High exo-content and yield of the product cannot be explained only by exoselective hydrolysis as reported by of Niwayama and Hiraga. Previously we reported exo-selective synthesis of 5-norbornene-2-carboxylic acid from endo-rich carboxylate in order to investigate the effect of endo/exo ratio on performance of photoresist prepared from tert-butyl 5- norbornene-2-carboxylate. Because of high cost of these reactions, practically pure exo-isomer is obtained by removing of endo-isomer through lactonization. Avenoza and Kawamura reported asymmetric Diels-Alder reaction of cyclopentadiene and chiral dienophile. Fraile reported asymmetric Diels-Alder reaction of furan with chiral acrylate. reported asymmetric Diels-Alder reaction by using antibody catalyst. Some of exo-selective syntheses of norbornene derivatives have been reported. As can be seen in the two examples, exo-selective synthesis of norbornene carboxylic acid derivatives is of importance from the practical viewpoint. In the case of photoresist monomer synthesis, endo-isomer provides undesired lactone by intramolecular cycloaddition to result in a low yield of desired photoresist monomer. Exo-isomer of norbornene carboxylic ester shows higher reactivity in living ROMP than endo-isomer. Norbornene derivatives are also useful as monomers or intermediates for photoresist materials. Polynorbornenes, which can be synthesized by vinyl polymerization or ring-opening metathesis polymerization (ROMP) of norbornene derivatives, show high thermal stability and transparency, and are useful for optical applications such as optical fibers, disk, lens and displays. It is well-known that Diels-Alder cycloaddiotion is endoselective due to secondary orbital overlap, and the selectivity is enhanced by Lewis acid. 2-Substituted norbornene compounds can be conventionally obtained by Diels-Alder cycloaddition between cyclopentadiene and acrylic compounds. The plausible reaction mechanism involving rapid equilibrium of thermodynamic isomerization and kinetically preferred hydrolysis of exo ester is proposed.ĥ-Norbornene-2-carboxylic acid and its derivatives are important as intermediates of pharmaceutically and biologically active compounds and monomers for advanced polymeric materials. Whereas the use of excess amount of water led to rapid and non-selective hydrolysis affording high endo content of the product. The exo selectivity for resulting NBCA was improved when the hydrolysis was conducted with equimolar water at room temperature in the presence of the stronger base (tBuONa) (endo/exo: 18/82). The hydrolyses of endo-rich MNBC (endo/exo = 80/20) under various conditions were carried out. Preliminary studies on base promoted isomerization of methyl 5-norbornene-2-carboxylate (MNBC) revealed that rapid isomerization was accomplished with sodium tert-butoxide (tBuONa), and the exo-content at the equilibrium was ca. Simple and efficient stereo-selective synthesis of exo-5-norbornene-2-carboxylic acid (NBCA) is reported. Keywords: Stereo-Selective Synthesis 2-Substituted Norbornene Isomerization Kinetically Selective Hydrolysis Graduate School of Bio-Applications and Systems Engineering, Tokyo University of Agriculture and Technology, Tokyo, JapanĮmail: Janurevised Februaccepted February 25, 2012
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