“Doubly enantiophobic” behavior during crystallization of racemic 1,5-dihydro-2H-pyrrol-2-one thioether

Abstract

The titled compound 7 demonstrates unusual “doubly enantiophobic” behavior during crystallization. Namely, the mentioned substance forms two polymorphic modifications 7a and 7b that appear to be racemic conglomerates in the space groups P2₁ and P6₅ (or P6₁), respectively. Both 7a and 7b are thermodynamically stable at certain temperature ranges. Hence, γ-lactam 7 is prone to spontaneous resolution of the racemate into the enantiomers in two different ways, which is an exceptional phenomenon. Phase behavior and structure of the crystalline modifications of 7 were investigated by means of single crystal and powder X-ray diffraction, differential scanning calorimetry, temperature-resolved vibration spectroscopy, and hot-stage microscopy.