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Scalable synthesis of β-truxinic acid (CBDA-4) was accomplished by capturing and photodimerizing a metastable crystalline solid of trans-cinnamic acid. This synthetic approach builds a foundation for investigating the properties and applications of the us

We developed a general method for the selective photochemical homo- and heterodimerization of cinnamic acid derivatives with the use of commercially available 1,8-dihydroxynaphthalene as a covalent template. A variety of symmetrical and unsymmetrical β-tr

Flavinium salts are frequently used in organocatalysis but their application in photoredox catalysis has not been systematically investigated to date. We synthesized a series of 5-ethyl-1,3-dimethylalloxazinium salts with different substituents in the positions 7 and 8 and investigated their application in light-dependent oxidative cycloelimination of cyclobutanes. Detailed mechanistic investigations with a coumarin dimer as a model substrate reveal that the reaction preferentially occurs via the triplet-born radical pair after electron transfer from the substrate to the triplet state of an alloxazinium salt. The very photostable 7,8-dimethoxy derivative is a superior catalyst with a sufficiently high oxidation power (E=2.26 V) allowing the conversion of various cyclobutanes (with Eox up to 2.05 V) in high yields. Even compounds such as all-trans dimethyl 3,4-bis(4-methoxyphenyl)cyclobutane-1,2-dicarboxylate can be converted, whose opening requires a high activation energy due to a missing pre-activation caused by bulky adjacent substituents in cis-position.

Mild [2 + 2] photodimerization of enone substrates was induced by donor-acceptor fluorophores. Enone substrates were activated efficiently for anti-head to head dimerizations with a high yield (up to 83%) and high selectivity. The adjustable excited state potential also allows donor-acceptor fluorophores to be used for isomerization of the above substrates, confirming the potential of donor-acceptor fluorophores as energy transfer photocatalysts.

The relative orientation of guests within ternary inclusion complexes is governed by the host-guest and guest-guest supramolecular interactions. Selectivity in 2+2 photocycloaddition between two alkenes included within a macrocyclic cavitand (γ-cyclodextrin) can be controlled using non-covalent interactions. In this manuscript, we report cavitand-mediated control of regioselectivity between alkyl cinnamates using non-covalent interactions. Using this method, we have shown that regioselectivity can be switched completely from a head-to-head dimer to a head-to-tail dimer. The reactions were also stereoselective in most cases. Stoichiometry experiments were performed to explore relative stabilities of the complexes, which indicate that the ternary complex is more stable than others. Selectivity in the photocycloaddition reaction was also applied retrospectively to deduce intermolecular orientations. Time-dependent conversion study we performed indicates that the observed reactivity of alkenes is representative of the intermolecular orientations in the bulk of the complex medium. Experimental observations and computational studies were used to qualitatively understand the complex structures, and relative magnitudes of the weak interactions. The reactions of complexes were studied in slurry form, and the extent of reaction control suggests a solid-state-like behavior.

The ability of γ-cyclodextrin to form ternary inclusion complexes has been utilized to mediate photo-heterodimerization between cinnamic acids and coumarins in the solid-state. Stabilizing steric and electronic interactions between the alkenes in the incl

Suzuki cross-coupling of a 1,8-dihalonaphthalene with 4-methoxy-3- methylphenylboronic acid or 4-acetamidophenylboronic acid and subsequent functional group transformation gave 1,8-bis(3′-methyl-4′-anilino) naphthalene, 16, and 1,8-bis(4′-anilino)naphthalene, 21, in 65% and 90% overall yield, respectively. These congested compounds exhibit two cofacial aniline rings that favor a proximate, parallel arrangement of covalently attached cinnamoyl units suitable for stereoselective photodimerization. The [2 + 2]cycloaddition was found to proceed with high yield and exclusive formation of cis,trans,cis-cyclobutane-1,2-dicarboxylic acids. Amide formation with cinnamoyl chloride and template 21 followed by photochemical dimerization and acidic hydrolysis gave β-truxinic acid, 10, in 69% overall yield. Coupling of 21 and (E)-3-(3,4-dimethylphenyl)acrylic acid in the presence of EDC, UV irradiation, and cleavage gave cis,trans,cis-3,4-bis(3,4-dimethylphenyl) cyclobutane-1,2-dicarboxylic acid, 26, in 60% yield. In both cases, the template was quantitatively recovered.

Photoreactions of the α- and β-polymorphs of trans-cinnamic acid were studied by 13C CPMAS solid-state nuclear magnetic resonance spectroscopy, and the reactants and products were spectroscopically characterized in detail. Chemical shifts and c

In the interest of expanding our knowledge of the interaction of cinnamic acid and its derivatives with ionizing radiation, (E)-cinnamic acid and several of its chlorinated and brominated derivatives were exposed to 60Co gamma radiation. Dimer yields were estimated from integration of the proton NMR signals of the irradiated material. (E)-Cinnamic acid itself is relatively unreactive. The largest yield of dimer was obtained with p-bromocinnamic acid where exposure to a dose of 116 megarads led to a 24% yield.

(Chemical Equation Presented) Cucurbit[8]uril and γ-cyclodextrin are able to align two olefin molecules in a head-head fashion within their large cavities. Excitation of such templated olefins results in syn head-head cyclobutanes in nearly quantitative yields. The methodology revealed here works with trans-cinnamic acids that do not dimerize either in solution or in the solid state and with the ones that yield only anti head-tail dimer in the solid state.

The 2:1 hydrogen-bonded cocrystals 1a·ox, la·su, 1a·pht, 1a·fu, 1b·ox, 1c·ox, 1d·ox between trans-cinnamamides (1a-1d) and dicarboxylic acids (ox, su, gl, fu, pht) were prepared and characterized by IR and powder X-ray techniques. The crystal structures of 1a·pht, 1a·ox and 1a·fu were solved by single crystal X-ray diffraction. Phthalic acid (pht) caused β-type photodimerization of trans-cinnamamide (1a) in the cocrystal and functioned as a non-covalent linker like gauche 1,2-diamines in photodimerization of trans-cinnamic acids. Oxalic acid (ox) enforced 1a to take a bilayer structure that is suitable for β-type photodimerization. In the case of fumaric acid (fu), cross photodimerization with 1a occurred to give a cycloadduct 4. For the cocrystals 1a·pht and 1a·fu, pedal-like motion was assumed to occur prior to the dimerization. (C) 2000 Elsevier Science Ltd.

The photochemistry of trans-cinnamic acid (trans-1) was studied in a cast film of dimethyldioctadecylammonium bromide (2), deposited from aqueous dispersions as a crystalline solid by the spontaneous vaporization of water. UV irradiation of the cast film resulted in a highly selective formation of the syn-Head-to-Head dimer, suggesting a parallel orientation of trans-1 within a bilayer film. Analyses with X-ray diffraction, differential scanning calorimetry, and IR spectra revealed the formation of a bilayer structure of 2 in which the molecules of trans-1 are dissolved to interact with 2 of the polar head groups. The photoreactivity of trans-1 in the cast film was found to be dramatically suppressed by heating at 40-60 °C, which is attributed to an improvement in the crystallinity of the bilayer.

UV irradiation of cinnamic acids 1 involving a complex with surfactant amine N-oxides (CnDAO, n = 12, 14 and 16) as vesicles in water leads to the formation of cyclodimers (i.e. β-, δ-truxinic and/or α-truxillic acids ?). Decreasing the molar ratios of 1 to CnDAO causes the vesicles to transform into rod-like micelles and the yield of the cyclodimers decreases. The addition of HCl or NaOH to aqueous solutions of 1 and CnDAO brings about sharp changes in the self-assembly structures from vesicles to micro emulsions or rod-like micelles, accompanied by a change in product distribution in the photolysis of the complex 1. Upon addition of photoinactive carboxylic acids, phenylpropionic and palmitic acids to the 1 and C16DAO system, the rod-like micelles change into vesicles by formation of a complex with C16DAO leading to the observation of a dilution effect in the photodimerization upon addition of phenylpropionic acid. However, no dilution effect is observed for the palmitic acid. This is found to be attributable to the difference in degrees of mixing of 1 with the acids in the vesicles. These results show that photodimerization of 1 incorporated in CnDAO is controlled by a variety of molecular assemblies, i.e. rod-like micelles and homogeneous or heterogeneous vesicles.

Stereoselectivity of photocyclodimers of unsaturated carboxylates is shown to be controlled by changing the site distances of clay interlayers.

Photocyclodimerization of unsubstituted and p-methoxy substituted cinnamic acids incorporated in micelles, vesicles or microemulsions formed by dodecyl-(C12DAO) and hexadecyl-dimethylamine oxides (C16DAO) has been studied in water. The dimerization proceeds in the vesicle much more efficiently than in the micelles with preferable formation of head-to-head dimers. The photoreactivity and the stereochemistry of cyclodimers are affected by structural change of the molecular aggregates.

By double salt formation, diamines can steer the solid-state photodimerization of trans-cinnamic acid (1).Thus, the yields for the photodimerization were significant only in three double salts, i.e., the ones with tn and t- and c-chxn, which are assumed to have an overlap structure.The resultant photodimer is generally β-truxinic acid, although in one case, ε-truxillic acid was formed. α-Truxillic acid was not produced from any of the double salts studied.The X-ray crystal structures of three double salts of low photoreactivity (1*en, 1*pen, 1*hen) were consistent with Schmidt's rule.

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Three- and four-membered ring compounds with functional groups and bulky substituents have proved to be a rewarding new source of inclusion hosts.These hosts form clathrates with a variety of uncharged organic molecules ranging from protic dipolar to apolar compounds (168 different inclusion species).Formation and selectivity depend in a systematic manner on structural parameters of the host, such as the nature, number, and position of functional groups, the substituents, and ring size.X-ray structure analyses of two inclusion compounds 12121; = 9.782 (1), b = 11.376 (1), c = 17.603 (1) Angstroem; Z = 4. 17*MeCN (1:1): Pbcn; a = 12.314 (1), b = 16.074 (1), c = 12.938 (1) Angstroem; Z = 4> and of a free host molecule 1; a = 7.339 (2), b = 11.657 (4), c = 9.149 (3) Angstroem; β = 110.070; Z = 2> are reported, revealing the building principles of the new clathrate family.The structures exhibit linear chains of inter-/intramolecular H bridges between carboxylic groups in the free host 1 and H-bridge aggregation of host and guest molecules in infinite helical chains for the 1*t-BuOH (1:1) inclusion.In 17*MeCN (1:1), the guest molecules are tightly enclosed by the host framework without further specific interactions.

Irradiation of trans-cinnamic acid (1) and its methyl ester (2) in 1% aq. cetyltirmethylammonium bromide gave dimeric products in 35 and 29% yields as a mixture of truxinic and truuxillic acids in a ratio of 19 : 1 and 3.8 : 1, respectively, while in homogeneous solutions (1) gave no photodimers and (2) gave dimeric products in 2.3% yield under similar reaction conditions.

One-electron reduction of dimethyl μ-truxinate (μ-DMT), dimethyl β-truxinate (β-DMT), and dimethyl α-truxillate (α-DMT) has been investigated by pulse radiolysis and 77 K matrix γ irradiation of the 2-methyltetrahydrofuran solutions.Cycloreversion of the radical anions formed by an electron attachment to these cyclobutanes was observed in all cases, even at 77 K.The orientation of the cycloreversion was dependent on the stereochemistry of the cyclobutanes, and the selectivity was reasonably explained by a so-called cis effect; the best possible release of steric hindrance decides the primary step of the reaction.In 77 K matrix γ irradiation of α-DMT, an intense IR absorption was found after the photobleaching of trapped electrons with light >690 nm.In other DMTs, the IR absorption band was not observed while the cycloreversion of DMT by mobile electrons occurred.Thus, the IR band in the case of α-DMT was assigned to an associated dimer anion due to the interaction between the radical anion and the neutral molecule pair of trans-methyl cinnamate originally formed by the cycloreversion of α-DMT.The dimer anion was presumed to be oriented in a head-to-tail structure in a solvent cage on the basis of the original configuration of α-DMT.

Irradiation of neat liquid ethyl cinnamate at room temperature and of ethyl cinnamate glasses at -80 and -196 deg C produces cyclodimers in high yield.Six of the possible eleven isomers have been identified in the products.Their contributions to the overa

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