Chiral Anthranyl Bis-sulfoxides with Modular Chiroptical Properties Controlled by an Ionic Stimulus

Abstract

New chiral fluorescent bis-sulfoxide receptors based on syn and anti anthracene atropisomers were synthesized. Their coordination complexes for silver­(I), sodium­(I), and cesium­(I) cations were investigated using NMR and chiroptical spectroscopies as well as quantum chemical calculations. Notably, the CPL signals of a pair of (R,R) and (S,S) syn atropisomers were reversibly almost quenched by CsBArF, enabling in situ nearly on/off modulation of the CPL response via an ionic stimulus.

Introduction

Chiral bis-sulfoxides are well-known C ₂-symmetric bidentate ligands for transition metals, which have the advantage of being stable in the presence of dioxygen and humidity (Figure a). , In general, the mode of metal coordination to the SO group follows the Hard and Soft Acids and Bases (HSAB) principle, leading to preferred binding to the oxygen atoms for hard cations (alkali, Ca²⁺) and to the sulfur lone pair for soft cations (Ag⁺, Pd²⁺, Cu⁺). Nevertheless, other types of coordination can be observed in the presence of additional coordinating atoms or when steric constraints exist. Several chiral bis-sulfoxide ligands have found applications in asymmetric catalysis, notably those based on Ru­(II), Pd­(II), Pt­(II), or Rh­(II) (Figure a). Recently, they have also been integrated into light-responsive systems. For example, a UV-photoswitchable chiral bis-sulfoxide Ru­(II) complex exhibited tunable coordination modes (S,S- versus S,O- or O,O-) depending on light and solvent stimuli. Additionally, chiral bis-sulfoxides have also been used to modulate chiroptical properties, especially Circularly Polarized Luminescence (CPL). For instance, Cuerva et al. reported that ortho-phenylene ethynylene oligomers bearing terminal bis-sulfoxides become CPL-active (dissymmetry factor: g_lum = 0.9–7.1 × 10^–3) upon coordination with hard and borderline metallic cations and subsequent folding (Figure b). , These findings contribute to the blossoming field of CPL switches based on small organic molecules (SOMs), which have potential applications in tunable detection and emissive devices. While numerous sophisticated or supramolecular systems such as conjugated oligomers, π-extended polyaromatics, macrocycles, and interlocked molecules already exist, there is a growing demand for new easily accessible molecules with modular CPL properties. Herein, new simple chiral bis-sulfoxide anthracenes are described with their tunable chiroptical properties controlled by cations.

1.

Chiral bis-sulfoxides have been used as ligands: (a) with transition metals in asymmetric catalysis; (b) in conjugated oligomers whose spatial arrangement, and resulting CPL emission, is modified upon binding metallic cations. (c) This work: new chiral o,o’-disubstituted diphenylanthracenes 1a and 1b whose CPL intensity is reversibly reduced by Ag⁺ and Na⁺ binding and almost quenched by Cs⁺.

Recently, we showed that 9,10-diphenylanthracenes (DPA) substituted in ortho,ortho’-positions with asymmetric carbons (−CH­(OH)­CF₃ groups) are CPL-active, with g_lum values of 0.6 × 10^–3 (λ_exc = 370 nm). NMR and DFT analyses revealed that both hindered chiral groups lie above the anthranyl fluorophore, enabling CPL emission from this polyaromatic core. Besides, we demonstrated that achiral o,o’-bis-thioether diphenylanthracenes act as ligands for silver­(I), affording efficient homogeneous catalysts in tandem reactions involving alkynes. To further investigate the chiroptical properties of DPA, we designed enantiopure diphenylanthracenes with chiral bis-sulfoxides in ortho,ortho’-positions, acting as a chiral bidentate ligand near the emitting anthracene core. We hypothesized that their chiroptical properties (Circular Dichroism CD and CPL) could be changed upon coordination of cations by the chiral centers near the fluorophore (Figure c). To favor this coordination, and in contrast to benchmark sulfoxide ligands (Ar-SO-Tol, ArSO-tBu), the anthracene scaffold was functionalized with less sterically hindered aryl-SO-n-alkyl units: Ar-S­(O)-Me (compound 1a) and a new polyether derivative (compound 1b) designed to enhance polydentate coordination with oxophilic cations (Figure c). The modulation of their CPL emission was evaluated in the absence and presence of cations, specifically Ag⁺ and the alkali ions Na⁺ and Cs⁺.

Results and Discussion

Synthesis of Chiral Anthranyl o,o’-Bis-sulfoxides

As reported for 9,10-diarylanthracenes substituted in the o,o’-positions, compounds 1 and 2 exist as stable atropisomers at room temperature. ,

A two-step synthesis was developed to access the new anthranyl o,o'-bis-sulfoxides 1a and 1b (Scheme ). For the first step, o,o'-bis-thioethers 2a and 2b were prepared from simple anthracene derivatives via a Suzuki–Miyaura coupling under standard conditions. As we previously reported, compound 2a was isolated exclusively as its syn atropisomer, in 32% yield. The new thioether 2b was obtained as its anti (42% yield) and syn (14% yield) atropisomers. The stereochemistry of anti 2b was unambiguously confirmed by X-ray crystallography (Figure a).

1. Two-Step Synthesis of Anthranyl Bis-sulfoxides 1, as syn and anti Atropisomers .

^a The enantiopure stereoisomers ((R,R), (S,S), and meso) of syn 1a, syn 1b, and anti 1b were separated by chiral HPLC.

2.

X-ray structures of syn and anti o,o‘-bis-thioethers 2b: a) anti atropisomer 2b, b) coordination complex formed between anti 2b and two silver­(I) triflate ions, and c) (1:1) coordination complex syn 2b.AgOTf showing the unique silver­(I) ion positioned above the anthracene core, at a distance of 3.07 Å.

For the second step, controlled oxidation of each thioether 2 afforded the three desired anthranyl bis-sulfoxides 1 in excellent yields (72–80%). Finally, the stereoisomers of syn 1a, syn 1b, and anti 1b were successfully separated by chiral HPLC with e.e., >99.5%, and their absolute configurations ((R,R), (S,S), and meso) were assigned by comparison between calculated and experimental electronic circular dichroism (ECD) spectra (see Electronic Supporting Information, ESI). The absorption and fluorescence emission spectra of ligands 1 and 2 were similar (λ_exc = 340 nm, λ_em = 380–510 nm in dichloromethane) and correspond to those reported for the parent 9,10-diphenylanthracene (see ESI). These results indicate that the chemical modification of the anthracene core in ligands 1 and 2 does not significantly affect these spectroscopic properties.

Binding Abilities toward Cations

To compare the ability of coordination of syn ligands versus the anti ones, attemps of crystallization for metal complexes were conducted with AgOTf, NaX, and CsX salts (X: BArF, BF₄, OTf). Despite no crystal being obtained with sulfoxides 1, we were delighted to obtain the X-ray structures of two coordination complexes between thioether ligands 2b and silver­(I) triflate in a different stoichiometry, i.e., anti 2b.2AgOTf and syn 2b.AgOTf (Figure b and c, respectively). For these complexes involving syn or anti atropisomers 2b, the coordination of Ag⁺ is achieved through the lone pairs of the thioether group (distance Ag⁺···S_ether = 2.47–2.63 Å), the two oxygen atoms from one polyether chain (distance Ag⁺···O_ether = 2.42–2.63 Å), and one oxygen atom from the triflate counterion. In detail, the anti 2b ligand formed a (1:2) complex with AgOTf, where its two independent binding units are located on opposite sides of the anthracene core. In contrast, syn 2b ligand presented a single coordination site with multiple binding units, combining the two sulfur atoms (close together at a distance of 4.7 Å) and one polyether chain, along with an additional strong stabilizing cation···π interaction with the anthracene core (distance Ag⁺···π = 3.07 Å). Thus, the solid-state structural studies of thioether complexes reveal that the anthracene core and the polyether chains play an important role in the coordination of silver­(I), but do not provide insight into the binding behavior of sulfoxides, particularly in solution.

In solution, the binding behavior of syn 1a and 1b was evaluated using (host:guest) titrations monitored by fluorescence emission (λ_exc = 340 nm and λ_em = 410 nm; CH₂Cl₂/MeCN, (100:0) or (99:1)) in the presence of AgOTf, NaBArF, or CsBArF. The BArF^– and OTf^– counterions were selected to offer loose ionic pairs, excellent solubility, and stability for the salts and the resulting complexes, especially those involving Ag­(I) species. Considering titrations, only the (syn 1a:Cs) complex exhibited a 1:1 stoichiometry (K = 109 M^–1) in CH₂Cl₂/MeCN. The 1:1 stoichiometry observed for Cs⁺ reflects the binding of the largest cation to the syn 1a receptor, which lacks polyether chains and contains only two sulfoxide groups. Consequently, syn 1a exhibits lower binding efficiency and distinct stoichiometric behavior, as Cs⁺ coordination is limited to a single cation, unlike the smaller Ag⁺ and Na⁺ cations. The other complexes have a 1:2 stoichiometry and exhibit a high initial association constant (K₁₁), while the second constant (K₁₂) is significantly lower (see Figure and SI). This particular behavior based on two distinct regimes allows for control of the (1:1) complex formation by using a (1:1) ratio of host and guest and preventing the occurrence of higher-order complexes. The controlled formation of (1:1) complexes between cations and syn 1a and 1b was confirmed by ¹H NMR (see SI) and enables the study of “cation catch-and-release” by controlling the stoichiometry of ligand relative to the cations in a (1:1) ratio.

3.

(Host:guest) titration between syn 1b and CsBArF in CH₂Cl₂/MeCN (99:1), monitored by fluorescence emission (λ_exc = 340 nm). Inset: titration data at λ_em = 410 nm highlighting the formation of a (1:2) complex with a high K₁₁ (>10⁺⁶ M^–1).

Quantum chemical calculations (MP2­(full)/def2-SVP//B3LYP/def2-SVP, see ESI for details) were then performed to gain deeper insight into the 3D structures of (1:1) complexes between bis-sulfoxide (R,R)-syn 1b and each cation, i.e., Na⁺, Cs⁺, and Ag⁺ (Figure and Table ). This approach has already been used for similar systems and has yielded results in agreement with experimental data. Indeed, B3LYP/def2-SVP provides reliable geometries for metal-ion complexes dominated by ion–dipole interactions, while MP2­(full) single-point calculations improve the description of electron correlation and noncovalent interactions, offering a well-established compromise between accuracy and computational cost.

4.

Optimized structures (most stable ones) obtained by DFT calculations for (1:1) complexes formed between bis-sulfoxide (R,R)-syn 1b and metal cations: a,b) Ag⁺, c) Na⁺, and d) Cs⁺. The results (except for b) mainly indicate hexacoordination involving all oxygen atoms, with no evidence of cation···π interaction (distance >4.0 Å). Insets: top views with partial CPK representation of the cations and binding groups, highlighting a more (Ag⁺, Na⁺) or less (Cs⁺) pronounced encapsulation of cations depending on its size.

1. Structural Data Obtained from DFT Calculations: Distance (Å) Measured within Optimized Geometry (1:1) Complexes between (R,R)-syn 1b and Different M⁺ Cations (M: Ag, Na, Cs) .

Distance	(syn 1b:Ag+)	(syn 1b:Na+)	(syn 1b:Cs+)
SO···M+	2.35, 2.37; none	2.28, 2.28	2.25, 2.30
O ETHER···M+	2.35–2.68; 2.47–2.56	2.28–2.56	3.25–3.46
π···M+	4.38; 4.00	4.32	5.40

^aDistances were measured using Mercury software (version 2024.3.1).

^bCoordination complex corresponding to Figure a (only oxygen atoms as binding sites for Ag⁺).

^cThe coordination complex corresponds to Figure b (one sulfur atom and four oxygen atoms as binding sites).

The optimized geometries indicated that the three cations are coordinated by (R,R)-syn 1b with the same coordinating mode, i.e., through the six available oxygen atoms from the two sulfoxide groups and the two polyether chains (Figure a, c,d). One exception was observed for Ag⁺ (Figure b): one of the two most stable structures presented coordination by one sulfur atom and the polyether chains, instead of all oxygen atoms. In all complexes, even if the cations sit above the anthracene core, no obvious cation···π interaction appears, as they are distal from more than 4.0 Å. This result highlights a different coordination mode between bis-sulfoxides 1 and bis-thioethers 2 ligands, controlled by structural effects.

However, the 3D structure of the cationic complexes revealed subtle differences associated with the cation size (Table ). Indeed, the Ag⁺ and Na⁺ ions which have similar ionic radii (1.15 and 1.02 Å, respectively) are strongly coordinated to the ligand through short O···M⁺ contacts, and they are fully encapsulated by the two surrounding polyether chains (see Figure , insets a–c). In contrast, in the Cs⁺ complex, this larger cation (ionic radius: 1.67 Å) sits farther above the anthracene (Cs⁺: 5.40 Å versus Ag⁺, Na⁺: 4.00–4.38 Å) and the arrangement of the binding groups results in a reduced encapsulation (see Figure , inset d) due to a slightly higher constraint. Notably, the distance between the oxygen atoms of two sulfoxide groups is significantly larger in this less compact 3D structure (Cs⁺: 6.0 Å versus Ag⁺, Na⁺: 3.7–4.1 Å with a similar binding mode).

According to quantum chemical calculations, bis-sulfoxide syn 1b may exhibit promising synergistic binding behavior toward cations. Furthermore, upon formation of these (1:1) complexes, the chiral fluorescent syn ligand could undergo significant geometric and electronic reorganizations to lead to a well-organized compact cationic structure. This structural change could therefore be exploited for chiroptical modulation through cationic complexation.

The binding abilities of bis-sulfoxides ligands syn 1a and 1b were then investigated in solution. Catch-and-release experiments were performed and monitored by ¹H NMR (CD₂Cl₂) using the same three cations with different ionic radii and ligand affinities: Ag⁺ (1.1 Å), Na⁺ (1.0 Å), and Cs⁺ (1.7 Å). The formation of each cationic complex was thus experimentally confirmed (Figure for Cs⁺ and ESI for other cations). To verify the reversibility of the binding, decomplexation was induced by then adding [18-crown-6] (1.1 equiv) as a stronger cation chelator. NMR monitoring of the two-step process (catch then release) revealed that syn 1a and syn 1b were complexing each cation in a reversible manner (Figure ), except for the less coordinating ligand syn 1a which showed limited coordination with the larger Cs⁺ cation (see ESI). As expected for metal coordination by the sulfoxide groups, significant changes in the chemical shifts were observed both in the aromatic region (corresponding to the 9,10-aryl substituents) and in the aliphatic region (polyether chain for syn 1b or methyl group for syn 1a). This reversible coordination/decoordination process was also monitored by emission of fluorescence (λ_exc = 340 nm) for the three Ag⁺, Na⁺, and Cs⁺ cations (Figure inset). This preliminary study reveals an optical spectroscopic effect associated with binding which paves the way for probing chiroptical modulation through complexation.

5.

Representative cation catch-and-release by bis-sulfoxide syn 2b toward CsBArF monitored by ¹H NMR (2 mM, CD₂Cl₂) and by emission of fluorescence (inset: 15 μM in CH₂Cl₂; λ_exc = 340 nm, λ_em = 410 nm). A competitive chelator ([18-crown-6], 1.5 equiv) was added to ensure the cation release.

Chiroptical Properties and Switchability

Chiroptical properties of enantiopure o,o'-bis-sulfoxides syn 1a and 1b (15 μM in CH₂Cl₂) were studied by electronic circular dichroism (ECD, Figure left) and circularly polarized luminescence (CPL, Figure right). For the ECD analysis, each enantiomer couples feature mirror-image spectra with similar opposite Cotton effects at the ground state, in the 235–280 nm region and the 340–410 nm (characteristic of the π–π* transition corresponding to the anthracene core). This result indicates that the chiral information carried by ortho,ortho'-sulfoxide groups is effectively transferred to the anthranyl chromophore unit thanks to this molecular design. A slightly more intense CD signal is observed for syn 1b than syn 1a, possibly due to differences in coordination multiplicity and in structural variations. The CD dissymmetry factors g_abs were measured at the maximum of CD intensity (λ_max = 256 nm) for the two ligands: 8.7 × 10^–4 for syn 1a and 10.7 × 10^–4 for syn 1b. Interestingly, in the presence of cations, the CD spectra show significant changes upon coordination (Figure left, ECD insets), with a different signal signature (black lines versus red lines) and a slight decrease in intensity, with g_abs values in the range of 3.9–7.8 × 10^–4 for syn 1a and 10.0–9.2 × 10^–4 for syn 1b (see SI).

6.

Chiroptical characterizations of anthranyl chiral bis-sulfoxide (R)- and (S)-syn 1b enantiomers (15 μM in CH₂Cl₂) under different conditions: a) alone and in the presence of the following cations (1 equiv): b) AgOTf; c) NaBArF; and d) CsBArF. Left: Electronic Circular Dichroism (ECD, solid line) and absorption (Abs., dashed line) spectra with insets showing an enlarged view in the 350–420 nm range. Right: CPL (solid line) and fluorescence (dashed line) emission spectra (λ_exc = 355 nm).

Regarding the CPL emission (Figure , right, Table ), based on Kasha’s rules, the compounds were excited at the lower-energy CD transition (λ_exc = 355 nm, λ_em > 380 nm) to access the highest intensity in fluorescence emission. In detail, bis-sulfoxides syn 1a and 1b exhibited similar |g_lum| values of 4.0 × 10^–4 and 3.6 × 10^–4, respectively, in dichloromethane when excited at 355 nm (Figure and Table ). These values indicate an efficient transfer of chirality from sulfoxide groups to the anthracene moiety in the excited state. The observed g_lum values fall within the typical range reported for discrete small organic molecules (g_lum = 10^–4–10^–2). , It is important to note that measurements of low rotational strengths are generally considered to be imprecise (both in value and sign). Nevertheless, the values reported here form a coherent data set showing the same trend, which reinforces their relevance. The CPL response of the two syn 1 ligands was then evaluated in the presence of cations and revealed a decrease in CPL intensity, with one case showing a nearly complete quenching for Cs⁺ and syn 1b (Figure d, Table ). The decrease in CPL signal induced by cations was more pronounced for syn 1b than for syn 1a, likely due to the polyether chain, which enables more efficient coordination. So, in the case of the complexes formed with syn 1b, the g_lum values ranged from 1.5 × 10^–4 with Na⁺, then 0.84 × 10^–4 with Ag⁺, and finally 0.16 × 10^–4 with Cs⁺, the latter being nearly zero.

2. Dissymmetry Factors of CPL (g_lum, ×10^–4) Determined for syn 1a and syn 1b Ligands, Alone and in the Presence of Different Cations (1 equiv) .

syn 1a	syn 1a.AgOTf	syn 1a.NaBArF	syn 1a.CsBArF
4.0	3.7	2.0	3.75
syn 1b	syn 1b.AgOTf	syn 1b.NaBArF	syn 1b.CsBArF
3.6	1.5	0.84	0.16

^ag_lum values were measured at the maximum of the CD spectra (λ = 430 nm for syn 1a and λ = 439 nm for syn 1b). The values reported here are the average of the absolute values for the (R) and (S) enantiomers.

The variations in CPL result from a slight variation in fluorescence intensity (see Figure , right, and Figure ) and from a change in the dissymmetry factor (the calculation of which includes normalization of the fluorescence intensity). These variations are interpreted as resulting from an overall structural change during complexation (i.e., nature of cation, atom orientation, and orientations of the electric and magnetic transition dipole moments). Since Cs⁺ is a larger cation, it likely promotes a three-dimensional arrangement that is slightly different than that of Ag⁺ and Na⁺, as suggested by the DFT calculations (Figure d), which results in a more pronounced decrease in the CPL response of this Cs⁺ complex.

7.

Representative cation catch-and-release by bis-sulfoxide syn 1b toward CsBArF monitored by CPL (15 μM in CH₂Cl₂,; λ_exc = 355 nm): a) ligand syn 1b, b) ligand syn 1b with CsBArF (1 equiv) forming the coordination complex, and c) 18-crown-6 (1.5 equiv) was added to ensure cation release, by a competitive chelator. The original CPL signal of ligand syn 1b was observed again.

A full cycle of CPL modulation was carried out to assess the reversibility of this process using the syn 1b/CsBArF pair (Figure ). Consecutive CPL spectra were recorded in the same cuvette: first for the free ligand syn 1b (Figure a), then after adding CsBArF (1 equiv), which led to a quenching of the CPL signal (Figure b), and, finally, after introducing [18-crown-6] (1.5 equiv), which sequesters the Cs⁺ cation and releases the original chiral ligand syn 1b (Figure c). In this final step, the CPL signal was thus fully restored. Even if these g_lum values are low, they can be accessed and adjusted with simple ligands.

Conclusion

In conclusion, we have demonstrated that new chiral anthranyl o,o‘-bis-sulfoxides syn 1a and especially syn 1b are capable of reversibly coordinating different types of cations such as Ag⁺, Na⁺, and Cs⁺. This coordination/decoordination process is controlled by the presence of [18-crown-6] which acts as a competitive chelating agent. Moreover, the CPL properties of these enantiopure simple ligands are modulated by cation binding, particularly with anthranyl syn 1b exhibiting a nearly on/off CPL behavior upon coordination with the heavier Cs⁺ cation.

Experimental and Computational Details

Synthesis

Unless specified, all reactions were performed under an argon atmosphere with magnetic stirring. Chemicals obtained from commercial suppliers were used directly without any further purification.

General Procedure for the Synthesis of Thioethers 2

A Suzuki–Miyaura coupling (Pd­(PPh₃)₄, K₂CO₃) was applied with optimized conditions (solvent, substrate) for each thioether 4a or 4b to get anthranyl o,o‘-bis-thioethers 2a and 2b (see ESI for details).

General Procedure for the Oxidation of Thioethers 2 into Sulfoxides 1

To a suspension of thioether 2 in glacial acetic acid was added hydrogen peroxide (35% aqueous solution, 2.5 equiv). The resulting mixture was stirred at room temperature for 12 h under an argon atmosphere. After the completion of the reaction (TLC monitoring), the solution was concentrated, and the crude product was purified by column chromatography on silica gel to allow the isolation of sulfoxides 1. Each stereoisomer of 1a and 1b was separated by chiral HPLC to provide enantiopure (R,R and S,S) and meso syn 1a, syn 1b, and anti 1b (see pages S14–S19).

X-ray Diffraction

Crystallographic data were acquired at CESAMO (Université de Bordeaux) on a Bruker APEX 2 DUO. A single crystal was mounted and immersed in a stream of nitrogen gas [T = 150(2) K]. Data were collected, using a microfocus sealed tube of Cu Kα radiation (k = 1.54184 Å) or Mo Kα radiation (k = 0.71073 Å) on a KappaCCD diffractometer. Data collection and cell refinement were performed using APEX2 2013.10–0 and SAINT v8.34A (Bruker AXS Inc.). Data reduction was performed using SAINT v8.34A. Correction for absorption was performed using multiscan integration as included in SADABS V2012/1 (Bruker AXS). Structure solutions were found by charge-flipping methods SUPERFLIP and EDMA and refined with SHELXL.

Titrations

All solutions were freshly prepared. Binding constants (K_ass) between (S,S)-syn 1a and 1b hosts and metallic guests were determined using titrations monitored by fluorescence emission of the host (λ_exc = 340 nm) in the chosen solvent. A solution (2.5 mL) of the host (1.5 × 10^–5 M) was introduced in a quartz cuvette at 20 °C. Increasing aliquots of the guest stock solution (1–1.1 × 10^–3 M in the solvent chosen for titration) were successively added to the host solution. The titration data (intensity of fluorescence emission at 410 nm (I_F) versus (host:guest) ratio) were fitted using the nonlinear curve-fitting procedure with a (1:1) or (1:2) binding equation using the Bindfit program.

Spectroscopic Measurements

UV–vis spectroscopy was performed on a Varian 5000 UV–vis-NIR spectrophotometer, and the fluorescence emission spectra were recorded using a Fluoromax-4 spectrofluorometer. Electronic circular dichroism (ECD) spectra were measured by J-815 (JASCO). Circularly polarized luminescence (CPL) spectra were obtained by CPL-300 (JASCO).

Quantum Chemistry

All quantum chemical calculations were performed with the Gaussian 16 package. The hybrid density functional B3LYP together with the def2-SVP basis set was used for the geometry optimizations. Vibrational frequency calculations were performed at the same level of theory to verify that a local minimum had no imaginary frequency. Single-point energy calculations were then conducted on every species at the post-HF MP2­(full)/def2-SVP level of theory, and Gibbs free energies were derived from this energy by adding the zero-point energy and the thermal corrections to Gibbs free energy obtained at the B3LYP/def2-SVP level. B3LYP and MP2 calculations were performed using the Polarizable Continuum Model (PCM) in its integral equation formalism variant (IEFPCM) to simulate the dichloromethane (CH₂Cl₂) environment.

The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsomega.6c07072.

• Experimental procedures; characterization data of compounds; crystallographic data; NMR, ECD, and CPL spectra; and DFT calculation details (PDF)

• Crystallographic data for anti 2b (CCDC number 2471890) (CIF)

• Crystallographic data for anti 2b.2AgOTf (CCDC number 2471891) (CIF)

• Crystallographic data for syn 2b.AgOTf (CCDC number 2471893) (CIF)

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School of Materials Science and Engineering, Hubei University, Wuhan 430062, China

The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript.

The authors declare no competing financial interest.