Study of optical rotation based on the molecular structure in fused oligomers of macrocycles

We designed a unique oligomer form in which several helically twisted macrocycles (M- or P-helicity) are arranged through fusion. We investigated the optical rotation of a series of fused oligomers of macrocycles with a difference in the number and arrangement of elements associated with point-chiral auxiliary. Some oligomers cooperatively attained a situation where an identical sense of twisting was preferred throughout the entire molecule. On the basis of these results, we estimated diastereomeric excess induced in each oligomer. We revealed that the molar optical rotation per element was modulated with a rotational angle between elements: an increase via 0° rotational arrangement, a decrease via 180° rotational arrangement, or a decrease via cyclic arrangement. Alternatively, for other oligomers in which several diastereomeric conformers coexist, we uniquely attempted to consider the optical rotation based on the molecular structure through the assessment of a change ratio of the absorption dissymmetry factor before and after complexation with an achiral guest. We found that molar optical rotation could be different based on the arrangement, although actual measured values were similar.

Conformational Control of ortho-Phenylenes by Terminal Amides

Control over the folding of oligomers, be it broad induction of a preferred helical handedness or subtle changes in the orientations of individual functional groups, is important for applications ranging from molecular recognition to long-range conformational communication. Here, we report a series of ortho-phenylene hexamers functionalized with achiral and chiral amides at their termini. NMR spectroscopy, taking advantage of ¹⁹F labeling, allows multiple conformers to be detected for each compound. In combination with CD spectroscopy and DFT calculations, specific geometries corresponding to each conformer have been identified and quantified. General conclusions about the effect of sterics and the amide linker on conformational behavior have been drawn, revealing some similarities to and key differences from previously reported imines. A model for twist sense control has been developed that is supported by computational models.

Optically active Ag(i): o-OPE helicates using a single homochiral sulfoxide as chiral inducer

In this work we describe the ability of a simple enantiopure sulfoxide group to promote folding of oligo ortho-phenylene ethynylenes (o-OPEs) with one helical sense. A family of foldamers with up to seven triple bonds was synthesized and fully characterized. Moreover, changes in structure and chiroptical properties caused by Ag(i) coordination have been studied by NMR, UV, VCD and ECD measurements. Quantum mechanical DFT calculations support experimental results.

Twist sense control in terminally functionalized ortho-phenylenes

Chiral groups induce opposite twist senses of o-phenylene helices depending on their positions in dynamic mixtures.

Many abiotic foldamers are based on achiral repeat units but adopt chiral geometries, especially helices. In these systems, there is no inherent preference for one handedness of the fold; however, it is well-established that the point chirality of substituents can be communicated to the helix. This capability represents a basic level of control over folding that is necessary for applications in molecular recognition and in the assembly of higher-order structures. The ortho-phenylenes are a structurally simple class of aromatic foldamers that fold into helices driven by arene–arene stacking interactions. Although their folding is now reasonably well-understood, access to o-phenylenes enriched in one twist sense has been limited to resolution, yielding conformationally dynamic samples that racemize over the course of minutes to hours. Here, we report a detailed structure–property study of chiral induction from o-phenylene termini using a combination of NMR spectroscopy, CD spectroscopy, and computational chemistry. We uncover mechanistic details of chiral induction and show that the same substituents can give effective twist sense control in opposite directions in mixtures of interconverting conformers; that is, they are “ambidextrous”. This behavior should be general and can be rationalized using a simple model based on sterics, noting that arene–arene stacking is, to a first approximation, unaffected by flipping either partner. We demonstrate control over this mechanism by showing that chiral groups can be chosen such that they both favor one orientation and provide effective chiral induction.

Sequence-defined oligo(ortho-arylene) foldamers derived from the benzannulation of ortho(arylene ethynylene)s

A Cu-catalyzed benzannulation reaction transforms ortho(arylene ethynylene) oligomers into ortho-arylenes.

A Cu-catalyzed benzannulation reaction transforms ortho(arylene ethynylene) oligomers into ortho-arylenes. This approach circumvents iterative Suzuki cross-coupling reactions previously used to assemble hindered ortho-arylene backbones. These derivatives form helical folded structures in the solid-state and in solution, as demonstrated by X-ray crystallography and solution-state NMR analysis. DFT calculations of misfolded conformations are correlated with variable-temperature ¹H and EXSY NMR to reveal that folding is cooperative and more favorable in halide-substituted naphthalenes. Helical ortho-arylene foldamers with specific aromatic sequences organize functional π-electron systems into arrangements ideal for ambipolar charge transport and show preliminary promise for the surface-mediated synthesis of structurally defined graphene nanoribbons.

Novel ortho-OPE metallofoldamers: binding-induced folding promoted by nucleating Ag(i)–alkyne interactions

Ag(i)–alkyne interactions induce the folding of o-OPE foldamers, yielding a new class of metallofoldamers.