Two stereoisomers of 5-methyl-6-phenyl-4-methyl-1,3,4-oxadiazinane-2-thione have been independently prepared from (1R,2S)-ephedrine and (1S,2R)-ephedrine.  Each enantiomer crystallizes as S.H hydrogen bonded dimers with two crystallographically independent molecules centered about a pseudo-2-fold axis of rotation.  Crystals from a racemic mixture of these thiones also contained S.H hydrogen bonded dimers; however, the asymmetric unit contains only a single molecule, with the heteroenantiomeric dimer forming about a crystallographic inversion center.  Curiously, this contrasts with the structure of the ketone congener, where the racemic crystal contains only homoenantiomeric dimers, centered about crystallographic two-fold axes of rotation.  Opposing enantiomers are related through crystallographic inversion centers between (not within) dimers.  This presentation will detail the synthesis and crystallography of these compounds.  The crystallographic packing will be further explored using the Full Interaction Maps analysis within the Cambridge Crystallographic Database System.

Evaluation of crystal packing motifs observed in structures of 5-methyl-6-phenyl-4-methyl-1,3,4-oxadiazinane-2-thione

2019 Spring National Meeting

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