CN118063418A - Preparation method of 2-methyl-7-nitrobenzofuran-4-formic acid - Google Patents
Preparation method of 2-methyl-7-nitrobenzofuran-4-formic acid Download PDFInfo
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- CN118063418A CN118063418A CN202410214794.5A CN202410214794A CN118063418A CN 118063418 A CN118063418 A CN 118063418A CN 202410214794 A CN202410214794 A CN 202410214794A CN 118063418 A CN118063418 A CN 118063418A
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- -1 2-methyl-7-nitrobenzofuran-4-formic acid Chemical compound 0.000 title claims abstract description 25
- 238000002360 preparation method Methods 0.000 title claims abstract description 23
- 238000006243 chemical reaction Methods 0.000 claims abstract description 29
- 229940125782 compound 2 Drugs 0.000 claims abstract description 22
- 238000000034 method Methods 0.000 claims abstract description 14
- 229940125904 compound 1 Drugs 0.000 claims abstract description 12
- 229940126214 compound 3 Drugs 0.000 claims abstract description 6
- 238000005695 dehalogenation reaction Methods 0.000 claims abstract description 6
- 230000026030 halogenation Effects 0.000 claims abstract description 6
- 238000005658 halogenation reaction Methods 0.000 claims abstract description 6
- 238000006460 hydrolysis reaction Methods 0.000 claims abstract description 6
- 238000007363 ring formation reaction Methods 0.000 claims abstract description 5
- 230000007062 hydrolysis Effects 0.000 claims abstract description 3
- 239000007858 starting material Substances 0.000 claims abstract description 3
- XEKOWRVHYACXOJ-UHFFFAOYSA-N Ethyl acetate Chemical compound CCOC(C)=O XEKOWRVHYACXOJ-UHFFFAOYSA-N 0.000 claims description 54
- 239000002904 solvent Substances 0.000 claims description 24
- RTZKZFJDLAIYFH-UHFFFAOYSA-N Diethyl ether Chemical compound CCOCC RTZKZFJDLAIYFH-UHFFFAOYSA-N 0.000 claims description 20
- WYURNTSHIVDZCO-UHFFFAOYSA-N Tetrahydrofuran Chemical group C1CCOC1 WYURNTSHIVDZCO-UHFFFAOYSA-N 0.000 claims description 18
- OKKJLVBELUTLKV-UHFFFAOYSA-N Methanol Chemical compound OC OKKJLVBELUTLKV-UHFFFAOYSA-N 0.000 claims description 15
- KWYUFKZDYYNOTN-UHFFFAOYSA-M Potassium hydroxide Chemical compound [OH-].[K+] KWYUFKZDYYNOTN-UHFFFAOYSA-M 0.000 claims description 15
- LQZMLBORDGWNPD-UHFFFAOYSA-N N-iodosuccinimide Chemical compound IN1C(=O)CCC1=O LQZMLBORDGWNPD-UHFFFAOYSA-N 0.000 claims description 14
- PMZURENOXWZQFD-UHFFFAOYSA-L Sodium Sulfate Chemical compound [Na+].[Na+].[O-]S([O-])(=O)=O PMZURENOXWZQFD-UHFFFAOYSA-L 0.000 claims description 14
- 239000012043 crude product Substances 0.000 claims description 14
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 12
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 claims description 10
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims description 10
- 239000003208 petroleum Substances 0.000 claims description 10
- 239000000741 silica gel Substances 0.000 claims description 10
- 229910002027 silica gel Inorganic materials 0.000 claims description 10
- YLQBMQCUIZJEEH-UHFFFAOYSA-N tetrahydrofuran Natural products C=1C=COC=1 YLQBMQCUIZJEEH-UHFFFAOYSA-N 0.000 claims description 9
- 238000001914 filtration Methods 0.000 claims description 8
- 239000012074 organic phase Substances 0.000 claims description 8
- WMFOQBRAJBCJND-UHFFFAOYSA-M Lithium hydroxide Chemical compound [Li+].[OH-] WMFOQBRAJBCJND-UHFFFAOYSA-M 0.000 claims description 6
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 claims description 6
- 238000001704 evaporation Methods 0.000 claims description 6
- 229910052938 sodium sulfate Inorganic materials 0.000 claims description 6
- 235000011152 sodium sulphate Nutrition 0.000 claims description 6
- FAPWRFPIFSIZLT-UHFFFAOYSA-M Sodium chloride Chemical class [Na+].[Cl-] FAPWRFPIFSIZLT-UHFFFAOYSA-M 0.000 claims description 5
- 238000010898 silica gel chromatography Methods 0.000 claims description 5
- AKHNMLFCWUSKQB-UHFFFAOYSA-L sodium thiosulfate Chemical class [Na+].[Na+].[O-]S([O-])(=O)=S AKHNMLFCWUSKQB-UHFFFAOYSA-L 0.000 claims description 5
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 claims description 4
- 239000003513 alkali Substances 0.000 claims description 4
- 238000007865 diluting Methods 0.000 claims description 4
- 238000001035 drying Methods 0.000 claims description 4
- BWHMMNNQKKPAPP-UHFFFAOYSA-L potassium carbonate Chemical compound [K+].[K+].[O-]C([O-])=O BWHMMNNQKKPAPP-UHFFFAOYSA-L 0.000 claims description 4
- 238000002390 rotary evaporation Methods 0.000 claims description 4
- 238000005406 washing Methods 0.000 claims description 4
- 239000002585 base Substances 0.000 claims description 2
- FJDQFPXHSGXQBY-UHFFFAOYSA-L caesium carbonate Chemical compound [Cs+].[Cs+].[O-]C([O-])=O FJDQFPXHSGXQBY-UHFFFAOYSA-L 0.000 claims description 2
- 229910000024 caesium carbonate Inorganic materials 0.000 claims description 2
- 238000004587 chromatography analysis Methods 0.000 claims description 2
- 239000003480 eluent Substances 0.000 claims description 2
- 239000012046 mixed solvent Substances 0.000 claims description 2
- 229910000027 potassium carbonate Inorganic materials 0.000 claims description 2
- 238000003756 stirring Methods 0.000 claims description 2
- 150000001875 compounds Chemical class 0.000 abstract description 3
- 238000000746 purification Methods 0.000 abstract description 3
- 239000003153 chemical reaction reagent Substances 0.000 abstract description 2
- 239000012265 solid product Substances 0.000 description 6
- 238000004440 column chromatography Methods 0.000 description 5
- 239000007787 solid Substances 0.000 description 5
- 150000001907 coumarones Chemical class 0.000 description 4
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 3
- 238000005481 NMR spectroscopy Methods 0.000 description 3
- 229910052739 hydrogen Inorganic materials 0.000 description 3
- 239000001257 hydrogen Substances 0.000 description 3
- JCRWXSMKXVKUCO-UHFFFAOYSA-N methyl 3-hydroxy-4-nitro-2-prop-2-enylbenzoate Chemical compound COC(=O)C1=CC=C([N+]([O-])=O)C(O)=C1CC=C JCRWXSMKXVKUCO-UHFFFAOYSA-N 0.000 description 3
- 239000000047 product Substances 0.000 description 3
- 238000001228 spectrum Methods 0.000 description 3
- 238000005160 1H NMR spectroscopy Methods 0.000 description 2
- IAZDPXIOMUYVGZ-WFGJKAKNSA-N Dimethyl sulfoxide Chemical compound [2H]C([2H])([2H])S(=O)C([2H])([2H])[2H] IAZDPXIOMUYVGZ-WFGJKAKNSA-N 0.000 description 2
- 239000002547 new drug Substances 0.000 description 2
- 238000011160 research Methods 0.000 description 2
- HEDRZPFGACZZDS-MICDWDOJSA-N Trichloro(2H)methane Chemical compound [2H]C(Cl)(Cl)Cl HEDRZPFGACZZDS-MICDWDOJSA-N 0.000 description 1
- 230000003288 anthiarrhythmic effect Effects 0.000 description 1
- 230000001387 anti-histamine Effects 0.000 description 1
- 230000000259 anti-tumor effect Effects 0.000 description 1
- 239000000739 antihistaminic agent Substances 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 230000004071 biological effect Effects 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 201000010099 disease Diseases 0.000 description 1
- 208000037265 diseases, disorders, signs and symptoms Diseases 0.000 description 1
- 239000003814 drug Substances 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000003379 elimination reaction Methods 0.000 description 1
- 150000002148 esters Chemical group 0.000 description 1
- 150000002391 heterocyclic compounds Chemical class 0.000 description 1
- 125000002887 hydroxy group Chemical group [H]O* 0.000 description 1
- 239000000543 intermediate Substances 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 229930014626 natural product Natural products 0.000 description 1
- 238000000655 nuclear magnetic resonance spectrum Methods 0.000 description 1
- ISWSIDIOOBJBQZ-UHFFFAOYSA-N phenol group Chemical group C1(=CC=CC=C1)O ISWSIDIOOBJBQZ-UHFFFAOYSA-N 0.000 description 1
- 230000001737 promoting effect Effects 0.000 description 1
- 238000012827 research and development Methods 0.000 description 1
- 238000001308 synthesis method Methods 0.000 description 1
- 238000003786 synthesis reaction Methods 0.000 description 1
Landscapes
- Nitrogen Condensed Heterocyclic Rings (AREA)
Abstract
The invention discloses a preparation method of a compound 2-methyl-7-nitrobenzofuran-4-formic acid. The preparation method comprises the following specific steps: (1) Compound 1 is taken as a starting material, and compound 2 is prepared through halogenation and cyclization; (2) The compound 2 is subjected to dehalogenation and hydrolysis under alkaline conditions to obtain a compound 3, namely the 2-methyl-7-nitrobenzofuran-4-formic acid. The preparation method provided by the invention has the advantages of short process flow, few types of reagents participating in the reaction, convenient operation, mild and easily controlled reaction conditions, easy realization of industrialization, single configuration of the prepared product, easy purification and higher yield.
Description
Technical Field
The invention relates to the technical field of synthesis of medical intermediates, in particular to a preparation method of 2-methyl-7-nitrobenzofuran-4-formic acid.
Background
Benzofuran compounds are a very large number of compounds with very strong biological activity and widely exist in natural and non-natural products.
Benzofuran compounds are common important heterocyclic compounds, and many benzofuran derivatives have proved to have medicinal values, including antihistaminic, antitumor and antiarrhythmic activities, and many active compounds are expected to become medicaments for treating related diseases. Therefore, in recent years, there has been a great deal of attention from researchers.
The research on the synthesis method of the benzofuran compounds can be used for promoting the progress of the research of related pharmaceutical chemistry, and providing more support for the development of related new drugs.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides a preparation method of 2-methyl-7-nitrobenzofuran-4-formic acid. The preparation method provided by the invention has the advantages of short process flow route, convenience in operation, mild and easily controlled reaction conditions, lower cost, easiness in realizing industrialization, avoidance of complex reactions with higher dangers, single configuration of the prepared product, easiness in purification and higher yield.
The technical scheme of the invention is as follows:
A preparation method of 2-methyl-7-nitrobenzofuran-4-formic acid, which is carried out according to the following flow:
The method comprises the following specific steps:
(1) Taking the compound 1 as a starting material, and carrying out halogenation and ring closure reaction to prepare a compound 2;
(2) The compound 2 is subjected to dehalogenation and hydrolysis under alkaline conditions to obtain a compound 3, namely the 2-methyl-7-nitrobenzofuran-4-formic acid.
Further, in the step (1), the specific process of the halogenation and ring closure reaction is as follows: dissolving the compound 1 in a solvent, adding N-iodosuccinimide at normal temperature, stirring overnight at normal temperature to obtain a reaction solution, removing the solvent by rotary evaporation under reduced pressure, diluting a crude product with water, extracting with ethyl acetate, washing an organic phase with saturated sodium thiosulfate to be colorless, washing with saturated sodium chloride, drying with anhydrous sodium sulfate, filtering to remove sodium sulfate, evaporating the solvent, and purifying by silica gel column chromatography to obtain the compound 2.
Further, the molar ratio of the compound 1 to the N-iodosuccinimide is 1:1.2-2.
Further, the solvent is tetrahydrofuran, and the tetrahydrofuran is used in an amount to ensure that the concentration of the compound 1 in tetrahydrofuran is 0.2-0.5mol/L.
Further, the silica gel in the silica gel column is 200-300 meshes; the eluent used in the chromatography is a mixed solvent of petroleum ether and ethyl acetate, and the volume ratio of the petroleum ether to the ethyl acetate is 5:1.
Further, in the step (2), the specific process of dehalogenation and hydrolysis reaction is as follows: dissolving the compound 2 in a solvent, adding alkali, reacting for 2-18h at 50-80 ℃ under normal pressure to obtain a reaction solution, evaporating the reaction solution, diluting a crude product with water, adjusting the pH to be less than 6 with dilute hydrochloric acid, extracting with ethyl acetate, drying an organic phase with anhydrous sodium sulfate, filtering to remove sodium sulfate, evaporating the solvent, and purifying by silica gel column chromatography to obtain the compound 3.
Further, the solvent comprises at least one of methanol and ethanol; the alkali comprises at least one of potassium hydroxide, sodium hydroxide, lithium hydroxide, cesium carbonate and potassium carbonate.
Further, the concentration of the compound 2 in the solvent is 0.1 to 0.5mol/L; the amount of the base is 1.0 to 3 equivalents of the compound 2.
Further, the concentration of the dilute hydrochloric acid is 0.5-2 mol/L.
The beneficial technical effects of the invention are as follows:
the invention firstly carries out halogenation on of an olefinic bond, then closes a ring with a phenolic hydroxyl group, then carries out dehalogenation under alkaline conditions, then carries out elimination reaction, and simultaneously carries out hydrolysis reaction on an ester functional group to obtain a target product.
The preparation method provided by the invention has the advantages of short process flow route, few reagent types participating in reaction, convenient operation, mild and easily controlled reaction conditions, easy realization of industrialization, easy purification of products and high yield, and the unreported molecules provide more possibility for the research and development of new drugs.
Drawings
FIG. 1 is a schematic illustration of the reaction scheme of the present invention.
FIG. 2 is a nuclear magnetic resonance hydrogen spectrum of the compound 2 prepared in example 1 of the present invention.
FIG. 3 is a nuclear magnetic resonance spectrum of 2-methyl-7-nitrobenzofuran-4-carboxylic acid prepared in example 1 of the present invention.
Detailed Description
The present invention will be described in detail below with reference to the drawings and examples.
Example 1
A preparation method of 2-methyl-7-nitrobenzofuran-4-formic acid comprises the following steps:
(1) Preparation of methyl 2- (iodomethyl) -7-nitro-2, 3-dihydrobenzofuran-4-carboxylate (Compound 2) to a 5mL one-necked flask was added methyl 2-allyl-3-hydroxy-4-nitrobenzoate (Compound 1) (0.1 g,0.42mmol,1.0 eq), N-iodosuccinimide (0.189 g,0.84mmol,2.0 eq) and tetrahydrofuran (1 mL), the reaction solution was stirred at room temperature for 18 hours to give a reaction solution, the solvent was distilled off under reduced pressure, the crude product was diluted with water, extracted with ethyl acetate, the organic phase was washed with saturated sodium thiosulfate to colorless, washed with saturated sodium chloride, dried over anhydrous sodium sulfate, the solvent was evaporated to dryness after filtration of the sodium sulfate removal, and the obtained crude product was purified by column chromatography (200 to 300 mesh silica gel, petroleum ether/ethyl acetate with a volume ratio of 5/1) to give a yellow solid product, yield 45.7% and purity 95%. The nuclear magnetic resonance hydrogen spectrum of 2- (iodomethyl) -7-nitro-2, 3-dihydrobenzofuran-4-carboxylic acid methyl ester (compound 2) is shown in figure 2.
As can be seen from fig. 2 ,1H NMR(400MHz,Chloroform-d)δ7.92(d,J＝8.8Hz,1H),7.52(d,J＝8.9Hz,1H),5.14–5.05(m,1H),3.89(s,3H),3.76(dd,J＝18.3,9.3Hz,1H),3.49(dd,J＝10.5,3.8Hz,1H),3.44–3.34(m,2H).
(2) Preparation of 2-methyl-7-nitrobenzofuran-4-carboxylic acid
Methyl 2- (iodomethyl) -7-nitro-2, 3-dihydrobenzofuran-4-carboxylate (compound 2) (0.02 g,0.055 mmol) is dissolved in methanol (0.5 mL), potassium hydroxide solid (0.0067 g,0.12 mmol) is added, the reaction is carried out for 2h at 50 ℃, after the reaction is finished, the crude product is diluted with water, the reaction solution is adjusted to pH <6 by 1mol/L hydrochloric acid, then extracted by ethyl acetate, the organic phase is dried by anhydrous sodium sulfate, the solvent is evaporated after filtering to remove sodium sulfate, and the crude product is purified by column chromatography (200-300 meshes of silica gel, volume ratio of petroleum ether/ethyl acetate of 1/1) to obtain yellow solid product 0.01g, and the yield is 82% and the purity is 95%. The nuclear magnetic resonance hydrogen spectrum of 2-methyl-7-nitrobenzofuran-4-carboxylic acid (compound 3) is shown in FIG. 3.
As can be seen from fig. 3 ,1H NMR(400MHz,DMSO-d6)δ7.94(d,J＝8.4Hz,1H),7.75(d,J＝8.4Hz,1H),7.33(d,J＝1.3Hz,1H),2.54–2.51(m,3H).
Example 2
A preparation method of 2-methyl-7-nitrobenzofuran-4-formic acid comprises the following steps:
(1) Preparation of methyl 2- (iodomethyl) -7-nitro-2, 3-dihydrobenzofuran-4-carboxylate (Compound 2)
To a 50mL single-necked flask, methyl 2-allyl-3-hydroxy-4-nitrobenzoate (compound 1) (1 g,4.2mmol,1.0 eq), N-iodosuccinimide (1.89 g,8.4mmol,2.0 eq) and dry tetrahydrofuran (10 mL) were added, the reaction was stirred at room temperature for 18 hours to give a reaction solution, the reaction solution was subjected to reduced pressure rotary evaporation to remove the solvent, the crude product was diluted with water, extracted with ethyl acetate, the organic phase was washed with saturated sodium thiosulfate to colorless, washed with saturated sodium chloride, dried over anhydrous sodium sulfate, the solvent was evaporated after filtration to dryness, and the obtained crude product was purified by column chromatography (200 to 300 mesh silica gel, petroleum ether/ethyl acetate in a volume ratio of 5/1) to give a yellow solid product, yield 71.9%, purity 95%.
(2) Preparation of 2-methyl-7-nitrobenzofuran-4-carboxylic acid
Methyl 2- (iodomethyl) -7-nitro-2, 3-dihydrobenzofuran-4-carboxylate (compound 2) (1 g,2.754 mmol) was dissolved in methanol (20 mL), potassium hydroxide solid (0.473 g, 8.433 mmol) was added, the reaction was carried out at 60℃for 12h, after the reaction was completed, the solvent of the reaction solution was evaporated to dryness, the residue was dissolved in water again, the solution was adjusted to pH <5 with 1mol/L hydrochloric acid, the solid was precipitated, filtered, washed with water and dried at 45 ℃. The crude product obtained is purified by silica gel column chromatography (200-300 meshes of silica gel, petroleum ether/ethyl acetate with the volume ratio of 1/1) to obtain 0.55g of yellow solid product with the yield of 90 percent and the purity of 95 percent.
Example 3
A preparation method of 2-methyl-7-nitrobenzofuran-4-formic acid comprises the following steps:
(1) Preparation of methyl 2- (iodomethyl) -7-nitro-2, 3-dihydrobenzofuran-4-carboxylate (Compound 2)
To a 5mL one-necked flask, methyl 2-allyl-3-hydroxy-4-nitrobenzoate (compound 1) (25.0 g,0.105mol,1.0 eq), N-iodosuccinimide (47.42 g,0.210mmol,2.0 eq) and dry tetrahydrofuran (500 mL) were added, and the reaction was stirred at room temperature for 18 hours to give a reaction solution, the reaction solution was subjected to rotary evaporation under reduced pressure to remove the solvent, the crude product was diluted with water, extracted with ethyl acetate, the organic phase was washed with saturated sodium thiosulfate to colorless, washed with saturated sodium chloride, dried over anhydrous sodium sulfate, the solvent was evaporated after filtration to dryness, and the obtained crude product was purified by column chromatography (200 to 300 mesh silica gel, volume ratio of petroleum ether/ethyl acetate 5/1) to give a yellow solid product of 34.7g, yield 90.8%, purity 95%.
(2) Preparation of 2-methyl-7-nitrobenzofuran-4-carboxylic acid
Methyl 2- (iodomethyl) -7-nitro-2, 3-dihydrobenzofuran-4-carboxylate (compound 2) (30.0 g,0.083 mol) is dissolved in methanol (600 mL), potassium hydroxide solid (13.9 g,0.248 mol) is added to react for 18 hours at 70 ℃, after the reaction is finished, the reaction solution is evaporated to dryness, the residue is dissolved in water again, the solution is adjusted to pH <5 by 1mol/L hydrochloric acid, the solid is separated out, filtered, washed with water and dried at 45 ℃, and the crude product is purified by column chromatography (200-300 meshes of silica gel, petroleum ether/ethyl acetate with the volume ratio of 1/1) to obtain 17.3g of yellow solid product with the yield of 94.7% and the purity of 95%.
The above is only a preferred embodiment of the present invention, and the present invention is not limited to the above examples. It is to be understood that other modifications and variations which may be directly derived or contemplated by those skilled in the art without departing from the spirit and concepts of the present invention are deemed to be included within the scope of the present invention.
Claims (9)
1. The preparation method of the 2-methyl-7-nitrobenzofuran-4-formic acid is characterized by comprising the following steps of:
The method comprises the following specific steps:
(1) Taking the compound 1 as a starting material, and carrying out halogenation and ring closure reaction to prepare a compound 2;
(2) The compound 2 is subjected to dehalogenation and hydrolysis under alkaline conditions to obtain a compound 3, namely the 2-methyl-7-nitrobenzofuran-4-formic acid.
2. The method according to claim 1, wherein in the step (1), the specific process of the halogenation and ring closure reaction is as follows: dissolving the compound 1 in a solvent, adding N-iodosuccinimide at normal temperature, stirring overnight at normal temperature to obtain a reaction solution, removing the solvent by rotary evaporation under reduced pressure, diluting a crude product with water, extracting with ethyl acetate, washing an organic phase with saturated sodium thiosulfate to be colorless, washing with saturated sodium chloride, drying with anhydrous sodium sulfate, filtering to remove sodium sulfate, evaporating the solvent, and purifying by silica gel column chromatography to obtain the compound 2.
3. The preparation method according to claim 2, wherein the molar ratio of the compound 1 to the N-iodosuccinimide is 1:1.2-2.
4. The preparation method according to claim 2, wherein the solvent is tetrahydrofuran, and the tetrahydrofuran is used in an amount to ensure a concentration of 0.2 to 0.5mol/L of the compound 1 in tetrahydrofuran.
5. The preparation method according to claim 2, wherein the silica gel in the silica gel column is 200-300 mesh; the eluent used in the chromatography is a mixed solvent of petroleum ether and ethyl acetate, and the volume ratio of the petroleum ether to the ethyl acetate is 5:1.
6. The method according to claim 1, wherein in the step (2), the specific process of dehalogenation and hydrolysis reaction is as follows: dissolving the compound 2 in a solvent, adding alkali, reacting for 2-18h at 50-80 ℃ under normal pressure to obtain a reaction solution, evaporating the reaction solution, diluting a crude product with water, adjusting the pH to be less than 6 with dilute hydrochloric acid, extracting with ethyl acetate, drying an organic phase with anhydrous sodium sulfate, filtering to remove sodium sulfate, evaporating the solvent, and purifying by silica gel column chromatography to obtain the compound 3.
7. The method according to claim 6, wherein the solvent comprises at least one of methanol and ethanol; the alkali comprises at least one of potassium hydroxide, sodium hydroxide, lithium hydroxide, cesium carbonate and potassium carbonate.
8. The method according to claim 6, wherein the concentration of the compound 2 in the solvent is 0.1 to 0.5mol/L; the amount of the base is 1.0 to 3 equivalents of the compound 2.
9. The method according to claim 6, wherein the concentration of the dilute hydrochloric acid is 0.5 to 2mol/L.
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