The analysis of spectra indicates that all the products (except for 7l with E/Z ratio 83:17) were obtained as single isomers. By the analysis of 2D NMR spectra (e.g. NOESY, see supporting information) it was deduced that hemiindigos 5a-5q and hemithioindigos 6a-6q obtained in the mechanochemical syntheses are in Z configurations (in agreement with the literature data for solution syntheses), the oxindoles 6a-6q are in E configuration (also in agreement with the literature data for solution syntheses). High stereoselectivity of the mechanochemical synthesis, especially for complex, conformationally labile molecules is quite an exception. This limitati on originates from inhibited molecular mobility in the solid state, which restricts intramolecular and intermolecular motion. Thus, multiple conformations are frozen and these different conformations can exhibit different stereochemical preferences during the reactions. Thus, the Curtin-Hammett principle is mostly violated under mechanochemical conditions. In this context, it is worth noting that in the current case, not only simple derivatives are obtained stereoselectively, but also macrocyclic derivatives 5-7p,q for which the reactions have to proceed stereoselectively at four spatially close centers, leading to C4 symmetric all-Z products (Fig. ).