Stable ketene imine pyridinium salt and preparation method thereof

Abstract

The invention relates to the technical field of organic chemical synthesis, in particular to a stable ketene imine pyridinium salt and a preparation method thereof.In the presence of a copper compound, a pyridine compound shown in the formula (II), a pyridine compound shown in the formula (II), a terminal alkynyl ketone compound shown in the formula (III) and a sulfonyl azide compound shown in the formula (IV) are subjected to a one-pot reaction, and the ketene imine pyridinium salt is obtained. The ketene imine pyridinium salt as shown in the formula (I) is obtained; according to the method, a copper compound is used as a catalyst, no oxidizing agent or reducing agent needs to be added, terminal alkyne ketone, sulfonyl azide and a pyridine compound react in an organic solvent, and ketene imine pyridinium salt is obtained through one-step reaction; the ketene imine pyridinium salt has the advantages that the ketene imine pyridinium salt is stable and can serve as a donor of a drug intermediate ketene imine, the preparation method is simple, purification is easy, the purity is high, and kilogram-level preparation can be achieved; the ketene imine pyridinium salt can be used as a stable ketene imine donor, so that the synthesis steps of the medicine are shortened, the development path of the new medicine is increased, and the ketene imine pyridinium salt has a wide medicine synthesis application prospect.

Description

Technical Field

[0001] The invention relates to the technical field of organic chemical synthesis, and in particular to a stable ketene imine pyridinium salt and a preparation method thereof. Background Art

[0002] Keteneamine is an important active intermediate and synthon for the synthesis of nitrogen-containing organic compounds. It has a long history of research and rich reactivity. It has broad application prospects in the synthesis and construction of various new nitrogen heterocycles. Keteneamine has always been a difficult and hot issue in its synthesis due to its high activity, easy self-polymerization and instability. Currently, keteneamine intermediates are mainly prepared through amides, isonitriles and alkynylamines. Some reagents that are easy to absorb moisture, unstable and highly toxic are generally used, or precious metal catalysts are used, which have the disadvantages of harsh reaction conditions, poor substrate applicability and poor functional group tolerance. Although the in situ generation of keteneamine strategy can solve the problem of preparing some unstable keteneamines and broaden the scope of substrate applicability, the raw materials that have not reacted completely, as well as the Lewis acid, catalyst, base and other reagents remaining in the reaction will affect the next reaction. Summary of the invention

[0003] The problem solved by the present invention is to provide a stable ketene imine pyridinium salt and a preparation method thereof. The ketene imine pyridinium salt has the advantages that the salt is stable and can be used as a donor of a drug intermediate ketene imine. The preparation method is simple, easy to purify, high in purity, and kilogram-level preparation can be achieved, thereby having broad application prospects in pharmaceutical synthesis.

[0004] In order to achieve the above-mentioned object, the present invention adopts the following technical scheme: a stable ketene imine pyridinium salt is prepared by reacting a pyridine compound as shown in formula (II), a terminal acetylenic ketone compound as shown in formula (III), and a sulfonyl azide compound as shown in formula (IV) in a one-pot manner in the presence of a copper compound to obtain the ketene imine pyridinium salt as shown in formula (I).

[0005]

[0006] The R1 is independently selected from any one of methyl, ethyl, C3-C8 alkyl, phenyl, 4-methylphenyl, 4-halophenyl, 4-hydroxyphenyl, 4-cyanophenyl, 4-methoxyphenyl, 4-nitrophenyl, methoxy, ethoxy, and tert-butoxy;

[0007] The R2 is independently selected from any one of methyl, ethyl, C3-C8 alkyl, 4-methylphenyl, 4-halophenyl, 4-hydroxyphenyl, 4-cyanophenyl, 4-methoxyphenyl, and 4-nitrophenyl;

[0008] The R3 is selected from any one of methyl, ethyl, dimethyl, halogen, dihalogen, and tert-butyl.

[0009] In a method for preparing a stable ketene imine pyridinium salt, a terminal acetylenic ketone compound (III) and a sulfonyl azide compound (IV) are first reacted with copper to generate a triazole intermediate A, which undergoes ring-opening rearrangement to obtain ketene imine B, which then undergoes nucleophilic addition with a pyridine compound (II) to obtain an intermediate C, and then undergoes an intramolecular cyclization reaction to obtain ketene imine pyridinium salt. The reaction mechanism is as follows:

[0010]

[0011] Preferably, the copper compound includes any one or more of copper acetate (Cu(OAc)2), copper chloride (CuCl2), copper bromide (CuBr2), copper acetylacetonate (Cu(acac)2), copper trifluoroacetate (Cu(TFA)2), copper trifluoromethanesulfonate (Cu(OTf)2), copper oxide (CuO), cuprous iodide (CuI), cuprous bromide (CuBr), cuprous chloride (CuCl), copper thiophene-2-carboxylate (CuTc), and cuprous acetate (CuOAc), preferably cuprous chloride (CuCl).

[0012] Preferably, the reaction is carried out in an organic solvent, which includes any one or more of acetonitrile, dichloroethane, N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMA), dichloromethane, chlorobenzene, benzene, xylene, dimethyl sulfoxide (DMSO), and N-methylpyrrolidone (NMP), preferably dichloromethane.

[0013] Preferably, the molar ratio of the compounds (II), (III), (VI) to the copper compound is 1:1-3:1-3:0.05-0.2, for example, 1:1.5:1.5:0.05, 1:2:2:0.1 or 1:3:3:0.2, preferably 1:2:2:0.1.

[0014] Preferably, the molar ratio of the pyridine compound (II), the terminal acetylenic ketone compound (III), and the sulfonyl azide compound (IV) is 1:1-3:1-3, for example, 1:1:1, 1:1.5:1.5, or 1:3:3.

[0015] Preferably, the ratio of the pyridine compound (II) to the solvent is 1, mmol:5-15, mL, for example, 1, mmol:5, mL, 1, mmol:8, mL, 1, mmol:10, mL, 1, mmol:12, mL or 1, mmol:15, mL.

[0016] Preferably, the reaction temperature is room temperature, and the reaction time is 0.5-8 hours, for example, 0.5 hours, 1 hour, 2 hours, 4 hours or 8 hours.

[0017] Preferably, after the reaction is completed, a post-treatment step is further included, and the post-treatment includes any one of filtration, crystallization, recrystallization, column chromatography purification or a combination of multiple treatment methods;

[0018] As an exemplary post-treatment method, for example, the reaction can be filtered after completion, the filter residue is washed with a mixture of petroleum ether and ethyl acetate, and vacuum dried to obtain the target product.

[0019] The beneficial effects of the present invention are as follows: by selecting a suitable reaction substrate and reacting under the action of a suitable catalyst, a pyridinium salt of enone imine of formula (I) is obtained through a one-pot reaction, the reaction conditions are simple, purification is easy, and a good yield is achieved, a new donor is provided for the preparation of enone imine, and the present invention has good application value and potential in industrial and drug synthesis. DETAILED DESCRIPTION

[0020] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0021] Embodiment 1

[0022] A stable ketene imine pyridinium salt is prepared by reacting a pyridine compound as shown in formula (II), a terminal acetylenic ketone compound as shown in formula (III), and a sulfonyl azide compound as shown in formula (IV) in a one-pot manner in the presence of a copper compound to obtain the ketene imine pyridinium salt as shown in formula (I).

[0023]

[0024] The R1 is independently selected from any one of methyl, ethyl, C3-C8 alkyl, phenyl, 4-methylphenyl, 4-halophenyl, 4-hydroxyphenyl, 4-cyanophenyl, 4-methoxyphenyl, 4-nitrophenyl, methoxy, ethoxy, and tert-butoxy;

[0025] The R2 is independently selected from any one of methyl, ethyl, C3-C8 alkyl, 4-methylphenyl, 4-halophenyl, 4-hydroxyphenyl, 4-cyanophenyl, 4-methoxyphenyl, and 4-nitrophenyl;

[0026] The R3 is selected from any one of methyl, ethyl, dimethyl, halogen, dihalogen, and tert-butyl.

[0027] A method for preparing a stable ketene imine pyridinium salt, the specific preparation method being:

[0028] Add the compounds of the above formula (II), (III), (IV) and copper acetate (Cu(OAc)2) to acetonitrile, then heat to 60°C and stir at this temperature for 4 hours;

[0029] The molar ratio of the compound of formula (II) to cuprous iodide (CuI) is 1:0.1; the molar ratio of the compound of formula (II) to the compounds of formula (III) and (IV) is 1:1.5:1.5; the ratio of the compound of formula (II) in millimole (mmol) to acetonitrile in milliliter (ml) is 1:8;

[0030] After the reaction is complete, the reaction system is naturally cooled to room temperature, a mixture of ethyl acetate and saturated brine in an equal volume ratio is added, and the mixture is shaken and extracted for 2-4 times. The organic layer is collected, dried, and concentrated by rotary evaporation to obtain a crude product. The crude product is chromatographed on a 200-300 mesh silica gel column using a mixture of ethyl acetate and petroleum ether as an eluent, wherein the volume ratio of ethyl acetate to petroleum ether is 1:5, thereby obtaining a white product, ketene imine pyridine salt, with a yield of 96%; a compound of formula (I) (C17H18N2O4S);

[0031] Nuclear magnetic resonance of the compound of formula (II): 1H, NMR, (400, MHz, CDCl3), δ, 8.06-8.02, (m, 2H), 8.01-7.87, (m, 2H), 7.47-7.20, (s, 5H), 5.52, (s, 1H), 3.86, (s, 2H), 2.63, (s, 3H), 1.12, (s, 3H);

[0032] 13C, NMR, (100, MHz, CDCl3), δ, 166.6, 154.7, 152.4, 143.8, 140.9, 137.8, 128.8, (3C), 128.7, (2C), 125.9, (2C), 87.2, 59.4, 20.1, 14.4.

[0033] Embodiment 2

[0034] A stable ketene imine pyridinium salt is prepared by reacting a pyridine compound as shown in formula (II), a terminal acetylenic ketone compound as shown in formula (III), and a sulfonyl azide compound as shown in formula (IV) in a one-pot manner in the presence of a copper compound to obtain the ketene imine pyridinium salt as shown in formula (I).

[0035]

[0036] The R1 is independently selected from any one of methyl, ethyl, C3-C8 alkyl, phenyl, 4-methylphenyl, 4-halophenyl, 4-hydroxyphenyl, 4-cyanophenyl, 4-methoxyphenyl, 4-nitrophenyl, methoxy, ethoxy, and tert-butoxy;

[0037] The R2 is independently selected from any one of methyl, ethyl, C3-C8 alkyl, 4-methylphenyl, 4-halophenyl, 4-hydroxyphenyl, 4-cyanophenyl, 4-methoxyphenyl, and 4-nitrophenyl;

[0038] The R3 is selected from any one of methyl, ethyl, dimethyl, halogen, dihalogen, and tert-butyl.

[0039] A method for preparing a stable ketene imine pyridinium salt, the specific preparation method being:

[0040]

[0041] Add the compounds of the above formula (II), (III), (IV) and copper acetate (Cu(OAc)2) to dichloromethane, then heat to 80°C and stir at this temperature to react for 8 hours;

[0042] The molar ratio of the compound of formula (II) to copper acetate (Cu(OAc)2) is 1:0.5; the molar ratio of the compound of formula (II) to the compounds (III) and (IV) is 1:2:2; the ratio of the compound of formula (II) in millimole (mmol) to dichloromethane in milliliters (ml) is 1:10;

[0043] After the reaction is complete, the reaction system is naturally cooled to room temperature, and a mixture of ethyl acetate and saturated brine in an equal volume ratio is added, and the mixture is shaken and extracted for 2-4 times. The organic layer is collected, dried, and concentrated by rotary evaporation to obtain a crude product. The crude product is chromatographed on a 200-300 mesh silica gel column using a mixture of ethyl acetate and petroleum ether as an eluent, wherein the volume ratio of ethyl acetate to petroleum ether is 1:6, thereby obtaining a white product 3-hydroxypyrrolidine diastereomer with a total yield of 92%. Compound of formula (C19H22N2O4S);

[0044] Nuclear magnetic resonance of the compound of formula (II): 1HNMR δ8.01 (t, J = 7.9 Hz, 1H), 7.97-7.83 (m, 2H), 7.45 (d, J = 7.9 Hz, 2H), 7.28 (d, J = 7.9 Hz, 2H), 5.54 (s, 1H), 3.85 (q, J = 7.1 Hz, 2H), 2.63 (s, 6H), 2.41 (s, 3 H), 1.13 (t, J=7.1Hz, 3H).13C{1H}NMR (151MHz) δ166.8, 154.8, 152.6, 143.4, 141.8, 129.5, 129.0(2C), 128.6, 127.2(2C), 125.7(2C), 86.2, 59.1, 21.5, 20.0(2C), 14.3.

[0045] Embodiment 3

[0046] A stable ketene imine pyridinium salt is prepared by reacting a pyridine compound as shown in formula (II), a terminal acetylenic ketone compound as shown in formula (III), and a sulfonyl azide compound as shown in formula (IV) in a one-pot manner in the presence of a copper compound to obtain the ketene imine pyridinium salt as shown in formula (I).

[0047]

[0048] The R1 is independently selected from any one of methyl, ethyl, C3-C8 alkyl, phenyl, 4-methylphenyl, 4-halophenyl, 4-hydroxyphenyl, 4-cyanophenyl, 4-methoxyphenyl, 4-nitrophenyl, methoxy, ethoxy, and tert-butoxy;

[0049] The R2 is independently selected from any one of methyl, ethyl, C3-C8 alkyl, 4-methylphenyl, 4-halophenyl, 4-hydroxyphenyl, 4-cyanophenyl, 4-methoxyphenyl, and 4-nitrophenyl;

[0050] The R3 is selected from any one of methyl, ethyl, dimethyl, halogen, dihalogen, and tert-butyl.

[0051] A method for preparing a stable ketene imine pyridinium salt, the specific preparation method being:

[0052]

[0053] Add the compound of formula (II) and (III) and cuprous iodide (CuI) to DMF, then heat to 100°C, stir and seal the mixture for 2 hours;

[0054] The molar ratio of the compound of formula (II) to cuprous iodide (CuI) is 1:0.15; the molar ratio of the compound of formula (II) to the compound of formula (III) is 1:1.2:1.2; the ratio of the compound of formula (II) in millimole (mmol) to dichloromethane in milliliter (ml) is 1:8;

[0055] After the reaction is complete, the reaction system is naturally cooled to room temperature, and a mixture of ethyl acetate and saturated brine in an equal volume ratio is added, and the mixture is shaken and extracted for 2-4 times. The organic layer is collected, dried, and concentrated by rotary evaporation to obtain a crude product. The crude product is chromatographed on a 200-300 mesh silica gel column using a mixture of ethyl acetate and petroleum ether as an eluent, wherein the volume ratio of ethyl acetate to petroleum ether is 1:8, thereby obtaining a white product 3-hydroxypyrrolidine diastereomer with a total yield of 88%. Compound of formula (I) (C17H17ClN2O4S);

[0056] Nuclear magnetic resonance of the compound of formula (I): 1HNMR (400 MHz, CDCl3) δ8.12 (d, J=8.2 Hz, 1H), 8.06-8.02 (m, 1H), 8.00-7.76 (m, 2H), 7.46-7.21 (s, 4H), 5.40 (s, 1H), 3.80 (s, 2H), 2.61 (s, 3H), 1.13 (s, 3H);

[0057] 13CNMR (100MHz, CDCl3) δ167.1, 155.2, 153.4, 144.2, 142.4, 136.6, 127.4(2C), 129.5(2C), 126.6(2C), 88.4, 60.2, 22.3, 15.6.

[0058] Embodiment 4

[0059] A stable ketene imine pyridinium salt is prepared by reacting a pyridine compound as shown in formula (II), a terminal acetylenic ketone compound as shown in formula (III), and a sulfonyl azide compound as shown in formula (IV) in a one-pot manner in the presence of a copper compound to obtain the ketene imine pyridinium salt as shown in formula (I).

[0060]

[0061] The R1 is independently selected from any one of methyl, ethyl, C3-C8 alkyl, phenyl, 4-methylphenyl, 4-halophenyl, 4-hydroxyphenyl, 4-cyanophenyl, 4-methoxyphenyl, 4-nitrophenyl, methoxy, ethoxy, and tert-butoxy;

[0062] The R2 is independently selected from any one of methyl, ethyl, C3-C8 alkyl, 4-methylphenyl, 4-halophenyl, 4-hydroxyphenyl, 4-cyanophenyl, 4-methoxyphenyl, and 4-nitrophenyl;

[0063] The R3 is selected from any one of methyl, ethyl, dimethyl, halogen, dihalogen, and tert-butyl.

[0064] A method for preparing a stable ketene imine pyridinium salt, the specific preparation method being:

[0065]

[0066] Add the compounds of the above formula (II), (III), (IV) and cuprous iodide (CuI) to DMF, then heat to 100svbb°C, stir and seal to react for 2 hours;

[0067] The molar ratio of the compound of formula (II) to cuprous iodide (CuI) is 1:0.15; the molar ratio of the compound of formula (II) to the compound of formula (III) is 1:1.2:1.2; the ratio of the compound of formula (II) in millimole (mmol) to dichloromethane in milliliter (ml) is 1:8;

[0068] After the reaction is complete, the reaction system is naturally cooled to room temperature, and a mixture of ethyl acetate and saturated brine in an equal volume ratio is added, and the mixture is shaken and extracted for 2-4 times. The organic layer is collected, dried, and concentrated by rotary evaporation to obtain a crude product. The crude product is chromatographed on a 200-300 mesh silica gel column using a mixture of ethyl acetate and petroleum ether as an eluent, wherein the volume ratio of ethyl acetate to petroleum ether is 1:8, thereby obtaining a white product 3-hydroxypyrrolidine diastereomer with a total yield of 88%. Compound of formula (I) (C21H26N2O4S);

[0069] Nuclear magnetic resonance of the compound of formula (I): 1HNMR (400MHz, CDCl3) δ8.15 (s, 1H), 8.08-8.02 (m, 1H), 7.49 (s, 2H), 7.40-7.34 (m, 2H), 7.27 (s, 1H), 5.48 (s, 1H), 3.84 (s, 2H), 2.73 (s, 3H), 2.69 (s , 6H), 1.12 (s, 3H); 13CNMR (100MHz, CDCl3) δ166.8, 154.7, 152.6, 143.7, 140.6, 1 37.2, 132.1, 131.6, 129.1, 125.9(3C), 125.6, 86.8, 59.2, 20.8, 20.1(2C), 14.4.

[0070] Embodiment 5

[0071] A stable ketene imine pyridinium salt is prepared by reacting a pyridine compound as shown in formula (II), a terminal acetylenic ketone compound as shown in formula (III), and a sulfonyl azide compound as shown in formula (IV) in a one-pot manner in the presence of a copper compound to obtain the ketene imine pyridinium salt as shown in formula (I).

[0072]

[0073] The R1 is independently selected from any one of methyl, ethyl, C3-C8 alkyl, phenyl, 4-methylphenyl, 4-halophenyl, 4-hydroxyphenyl, 4-cyanophenyl, 4-methoxyphenyl, 4-nitrophenyl, methoxy, ethoxy, and tert-butoxy;

[0074] The R2 is independently selected from any one of methyl, ethyl, C3-C8 alkyl, 4-methylphenyl, 4-halophenyl, 4-hydroxyphenyl, 4-cyanophenyl, 4-methoxyphenyl, and 4-nitrophenyl;

[0075] The R3 is selected from any one of methyl, ethyl, dimethyl, halogen, dihalogen, and tert-butyl.

[0076] A method for preparing a stable ketene imine pyridinium salt, the specific preparation method being:

[0077]

[0078] Add the compounds of the above formula (II), (III), (IV) and cuprous iodide (CuI) to a dimethyl sulfoxide solvent, then heat to 120°C and stir in a sealed container for reaction for 12 hours at this temperature;

[0079] Wherein, the molar ratio of the compound of formula (II) to cuprous iodide (CuI) is 1:0.25; the molar ratio of the compound of formula (II) to the compound of formula (III) is 1:2.5:2.5; the ratio of the compound of formula (II) in millimole (mmol) to dichloromethane in milliliter (ml) is 1:12;

[0080] After the reaction is complete, the reaction system is naturally cooled to room temperature, and a mixture of ethyl acetate and saturated brine in an equal volume ratio is added, and the mixture is shaken and extracted for 2-4 times. The organic layer is collected, dried, and concentrated by rotary evaporation to obtain a crude product. The crude product is chromatographed on a 200-300 mesh silica gel column using a mixture of ethyl acetate and petroleum ether as an eluent, wherein the volume ratio of ethyl acetate to petroleum ether is 1:7, thereby obtaining a white product 3-hydroxypyrrolidine diastereomer with a total yield of 86%. Compound of formula (I) (C26H26N2O5S);

[0081] Nuclear magnetic resonance of the compound of formula (I): 1HNMR (400 MHz, CDCl3) δ8.06-8.02 (m, 1H), 8.00 (s, 2H), 7.47 (s, 4H), 5.52 (s, 1H), 3.86 (s, 2H), 2.63 (s, 6H), 1.12 (s, 3H); 13C NMR (100 MHz, CDCl3) δ166.6, 154.7, 152.4, 143.8, 140.9, 137.8, 128.8 (3C), 128.7 (2C), 125.9 (2C), 87.2, 59.4, 20.1 (2C), 14.4.

[0082] In summary, it can be clearly seen from all the above embodiments that when the method of the present invention is adopted, the compounds of formula (III) and (IV) can react smoothly with the compound (V) to obtain the target product with good yield and simple post-treatment. The achievement of these effects depends on the comprehensive synergistic effect of multiple factors such as catalysts and solvents.

[0083] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A stable ketene imine pyridinium salt, characterized in that: In the presence of a copper compound, a pyridine compound as shown in formula (II), a terminal acetylenic ketone compound as shown in formula (III), and a sulfonyl azide compound as shown in formula (IV) are reacted in one pot to obtain an enone imine pyridinium salt as shown in formula (I). The R1 is independently selected from any one of methyl, ethyl, C3-C8 alkyl, phenyl, 4-methylphenyl, 4-halophenyl, 4-hydroxyphenyl, 4-cyanophenyl, 4-methoxyphenyl, 4-nitrophenyl, methoxy, ethoxy, and tert-butoxy; The R2 is independently selected from any one of methyl, ethyl, C3-C8 alkyl, 4-methylphenyl, 4-halophenyl, 4-hydroxyphenyl, 4-cyanophenyl, 4-methoxyphenyl, and 4-nitrophenyl; The R3 is selected from any one of methyl, ethyl, dimethyl, halogen, dihalogen, and tert-butyl.

2. The method for preparing a stable ketene imine pyridinium salt according to claim 1, characterized in that: First, the terminal acetyl ketone compound (III) reacts with the sulfonyl azide compound (IV) under the catalysis of copper to generate the triazole intermediate A, which undergoes ring-opening rearrangement to obtain the enone imine B, which then undergoes nucleophilic addition with the pyridine compound (II) to obtain the intermediate C, followed by an intramolecular cyclization reaction to obtain the enone imine pyridinium salt. The reaction mechanism is as follows:

3. The method for preparing a stable ketene imine pyridinium salt according to claim 1, characterized in that: The copper compound includes any one or more of copper acetate, copper chloride, copper bromide, copper acetylacetonate, copper trifluoroacetate, copper trifluoromethanesulfonate, copper oxide, cuprous iodide, cuprous bromide, cuprous chloride, copper thiophene-2-carboxylate, and cuprous acetate.

4. The method for preparing a stable ketene imine pyridinium salt according to claim 3, characterized in that: The reaction is carried out in an organic solvent, and the organic solvent includes any one or more of acetonitrile, dichloroethane, N,N-dimethylformamide, N,N-dimethylacetamide, dichloromethane, chlorobenzene, benzene, xylene, dimethyl sulfoxide, and N-methylpyrrolidone.

5. The method for preparing a stable ketene imine pyridinium salt according to claim 1, characterized in that: The molar ratio of the compounds (II), (VI), (V) to the copper compound is 1:1-3:1-3:0.05-0.

2.

6. A stable ketene imine pyridinium salt and a preparation method thereof according to claim 1, characterized in that: The ratio of the pyridine compound to the organic solvent is 1, mmol: 5-15, mL.

7. A stable ketene imine pyridinium salt and a preparation method thereof according to claim 1, characterized in that: The reaction temperature is room temperature.

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