Syntheses and Crystal Structures of Three Chiral Oxazolidinones with Different Ring Conformations

The preparation of new, enantiomerically pure, alpha-amino acids from easily available starting materials is an ongoing challenge in synthetic organic chemistry. Here, we describe the syntheses and crystal structures of three chiral oxazolidinone derivatives prepared from L-alanine and pivalaldehyde to form a Schiff base intermediate and then reaction with the appropriate acid chloride to form the heterocycle. In each compound, the methyl and tert-butyl substituents lie to the same side of the molecule: these homochiral 'cis' structures were separated from their trans diastereomers by fractional crystallisation. The five-membered rings in these structures adopt various conformations including envelopes with either a C or O atom as the flap and twisted about a C-O bond. The extended structures of two of these compounds feature C(6) chains of molecules linked by C-H center dot center dot center dot O hydrogen bonds: one of these has a notably short H center dot center dot center dot O separation of 2.24 (3) angstrom.

Automated summary

This article discusses the synthesis and crystal structures of three chiral oxazolidinone derivatives prepared from L-alanine and pivalaldehyde, revealing their homochiral structures and various conformations in the five-membered rings. The extended structures of two compounds are linked by C-H···O hydrogen bonds, with one exhibiting a notably short H···O separation distance.