Reductive synthesis, polymer-immobilized

Combinatorial parallel synthesis of head-to-tail bisbenzimidazoles 41 has been performed using polymer-immobilized 1,2-diaminobenzenes (Fig. 2). The PEG-bound diamines were hf-acylated at the primary aromatic amino group with 4-fluoro-3-nitrobenzoic acid. The substituted amides were cy-clized to benzimidazoles under acidic conditions. Successive reduction and cyclization with various aldehydes yielded 5-(benzimidazol-2-yl)benzimid-azoles. Finally, the desired products 41 were released from the polymer support to afford the bisbenzimidazoles in good yields and with high purity [46]. 

D. Synthesis of Polymer-Immobilized Nanoparticles by Reductive Methods... 

The ozonolysis of cyclic alkenes in protic solvents followed by reductive decomposition of the hydroperoxides formed is a classical method for dialdehydes synthesis [70], This method is applied for the preparation of 3-ethoxycarbonylglutaric dialdehyde by ozonolysis of ethyl 3-cyclo-pentenecarboxylate. The dialdehyde is an intermediate in the sjmthesis of dolazetrone mesitilate, which is an active medical substance in AN-ZEMET anti-emetik. Zn/AcOH, phosphines, amines and sulfides such as 3, 3 -thiodipropionic acid and its salts are the most suitable redactors for this system. Their efficiency is comparable to that of methyl sulphide but without its shortcomings. The polymer immobilized 3,3 -thiodipropionic acid is also very active in this reduction reaction [70]. 

Yoshida and coworkers described the control of free-radical reactivity during reduction by dynamic coordination pyridylethyl-substituted tin hydrides (123, 124) appear to selectively reduce alkyl iodides and bromides in preference to chlorides, as illustrated in equations 102 and 103805. Dumartin and his associates reported the immobilization of substrates required for the synthesis of 17a-(iodovinyl)estradiol through hydrostannylation with a polymer-supported tin hydride (equation 104)803. Baba and coworkers described the use of Bu2SnIH in the synthesis of nitrogen heterocycles (e.g. 125) (equation 105)804. 

Phase transfer catalysts have been grafted onto the surface of porous capsules to facilitate product purification after reaction, and many types of immobilized cells, mycelia, enzymes, and catalysts have been encapsulated in polymers such as PDMS, PVA, or cellulose. In the specific case of PVA, they are named Lenti-kats, as commercialized by Genialab and used for nitrate and nitrite reduction and in the synthesis of fine chemicals. These beads show minimized diffusion limitations caused by the swelling of the polymeric environment under the reaction conditions. To avoid catalyst leaching, enlargement can be realized by linking them to, e.g., chitosan. 

Kunz and coworkers reported the application of an immobilized chiral galacto-sylamine in diastereoselective synthesis of piperidine and amino acid derivates [14]. Preparation of the galactosylamine auxiliary from 1,6-hexandiol and P-D-galactopyranosyl azide (1) required a six-step synthesis protocol. The precursor 2 was loaded onto a polymer bound silane. Reduction of the azide function gave the corresponding immobilized amine 3 (Scheme 12.2). 

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