Cinnamate esters, functional groups

Accordingly, the synthesis of novel cinnamate polymers with high functionality and performance is very important from the viewpoint of both polymer chemistry and practical use. Recently, we have reported the synthesis of polymers with pendant photosensitive moieties such as cinnamic ester and suitable photosensitizer groups by radical copolymerizations of 2-(cinnamoyloxy) ethyl methacrylate with photosensitizer monomers (9), by copolymerizations of chloromethylated styrene with the photosensitizer monomers followed by the reactions of the copolymers with salts of... 

In 2006, Ukai et al. proposed an interesting alternative with a rhodium(I)-catalyzed carboxylation of aryl- and alkenylboronic esters proceeding under mild conditions, and leaving ancillary reactive functional groups such as carbonyl- and cyano unreacted [51] (Scheme 5.13). Considering that organoboronic esters are easily available, and that various functional groups are tolerated, this reaction appeared to be particularly useful for the preparation of functionalized arylcarboxylic acids, such as benzoic and cinnamic acid derivatives. 

In Fig. 3 one finds a variety of functional groups that may be subdivided as follows haloalkyl groups [14-16], saturated esters (acetate [17], and benzoate [18,19]) unsaturated esters (methacrylate [19,20], acrylate [21], cinnamate [20], and others [21]) malonate and related esters [22-24] ethers and oligo(oxyethylenes) [25-28] imides [29,30] alkylsilyloxy groups [31] perfluoroalkyls [32-34] and protected carbohydrate groups [35]. Vinyl ethers with mesogenic (liquid-crystal forming) substituents will be treated separately in Section II. B.2. 

The order of reactivity of this Ru/silane combination to various functional groups differs greatly from that of its Pd/silane/ZnCh analog. While the latter is very useful for allylic reductions and essentially useless for unsaturated esters, the Ru-based system exhibits opposite reactivity. This complementary che-moselectivity is illustrated by the reduction of cinnamyl cinnamate (Scheme 59), a substrate containing both an allylic carboxylate and an a, -unsaturated ester.Each of these can be reduced separately by silicon hydride and the appropriate transition metal catalyst. 

The reaction was successfully applied to both electron-rich and electron-poor 4-nitrophenyl carboxylates among them, the conversion of the electron-deficient esters was found to be faster and more efficient. Many functional groups are tolerated on both the side of the carboxylic ester (halo, keto, formyl, ester, cyano, nitro and protected amino groups, heterocyclic and a,-unsaturated carboxylic esters) and of the alkene (electron-rich alkyl-substituted alkenes, electron-poor acrylate derivatives, trimethylvinylsilane as an ethylene surrogate). The cinnamate derivatives could become particularly useful substrates, since the availability of the synthetically equivalent vinyl halides is rather limited. In analogy to conventional Mizoroki-Heck chemistry, linear (Zi)-substituted alkenes are predominantly but not exclusively obtained. Selected examples are shown in Table 4.1. 

Examples of photosensitive functional groups which have been attached to or incorporated within polymer chains are olefinic, cinnamate, sulfoazide, azido, diazoketone. Units used for attaching or condensing photosensitive groups to polymer chains can be drawn from esters, carbonates, phosphonates, urethanes, ethers, amides and sulfonamides. 

The pendant functions listed in Figure 3 are often useful and of synthetic interest per se. For example, methacrylate and acrylate esters are polymerizable (cross-linking sites) [19-21] the cinnamate is photorespon-sive (for the photo-induced dimerization of its unsaturated groups) [20] oligo(oxyethylene) [25-27] and carbohydrate groups [35] give hydrophilic and water-soluble polymers, whereas perfluoroalkyl moieties [32-34] enhance hydrophobicity. Thus, poly(vinyl ethers) with cinnamate functions... 

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