Preparative Resolution of Heterocyclic Acetals Derived from Glycine, Mercapto‐acetic Acid, β‐Alanine, and Formyl‐ or Acetylacetic Acid by Recycling Chromatography onChiraspherand Temperature Dependence of Separation Factors

Chiraspher, a polymer of ethylN‐acryloylphenylalanine on spherical silica gel, is used for the preparative separation by recycling chromatography of the enantiomers of oxazolidinonesrac‐5, thioxolanonerac‐6, per‐hydropyrimidinonerac‐7, and dioxinonesrac‐9and10derived from the acids listed in the title (Figs.1–5). The oxazolidinonesrac‐1a,‐2, and‐4show a peculiar peak of the separation efficiences upon lowering theChiraspher‐column temperature to 15° (Fig.6). In some cases, multigram amounts of enantiomerically pure heterocycles could thus be prepared. The absolute configurations of most enantiomers are assigned. First applications of thetert‐butyl 5‐oxo‐2‐phenyloxazolidine‐3‐carboxylate (5) as a nucleophilic chiral glycine building block are described (products13–16,Scheme 2). A list of enantiomerically pure 1,3‐dioxinones is presented (Table 1), showing a correlation between their absolute configuration, sense of optical rotation, and elution behavior onChiraspher.