Carboxylate complexes cinnamates

The chiral center would be installed from either Unear carbamate 15 or branched carbamate 16 via the asymmetric addition of malonate anion to the 7i-allyl Mo complex reported by Trost et al. [11] to afford the branched chiral malonate derivative 17. Decarboxylation of 17 should provide the mono-carboxylic acid 18. Masa-mune homologation with 18 affords our common precursor 14. Linear carbamate 15 was obtained from the corresponding cinnamic acid, and branched 16 was prepared in one pot from the corresponding aldehyde. 

Cinnamoyl- 6-CD (6-CiO-/3-CD) was sparingly soluble in water, although most 6-substituted 6-CDs are soluble. However, 6-CiO-/3-CD was solubilized in water on the addition of adamantane carboxylic acid or p-iodoaniline which could be included in a 6-CD cavity. These results suggest that 6-CiO-/l-CD formed supramolecular polymers in the solid state, as shown in the proposed structure in Fig. 17. The X-ray powder pattern of 6-CiO-/l-CD was similar to that of the complex between p-CD and ethyl cinnamate, in which /3-CDs formed a layer structure. The crystal structure of 6-aminocinnamoyl-/3-CD (6-aminoCiO-/l-CD) is shown in Fig. 12 and we discussed the relationship between crystal packing and the substituent group in Sect. 2.8. 

According to the results reported previously, carboxylic acids R-COOH could be conveniently employed as complexing species. Prehydrolyzed titanium butoxide (HiO/Ti =1) oligomers have been complexed with unsaturated organic acids, such as cinnamic acid (C6H5-CH=CH-COOH). Copolymerization was then performed with styrene in the presence of benzoyl peroxide. Transparent brown polymers were thus obtained. They are very stable against water and cannot be dissolved in most organic solvents [43]. 

Considering that in the latters the complexation and the reaction take place at different and rather well separated sites (substrate phenyl ring and carboxyl group respectively) one can conclude that steric hindrance plays no significant role in the complexation effect. The equilibrium constant values determined by kinetics and UV spectroscopy are in good agreement for the cinnamate ester, except for large donor molecules where This relationship remains valid for all complexes studied... 

Conductometric and n.m.r. spectrometric data have allowed calculation of formation constants (at 30 °C) of cyclohexa-amylose-4-methyl cinnamate anion complexes with 1 1 and 2 1 stoicheiometries. The data suggest direct binding of the carboxylate terminal of 4-methyl cinnamate by cyclohexa-amylose in the 1 1 complex, while the structure of the 2 1 complex involves occlusion of the anion between two cyclohexa-amylose molecules in a head-to-head orientation. 

One of the standard methods for preparing enantiomerically pure compounds is the enantioselective hydrogenation of olefins, a,/3-unsaturated amino acids (esters, amides), a,/3-unsaturated carboxylic acid esters, enol esters, enamides, /3- and y-keto esters etc. catalyzed by chiral cationic rhodium, ruthenium and iridium complexes ". In isotope chemistry, it has only been exploited for the synthesis of e.p. natural and nonnatural H-, C-, C-, and F-labeled a-amino acids and small peptides from TV-protected a-(acylamino)acrylates or cinnamates and unsaturated peptides, respectively (Figure 11.9). This methodology has seen only hmited use, perhaps because of perceived radiation safety issues with the use of hydrogenation procedures on radioactive substrates. Also, versatile alternatives are available, including enantioselective metal hydride/tritide reductions, chiral auxiliary-controlled and biochemical procedures (see this chapter. Sections 11.2.2 and 11.3 and Chapter 12). 

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