Disulfide exchange in hydrogen-bonded cyclic assemblies: Stereochemical self-selection by double dynamic chemistry

Stereoselective cyclization of cystine-based bifunctional 2-ureido-4[1H]-pyrimidinone derivatives in CDCl3 solutions was demonstrated by H-1 NMR spectroscopy. Thiolate-catalyzed disulfide exchange in solution led to the equilibration of different diastereomers of 1. At low concentrations, where formation of cyclic assemblies is the dominant mode of association, the molecules act as their own template. At these concentrations the meso diastereomer is formed preferentially, indicating a higher stability of its cyclic assemblies under the applied conditions, in comparison to the other diastereomers.