A spherical chiral covalent organic framework and a preparation method and application thereof

Abstract

The present application relates to a kind of spherical chiral covalent organic framework and its preparation method and application, the spherical chiral covalent organic framework of proline fragment-containing spherical chiral L DTP-TAPB COF material, the L DTP-TAPB COF material has higher crystallinity, spherical morphology, and contains abundant tetrahydropyrrole chiral catalytic sites, can be applied in asymmetric aldol reaction and shows excellent catalytic activity. In the reaction of catalyzing p-nitrobenzaldehyde and cyclohexanone, the reaction yield is as high as 96%, and the ee value can reach 87%, higher than the catalytic performance of most reported chiral COFs and chiral metal organic framework catalysts. At the same time, it also presents excellent recycling property.

Description

Technical Field

[0001] The present 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 exhibit significant differences in physical, chemical, and biological properties. Asymmetric catalysis provides a highly efficient, highly selective, economical, and environmentally friendly method for the preparation of pure chiral compounds. Proline, a common natural chiral small molecule, is widely used in many asymmetric synthetic reactions. However, as a small molecule catalyst, proline also has some drawbacks, such as its catalytic efficiency being inferior to that of metal-organic frameworks (MOFs), organic cages, and composite materials. Furthermore, as a homogeneous catalytic reaction, proline catalysts are difficult to separate and recycle. Therefore, the development of novel heterogeneous chiral catalysts with high catalytic activity, stereoselectivity, and excellent recyclability is a highly desired and important research topic.

[0003] Since Yaghi et al. first reported covalent organic frameworks (COFs) in 2005, COFs have seen rapid development in applications such as gas storage, catalysis, sensing, optoelectronics, adsorption, and separation. Chiral COFs can be constructed by incorporating chirality into COF frameworks. This new class of chiral materials has demonstrated promising applications in chiral separation, chiral recognition, and chiral optics. In particular, the application of chiral COFs in asymmetric catalysis has garnered significant attention. This is due to their high surface area, excellent chemical stability, and inherent chirality. Their large pore volume and one-dimensional chiral channels facilitate the efficient access of reactants to catalytic sites, promoting the transport of reactants and products. Consequently, chiral COFs have been demonstrated to be useful in asymmetric catalytic reactions such as aldol condensation, Michael addition, and Henry reaction. Despite significant progress in asymmetric catalysis, chiral COFs still suffer from long reaction times (up to 4-7 days), low yields, and low 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 response to 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 solutions:

[0006] The first aspect of the present invention provides a spherical chiral covalent organic framework, 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):

[0007] , formula (1).

[0008] The second aspect of the present invention provides a method for preparing the above-mentioned spherical chiral covalent organic framework, comprising the steps of:

[0009] At room temperature, acetonitrile was used as solvent. L -DTP-Boc monomer and 1,3,5-tris(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 the -DTP-Boc monomer is shown in formula (2):

[0010] , where Boc is tert-butyloxycarbonyl, formula (2).

[0011] Further, according to the molar ratio, the chiral monomer L -DTP-Boc: 1,3,5-tris(4-aminophenyl)benzene = 3: (1.5~2.5).

[0012] Furthermore, during the preparation process, the final product is controlled by adjusting the amount of catalyst acetic acid. L -DTP-TAPB COF particle size.

[0013] Further, according to the molar ratio, the chiral monomer L -DTP-Boc: 1,3,5-tris(4-aminophenyl)benzene: acetic acid = 3: (1.5~2.5): 18~48.

[0014] Furthermore, the concentration of the acetic acid solution is 12 M.

[0015] The monomer L -DTP-Boc was synthesized by the following method:

[0016] 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;

[0017] 2) The obtained light yellow powder compound, (4-formylphenyl)boronic 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 the reaction mixture was heated under reflux to obtain L -DTP-Boc monomer.

[0018] Furthermore, in the step 1), the molar ratio of N-tert-butyloxycarbonyl-L-proline: 2,5-dibromoaniline: EDCI is 6: (4-5): (5-7).

[0019] Furthermore, in the step 2), the molar ratio of pale yellow powder compound: (4-formylphenyl)boric acid: K2CO3: Pd(PPh3)4 is 1: (2.8-3.2): (2.8-3.2): 1.

[0020] 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.

[0021] Preferably, the catalytic reaction is an aldol condensation reaction of a ketone and an aldehyde.

[0022] 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, glycolic acid, formic acid, benzoic acid or p-nitrobenzoic acid, etc.

[0023] Further preferably, the added amount of the spherical chiral covalent organic framework is 30 mol % of the aldehyde.

[0024] 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).

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] The present invention synthesizes chiral building blocks derived from natural proline ( L -DTP-Boc), and then reacted with 1,3,5-tris(4-aminophenyl)benzene (TAPB) under room temperature to undergo Schiff base reaction, successfully constructing a new type of spherical chiral L -DTP-TAPB-Boc COF. After removing the Boc protecting group of the chiral COF, the obtainedL -DTP-TAPB COF still has high crystallinity, maintains spherical morphology, and contains abundant tetrahydropyrrole chiral catalytic sites, which makes it applicable to asymmetric aldol reaction 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, with only slight changes in reaction yield and ee value after three cycles. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 for L -DTP-TAPB-Boc COF and L -Synthesis route of DTP-TAPB COF;

[0028] 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;

[0029] Figure 3 (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);

[0030] 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 -DTP-TAPB COF solid-state 13C CP-MAS NMR spectrum; (c)L -DTP-TAPB-Boc COF and L -DTP-TAPB COF TGA curve under nitrogen atmosphere; (d) L -Scanning electron microscopy image of DTP-TAPBCOF;

[0031] Figure 5 for L -DTP-TAPB COF cyclic test results in asymmetric aldol condensation reaction. DETAILED DESCRIPTION

[0032] To facilitate understanding of the present invention, the present invention will be described more fully below with reference to the accompanying drawings and examples. Preferred embodiments of the present invention are provided in the examples. However, the present invention can be implemented in many different forms and is not limited to the examples described herein. Rather, these examples are provided to provide a more thorough and comprehensive understanding of the disclosure of the present invention.

[0033] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this invention pertains. The terms used herein in the specification of the present invention are for the purpose of describing specific embodiments only and are not intended to limit the present invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0034] 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.

[0035] Materials and instruments

[0036] 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.

[0037] Liquid 1H and 13C NMR spectra were measured on a Bruker Avance NEO 600 MHz NMR spectrometer. 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 performed on a PerkinElmer Spectrum Two FT-IR spectrometer in Germany at 4000–400 cm -1. The thermal properties of the COF were evaluated in the temperature range of 30–800°C using a Netzsch TG 209 F3 thermal analyzer at a heating rate of 10°C / min in a nitrogen atmosphere. Nitrogen adsorption–desorption isotherms were measured at 77 K using a Mike ASAP 2460 surface area and porosity analyzer. Scanning electron microscopy (SEM) images were obtained on a Carl Zeiss Gemini 500 field emission scanning electron microscope.

[0038] The analytical column TZ1 (250 × 4.6 mm, 5 μm) was provided by Guangdong Langsim Biochemical Technology Co., Ltd. and packed with amylose tris-(3,5-dimethylphenylcarbamate)-coated silica. Enantiomeric excess (ee) values ​​were determined using the TZ1 analytical column on a Shimadzu LC-20ADXR system.

[0039] Example 1 Spherical Chirality L -Synthesis of DTP-TAPB COF Materials

[0040] refer to Figure 1 , the embodiment of the present invention L The synthesis of DTP-TAPB COF includes the following steps:

[0041] 1.1 Synthesis of precursors

[0042] The precursor synthesis is shown in formula (3):

[0043] , formula (3).

[0044] 1.1.1 tert-Butyl 2-((2,5-dibromophenyl)carbamoyl)pyrrolidine-1-carboxylate (1):

[0045] Will N -tert-Butyloxycarbonyl- L 1-Proline (1.03 g, 4.8 mmol) and 2,5-dibromoaniline (1.0 g, 4.0 mmol) were dissolved in CH2Cl2 (70 mL). 1-(3-Dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDCI, 1.07 g, 5.6 mmol) was added and stirred at room temperature for 24 hours. The mixture was then added to H2O and extracted with CH2Cl2. The combined organic phases were washed with water, dried over Na2SO4, and concentrated in vacuo. The product was purified by column chromatography to afford compound 1 (1.48 g, 83% yield) as a pale 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).

[0046] 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):

[0047] 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 mixture of degassed 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 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, 91% yield). 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).

[0048] 1.2 Synthesis of chiral COF

[0049] 1.2.1 L -DTP-TAPB-Boc COF:

[0050] 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 vial and sonicated for 10 min. Acetic acid solution (150-400 μL, 12 M) was then added and vigorously shaken on a vortex mixer for 10 s. The resulting precipitate was isolated by filtration and washed with DMF, THF, methanol, and acetone. It was then 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.

[0051] 1.2.2 L -DTP-TAPB COF:

[0052] Will L -DTP-TAPB-Boc COF (30 mg) and 1.0 mL of 4 M HCl / 1,4-dioxane were added to a 10 mL reaction vial. The resulting suspension was stirred at room temperature for 2 hours. 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).

[0053] 1.3 Results and Discussion

[0054] The synthesized products were characterized by scanning electron microscopy, powder X-ray diffraction (PXRD), FT-IR infrared and solid-state 13C CP-MAS NMR, thermal analyzer, specific surface area and porosity analyzer. L -DTP-TAPB-Boc COF and L -DTP-TAPB COF were analyzed and the results were as follows Figure 2-4 shown.

[0055] It can be seen that the embodiment of 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 L-DTP-Boc and TAPB monomers are dissolved in acetonitrile solvent and reacted at room temperature for three days with acetic acid solution as catalyst to obtain the product. 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.

[0056] Moreover, through Figure 2 Spherical particles prepared with different amounts of acetic acid catalyst L -DTP-TAPB-Boc COF scanning electron microscopy images show that the amount of catalyst affects the particle size of the resulting spherical chiral COFs. When the amount of acetic acid solution (12 M) increases from 150 μL to 400 μL, the resulting spherical chiral L The particle size of -DTP-TAPB-Boc COF decreased from 650 nm to 430 nm. Moreover, when 250 μL of acetic acid solution (12 M) was used as the catalyst, the L -DTP-TAPB-Boc COF has the best crystallinity.

[0057] Powder X-ray diffraction (PXRD) analysis was used 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 similar PXRD patterns, and the 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 similar crystal structure. Using Materials Studio software to simulate the two classic stacking models of 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 LThe 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°.

[0058] 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 bond. 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 indicates that the Boc protecting group has been successfully removed. Thermogravimetric analysis (TGA) shows that these chiral COFs exhibit 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 approximately 12.6%, which is consistent with the theoretical value (12.6%).

[0059] 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 is basically unchanged (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 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 the DTP-TAPB COFs are 27 and 21 m 2 g -1 .

[0060] Example 2 Asymmetric catalysis experiment

[0061] Experimental methods:

[0062] Asymmetric aldol condensation reaction:

[0063] At room temperature, in the presence of L A reaction flask containing 0.03 mmol of -DTP-TAPB COF, aldehyde (0.1 mmol), and various additives (0.03 mmol) was added with 1.0 mL of DMF, 0.3 or 1 mL of H2O, and 0.3 mL of cyclohexanone. The mixture was stirred at room temperature for approximately 3 days. After completion of the reaction (monitored by TLC), the catalyst was separated by centrifugation and washed thoroughly with MeOH (10 mL) five times. The combined organic phases were evaporated under vacuum to yield the crude product. Purification by silica gel column chromatography (PE / EtOAc = 4 / 1) afforded the corresponding aldol product. The dr value was determined by H NMR. The ee value was determined by HPLC on a TZ1 analytical column. Yields are reported as isolated yields.

[0064] Cycle test experimental steps:

[0065] 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 resulting COF powder was dried under vacuum at room temperature and then used for the next cycle.

[0066] Table 1. L -Test of the catalytic activity of DTP-TAPB COF in asymmetric aldol condensation reaction

[0067]

[0068] 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.

[0069] 2.1 Effects of various additives on aldol condensation reaction

[0070] It can be seen from the test results of Example 1 that the L -DTP-TAPB COF has good crystallinity, certain porosity and abundant tetrahydropyrrole chiral catalytic sites. Therefore, it was further explored as a chiral catalyst for the aldol condensation reaction of cyclohexanone and p-nitrobenzaldehyde.

[0071] Based on previous work, the yield and ee value obtained when the solvent was DMF / H2O (1 mL / 0.3 mL) were relatively high. Therefore, DMF / H2O (1 mL / 0.3 mL) was used as the solvent in the examples. In order to improve the reaction activity and obtain a high ee value, 30 mol% L Using -DTP-TAPB COF as the catalyst and DMF / H₂O (1 mL / 0.3 mL) as the solvent, the effects of various additives on the aldol condensation reaction were systematically evaluated. 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.

[0072] First, using acetic acid as an additive, the aldol condensation reaction yielded 75% and an ee of 68%. Switching to glycolic acid increased the yield to 88% and the ee to 82%. Using formic acid as an additive significantly improved the catalytic activity, achieving a yield of 92% and an ee of 85%, respectively. Next, switching to benzoic acid and p-nitrobenzoic acid resulted in slightly improved yields of 95% and 96%, respectively. With benzoic acid as the additive, the ee dropped to 77%, while using p-nitrobenzoic acid resulted in an ee of 87%. Finally, in the absence of any additive, only trace amounts of product were observed (Table 1, entry 6).

[0073] 2.2 Effect of different solvents on catalytic reaction performance.

[0074] 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.

[0075] Table 2. Aldol condensation reaction tests in different solvents

[0076]

[0077] 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 high performance liquid chromatography.

[0078] 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).

[0079] Subsequent attempts to use pure solvents MTBE, MeOH, and ACN yielded the desired product after 3 days of reaction, but the yield and ee values ​​were relatively moderate (Table 2, entries 2, 3, and 4).

[0080] 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 the yield and ee value reaching 96% and 87%, respectively.

[0081] Among all chiral COFs asymmetric catalytic aldol condensation reactions of cyclohexanone and p-nitrobenzaldehyde, 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 days 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.

[0082] 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 the yield and ee value reaching 96% and 87%, respectively.

[0083] Then, the invention was tested in an asymmetric aldol condensation reaction to determine the optimal conditions. L -DTP-TAPBCOF recyclability, 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, with only slight changes in reaction yield and ee value after three cycles.

[0084] In summary, it can be seen that 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, chiral L -DTP-Boc monomer reacted with 1,3,5-tris(4-aminophenyl)benzene (TAPB) to successfully construct 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 and a tetrahydropyrrole-rich chiral catalytic site was successfully obtained. 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.

[0085] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned 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.

[0086] The above-described embodiments merely illustrate several implementations of the present invention, and while their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention shall be determined by the appended claims.

Claims

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

2. The method for preparing a spherical chiral covalent organic framework according to claim 1, wherein: Including steps: At room temperature, acetonitrile is used as a solvent, L-DTP-Boc monomer and 1,3,5-tris(4-aminophenyl)benzene are used as raw materials, and acetic acid solution is used as a catalyst to react to obtain chiral L-DTP-TAPB-Boc COF; finally, the L-DTP-TAPB-Boc COF is subjected to a Boc removal treatment using an HCl / dioxane solution at room temperature to obtain the L-DTP-TAPB COF material; the structural formula of the L-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 L-DTP-Boc monomer: 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 particle size of the final product L-DTP-TAPB COF was controlled by adjusting the amount of catalyst acetic acid.

5. The preparation method according to claim 4, characterized in that According to the molar ratio, the L-DTP-Boc monomer: 1,3,5-tris(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 12M.

7. The preparation method according to claim 2, characterized in that The L-DTP-Boc monomer is synthesized by the following method: 1) N-tert-Butyloxycarbonyl-L-proline and 2,5-dibromoaniline were dissolved in a CH2Cl2 solution, EDCI was added, and the mixture was stirred at room temperature to obtain a light yellow powder compound; 2) The obtained light yellow powder compound, (4-formylphenyl)boronic 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 the reaction mixture was heated under reflux to prepare L-DTP-Bo c monomer.

8. The preparation method according to claim 7, characterized in that In the step 1), the molar ratio is 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 the light yellow powder compound: (4-formylphenyl)boric acid: K2CO3: Pd(PPh3)4 is 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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