Spherical chiral covalent organic framework as well as preparation method and application thereof

Abstract

The invention relates to a spherical chiral covalent organic framework and a preparation method and application thereof.The spherical chiral covalent organic framework is a spherical chiral L-DTP-TAPB COF material containing a proline fragment, and the L-DTP-TAPB COF material has high crystallinity and spherical morphology, contains rich tetrahydropyrrole chiral catalytic sites, and has the advantages of being high in catalytic activity and high in catalytic activity. The catalyst can be applied to asymmetric aldol reaction and shows excellent catalytic activity. In catalysis of a reaction of p-nitrobenzaldehyde and cyclohexanone, the reaction yield is up to 96%, the ee value can reach 87%, and the catalytic performance of the chiral COFs and chiral metal organic framework catalysts is higher than that of most reported chiral COFs and chiral metal organic framework catalysts. And meanwhile, excellent recycling performance is also shown.

Description

Technical Field

[0001] The invention belongs to the field of organic functional materials, and in particular relates to a spherical chiral covalent organic framework and a preparation method and application thereof. Background Art

[0002] Chirality is a ubiquitous phenomenon in nature, and chiral enantiomers of different configurations often have significant differences in physical, chemical and biological properties. Among them, asymmetric catalysis provides a highly efficient, highly selective, economical and environmentally friendly method for the preparation of pure chiral compounds. Proline, as a common natural chiral small molecule, is widely used in many asymmetric synthetic reactions. However, as a small molecule catalyst, proline also has some disadvantages, such as its catalytic efficiency is not as good as that of metal organic frameworks (MOFs), organic cages and composite materials. And as a homogeneous catalytic reaction, proline catalysts also have shortcomings such as difficulty in separation and recovery. Therefore, the development of new heterogeneous chiral catalysts with high catalytic activity, stereoselectivity and excellent recyclability is a very desirable and important research topic.

[0003] Since Yaghi et al. first reported covalent organic frameworks (COFs) in 2005, COFs materials have developed rapidly in the fields of gas storage, catalysis, sensing, optoelectronics, adsorption and separation. If chiral characteristics are introduced into the COFs framework, chiral COFs materials can be constructed. This type of new chiral material has been proven to have good application prospects in the fields of chiral separation, chiral recognition and chiral optics. In particular, the application of chiral COFs in asymmetric catalysis has also attracted widespread attention. This is because chiral COFs materials have the advantages of high specific surface area, excellent chemical stability and inherent chiral characteristics. Their large pore volume and one-dimensional chiral pores are conducive to the effective entry of reactants into the contact catalytic sites and promote the transport of reactants and products. Therefore, chiral COFs materials have been shown to be used in asymmetric catalytic reactions such as aldol condensation reaction, Michael addition reaction, and Henry reaction. Although chiral COFs have made considerable research progress in the field of asymmetric catalysis, there are still problems such as long catalytic reaction time (reaction time is as long as 4-7 days), low reaction yield and stereoselectivity. It can be seen that the development of chiral COFs catalysts with high catalytic activity, stereoselectivity and excellent recyclability for the synthesis of pure chiral organic compounds is a topic worthy of research, but there are still great challenges. Summary of the invention

[0004] In view of the above problems existing in the prior art, the present invention provides a spherical chiral covalent organic framework and a preparation method and application thereof.

[0005] The present invention adopts the following technical solution: In a first aspect of the present invention, a spherical chiral covalent organic framework is provided, wherein the spherical chiral covalent organic framework is a spherical chiral covalent organic framework containing a proline fragment. L -DTP-TAPB COF material, the structural formula is shown in formula (1): , formula (1).

[0006] The second aspect of the present invention provides a method for preparing the above-mentioned spherical chiral covalent organic framework, comprising the steps of: At room temperature, acetonitrile was used as the solvent. L -DTP-Boc monomer and 1,3,5-tri(4-aminophenyl)benzene are used as raw materials and acetic acid solution is used as catalyst to obtain chiral L -DTP-TAPB-Boc COF; Finally, L -DTP-TAPB-BocCOF was treated with HCl / dioxane solution at room temperature to remove Boc to obtain the L -DTP-TAPB COF material; L The structural formula of -DTP-Boc monomer is shown in formula (2): , wherein Boc is tert-butyloxycarbonyl, formula (2).

[0007] Further, according to the molar ratio, the chiral monomer L -DTP-Boc: 1,3,5-tris(4-aminophenyl)benzene = 3: (1.5~2.5).

[0008] Furthermore, during the preparation process, the final product is controlled by adjusting the amount of catalyst acetic acid. L -Particle size of DTP-TAPB COF.

[0009] Further, according to the molar ratio, the chiral monomer L -DTP-Boc: 1,3,5-tri(4-aminophenyl)benzene: acetic acid = 3: (1.5~2.5): 18~48.

[0010] Furthermore, the concentration of the acetic acid solution is 12 M.

[0011] The monomer L -DTP-Boc was synthesized by the following method: 1) Dissolve N-tert-butyloxycarbonyl-L-proline and 2,5-dibromoaniline in CH2Cl2 solution, add EDCI, and stir at room temperature to prepare a light yellow powder compound; 2) The obtained light yellow powder compound, (4-formylphenyl)boric acid, K2CO3 and Pd(PPh3)4 were mixed to obtain a mixture, and then degassed 1,4-dioxane and H2O were added under argon protection, and then the reaction mixture was heated under reflux to prepare L -DTP-Boc monomer.

[0012] Furthermore, in the step 1), the molar ratio of N-tert-butyloxycarbonyl-L-proline: 2,5-dibromoaniline: EDCI is 6: (4-5): (5-7).

[0013] Furthermore, in the step 2), the molar ratio of light yellow powder compound: (4-formylphenyl)boric acid: K2CO3: Pd(PPh3)4 is 1:(2.8~3.2):(2.8~3.2):1.

[0014] The third aspect of the present invention provides the use of the spherical chiral covalent organic framework and the spherical chiral covalent organic framework prepared by the above preparation method in the asymmetric catalytic reaction of aldol condensation.

[0015] Preferably, the catalytic reaction is an aldol condensation reaction of a ketone and an aldehyde.

[0016] Further preferably, the catalytic reaction is an aldol condensation reaction of cyclohexanone and p-nitrobenzaldehyde, the solvent can be a common solvent such as DMF / H2O solution, pure solvent MTBE, MeOH or ACN; the additive can be acetic acid, hydroxyacetic acid, formic acid, benzoic acid or p-nitrobenzoic acid, etc.

[0017] Further preferably, the added amount of the spherical chiral covalent organic framework is 30 mol % of the aldehyde.

[0018] In one preferred embodiment, the reaction solvent is DMF / H2O, and the additive is p-nitrobenzoic acid. In one specific embodiment, the additive is p-nitrobenzoic acid, and the solvent is DMF / H2O (1 mL / 0.3 mL).

[0019] Compared with the prior art, the present invention has the following beneficial effects: The present invention synthesizes a chiral building block derived from natural proline ( L -DTP-Boc), and then reacted with 1,3,5-tri(4-aminophenyl)benzene (TAPB) under room temperature to successfully construct a new type of spherical chiral L -DTP-TAPB-Boc COF. After the Boc protecting group of the chiral COF is removed, the obtained L-DTP-TAPB COF still has high crystallinity, maintains a spherical morphology, and contains abundant tetrahydropyrrole chiral catalytic sites, which makes it useful in asymmetric aldol reactions and exhibits excellent catalytic activity. In the catalytic reaction of p-nitrobenzaldehyde with cyclohexanone, L -DTP-TAPBCOF exhibits excellent catalytic performance, with a reaction yield of up to 96% and an enantiomeric excess (ee) value of 87%, which is higher than the catalytic performance of most reported chiral COFs and chiral metal-organic frameworks (MOFs) catalysts. L -DTP-TAPB COF also exhibits excellent recyclability. After three cycles of use, its reaction yield and ee value only change slightly. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 for L -DTP-TAPB-Boc COF and L -Synthesis route of DTP-TAPB COF; Figure 2 The spherical particles prepared with 150, 200, 250 and 400 μL of acetic acid solution (12 M) as catalyst L -SEM images of DTP-TAPB-Boc COF; sizes are: (a, e) 650 nm, (b, f,) 530 nm, (c, g) 450 nm and (d, h) 430 nm, respectively; Figure 3 For (a) L -DTP-TAPB-Boc COF and (b) L -PXRD results of DTP-TAPB COF (experimental data; Pawley refined data; AA-overlapping type, orange curve; AB-staggered type, green curve; difference, yellow curve; Bragg position cyan curve; AA, top view; AB, top view); Figure 4 (a) TAPB, L -DTP-Boc, L -DTP-TAPB-Boc COF and L -FT-IR spectrum data of DTP-TAPB COF; (b) L -DTP-TAPB-Boc COF and L -Solid-state 13C CP-MAS NMR spectrum of DTP-TAPB COF; (c) L -DTP-TAPB-Boc COF and L-TGA curve of DTP-TAPB COF in nitrogen atmosphere; (d) L -Scanning electron microscopy image of DTP-TAPBCOF; Figure 5 for L -DTP-TAPB COF cyclic test results in asymmetric aldol condensation reaction. DETAILED DESCRIPTION

[0021] In order to facilitate the understanding of the present invention, the present invention will be described more fully below with reference to the relevant drawings and embodiments. Preferred embodiments of the present invention are given in the embodiments. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosure of the present invention more thorough and comprehensive.

[0022] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those generally understood by those skilled in the art of the present invention. The terms used herein in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more related listed items.

[0023] The reagents used in the following examples, unless otherwise specified, are all commercially available; the methods used in the following examples, unless otherwise specified, are all conventional methods that can be achieved. Materials and instruments 1,3,5-Tris(4-aminophenyl)benzene (TAPB) was purchased from Shanghai Kaiyulin Co., Ltd. Other materials were purchased from commercial sources and, if necessary, purified by standard techniques before use.

[0024] Liquid 1H and 13C NMR spectra were measured on a Bruker Avance NEO 600 MHz NMR instrument. Powder X-ray diffraction spectra were measured on a Rigaku Ultima IV X-ray powder diffractometer using Cu Kα (λ=1.5406 Å) radiation. Fourier transform infrared spectroscopy (FT-IR) was measured on a PerkinElmer Spectrum Two FT-IR spectrometer in Germany at 4000–400 cm -1. The thermal properties of COF were evaluated in the temperature range of 30~800℃ using a Netzsch TG 209 F3 thermal analyzer in a nitrogen atmosphere with a heating rate of 10℃ / min. Nitrogen adsorption-desorption isotherms at 77 K were measured using an American Mike ASAP 2460 specific surface area and porosity analyzer. Scanning electron microscopy (SEM) images were taken on a Carl Zeiss Gemini 500 field emission scanning electron microscope.

[0025] The analytical column TZ1 (250×4.6 mm, 5 μm) was provided by Guangdong Langsim Biochemical Technology Co., Ltd. and used amylose tris-(3,5-dimethylphenylcarbamate) coated silica gel packing. The enantiomeric excess (ee) value was determined using the TZ1 analytical column on the Shimadzu LC-20ADXR system.

[0026] Example 1 Spherical chirality L -Synthesis of DTP-TAPB COF Materials refer to Figure 1 , the embodiment of the present invention L The synthesis of -DTP-TAPB COF includes the following steps: 1.1 Synthesis of precursors The precursor synthesis is shown in formula (3): , formula (3).

[0027] 1.1.1 tert-Butyl 2-((2,5-dibromophenyl)carbamoyl)pyrrolidine-1-carboxylate (1): Will N -tert-Butyloxycarbonyl- L -Proline (1.03 g, 4.8 mmol) and 2,5-dibromoaniline (1.0 g, 4.0mmol) were dissolved in CH2Cl2 (70 mL) solution, 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDCI, 1.07 g, 5.6 mmol) was added, and the mixture was stirred at room temperature for 24 hours, added to H2O, extracted with CH2Cl2, the organic phases were combined, washed with water, dried with Na2SO4, and concentrated in vacuo. The product was purified by column chromatography to obtain compound 1 (1.48 g, yield 83%) as a light yellow powder. 1 H NMR (600 MHz, DMSO- d6), δ = 9.52 (d, 1H), 7.92 (d, 1H),7.62 (d, 1H), 7.33 (d, 1H), 4.46 – 4.32 (m, 1H), 3.43 (ddd, 1H), 3.38 – 3.34(m, 1H), 2.30 – 2.10 (m, 1H), 2.06 – 1.75 (m, 3H), 1.38 (d, 9H). 1.1.2 (S)-2-((4,4''-diformyl-[1,1':4',1''-terphenyl]-2'-yl)carbamoyl)pyrrolidine-1-carboxylic acid tert-butyl ester ( L -DTP-Boc): Compound 1 (900 mg, 2.0 mmol), (4-formylphenyl)boronic acid (900 mg, 6.0 mmol), K2CO3 (830 mg, 6.0 mmol) and Pd(PPh3)4 (233 mg, 0.2 mmol) were added to a two-necked flask. Under argon protection, a degassed mixture of 1,4-dioxane (10 mL) and H2O (2.5 mL) was added to the flask. The reaction mixture was heated to reflux at 100 °C for 24 h. After cooling to room temperature, it was first extracted with dichloromethane and saturated NaHCO3 solution. The organic phase was dehydrated with anhydrous sodium sulfate and concentrated in vacuo to obtain a crude product. The crude product was purified by silica gel column chromatography to obtain a yellow powder. L -DTP-Boc (1.72 g, yield 91%). 1 H NMR (600 MHz, DMSO- d 6), δ = 10.08 (d, 2H), 9.56 (d, 1H), 8.05 (t, 2H), 8.02 – 7.88 (m, 5H), 7.76 – 7.62 (m, 3H), 7.54 (d, 1H), 4.19(ddd, 1H), 3.34 – 3.22 (m, 2H), 2.15 – 1.98 (m, 1H), 1.87 – 1.67 (m, 3H), 1.35 (d, 9H). 1.2 Synthesis of chiral COF 1.2.1 L -DTP-TAPB-Boc COF: First, acetonitrile (5 mL), TAPB (7.0 mg, 0.02 mmol), L-DTP-Boc (14.9 mg, 0.03 mmol) was added to a 10 mL glass bottle and ultrasonicated for 10 min. Then, acetic acid solution (150-400 μL, 12 M) was added, and the mixture was vigorously shaken on a vortex mixer for 10 s and placed at room temperature for 72 h. The resulting precipitate was separated by filtration and washed with DMF, THF, methanol and acetone. Then, it was dried under vacuum at 80 °C overnight to obtain the chiral L -DTP-TAPB-Boc COF Yellow solid. Further purification L -DTP-TAPB-Boc COF was extracted with THF by Soxhlet for 24 h and dried at 80 °C in vacuo.

[0028] 1.2.2 L -DTP-TAPB COF: Will L -DTP-TAPB-Boc COF (30 mg) and 1.0 mL 4 M HCl / 1,4-dioxane were added to a 10 mL reaction bottle. The resulting suspension was stirred at room temperature for 2 h. The mixture was filtered and THF (1 × 6 mL), MeOH (containing 2% Et3N) (2 × 6 mL), H2O (1 × 6 mL), THF (1 × 6 mL) and Et2O (1 × 6 mL) were added in sequence. L -DTP-TAPB COF was further purified by Soxhlet extraction in THF for 24 h and then dried under vacuum at 80 °C to obtain a light yellow powder (22.4 mg, 75% yield).

[0029] 1.3 Results and Discussion The synthesized samples were characterized by scanning electron microscopy, powder X-ray diffraction (PXRD), FT-IR infrared, solid-state 13C CP-MAS NMR, thermal analyzer, specific surface area and porosity analyzer. L -DTP-TAPB-Boc COF and L -DTP-TAPB COF was analyzed and the results were as follows Figure 2-4 shown.

[0030] It can be seen that the present invention uses a simple amidation reaction and Suzuki reaction to synthesize a chiral proline fragment containing a natural chiral L -DTP-Boc monomer. Then, acetonitrile was used as solvent and the chiral monomer was reacted at room temperature. L -DTP-Boc and TAPB monomers are dissolved in acetonitrile solvent, acetic acid solution is used as catalyst, and the reaction is carried out at room temperature for three days to obtain L-DTP-TAPB-Boc COF. Finally, L -DTP-TAPB-Boc COF was treated with 4 M HCl / dioxane solution at room temperature to successfully obtain a chiral proline fragment. L -DTP-TAPB COF.

[0031] Moreover, through Figure 2 Spherical particles prepared with different amounts of acetic acid catalyst L -DTP-TAPB-Boc COF scanning electron microscopy images, it can be seen that the amount of catalyst affects the particle size of the resulting spherical chiral COFs. When the amount of acetic acid solution (12 M) increased from 150 μL to 400 μL, the resulting spherical chiral L -DTP-TAPB-Boc COF particle size decreased from 650 nm to 430 nm. Moreover, when 250 μL acetic acid solution (12 M) was used as the catalyst, L -DTP-TAPB-Boc COF has the best crystallinity.

[0032] Powder X-ray diffraction (PXRD) analysis was performed to determine L -DTP-TAPB-Boc COF and L -DTP-TAPBCOF crystal structure. Figure 3 As shown, L The PXRD spectrum of -DTP-TAPB-Boc COF shows obvious diffraction peaks at 2θ = 2.06° and 3.94°, which are attributed to the (100) and (200) crystal planes, respectively. L -DTP-TAPB COF has a similar PXRD spectrum, and its diffraction peaks at 2θ = 2.17° and 4.11° are also attributed to the (100) and (200) crystal planes, respectively, which indicates that L -DTP-TAPB COF has L -DTP-TAPB-Boc COF-like crystal structure. Materials Studio software was used to simulate two classic stacking models, overlapping AA stacking and staggered AB stacking, to analyze the crystal structure. The structural simulation results show that the simulated PXRD pattern generated by the AA stacking mode is similar to L -DTP-TAPB-Boc COF and L The experimental PXRD pattern of -DTP-TAPB COF is more consistent, while the staggered AB stacking pattern does not match the experimental PXRD pattern well. Pawley refinement was performed based on the AA stacking pattern, and the results showed that the refined spectrum had only a small error with the experimental PXRD spectrum (L -DTP-TAPB-BocCOF Rwp = 2.03%, Rp = 1.56%; L -DTP-TAPB COF Rwp = 3.04%, Rp = 2.36%). And the optimized unit cell parameters were obtained, L -DTP-TAPB-Boc COF results are a = b = 51.93 Å, c = 4.118 Å, α = β = 90°, γ = 120°; L -DTP-TAPB COF results are a = b = 52.09 Å, c = 3.601 Å, α = β = 90°, γ = 120°.

[0033] By FT-IR spectroscopy ( Figure 4 a) and solid state 13 C CP-MAS NMR( Figure 4 b) The analysis confirmed L -DTP-TAPB-BocCOF and L -DTP-TAPB COF chemical composition. L -DTP-Boc compared to L -DTP-TAPB-Boc COF and L -DTP-TAPB COF at 1622 cm −1 New characteristic peaks appeared at both ends, which were attributed to the stretching vibration of the imine bond C=N, indicating that both chiral COFs are imine COFs. 13 In the C CP-MAS NMR spectrum, L -DTP-TAPB-Boc and L Both chiral COFs, -DTP-TAPB, have characteristic peaks of imine carbon at 160 ppm, further confirming the formation of C=N bonds. The peaks at 170, 62, 47, 30, and 24 ppm can be attributed to the carbon atoms of the proline fragment. L -DTP-TAPB 13 In the C CP-MASNMR spectrum, the disappearance of the signal peaks at 155, 80, and 28 ppm indicated that the Boc protecting group had been successfully removed. Thermogravimetric analysis (TGA) showed that these chiral COFs exhibited good thermal stability within 300 °C ( Figure 4 c) For L -DTP-TAPB-Boc COF, the decomposition of the Boc group was observed in the range of 190–267 °C, with a weight loss of about 12.6%, which is consistent with the theoretical value (12.6%).

[0034] Scanning electron microscope (SEM) images show that the synthesized L -DTP-TAPB-Boc COF has a spherical morphology and a particle size of about 450 nm, and the L The spherical morphology of -DTP-TAPB COF is still retained, and the particle size has basically not changed (Figure 4d). The chirality of the activated sample was studied by measuring the N2 adsorption-desorption at 77 K. L -DTP-TAPB-Boc COF and L -Porosity of DTP-TAPB COF. The adsorption curves of these two chiral COFs exhibit classic type IV isotherms, indicating that they are both mesoporous materials. L -DTP-TAPB-Boc COF and L The Brunauer−Emmett−Teller (BET) surface areas of -DTP-TAPB COF are 27 and 21 m 2 g -1 .

[0035] Example 2 Asymmetric catalysis experiment Experimental methods: Asymmetric aldol condensation reaction: At room temperature, in the presence of L -DTP-TAPB COF (0.03 mmol), aldehyde (0.1 mmol) and different additives (0.03 mmol) were added to a reaction bottle with 1.0 mL DMF, 0.3 or 1 mL of H2O and 0.3 mL cyclohexanone. The mixture was stirred at room temperature for about 3 days. After the reaction was completed (monitored by TLC), the catalyst was separated by centrifugation and washed thoroughly with MeOH (10 mL) 5 times. The combined organic phases were evaporated under vacuum to obtain the crude product. Purification by silica gel column chromatography (PE / EtOAc = 4 / 1) gave the corresponding aldehyde product. The dr value was determined using 1H NMR. The ee value was determined using HPLC on a TZ1 analytical column. The yield is the isolated yield.

[0036] Cycle test experimental steps: The asymmetric aldol condensation reaction of cyclohexanone and p-nitrobenzaldehyde was tested. L -DTP-TAPBCOF is recyclable. After each cycle, it is recovered by centrifugation. L -DTP-TAPB COF, washed with THF and methanol. The obtained COF powder was dried under vacuum at room temperature and then used for the next cycle.

[0037] Table 1.L -Test of the catalytic activity of DTP-TAPB COF in asymmetric aldol condensation reaction

[0038] a Reaction conditions: aldehyde (0.1 mmol), cyclohexanone (0.3 mL), chiral COF (0.03 mmol), additive (0.03 mmol) and DMF / H2O (1 mL / 0.3 mL) were reacted at room temperature for 3 days. b Separation yield. c Confirmed by chiral HPLC. d pass 1 Confirmed by H NMR spectroscopy.

[0039] 2.1 Effects of various additives on the aldol condensation reaction It can be seen from the test results of Example 1 that L -DTP-TAPB COF has good crystallinity, certain porosity and abundant tetrahydropyrrole chiral catalytic sites. Therefore, it is further explored as a chiral catalyst for catalyzing the aldol condensation reaction of cyclohexanone and p-nitrobenzaldehyde.

[0040] Based on previous work, the yield and ee value obtained when the solvent is DMF / H2O (1 mL / 0.3 mL) are relatively high. Therefore, DMF / H2O (1 mL / 0.3 mL) is used as the solvent in the embodiment. In order to improve the reaction activity and obtain a high ee value, 30 mol% L -DTP-TAPB COF was used as the catalyst and DMF / H2O (1 mL / 0.3 mL) as the solvent to systematically evaluate the effects of various additives on the aldol condensation reaction. Acetic acid, glycolic acid, formic acid, benzoic acid, and p-nitrobenzoic acid (Table 1, entries 1-5) were used to evaluate their effects on the aldol condensation reaction.

[0041] First, the yield of the aldol condensation reaction was 75% and the ee value was 68% using acetic acid as the additive. When the additive was changed to glycolic acid, the yield increased to 88% and the ee value also increased to 82%. When formic acid was used as the additive, the catalytic ability was significantly improved, with a yield and ee value of 92% and 85%, respectively. Next, we changed the additive to benzoic acid and p-nitrobenzoic acid, and the yields were slightly improved to 95% and 96%, respectively. When the additive was benzoic acid, the ee value dropped to 77%, while the ee value of 87% was obtained under the conditions of p-nitrobenzoic acid. Finally, only trace amounts of product were observed in the absence of any additives (Table 1, entry 6).

[0042] 2.2 Effect of different solvents on catalytic reaction performance.

[0043] In order to further find better catalytic conditions and further evaluate the effects of different solvents on catalytic reaction performance, please refer to Table 2 for details.

[0044] Table 2. Tests of aldol condensation reaction in different solvents

[0045] a Reaction conditions: aldehyde (0.10 mmol), cyclohexanone (0.3 mL), L -DTP-TAPB COF (0.03 mmol), p-nitrobenzoic acid (0.03 mmol) and solvent were reacted at room temperature for 3 days. b Isolated yield. c Determined by chiral high performance liquid chromatography. d Determined by chiral HPLC.

[0046] First, the solvent ratio was changed from DMF / H2O (1 mL / 0.3 mL) to DMF / H2O (1 mL / 1 mL), and it was found that both the yield and ee value decreased significantly (Table 2, entry 1).

[0047] Subsequent attempts to use pure solvents MTBE, MeOH, and ACN resulted in the desired product after 3 days of reaction, but the yield and ee values ​​were relatively moderate (Table 2, entries 2, 3, and 4).

[0048] Finally, it was determined that when p-nitrobenzoic acid was used as the additive and the solvent was DMF / H2O (1 mL / 0.3 mL), the best asymmetric aldol condensation catalytic performance was obtained, with a yield and ee value of up to 96% and 87%, respectively.

[0049] Among all chiral COFs, the asymmetric aldol condensation of cyclohexanone and p-nitrobenzaldehyde is L -DTP-TAPB COF only needs 3 days to react, while the reported DMTA-TPB1 / n' COF (n = 2, 3 and 4) and L-HPP-TZ-NHCOF need 4 and 7 days to react, respectively, indicating that L -DTP-TAPB COF catalyst showed a more efficient asymmetric catalytic efficiency. In addition, compared with other reported chiral MOFs containing tetrahydropyrrole sites, such as S-Cd-MOF, RR-DUT-136amine, UiO-66-LP-120, UIO-68-NHPro, IRMOF-Pro, Cd-TBT and CMIL-1-Pro, the one synthesized in this work L-DTP-TAPB COF exhibits better chiral stereoselectivity.

[0050] Furthermore, under the optimal conditions determined, when p-nitrobenzoic acid was used as the additive and the solvent was DMF / H2O (1mL / 0.3 mL), the best asymmetric aldol condensation catalytic performance was obtained, with a yield and ee value of up to 96% and 87%, respectively.

[0051] Then, the invention was tested in an asymmetric aldol condensation reaction to determine the optimal conditions. L -The recyclability of DTP-TAPBCOF, the results are as follows Figure 5 As shown, it can be seen that the chirality of the present invention L -DTP-TAPB COF also exhibits excellent recyclability. After three cycles of use, its reaction yield and ee value only change slightly.

[0052] In summary, it can be seen that the scheme of the present invention synthesizes chiral proline fragments containing natural chiral proline fragments through simple amidation reaction and Suzuki reaction. L -DTP-Boc monomer. Then, at room temperature, using chiral L -DTP-Boc monomer and 1,3,5-tri(4-aminophenyl)benzene (TAPB) reacted to form a new chiral L -DTP-TAPB-Boc COF materials. L -DTP-TAPB-Boc COF, it was found that the particle size of spherical chiral COFs could be changed by adjusting the amount of catalyst. L -DTP-TAPB-Boc COF was deprotected to successfully obtain a tetrahydropyrrole-rich chiral catalytic site L -DTP-TAPB COF. L -DTP-TAPB COF can be used as a heterogeneous catalyst and exhibits excellent catalytic performance in the asymmetric aldol reaction of cyclohexanone and p-nitrobenzaldehyde. After 3 days of reaction, its conversion rate and ee value can reach as high as 96% and 87%, respectively, which are higher than the catalytic performance of most reported chiral COFs and chiral MOFs for asymmetric aldol condensation reactions.

[0053] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0054] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A spherical chiral covalent organic framework, characterized in that: The spherical chiral covalent organic framework is a spherical chiral covalent organic framework containing a proline fragment. L -DTP-TAPB COF material, the structural formula is shown in formula (1): , formula (1).

2. The method for preparing a spherical chiral covalent organic framework according to claim 1, characterized in that: Includes steps: At room temperature, acetonitrile was used as the solvent. L -DTP-Boc monomer and 1,3,5-tri(4-aminophenyl)benzene are used as raw materials and acetic acid solution is used as catalyst to obtain chiral L -DTP-TAPB-Boc COF; Finally, L -DTP-TAPB-Boc COF was treated with HCl / dioxane solution at room temperature to remove Boc to obtain the L -DTP-TAPB COF material; L The structural formula of -DTP-Boc monomer is shown in formula (2): , wherein Boc is tert-butyloxycarbonyl, formula (2).

3. The preparation method according to claim 2, characterized in that: According to the molar ratio, the chiral monomer L -DTP-Boc: 1,3,5-tris(4-aminophenyl)benzene = 3: (1.5~2.5).

4. The preparation method according to claim 2, characterized in that: During the preparation process, the final product is controlled by adjusting the amount of catalyst acetic acid. L -Particle size of DTP-TAPB COF.

5. The preparation method according to claim 4, characterized in that: According to the molar ratio, the chiral monomer L -DTP-Boc: 1,3,5-tri(4-aminophenyl)benzene: acetic acid = 3: (1.5~2.5): 18~48.

6. The preparation method according to claim 5, characterized in that: The concentration of the acetic acid solution is 12 M.

7. The preparation method according to claim 2, characterized in that: The sexual monomer L -DTP-Boc was synthesized by the following method: 1) Dissolve N-tert-butyloxycarbonyl-L-proline and 2,5-dibromoaniline in CH2Cl2 solution, add EDCI, and stir at room temperature to prepare a light yellow powder compound; 2) The obtained light yellow powder compound, (4-formylphenyl)boric acid, K2CO3 and Pd(PPh3)4 were mixed to obtain a mixture, and then degassed 1,4-dioxane and H2O were added under argon protection, and then the reaction mixture was heated under reflux to prepare L -DTP-Boc monomer.

8. The preparation method according to claim 7, characterized in that: In the step 1), according to the molar ratio, N-tert-butyloxycarbonyl- L -Proline: 2,5-dibromoaniline: EDCI = 6: (4~5): (5~7).

9. The preparation method according to claim 7, characterized in that: In the step 2), the molar ratio of pale yellow powder compound: (4-formylphenyl)boric acid: K2CO3: Pd(PPh3)4 = 1: (2.8~3.2): (2.8~3.2):

1.

10. Use of the spherical chiral covalent organic framework according to claim 1 and the spherical chiral covalent organic framework prepared by the preparation method according to any one of claims 2 to 9 in asymmetric catalytic reaction of aldol condensation.

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