. The relationship between the occurrence of this enantiomeric resolution phenomenon and the crystal properties has been investigated with respect to SN and its aryl-and alkylsulfonate derivatives. The mode of enantiomeric resolution of (±)-SN was similar to that of para-substituted benzenesulfonate derivatives (±)-ST (4-MeC 6 H 4 SO 3 -) and (±)-SC (4-ClC 6 H 4 SO 3 -) previously reported, whereas the unsubstituted derivative (±)-SB (C 6 H 5 SO 3 -) and alkylsulfonate derivatives (±)-SO (n-C 8 H 17 SO 3 -) and (±)-SM (CH 3 SO 3 -) did not show such an enantiomeric resolution phenomenon. The crystalline form of the former racemates that underwent the enantiomeric resolution was racemic compounds, while the latter were mixed crystals (solid solutions) composed of the respective optical antipodes.