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Figure from:A Facile and Green Synthesis of 2,4,6-Triarylpyridine Derivatives Using the Modified Mesoporous Organic Polymer Based on Calix [4]Resorcinarene: As an Efficient and Reusable Heterogeneous Acidic Catalyst

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Scheme 2. Synthesis of 2,4,6-trisubstituted pyridines

Figure 4 Synthesis of 2,4,6-trisubstituted pyridines

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Scheme 1. Synthesis of calix [4]resorcinarene 1, 3D-network polymer 2, amine-functionalized polymer 3 and the N-pr« pyl sulfamic acid functionalized polymeric catalyst 4. Immobilization of SO,;H—acidic group on highly efficient mesoporous materials provides the system that combines the advantages of homogeneous acidic catalysts with those of heterogeneous systems. In this project, attention was focused on the catalytic activity of the novel porous organic polymer based on calix [4]resorcinarene functionalized by sulfamic acid. The preparation of 2,4,6-trisubstituted pyridine derivatives served as a model reaction. The multi-step functional- ization process involved in the catalyst preparation is designated in Scheme I. 2,4,6-Triphenyipyridine (8a): white crystals, yield 10%, m.p. 134—136°C (from EtOH), MS m/z: 307
Scheme 1. Synthesis of calix [4]resorcinarene 1, 3D-network polymer 2, amine-functionalized polymer 3 and the N-pr« pyl sulfamic acid functionalized polymeric catalyst 4. Immobilization of SO,;H—acidic group on highly efficient mesoporous materials provides the system that combines the advantages of homogeneous acidic catalysts with those of heterogeneous systems. In this project, attention was focused on the catalytic activity of the novel porous organic polymer based on calix [4]resorcinarene functionalized by sulfamic acid. The preparation of 2,4,6-trisubstituted pyridine derivatives served as a model reaction. The multi-step functional- ization process involved in the catalyst preparation is designated in Scheme I. 2,4,6-Triphenyipyridine (8a): white crystals, yield 10%, m.p. 134—136°C (from EtOH), MS m/z: 307
Table 1. Elemental analysis data for polymer 2, NH,-fimctionalized polymer 3 and the sulfamic acid functionalized cata- lyst 4
Table 1. Elemental analysis data for polymer 2, NH,-fimctionalized polymer 3 and the sulfamic acid functionalized cata- lyst 4
Fig. 1. The comparative FT-IR spectra for polymeric network 2 (a), amine functionalized polymer 3 (5), catalyst 4 (c).
Fig. 1. The comparative FT-IR spectra for polymeric network 2 (a), amine functionalized polymer 3 (5), catalyst 4 (c).
Fig. 2. TGA profile of the synthesized catalyst 4.
Fig. 2. TGA profile of the synthesized catalyst 4.
Fig. 4. Nitrogen adsorption—desorption isotherm of N-pro- pyl sulfamic acid functionalized polymeric catalyst 4. methodology. The reaction was carried out under optimized conditions for a variety of substituted aro- matic aldehydes and in each case, the corresponding 2,4,6-trisubstituted pyridines were obtained in good to excellent yields. The remarkable point is that aromatic aldehydes bearing electron-withdrawing groups (such
Fig. 4. Nitrogen adsorption—desorption isotherm of N-pro- pyl sulfamic acid functionalized polymeric catalyst 4. methodology. The reaction was carried out under optimized conditions for a variety of substituted aro- matic aldehydes and in each case, the corresponding 2,4,6-trisubstituted pyridines were obtained in good to excellent yields. The remarkable point is that aromatic aldehydes bearing electron-withdrawing groups (such
Fig. 3. FE-SEM (a) and TEM (b) images of the synthesized catalyst 4.
Fig. 3. FE-SEM (a) and TEM (b) images of the synthesized catalyst 4.
Table 2. Optimization of the reaction conditions * Reported yields.
Table 2. Optimization of the reaction conditions * Reported yields.
Table 3. One-pot synthesis of 2,4,6-trisubstituted pyridines*
Table 3. One-pot synthesis of 2,4,6-trisubstituted pyridines*
Scheme 3. Plausible mechanism for the synthesis of 2,4,6-trisubstituted pyridines catalyzed by catalyst 4. * Reaction conditions: aromatic aldehyde (1 mmol), acetophenone (2 mmol), NH4,OAC (1.3 mmol), catalyst (0.05 mmol), 60—70°C solvent-free. ** Tsolated yields.
Scheme 3. Plausible mechanism for the synthesis of 2,4,6-trisubstituted pyridines catalyzed by catalyst 4. * Reaction conditions: aromatic aldehyde (1 mmol), acetophenone (2 mmol), NH4,OAC (1.3 mmol), catalyst (0.05 mmol), 60—70°C solvent-free. ** Tsolated yields.
Table 4. The comparison of this work catalyst with reported catalysts in the synthesis of triarylpyridines * 2,4,6-Triphenylpyridine as the base product in all reported yields.
Table 4. The comparison of this work catalyst with reported catalysts in the synthesis of triarylpyridines * 2,4,6-Triphenylpyridine as the base product in all reported yields.
Fig. 5. Recyclability of the catalyst 4.
Fig. 5. Recyclability of the catalyst 4.