Photocyclodimerization Of 2-anthracenecarboxylic Acid Research Articles

Supramolecular Architecture of an Amphiphilic Amino Alcohol as a Versatile Chiral Environment for Stereocontrolled Photoreaction of Various Anthracenes.

The photocyclodimerization of 2-anthracenecarboxylic acid has been extensively studied as a model reaction of asymmetric photochemistry. So far, numerous chiral environments have been employed to control this photoreaction, while the scope of photoreactants has been limited only to 2-anthracenecarboxylic acid and its simple esters and amides. Here, we developed a systematic series of photoreactants (2 a-d) by introducing various substituents to 2-anthracenecarboxylic acid, which showed different reactivities and selectivities depending on the substituents. By using the photoreactants 2 a-d, we evaluated the performance of a chiral environment composed of an amphiphilic amino alcohol (1), where the photocyclodimerization of 2 a-d generally proceeded in excellent regio- and enantioselectivities (71-98 % regio ratio, 76-86 % ee). Furthermore, by reacting 2 a and 2 b together in the chiral environment of 1, we succeeded in the first stereocontrolled cross-photocyclodimerization between two prochiral anthracenes (58 % chemo ratio, 83 % regio ratio, 90 % ee).

Supramolecular Enantiodifferentiating Photocyclodimerization of 2-Anthracenecarboxylic Acid Mediated by Bridged β-Cyclodextrins: Critical Effects of the Host Structure, pH and Co-Solvents.

Several sulfoxide- and sulfone-bridged β-cyclodextrin (CD) dimers were synthesized for mediating the enantiodifferentiating [4+4] photocyclodimerization of 2-anthracenecarboxylic acid (AC). The complexation behavior of these chiral hosts with AC was investigated by UV-vis, circular dichroism, fluorescence, and NMR spectroscopies and certified the formation of 1 : 1 and 1 : 2 host-guest complexes. The product distribution and enantioselectivity of the photoreaction turned out to be a critical function of the chemical structure of bridged CDs. Comparing to the sulfur-bridged 2AX -3GX β-CD dimer 7, the conversion of the photolyzes with sulfoxide-bridged was significantly improved, and the ee of cyclodimer 2 was remarkably increased from -82.8% with 7 to -96.7% with the sulfoxide-bridged 2AX -3GX β-CD dimer 8. The relative yields and ee values of the slipped cyclodimers 5 and 6 were greatly enhanced in the presence of 6 M CsCl. The reaction selectivity is susceptible to the pH variation of the aqueous buffer solution, demonstrating that the supramolecular photochirogenesis is controlled by multidimensional factors, including the chemical structure of the chiral host, solvent, and pH conditions.

Switched enantioselectivity by solvent components and temperature in photocyclodimerization of 2-anthracenecarboxylate with 6A,6X-diguanidio−γ-cyclodextrins

A series of 6A,6X-diguanidio-γ-cyclodextrins (CDs) were used as chiral hosts for mediating the enantiodifferentiating [4+4] photocyclodimerization of 2-anthracenecarboxylic acid (AC). These γ-CD derivatives form stable 1:2 ternary complexes with AC in aqueous ammonia solutions and the head-to-head photodimers 3 and 4 were greatly enhanced in the presence of these diguanidio-γ-CDs. The enantioselectivity of chiral photodimers 2 and 3 is a critical function of the temperature and the ammonia contents, showing inverted product chirality by changing these external factors.

Regioselective Molecularly Imprinted Reaction Field for [4 + 4] Photocyclodimerization of 2-Anthracenecarboxylic Acid.

Molecularly imprinted cavities have functioned as a regioselective reaction field for the [4 + 4] photocyclodimerization of 2-anthracenecarboxylic acid (2-AC). Molecularly imprinted polymers were prepared by precipitation polymerization of N-methacryloyl-4-aminobenzamidine as a functional monomer to form a complex with template 2-AC and ethylene glycol dimethacrylate as a crosslinking monomer. The 2-AC-imprinted cavities thus constructed preferentially bound 2-AC with an affinity greater than that toward structurally related 9-anthracenecarboxylic acid, 2-aminoanthracene, and unsubstituted anthracene. Moreover, from the four possible regioisomeric cyclodimers, they mediated the [4 + 4] photocyclodimerization of 2-AC specifically to the anti-head-to-tail (anti-HT) isomer. This indicates that the imprinted cavities accommodate two 2-AC molecules in an anti-HT manner, thereby facilitating the subsequent regioselective photocyclodimerization.

Catalytic Enantiodifferentiating Photocyclodimerization of 2‐Anthracenecarboxylic Acid Mediated by a Non‐Sensitizing Chiral Metallosupramolecular Host

Cap in hand: Combined use of diamino-γ-cyclodextrin (CD) and Cu(ClO4)2 resulted in the first catalytic supramolecular photochirogenesis in the photocyclodimerization of 2-anthracenecarboxylic acid. The anti-head-to-head cyclodimer formed in 64–70 % enantiomeric excess and about 50 % yield; these values are the highest ever reported for CD-mediated photochirogenesis. Detailed facts of importance to specialist readers are published as ”Supporting Information”. Such documents are peer-reviewed, but not copy-edited or typeset. They are made available as submitted by the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Catalytic Enantiodifferentiating Photocyclodimerization of 2‐Anthracenecarboxylic Acid Mediated by a Non‐Sensitizing Chiral Metallosupramolecular Host

Catalytic Enantiodifferentiating Photocyclodimerization of 2‐Anthracenecarboxylic Acid Mediated by a Non‐Sensitizing Chiral Metallosupramolecular Host

Supramolecular Enantiodifferentiating Photocyclodimerization of 2-Anthracenecarboxylate Mediated by Capped γ-Cyclodextrins: Critical Control of Enantioselectivity by Cap Rigidity

A series of gamma-cyclodextrins (CDs) modified with capping and noncapping aromatic group(s) were synthesized to mediate the enantiodifferentiating [4 + 4] photocyclodimerization of 2-anthracenecarboxylic acid (AC). The complexation behavior of these gamma-CDs with AC was studied by circular dichroism, UV-vis, and NMR spectroscopy to reveal the formation of stable 1:2 host-guest complexes in all cases. The capped gamma-CD with a biphenyl group bridging the A and D glucose units was shown to confine the included AC molecules most strictly among the capped and noncapped gamma-CDs examined. Photocyclodimerization of AC mediated by capped gamma-CDs considerably improved the yield and enantiomeric excess (ee) of the head-to-head photodimer 3. The ee and the absolute configuration of syn-head-to-tail photodimer 2 critically depended on the rigidity of capping. Thus, the flexibly capped and rim-substituted gamma-CDs afforded 2 in moderate ee's of around 40%, whereas gamma-CD with a rigid biphenyl cap gave the antipodal 2 in -58% ee. Interestingly, the ee of 2 mediated by flexibly capped gamma-CDs was highly sensitive to the temperature variation as a consequence of large differential entropy changes in the enantiodifferentiation process. In contrast, the entropy effect does not appear to play a significant role in the photocyclodimerization of AC with rigidly capped gamma-CDs. The differential enthalpy and entropy changes obtained for the enantiodifferentiating photocyclodimerization mediated by native and most of the modified gamma-CDs gave an excellent enthalpy-entropy compensation plot with an exception of the biphenyl-capped gamma-CD, indicating the operation of significantly different enantiodifferentiation mechanism within the rigidly capped cyclodextrin cavity.

Solvent Switching of Stereoselectivity in [4 + 4] Photocyclodimerization of 2-Anthracenecarboxylic Acid

Abstract Stereochemistry of the major photocyclodimer is switched from 52% anti-head-to-head to 51% anti-head-to-tail among the four stereoisomers produced upon irradiation of 2-anthracenecarboxylic acid at low temperatures by changing the solvent from dichloromethane to methanol, through a critical control of the hydrogen bonding and dipole–dipole interactions.

Enantiodifferentiating [4 + 4] photocyclodimerization of 2-anthracenecarboxylate catalyzed by 6 A,6 X-diamino-6 A,6 X-dideoxy-γ-cyclodextrins: Manipulation of product chirality by electrostatic interaction, temperature and solvent in supramolecular photochirogenesis

6 A,6 X-Dideoxy-6 A,6 X-diamino-γ-cyclodextrins (X = B, C, D and E) 5a– d were synthesized as chiral hosts for catalyzing the enantiodifferentiating [4 + 4] photocyclodimerization of 2-anthracenecarboxylic acid (ACA). The electrostatic interaction between 5a– d and ACA efficiently affected the preorganization of two ACA molecules within the γ-CD cavity, and improved the yields of head-to-head cyclodimers. By lowering the reaction temperature or solvent polarity, the electrostatic interaction was further enhanced. The anti-to-syn ratio of the head-to-head isomers gradually increased by changing the host from 5a to 5d (with increasing distance between the two amino groups on the CD rim), demonstrating a good structure–function relationship in this supramolecular photoreaction system. The chiral sense and enantiomeric excess of the photoproducts obtained are significantly affected, and even inverted, by solvent composition and reaction temperature. This temperature- and solvent-controlled chirality switching behavior is proven to originate from the contribution of non-zero differential entropy (ΔΔ S ‡) in the enantiodifferentiating process. This finding is the first example of a chirality inversion driven by entropy-related factors, such as solvent and temperature, in a non-sensitized asymmetric photoreaction. The sign of ΔΔ S ‡ was switched by the composition of solvent and exhibited an excellent compensatory relationship against the differential enthalpy (ΔΔ H ‡), revealing that the photoenantiodifferentiation is governed not only by enthalpy but also by entropy, and also that the enantiodifferentiation mechanism does not vary throughout the whole system, irrespective of the condition changes.