Crystal structures of (2-substituted-5-N-tosyl)bicyclo[3.3.0]-5-azacyclooct-2-enone: a pseudo achiral crystal from enantiopure compound and a counter-example of Wallach's rule

An unusual crystallization affording an apparently pseudoachiral crystal from single enantiomers 1a and 1b was observed. In cases of enantiopure molecules such as 1a and 1b with structural flexibility, the tendency toward a centrosymmetric arrangement was so overwhelming that apparently achiral crystals were formed even by homochiral compounds via the formation of a pseudo-centrosymmetric asymmetric unit accompanying structural adjustment. In addition, these crystals of 1a constitute as a counter-example of Wallach's rule.