3. Discrimination of Mobile Supramolecular Chirality: Kinetic Resolution of Mechanically Planar Chiral Rotaxanes by Organocatalysis

Among the fields of asymmetric synthesis approaching the mature science, asymmetric discrimination and catalytic synthesis of chiral supramolecules still stand as unsolved problems. Supramolecules such as rotaxanes and catenanes are known to possess mechanical chirality when each of the axis and/or ring components has dissymmetry (Fig. 3.1) (Frisch and Wasserman in J Am Chem Soc 83:3789–3795, 1961, [1]; Schill in Catenanes, rotaxanes and knots, Academic Press, New York, 1971, [2]). The extreme difficulty in asymmetric synthesis of such supramolecules may be resulting from conformational diversity and movability of mechanically chiral supramolecules. I have achieved the first example of highly enantioselective synthesis of mechanically planar chiral rotaxanes by acylative kinetic resolution of the racemate. In the presence of catalyst 1c, an acylative kinetic resolution of a racemic rotaxane 10 afforded a mechanically planar chiral rotaxane 10 with perfect enantiopurity (>99% ee) in 29% yield (the theoretical maximum yield of kinetic resolution of racemate is 50%) (Fig. 3.2). The catalysts enabled to discriminate mobile mechanical chirality of the rotaxanes with the excellent selectivity in up to 16.