An Approach to Helical Tubular Self-Aggregation Using C₂-Symmetric Self-Complementary Hydrogen-Bonding Cavity Molecules

Abstract

In an approach to helical self-aggregation, C2-symmetric cavity compounds based on the fusion of the bicyclo[3.3.1]nonane and indole framework and incorporating two 2-pyridone hydrogen-bonding motifs, compounds (-)-4 (pyrrole N-butyl) and (-)-5 (pyrrole N-decyl), have been synthesized. The 2-pyridone AD-DA hydrogen-bonding motif failed to operate in the solid state as demonstrated by X-ray diffraction analysis of (-)-4. Instead, the hydrogen-bonded (D-A) chains ...O=C-N-H...O=C-N-H...O=C-N-H..., interconnecting columnar stacks, comprise helices of the right-handed (P) chirality motif. In solution, the aggregation of (-)-5 was studied by NMR, electronic, and CD spectroscopies, and VPO measurements. These investigations strongly suggest that (-)-5 associates to oligomers in CHCl3 and CH2Cl2 using the 2-pyridone motif, fitting the equal K model, and that pi-stacking can be ruled out as a mode of aggregation. We conclude that the so formed aggregates of (-)-5 have a helical structure, based on the fact that only helical tubular structures can result when enantiomerically pure 5 uses its 2-pyridone AD-DA hydrogen-bonding motifs for aggregation.

Synthesis and Self‐Aggregation of Enantiopure and Racemic Molecular Tweezers Based on the Bicyclo[3.3.1]nonane Framework

“…The product was collected by filtration with a Pasteur pipette clogged with cotton wool. The product was washed with EtOAc, eluted with CH 2 (21)), 36.59 (C-7(18)), 36.14 (C-11 (22) H NMR spectra was recorded. CDCl 3 (typically 100-300 mL) was sequentially added to the solution.…”

“…[33] Within the field of supramolecular chemistry, 3 has been used to introduce chirality into crown ethers, [34,35] as a backbone in self-complimentary hydrogen-bonding cleft molecules, [36,37] and has served as lattice-inclusion hosts. [38,39] During the course of our investigations into the development of various supramolecular architectures, we herein report on the synthesis of an enantiomerically pure pair of molecular tweezers ((R,R,R,R)-4) from the enantiopure bicycloA C H T U N G T R E N N U N G [3.3.1]nonane framework containing a pyrazine tether and quinoline arms (Scheme 2) and their self-aggregating properties in solution.…”

Topology Selection and Tautoleptic Aggregation: Formation of an Enantiomerically Pure Supramolecular Belt over a Helix

“…In fact, when the same chiral angle bar, the bicyclo[3.3.1]nonane framework, was used and a hydrogen-bonding motif was placed in a different position, the aggregation resulted in helical tubular oligomers (Figure 1, compound 3). [22] Moreover, for the first time an enantiomerically pure molecular belt has been assembled on the basis of hydrogen bonding, and for the first time an inherently nonself-complementary three-hydrogen-bond motif has been involved in cyclic homoleptic aggregation. In this process enantiomerically pure monomer 2 aggregated by induced tautomerization to include the DDA and AAD hydrogenbonding motifs of isocytosine at one end each, thus forming an unusually stable cyclic tetrameric structure.…”

Stimuli-controlled self-assembly of diverse tubular aggregates from one single small monomer

“…3) and with the shape from almost ideally spherical to non-symmetrical, such as the ‘banana'- or ‘S'-shape4. At the same time another important and structurally related topology, H-bonded organic nanotubes, has recently been addressed5678; however, with limited success in terms of the generality and simplicity of the strategy for the self-assembly process. As a rule, more structurally elaborated monomers give more predictable outcomes of the self-assembly, but unfortunately at the expense of synthetic efforts involved in their preparation.…”

“…Such aggregation-induced tautomer/conformer shift is expected to be extremely favourable in cyclic systems to fulfill the maximum occupancy of H-bonding sites in response to geometric constraints in the monomer. The use of enantiomerically pure building blocks could further secure the tubular aggregation mode over the open linear one7.…”