Carboxylate-bearing

Gimenez S, Ponsart S, Coudane J, Vert M (2001) Synthesis, properties and in vitro degradation of carboxyl-bearing PCL. J Bioact Compat Polym 16 32 6... 

These mechanisms were finally discounted by Loftfield [3047, who used the isotopically labelled compound 15) and showed that only half of the label appeared at the carboxyl-bearing carbon in the product. A mechanism involving the reactive cyclopropanone intermediate (16) accounts for the isotopic distribution, and has gained general acceptance... 

The stereoselectivity can be explained by the occurrence of a metal-carbene intermediate in which one of the two enantiotopic faces of the trigonal carbene C-atom is shielded by the chiral ligand such that the olefin preferentially approaches from the less hindered side (Fig. 1). Consequently, the cis- and the trans-product have the same absolute configuration at the carboxyl-bearing carbon atom. 

Palladium-catalyzed cyclizations of 6,7-unsaturated carboxylates bearing an additional electron-withdrawing functionality at C-2 are achieved with aryl halides after prior treatment of the substrate with sodium hydride34-36,82. Only cyclopentanc products are obtained as mixtures of diastereomers (70 30 when Z = GOOCH, and 80 20 when Z = S02C6H5, no further structural information given). No cyclization occurs with similar 4,5-unsaturated systems. 

With the aim of elaborating polymers with an anisotropic columnar structure and containing a quantitative ratio of metal centers incorporated to study their optical properties, in situ polymerization of reactive low-molar-mass liquid crystals oriented in their mesophase has been developed. Cu, Mg, and Zn carboxylates bearing terminal acrylate functions and their subsequent... 

The absence of mesomorphism in these compounds was explained on the basis of space-filling requirements. Thus, the intercalation of pyrazine between the binuclear units creates free volume which needs to be filled to obtain a stable, condensed phase when the carboxylates bear only one chain, the interdimeric space is likely filled by the aliphatic chains belonging to a different polymeric chain, giving rise to a crossed structure which prevents the formation of a columnar mesophase. However, as will be seen later, liquid-crystalline behavior was induced in the case of mixed-valence diruthenium(II,III) carboxylate complexes with bulky equatorial Kgands bearing two and three aliphatic chains as with such ligands, it was possible to fill the interdimeric space and thus to induce a thermotropic columnar mesophase. Very recently, the synthesis, characterization, and mesomorphic properties of pyrazine-polymerized divalent rhodium benzoates have also been reported (99). " Most of these compounds exhibit columnar (Colh, Coir, CoIn) and cubic mesophases with melting transition temperatures close to, or even below, room temperature. 

DDQ was proved to be the optimal stoichiometric oxidant, and the copper salts were not necessary. A chiral organic contact ion-pair interaction was proposed for the reaction. The enamine intermediate is generated from the ketone and the primary amine moiety of the L-phenylalanine. The interae-tion between the carboxylate-bearing enamine intermediate and the imin-ium cation from the oxidation probably contributes to the diastereomerie discrimination, which furnishes this asymmetric CDC process. 

Poly(amino-acids).—The rate of hydrolysis of 4-nitrophenyl carboxylates bearing a long alkyl chain is enhanced by 55 -bis(cycloglycyl-L-hemicystylglycyl-L-histidyl-6-aminohexanyl-cis-aminoundecanoyl). The pH-rate profile for the hydrolysis of... 

A nitrile enolate can react with a carboxyl-bearing electrophile, allowing the... 

Perhaps an even more interesting class of copolymers studied was that with carboxyl bearing moieties. Copolymer XII that was synthesized using an unprotected carboxylic acid containing monomer. High molecular weight copolymers with carboxyl group content up to 50 mol% were synthesized and characterized [20]. 

Yuan described the synthesis of A -substituted 5-trifluoromethylimidazole-4-carboxylates via the base-induced cycloaddition of ethyl isocyanoacetates to trifluo-roacetimidoyl chlorides followed by aromaticity-driven intramolecular cyclization via 1,1-addition of the amino group to the isocyano functionality (Scheme 39) [53]. A wide variety of 5-trifluoromethylimidazole carboxylates, bearing an alkyl or aryl group at iV-1, was prepared using this method. Moreover, the electronic nature of the aryl group did not significantly affect the course of reaction. 

Cinnamoyl groups were introduced into the amino- and carboxyl-bearing blocks of the copolymers, because we initially intended to take advantage of the photodimerization reaction of the cinnamoyl units (Guo et al, 1996 Liu et al, 1999 Stewart and Liu, 2000) and thus stitch together the associated polymer chains. However, the amidization reaction was later found to be more efficient than the cinnamoyl dimerization reaction. Therefore, the cinnamoyl units performed no apparent function in this study. 

Carboxylic elastomers have also been prepared by the addition of a carboxyl-bearing molecule such as thioglycollie acid, maleic anhydride, or acrylic acid to rubber in solvent, on the mill, or in latex. The preparation of a carboxylic polymer from a butadiene-acrylonitrile copolymer in an internal or Banbury mixer has been mentioned in the adhesives patent literature. The carboxylation of vulcanized natural rubber and of butadiene-styrene copolymers, including reclaimed stocks of these elastomers, by treatment with maleic an-... 

In the addition of ketoesters to nitrostyrenes, two stereocenters are formed. The carboxylate-bearing center is formed as a 1 1 mixture of diastereomers, and the selectivity refers to the aryl-bearing center. 

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