Shape-Persistent and Shape-Adaptable Macrocycles Based on Restricted Rotation: Studies Building Toward ‘Macromolecular Playdough’

Abstract

A rigid 48-membered macrocycle 1 was synthesized and studied that comprises two atropisomeric N,N′-diarylnaphthalenediimide building blocks that adopt stable syn and anti conformations due to restricted rotation about two C_aryl-N_imide bonds. The resulting macrocycle maintains three distinct conformations: anti/anti, syn/anti and syn/syn conformers that are stable and separable at room temperatures, and each with distinct shapes and sizes as measured by GPC. At elevated temperatures, macrocycle 1 was conformationally flexible and showed interconversion of the respective isomers. Conformational preferences established at higher temperatures were preserved on cooling to room temperature as the restricted rotation was reestablished and the macrocycle becomes conformationally rigid.

Key words

restricted rotation - atropisomerism - foldamers - macrocycles - cyclizations - conformation

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17

In this system, there are fewer than 2n conformations due to the symmetry of the molecules.

19

Calculated from the Arrhenius equation assuming an ideal value of A = 2.08·10¹⁰s^-1deg^-1.

23

Molecular weight estimates were made based on polystyrene standard. GPC conditions were Waters Styragel HR 4E in CHCl₃ at 1 mL min^-1.