Chiral heterocycles occur in many compounds of interest, but their efficient synthesis is challenging. This study concerns the enantioselective and diastereoselective synthesis of densely substituted chiral pyran derivatives. Diastereodivergence of the oxa-Diels-Alder reaction is achieved by using either a bifunc-tional amino-thiourea or a monofunctional quinine organocatalyst under ball-milling conditions. Liquid-assisted grinding proves a highly efficient means of affording pyrans in high yield, with high enantiomeric purities and short reaction times.

Herein, we present the synthesis and utilization of derivatives of 4H-benzo[b][1,4]thiazine-3-carboxylic acid. These benzothiazine compounds were assembled via the coupling of aminothiols and bromopyruvates. Oxidative dimerization of these starting materials was also observed and the corresponding benzothiazine dimers were isolated. Moreover, the coupling of benzothiazines with amino acids was realized. In doing so, an enantioselective synthesis of the nonproteinogenic amino acid 2-amino-3-propylhexanoic acid was accomplished.