A planar-chiral pyridinophane is a structurally unique molecule whose enantiomerically pure form is available via crystallization-induced asymmetric transformation. We have synthesized novel enantiomerically enriched pyridines (Sp, R)-2  and (Rp, S)-3  from previously reported pyridinophane (Sp)-1  and carried out organocatalytic asymmetric cyclopropanation of electron-deficient malononitriles with haloacetates 4  in the presence of the pyridine catalysts 1  -3  to correlate their structures with enantioselectivity of dicyanocyclopropane 5  in pyridinium ylide-catalyzed reactions. The catalytic cyclopropanation proceeded to give optically active 5  whose enantiomeric excesses were obviously dependent on structures of the catalyst used: pyridinophane (Sp)-1  having a flexible ansa-bridge afforded (1R, 3S)-5  with 94% ee, whereas (Sp, R)-2  and (Rp, S)-3  with partially restricted dynamism of the bridge allowed (1R, 3S)-5  and its enantiomer with 67% ee and 90% ee, respectively.

Structure, dynamism, and enantioselectivity of planar-chiral pyridines for ylide-catalyzed asymmetric cyclopropanation of malononitriles

248th National Meeting (2014)

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