Cinnamic acid derivative, photochem

Polyesters of cinnamic acid derivatives used as photorresists, whose main photochemical feature is [2tt -I- 2-77] dimerization, are reported to experiment PFR along with trans-cis isomerization as secondary reactions [234-240]. 

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-... 

The photochemical desulfurization of 4-amino-l,3 tWazolium salts 224 or mesoionic 2,3,5-triaryl-l,3-thiazolium-4-olates 228 in the presence of trialkylphosphite or trialkylphosphine, affording ring-opened cinnamic acid derivatives 226 [88JCS(P1)189] and 230 (83JHC245) or quinolinones 231 [88JCS(PI)189] is assumed to proceed via intermediate azetine derivatives 225 and 229, respectively (Scheme 62). 

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. " ... 

In actual photochemical polymerizations, on the other hand, sterically pure products can occasionally be produced, since here every propagation step must be photochemically controlled. A prerequisite for this, however, is that the density difference between polymer and monomer crystals be very small. An example of this is the polymerization of cinnamic acid derivatives, which, according to the crystal structure of the monomer, lead to a- or j3-truxinic acid products ... 

It is important to point out that it is possible to carry out photochemical transformations in mild conditions in order to maintain the activity of the biological molecules or encapsulated cells. For such purposes the photo-transformation of HA is carried out in the presence of several compounds, such as cinnamic acid derivatives, coumarin, thymine, methacrylic anhydride, glycidyl methacrylate and styrene. Figure 5.10 shows how methacrylic esters undergo photopolymerization in the presence of HA to form a grafted polymer [46]. 

Yamamoto, M., Furuyama, N., and Itoh, K., Hydrogen bonding and photochemical processes of a cinnamic acid derivative in Langmuir-Blodgett films,/. Phys. Chem., 100,18483,1996. 

The photochemical behavior of cinnamic acid derivatives 32a-g (Scheme 14) has been investigated by employing y-CD or CB [8] as photodimerization templates [76,81]. Solid-state complexes of 32a-g with y-CD cannot be prepared by the... 

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. 

Cinnamates occupy an important place in the history of photochemistry. Schmidt and his co-workers [18] used the solid state photochemistry of cinnamic acid and its derivatives to develop the idea of topochemical control of photochemistry in the crystalline state. Minsk [19] developed poly(vinyl cinnamate) as the first polymer for photoimaging. The cinnamate chromophore is still commonly incorporated in photopolymers of all types, including LC polymers, to enable them to be photochemically cross-linked [20], and a number of reports of the photochemistry of such MCLC and SCLC polymers are summarized below. 

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-... 

The photochemical (2 + 2)-dimerization between raw -cinnamates contained within a photocrosslinkable dendrimer has been reported. The cycloaddition is accompanied by trans-cis isomerism. The (3-form of raw -2,4-dichlorocinnamic acid dimerizes on irradiation to give the (3-truxinic acid derivative in a first-order kinetic process. Others have studied the influence of substituents on the aryl ring of cinnamic acid, with a view to control crystal engineering. Ito et alJ have reported the photodimerization in the solid state of cinnamic acids (1) as their... 

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. 

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