Irradiation cinnamate derivatives

Intramolecular Cycloadditions. - Intramolecular (2 + 2)-photocycloaddi-tion has been reported within diene 1,1-dicarbonitriles. Both direct and sensitized irradiation is effective. Unlike the singlet process, where an exciplex is involved, the sensitized process proceeds via 1,4-biradicals. The singlet and triplet reactivity has been investigated for a series of 1-alkene-1,1-dicarbonitriles with additional unsaturation at the 5, 6 or 7 positions. The cyclophane moiety shown in the derivative (23) has been suggested as a useful reaction control system. The irradiation of this cinnamate derivative affords the (3-truxinic acid derivative (24), which can be uncoupled from the paracyclophane. ... 

Irradiation of cinnamate derivatives in chiral host environments has long attracted attention as a gateway to asymmetric photochemical synthesis. The use of a nonchiral host induced to crystallize in a chiral space group represents an example of absolute asymmetric synthesis, as described by Vaida et al. for the cinnamamide/cinnamic acid host/guest system and by Hasegawa et al. - for the cross dimerization of 5 (which spontaneously crystallizes in a chiral space group). It should be noted that even apparently minor modifications, at times, have a profound impact on the outcome of sohd-state reactions. In the previous example, the methyl ester derivative of 5 gives, upon irradiation, hnear polymers. 

The greater intensity of the band of the metabolite at 220 mis probably due to the presence of a second, superimposed chromophore which could also account for the shift of the minimum. On the other hand, the band near 300 m/u. has the expected intensity. Its broadness and displacement towards longer wavelength are probably due to the presence of a substituent on the double bond or benzenoid ring. That the assignment to a coumaroyl chromophore is essentially correct is evidenced by the fact that both M and the model compound underwent the same type of reaction on irradiation in the near-ultraviolet (Figure 4). The observed isosbestic points imply that the photoreaction is a simple one, such as A -> B or A = B, and is obviously the well-known light-induced trans- to c/r-isomerization (7) of cinnamic acid derivatives. 

Similar behaviour has been observed in the photoreaction of methyl a-cyano-4-[2-(2-pyridyl)ethenyl]cinnamate (7 OMe) crystals in which the yield of [2.2] paracyclophane reached 65% on irradiation at — 78°C (see Scheme 10 p. 153) (Hasegawa et al., 1989b). From the crystal structure analysis of the same type of [2.2] paracyclophane, which is topochemically derived from alkyl a-cyano-4-[2-(4-pyridyl)ethenyl]cinnamate crystals, a highly strained molecular shape is confirmed in which two phenylene rings are severely bent (Maekawa et al., 1991b). 

Intermolecular photocycloadditions of alkenes can be carried out by photosensitization with mercury or directly with short-wavelength light.179 Relatively little preparative use has been made of this reaction for simple alkenes. Dienes can be photosensitized using benzophenone, butane-2,3-dione, and acetophenone.180 The photodimerization of derivatives of cinnamic acid was among the earliest photochemical reactions to be studied.181 Good yields of dimers are obtained when irradiation is carried out in the crystalline state. In solution, cis-trans isomerization is the dominant reaction. 

For instance, head-head photodimers are predicted from the crystal structures of 9-cyanoanthracene and 9-anthraldehyde, but the head-tail isomer is produced. Craig and Sarti-Fantoni and later others found that photoreactions of 9-cyanoanthracene and 9-anthraldehyde take place at defect sites [96,215], Systematic photochemical and crystallographic studies by Schmidt and co-workers uncovered many cases of substituted anthracenes which behave in an unexpected fashion (Scheme 40) [216,217]. Examples shown in Scheme 40 clearly illustrate that, unlike cinnamic acid derivatives, the stereochemistry of the product dimer from anthracenes cannot be predicted on the basis of crystal packing. An example from the laboratories of Venkatesan is noteworthy in this context [218], Irradiation of crystals of 7-... 

Photo-crosslinking and the reverse process of photodissociation of pre-existing crosslinks relies on a cycloaddition reaction (and on the reverse dissociation of the cyclic adduct). For example, derivatives of vinyl cinnamic acid can form crosslinks which are dissociated by irradiation with short wavelength light (e.g. 254 nm produced by low-pressure mercury arcs). In this process the polymer chains become separated, and the polymer itself is then soluble in organic solvents. 

Cinnamic acid derivative 36 crystallizes in the chiral space group P2t and gives the optically pure dimer 37 upon irradiation in the solid state [22], Chiral crystals of 38 gave, upon irradiation, the optically active dimer 39 of 90% ee, whereas the corresponding methyl ester gave a highly crystalline linear polymer through a typical [2 + 2] topochemical photopolymerization [23],... 

Crystalline traras-cinnamic acid forms cyclobutane derivatives upon irradiation of the crystal when C=C double bonds in neighboring molecules interact with each other to give cyclobutane derivatives, as illustrated in Figure 18.1. In solution or in the molten state, the only reaction observed is isomerization from trans- to cfs-cinnamic acid, but in the crystalline state the stereospecific reaction to form cyclobutane derivatives may occur. 

The development of the principles of solid-state reactions of substituted cinnamic acids was pioneered by Gerhard M. J. Schmidt. The trans-SLcid was found to be polymorphic, and three different crystal forms (designated a, and 7) were identified by him. The finding that the nature of the cyclobutane derivatives formed by the solid-state photochemical reaction on crystals of frans-cinnamic acid depend on which polymorph is irradiated was of great interest. The products of the photo-... 

Intramolecular Additions - The truxinic acid derivative (23) is formed on irradiation of (24) in methanol using a Pyrex filter. The reaction is quantitative and has a quantum yield of 0.55. Similar reactivity is observed when crystals of (24) are irradiated. The use of a benzene ring as a constraint has provided a method for the formation of a single stereoisomer in high yield this is seen best of all with the yield this is cinnamate ester (25). Irradiation of (25) for 21 h in methylene chloride solution affords an 88% yield of (26). A less efficient reaction... 

Another example of control over the (2+2)-photodimerization of cinnamates has been published. In these examples the conformation tether is a dioxane system as shown in (31). The irradiation of these affords mixtures from which cyclobutane derivatives (32), (33), (34) and (35) can be isolated. ... 

A review has highlighted the photocycloaddition reactions of alkenes with aromatic esters and nitriles. Cycloadditions occur by a (3+2)-mode and provides a path to medium size ring systems. When the cinnamic acid derivative (9) is irradiated at 359 nm in ethanol with added Ti02 the product (10) is formed in 30% yield. Analogous products are formed from other straight chain alcohols such as (11) from propan-l-ol. Benzonitrile can be photochemically hydrated in the presence of oxophosphorus porphyrins. " ... 

The cinnamates (177) are photochemically reactive in micelles. Irradiation brings about C-O bond fission and recombination within the radical pair affords the chalcones (178). The EZ isomerization of the enone (179) is followed by the photochemical isomerization into the cyclopentenone derivative (180). This occurs by amide bond fission followed by recombination within the biradical. ... 

This work focused on frans-cinnamic acid and some of its ring substituted derivatives. In homogeneous solution, the distribution of the photoproducts is dependent on the steric and electronic effects of the reagents. Irradiation of a melt or solution of frans-cinnamic acid does not cause dimerization, only isomerization (9,10). Dimers of frans-cinnamic acid can form in the solid state with retention of crystal symmetry because the monomers are held rigidly within the lattice in a uniform and repeating manner forcing an association between monomers. 

Cyanoanthracene has a 3-type crystal structure but produces a head-to-tail photodimer. Unlike cinnamic acids and their derivatives, the stereochemistry of the photoproduct dimer from anthracenes cannot often be predicted on the basis of their crystal packing [78]. 9-Methoxyanthracene has a photostable y-type crystal structure. 9-CNA host crystals doped with 9-MeOA form a solid solution, which upon irradiation yield a heterodimer (3> = 0.12). A reaction mechanism via an exciplex is proposed. The exciplex fluorescence was observed [32] ... 

In plants at the present time, SA is thought to be derived from phenylalanine, via trans-cinnamic acid (CA) and benzoic acid (BA) as shown in Fig. 2 [17-19]. In tobacco plants (Nicotiana tabaccum) the accumulation of SA has been studied in some more detail and various stress factors, such as UV-irradiation, ozone [20], hydrogen peroxide [21] and elicitation with a Phytopthora megasperma preparation [22], have been shown to induce SA accumulation. 

Cinnamic alcohol and its derivatives are starting materials for the synthesis of coumarin dyes used in food industries and as laser dyes. By irradiation at 254 nm cinnamic acid or the alcohol exhibits an extremely complex reaction spectrum using UWVis-spectroscopy. A comparison of the reaction chromatograms for different irradiation conditions in various solvents... 

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