Method for synthesizing lignin-based carbazole derivative by one-pot two-step method

Abstract

The invention provides a method for synthesizing a lignin-based carbazole derivative by a one-pot two-step method, and belongs to the technical field of compound synthesis. The method comprises the following steps: step 1, taking a lignin beta-O-4 model compound and an N-methyl-3-indole formaldehyde compound as reaction raw materials, and reacting for a certain time in a solvent under the action of alkali; and 2, adding acetic acid, a Fe-based catalyst, 2, 2, 6, 6-tetramethylpiperidine oxide, a 4-chlorobutanone compound and an additive into the system, and reacting for a certain time to finally obtain the carbazole compound. The synthetic method for preparing the carbazole derivative has the advantages of being economical, low in cost, simple to operate, mild in reaction condition, high in product selectivity and the like, and a novel green way is provided for preparation of carbazole compounds.

Description

Technical Field

[0001] The invention belongs to the technical field of organic compound synthesis and relates to a one-pot two-step method for synthesizing lignin-based carbazole derivatives. Background Art

[0002] Carbazole and its derivatives are a special class of nitrogen-containing aromatic heterocyclic molecules that are widely found in the fields of natural products, drugs and functional materials. They can also be used to construct fluorescent molecular probes or sensors, light-emitting diodes or organic light-emitting electronic devices. As important fine chemical intermediates, they are widely used in high-end organic pigments, dyes, pesticides, polymer materials and other fields.

[0003] Currently, a variety of synthetic strategies have been applied to the preparation of carbazole derivatives in the literature. Early methods include the Graebe-Ullmann reaction, the Borsche-Drechsel cyclization, and the Fischer-Borsche carbazole synthesis. These methods suffer from harsh reaction conditions and long reaction steps. In recent years, noble metal and transition metal catalysts have been applied to the synthesis of carbazole and its derivatives, enriching the synthetic methods of carbazole. One method is to construct nitrogen heterocycles from biphenyl derivatives. However, this method requires prefunctionalization and the product structure is limited. Another method is to construct the carbazole ring from indole derivatives through cyclization reactions. This is one of the ways to quickly and efficiently obtain structurally diverse carbazole derivatives. Among them, the following strategies can be adopted for the construction of carbazoles through indole cyclization reactions: [2+2'+2'] cyclization reaction (Org. Chem. 2009, 74, 7481), [2+2'+2"] cyclization reaction (Org. Lett. 2016, 18, 5384), and [4+2] cycloaddition reaction (Adv. Synth. Catal. 2014, 557). However, most of these methods have limitations such as heavy metal residues, low yields, and complex operations.

[0004] Therefore, the research and development of a novel, efficient, low-energy, environmentally friendly, easy-to-operate, and sustainable synthesis method for carbazole derivatives has become an important topic that needs to be studied urgently. Summary of the Invention

[0005] In order to solve the problems existing in the prior art, the purpose of the present invention is to provide a one-step method for preparing carbazole derivatives from lignin model compounds. This method has the advantages of simple operation, mild reaction conditions, and high product selectivity, and provides a new green route for the preparation of carbazole compounds.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

[0007] A one-pot two-step method for synthesizing lignin-based carbazole derivatives comprises the following steps:

[0008] Step 1: Add lignin β-O-4 model compound 1a0, N-methylindole-3-carboxaldehyde compound 2a0, and base to a solvent and react for a certain period of time to obtain a mixture, which is then cooled to room temperature and set aside. In this step, 1a0 and 2a0 react to synthesize an alkenyl indole intermediate.

[0009] In the second step, acid is added to the mixture and reacted for a while. Then, an Fe-based catalyst, 2,2,6,6-tetramethylpiperidinyl oxide (TEMPO), 4-chlorophenylbutyronitrile compounds and additives are added, and the temperature is raised to a certain level for reaction to obtain a reaction mixture. After separation and purification, the carbazole derivative 4a0 is obtained, that is, a carbazole compound is obtained. This reaction is based on a C / H activation-cyclization strategy, and a novel polycarbonyl carbazole derivative is successfully synthesized through an indole enylation-Diels-Alder cycloaddition-dehydrogenation aromatization reaction.

[0010] Furthermore, in the first step, the molar ratio of the lignin β-O-4 model compound to the N-methylindole-3-carboxaldehyde compound is 1 to 10:1; the molar ratio of the base to the N-methylindole-3-carboxaldehyde compound is 1 to 10:1;

[0011] Furthermore, in the second step, the molar ratio of the N-methylindole-3-carboxaldehyde compound to 4-chlorobutyrophenone is 1:1-5; the molar ratio of the base to the acid is 1:1; the molar ratio of the 2,2,6,6-tetramethylpiperidinyl oxide (TEMPO) to the N-methylindole-3-carboxaldehyde compound is 3:1; and the molar ratio of the additive 1,10-phenanthroline to the Fe-based catalyst is 1.5:1, wherein the amount of the Fe-based catalyst is 1-20 mol%.

[0012] Furthermore, the base in the first step is one or more of NaOH, KOH, CsCO3, t-BuOK, and CH3CHONa, preferably NaOH.

[0013] Furthermore, the solvent in the first step is toluene.

[0014] Furthermore, the solvent in the second step is one or more of toluene, tert-amyl alcohol, water, 1,4-dioxane, acetonitrile, methanol, ethanol, isopropanol, dimethyl sulfoxide, and dimethylformamide, preferably toluene.

[0015] Furthermore, the Fe-based catalyst in the second step is one or more of Fe(NO3)3·9H2O, FeCl3, FeCl2, FeBr2, Fe(CH3COO)2, and Fe(C5H7O2)3, preferably Fe(NO3)3·9H2O.

[0016] Furthermore, the additive in the second step is 1,10-phenanthroline.

[0017] Furthermore, the acid in the second step is acetic acid (HOAc).

[0018] Furthermore, the reaction temperature of the first step is 110-130° C., and the reaction time is 0.5-4 h;

[0019] Furthermore, the reaction temperature of the second step is 80-150° C., and the reaction time is 0.5-14 h; the reaction temperature is preferably 120° C., and the reaction time is preferably 8 h.

[0020] The reaction formula of the present invention is:

[0021]

[0022] The R 1 is an alkyl group having 1 to 10 carbon atoms, an alkoxy group, a halogen group, a nitro group, an ester group, a benzyl group, an aryl group having 6 to 18 carbon atoms, an amino group, a hydroxyl group or hydrogen; 2 is hydroxymethyl or hydrogen; said R 3 is an alkyl group having 1 to 10 carbon atoms, an alkoxy group, a halogen group, a nitro group, an ester group, a benzyl group, an aryl group having 6 to 18 carbon atoms, an amino group, a hydroxyl group or hydrogen; 4 is an alkyl group having 1 to 10 carbon atoms, an alkoxy group, a halogen group, a nitro group, an ester group, a benzyl group, an aryl group having 6 to 18 carbon atoms, an amino group, a hydroxyl group or hydrogen; 5 It is an alkyl group having 1 to 10 carbon atoms, an alkoxy group, a halogen group, a nitro group, an ester group, a benzyl group, an aryl group having 6 to 18 carbon atoms, an amino group, a hydroxyl group or hydrogen.

[0023] The beneficial effects of the present invention are:

[0024] (1) The present invention is different from the traditional indole substrate synthesis method. It uses a lignin model compound as a substrate with a wide source and is environmentally friendly. It is different from the traditional palladium-copper noble metal catalysis. It uses an iron-based catalyst to ensure the catalytic effect while having economic benefits and low residue. It adopts a one-pot two-step method for reaction, which is convenient to feed and easy to operate.

[0025] (1) The synthetic method for preparing carbazole compounds described in the present invention has the advantages of being economical, simple to operate, mild reaction conditions, and high product selectivity, and provides a new green approach for the preparation of carbazole compounds. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 The carbazole product 4a prepared in Example 1 1 H-NMR nuclear magnetic spectrum.

[0027] Figure 2 The carbazole product 4b prepared in Example 11 1 H-NMR nuclear magnetic spectrum.

[0028] Figure 3 The carbazole product 4c prepared in Example 12 1 H-NMR nuclear magnetic spectrum.

[0029] Figure 4 The carbazole product 4d prepared in Example 13 1 H-NMR nuclear magnetic spectrum.

[0030] Figure 5 The carbazole product 4e prepared in Example 14 1 H-NMR nuclear magnetic spectrum.

[0031] Figure 6 The carbazole product 4f prepared in Example 15 1 H-NMR nuclear magnetic spectrum.

[0032] Figure 7 4g of the carbazole product prepared in Example 16 1 H-NMR nuclear magnetic spectrum. DETAILED DESCRIPTION

[0033] The present invention is described in detail below with reference to the embodiments, but the embodiments of the present invention are not limited thereto. Obviously, the embodiments described below are only some embodiments of the present invention. For those skilled in the art, other similar embodiments obtained without creative work all fall within the scope of protection of the present invention.

[0034] Example 1:

[0035] In a 35 ml pressure bottle, under air, 2-(2-methoxyphenoxy)-1-benzyl alcohol 1a (0.2 mmol), N-methylindole-3-carbaldehyde 2a (0.1 mmol), and NaOH (0.8 mmol) were added to 2 mL of toluene in sequence. The mixture was heated to 120°C, stirred for 2 h, and then cooled to room temperature.

[0036] Continue to add acetic acid (0.8mmol), wait for a while, then add 2mL of toluene, 4-chlorophenyl ketone 3a (0.1mmol), Fe(NO3)3·9H2O (0.02mmol, 8mg), TEMPO (0.3mmol) and 1,10-phenanthroline (0.03mmol) to the reaction solution, heat to 120℃ and stir to react for 10h. After the reaction is completed, cool to room temperature and separate by silica gel column chromatography (eluent is petroleum ether / ethyl acetate, v / v=50:1) and then recrystallize to obtain the target solid product 4a (74.72mg, yield 90%). The target product was confirmed by nuclear magnetic resonance spectroscopy and high-resolution mass spectrometry. The reaction formula is as follows. 1,3-di(benzophenone)-9-methylcarbazole 1 H-NMR characterization is shown in the attached Figure 1 ,from Figure 1 The product can be identified as 4a.

[0037]

[0038] Example 2

[0039] In a 35 ml pressure bottle, under air, 2-(2-methoxyphenoxy)-1-benzyl alcohol 1a (0.2 mmol), N-methylindole-3-carbaldehyde 2a (0.1 mmol), and NaOH (1.0 mmol) were added to 2 mL of toluene in sequence. The mixture was heated to 110°C, stirred for 4 h, and then cooled to room temperature.

[0040] Acetic acid (1.0 mmol) was added, followed by a short wait. 2 mL of ethanol, 4-chlorobutyrophenone 3a (0.1 mmol), Fe(NO₃)₃·9H₂O (0.01 mmol, 4 mg), TEMPO (0.3 mmol), and 1,10-phenanthroline (0.0015 mmol, 2.7 mg) were added to the reaction solution. The mixture was heated to 80°C and stirred for 24 h. After completion, the reaction was cooled to room temperature and separated by silica gel column chromatography (eluent: petroleum ether / ethyl acetate, v / v = 50:1) followed by recrystallization to afford the desired solid product 4a (70.62 mg, 85% yield).

[0041] Example 3

[0042] In a 35 ml pressure bottle, under air, 2-(2-methoxyphenoxy)-1-benzyl alcohol 1a (0.2 mmol), N-methylindole-3-carbaldehyde 2a (0.1 mmol), and NaOH (0.1 mmol) were added to 2 mL of toluene in sequence. The mixture was heated to 130°C, stirred for 0.5 h, and then cooled to room temperature.

[0043] Acetic acid (0.1 mmol) was added, and after a short pause, 2 mL of chlorobenzene, 4-chlorobutyrophenone 3a (0.1 mmol), FeCl3 (0.02 mmol, 3.25 mg), TEMPO (0.3 mmol), and 1,10-phenanthroline (0.03 mmol) were added to the reaction solution. The mixture was heated to 150°C and stirred for 0.5 h. After completion of the reaction, the mixture was cooled to room temperature and separated by silica gel column chromatography (eluent: petroleum ether / ethyl acetate, v / v = 50:1) followed by recrystallization to afford the desired solid product 4a (62.27 mg, 75% yield).

[0044] Example 4

[0045] In a 35 ml pressure bottle, under air, 2-(2-methoxyphenoxy)-1-benzyl alcohol 1a (0.2 mmol), N-methylindole-3-carbaldehyde 2a (0.1 mmol), and KOH (0.5 mmol) were added to 2 mL of toluene in sequence. The mixture was heated to 130°C, stirred for 2 h, and then cooled to room temperature.

[0046] Acetic acid (0.5 mol) was added, followed by a short wait. Afterward, 2 mL of N,N-dimethylformamide, 4-chlorobutyrophenone 3a (0.1 mmol), FeCl2 (0.02 mmol, 2.54 mg), TEMPO (0.3 mmol), and 1,10-phenanthroline (0.03 mmol) were added to the reaction solution. The mixture was heated to 80°C and stirred for 14 h. After completion of the reaction, the mixture was cooled to room temperature and separated by silica gel column chromatography (eluent: petroleum ether / ethyl acetate, v / v = 50:1) followed by recrystallization to afford the desired solid product 4a (68.08 mg, 82% yield).

[0047] Example 5

[0048] In a 35 ml pressure bottle, under air, 2-(2-methoxyphenoxy)-1-benzyl alcohol 1a (0.2 mmol), N-methylindole-3-carboxaldehyde 2a (0.1 mmol), and CsCO3 (0.8 mmol) were added to 2 mL of toluene in sequence, heated to 120 ° C, stirred for 4 h, and then cooled to room temperature.

[0049] Acetic acid (0.8 mol) was added, followed by a short wait. 2 mL of acetonitrile, 4-chlorobutyrophenone 3a (0.1 mmol), FeBr2 (0.02 mmol, 4.3 mg), TEMPO (0.3 mmol), and 1,10-phenanthroline (0.03 mmol) were added to the reaction solution. The mixture was heated to 150°C and stirred for 0.5 h. After completion, the reaction was cooled to room temperature and separated by silica gel column chromatography (eluent: petroleum ether / ethyl acetate, v / v = 50:1) followed by recrystallization to afford the desired solid product 4a (66.42 mg, 80% yield).

[0050] Example 6

[0051] In a 35 ml pressure bottle, under air, 2-(2-methoxyphenoxy)-1-benzyl alcohol 1a (0.2 mmol), N-methylindole-3-carbaldehyde 2a (0.1 mmol), and t-BuOK (0.8 mmol) were added to 2 mL of toluene in sequence. The mixture was heated to 120°C, stirred for 4 h, and then cooled to room temperature.

[0052] Acetic acid (0.8 mol) was added, followed by a short wait. Afterward, 2 mL of isopropanol, 4-chlorobutyrophenone 3a (0.1 mmol), Fe(CH3COO)2 (0.02 mmol, 3.48 mg), TEMPO (0.3 mmol), and 1,10-phenanthroline (0.03 mmol) were added to the reaction solution. The mixture was heated to 120°C and stirred for 10 h. After completion, the reaction was cooled to room temperature and separated by silica gel column chromatography (eluent: petroleum ether / ethyl acetate, v / v = 50:1) followed by recrystallization to afford the desired solid product 4a (66.42 mg, 80% yield).

[0053] Example 7

[0054] In a 35 ml pressure bottle, under air, 2-(2-methoxyphenoxy)-1-benzyl alcohol 1a (0.2 mmol), N-methylindole-3-carbaldehyde 2a (0.1 mmol), and CH3CHONa (0.8 mmol) were added to 2 mL of toluene in sequence. The mixture was heated to 120°C, stirred for 4 h, and then cooled to room temperature.

[0055] Acetic acid (0.8 mol) was added, followed by a short wait. Afterward, 2 mL of methanol, 4-chlorobutyrophenone 3a (0.1 mmol), Fe(C5H7O2)3 (0.05 mmol, 8 mg), TEMPO (0.3 mmol), and 1,10-phenanthroline (0.03 mmol) were added to the reaction solution. The mixture was heated to 100°C and stirred for 2 h. After completion of the reaction, the mixture was cooled to room temperature and separated by silica gel column chromatography (eluent: petroleum ether / ethyl acetate, v / v = 50:1) followed by recrystallization to afford the desired solid product 4a (63.10 mg, 76% yield).

[0056] Example 8

[0057] In a 35 ml pressure bottle, under air, 2-(2-methoxyphenoxy)-1-benzyl alcohol 1a (2.0 mmol), N-methylindole-3-carbaldehyde 2a (0.1 mmol), and NaOH (0.8 mmol) were added to 2 mL of toluene in sequence. The mixture was heated to 120°C, stirred for 4 h, and then cooled to room temperature.

[0058] Acetic acid (0.8 mol) was added, and after a short pause, 2 mL of 1,4-dioxane, 4-chlorobutyrophenone 3a (0.5 mmol), Fe(NO₃)₃·9H₂O (0.02 mmol, 8 mg), TEMPO (0.3 mmol), and 1,10-phenanthroline (0.03 mmol) were added to the reaction solution. The mixture was heated to 120°C and stirred for 10 h. After completion of the reaction, the mixture was cooled to room temperature and separated by silica gel column chromatography (eluent: petroleum ether / ethyl acetate, v / v = 50:1) followed by recrystallization to afford the desired solid product 4a (58.98 mg, 71% yield).

[0059] Example 9

[0060] In a 35 ml pressure bottle, under air, 2-(2-methoxyphenoxy)-1-benzyl alcohol 1a (0.1 mmol), N-methylindole-3-carbaldehyde 2a (0.1 mmol), and NaOH (0.8 mmol) were added to 2 mL of toluene in sequence. The mixture was heated to 120°C, stirred for 4 h, and then cooled to room temperature.

[0061] Acetic acid (0.8 mol) was added, followed by a short pause. Afterward, 2 mL of tert-amyl alcohol, 4-chlorobutyrophenone 3a (0.1 mmol), Fe(NO₃)₃·9H₂O (0.01 mmol, 8 mg), TEMPO (0.3 mmol), and 1,10-phenanthroline (0.03 mmol) were added to the reaction solution. The mixture was heated to 120°C and stirred for 10 h. After completion of the reaction, the mixture was cooled to room temperature and separated by silica gel column chromatography (eluent: petroleum ether / ethyl acetate, v / v = 50:1) followed by recrystallization to afford the desired solid product 4a (59.81 mg, 72% yield).

[0062] Example 10

[0063] In a 35 ml pressure bottle, under air, 2-(2-methoxyphenoxy)-1-benzyl alcohol 1a (0.2 mmol), N-methylindole-3-carbaldehyde 2a (0.1 mmol), and NaOH (0.8 mmol) were added to 2 mL of toluene in sequence. The mixture was heated to 120°C, stirred for 4 h, and then cooled to room temperature.

[0064] Acetic acid (0.8 mol) was added, followed by a short wait. Afterward, 2 mL of water, 4-chlorobutyrophenone 3a (0.1 mmol), Fe(NO₃)₃·9H₂O (0.2 mmol, 8 mg), TEMPO (0.3 mmol), and 1,10-phenanthroline (0.03 mmol) were added to the reaction solution. The mixture was heated to 120°C and stirred for 10 h. After completion of the reaction, the mixture was cooled to room temperature and separated by silica gel column chromatography (eluent: petroleum ether / ethyl acetate, v / v = 50:1) followed by recrystallization to afford the desired solid product 4a (68.91 mg, 83% yield).

[0065] Example 11

[0066] In a 35 ml pressure bottle, under air, 1a (0.2 mmol), 2b (0.1 mmol), and NaOH (0.8 mmol) were added to 2 mL of toluene in sequence, heated to 120°C, stirred for 4 h, and then cooled to room temperature.

[0067] Acetic acid (0.8 mol) was added, and after a short wait, 2 mL of toluene, 3a (0.1 mmol), Fe(NO₃)₃·9H₂O (0.02 mmol, 8 mg), TEMPO (0.3 mmol), and 1,10-phenanthroline (0.03 mmol) were added to the reaction solution. The mixture was heated to 120°C and stirred for 10 h. After completion of the reaction, the mixture was cooled to room temperature and separated by silica gel column chromatography (eluent: petroleum ether / ethyl acetate, v / v = 50:1) followed by recrystallization to obtain the target solid product 4b (63.10 mg, 76% yield). The target product was confirmed by nuclear magnetic resonance spectroscopy and high-resolution mass spectrometry. The reaction equation is shown below.

[0068]

[0069] Example 12

[0070] In a 35 ml pressure bottle, under air, 1a (0.2 mmol), 2c (0.1 mmol), and NaOH (0.8 mmol) were added to 2 mL of toluene in sequence, heated to 120°C, stirred for 4 h, and then cooled to room temperature.

[0071] Acetic acid (0.8 mol) was added, and after a short wait, 2 mL of toluene, 3a (0.1 mmol), Fe(NO₃)₃·9H₂O (0.02 mmol, 8 mg), TEMPO (0.3 mmol), and 1,10-phenanthroline (0.03 mmol) were added to the reaction solution. The mixture was heated to 120°C and stirred for 10 h. After completion of the reaction, the mixture was cooled to room temperature and separated by silica gel column chromatography (eluent: petroleum ether / ethyl acetate, v / v = 50:1) followed by recrystallization to afford the target solid product 4c (60.60 mg, 73% yield). The target product was confirmed by nuclear magnetic resonance spectroscopy and high-resolution mass spectrometry. The reaction equation is shown below.

[0072]

[0073] Example 13

[0074] In a 35 ml pressure bottle, under air, 1b (0.2 mmol), 2a (0.1 mmol), and NaOH (0.8 mmol) were added to 2 mL of toluene in sequence, heated to 120°C, stirred for 4 h, and then cooled to room temperature.

[0075] Acetic acid (0.8 mol) was added, and after a short pause, 2 mL of toluene, 3a (0.1 mmol), Fe(NO₃)₃·9H₂O (0.02 mmol, 8 mg), TEMPO (0.3 mmol), and 1,10-phenanthroline (0.03 mmol) were added to the reaction solution. The mixture was heated to 120°C and stirred for 10 h. After completion of the reaction, the mixture was cooled to room temperature and separated by silica gel column chromatography (eluent: petroleum ether / ethyl acetate, v / v = 50:1) followed by recrystallization to yield the target solid product 4d (73.06 mg, 88% yield). The target product was confirmed by nuclear magnetic resonance spectroscopy and high-resolution mass spectrometry. The reaction equation is shown below.

[0076]

[0077] Example 14

[0078] In a 35 ml pressure bottle, under air, 1c (0.2 mmol), N-methylindole-3-carboxaldehyde 2a (0.1 mmol), and NaOH (0.8 mmol) were added to 2 mL of toluene in sequence, heated to 120°C, stirred for 4 h, and then cooled to room temperature.

[0079] Acetic acid (0.8 mol) was added, and after a short wait, 2 mL of toluene, 3a (0.1 mmol), Fe(NO₃)₃·9H₂O (0.02 mmol, 8 mg), TEMPO (0.3 mmol), and 1,10-phenanthroline (0.03 mmol) were added to the reaction solution. The mixture was heated to 130°C and stirred for 10 h. After completion of the reaction, the mixture was cooled to room temperature and separated by silica gel column chromatography (eluent: petroleum ether / ethyl acetate, v / v = 50:1) followed by recrystallization to afford the target solid product 4e (58.11 mg, 70% yield). The target product was confirmed by nuclear magnetic resonance spectroscopy and high-resolution mass spectrometry. The reaction equation is shown below.

[0080]

[0081] Example 15

[0082] In a 35 ml pressure bottle, under air, 1a (0.2 mmol), 2a (0.1 mmol), and NaOH (0.8 mmol) were added to 2 mL of toluene in sequence, heated to 115°C, stirred for 4 h, and then cooled to room temperature.

[0083] Acetic acid (0.8 mol) was added, and after a short wait, 2 mL of toluene, 3b (0.1 mmol), Fe(NO₃)₃·9H₂O (0.02 mmol, 8 mg), TEMPO (0.3 mmol), and 1,10-phenanthroline (0.03 mmol) were added to the reaction solution. The mixture was heated to 120°C and stirred for 10 h. After completion of the reaction, the mixture was cooled to room temperature and separated by silica gel column chromatography (eluent: petroleum ether / ethyl acetate, v / v = 50:1) followed by recrystallization to afford the target solid product 4f (58.94 mg, 71% yield). The target product was confirmed by nuclear magnetic resonance spectroscopy and high-resolution mass spectrometry. The reaction equation is shown below.

[0084]

[0085] Example 16

[0086] In a 35 ml pressure bottle, under air, 1a (0.2 mmol), 2a (0.1 mmol), and NaOH (0.8 mmol) were added to 2 mL of toluene in sequence, heated to 110°C, stirred for 4 h, and then cooled to room temperature.

[0087] Acetic acid (0.8 mol) was added, and after a short pause, 2 mL of toluene, 3c (0.1 mmol), Fe(NO₃)₃·9H₂O (0.02 mmol, 8 mg), TEMPO (0.3 mmol), and 1,10-phenanthroline (0.03 mmol) were added to the reaction solution. The mixture was heated to 120°C and stirred for 10 hours. After completion of the reaction, the mixture was cooled to room temperature and separated by silica gel column chromatography (eluent: petroleum ether / ethyl acetate, v / v = 50:1) followed by recrystallization to yield 4 g (69.74 mg, 84% yield) of the desired solid product. The desired product was confirmed by nuclear magnetic resonance spectroscopy and high-resolution mass spectrometry. The reaction equation is shown below.

[0088]

[0089] The above-described embodiments merely express the implementation methods of the present invention, but should not be understood as limiting the scope of the patent of the present invention. It should be pointed out that for those skilled in the art, several variations and improvements can be made without departing from the concept of the present invention, and these all fall within the scope of protection of the present invention.

Claims

1. A one-pot two-step method for synthesizing lignin-based carbazole derivatives, characterized in that: The method comprises the following steps: Step 1: Adding lignin β-O-4 model compound 1a0, N-methylindole-3-carboxaldehyde compound 2a0, and a base to a solvent to react and synthesize an alkenyl indole intermediate to obtain a mixture; In the second step, an acid is first added to the mixture to react for a while, and then an Fe-based catalyst, 2,2,6,6-tetramethylpiperidinyl oxide TEMPO, a 4-chlorobutyrophenone compound, and an additive are added to react to obtain a reaction mixture, which is separated and purified to obtain a carbazole derivative 4a0, i.e., a carbazole compound.

2. The one-pot two-step method for synthesizing lignin-based carbazole derivatives according to claim 1, characterized in that: The general reaction formula of the method is: The R 1 is an alkyl group having 1 to 10 carbon atoms, an alkoxy group, a halogen group, a nitro group, an ester group, a benzyl group, an aryl group having 6 to 18 carbon atoms, an amino group, a hydroxyl group or hydrogen; 2 is hydroxymethyl or hydrogen; said R 3 is an alkyl group having 1 to 10 carbon atoms, an alkoxy group, a halogen group, a nitro group, an ester group, a benzyl group, an aryl group having 6 to 18 carbon atoms, an amino group, a hydroxyl group or hydrogen; 4 is an alkyl group having 1 to 10 carbon atoms, an alkoxy group, a halogen group, a nitro group, an ester group, a benzyl group, an aryl group having 6 to 18 carbon atoms, an amino group, a hydroxyl group or hydrogen; 5 It is an alkyl group having 1 to 10 carbon atoms, an alkoxy group, a halogen group, a nitro group, an ester group, a benzyl group, an aryl group having 6 to 18 carbon atoms, an amino group, a hydroxyl group or hydrogen.

3. The one-pot two-step method for synthesizing lignin-based carbazole derivatives according to claim 1, characterized in that: In the first step, the molar ratio of the lignin β-O-4 model compound to the N-methylindole-3-carboxaldehyde compound is 1 to 10:1; and the molar ratio of the base to the N-methylindole-3-carboxaldehyde compound is 1 to 10:

1.

4. The one-pot two-step method for synthesizing lignin-based carbazole derivatives according to claim 1, characterized in that: In the first step, the molar ratio of the N-methylindole-3-carboxaldehyde compound to 4-chlorobutyrophenone is 1:1-5; the molar ratio of the base to the acid is 1:1; the molar ratio of the 2,2,6,6-tetramethylpiperidinyl oxide TEMPO to the N-methylindole-3-carboxaldehyde compound is 3:1; the molar ratio of the additive to the Fe-based catalyst is 1.5:1, wherein the amount of the Fe-based catalyst is 1-20 mol%.

5. The one-pot two-step method for synthesizing lignin-based carbazole derivatives according to claim 1, characterized in that: In the method: In the first step, the base is one or more of NaOH, KOH, CsCO3, t-BuOK, and CH3CHONa; In the first step, the solvent is toluene; In the second step, the solvent is one or more of toluene, tert-amyl alcohol, water, 1,4-dioxane, acetonitrile, methanol, ethanol, isopropanol, dimethyl sulfoxide, and dimethylformamide; In the second step, the Fe-based catalyst is one or more of Fe(NO3)3·9H2O, FeCl3, FeCl2, FeBr2, Fe(CH3COO)2, and Fe(C5H7O2)3; In the second step, the additive is 1,10-phenanthroline and the acid is acetic acid (HOAc).

6. The one-pot two-step method for synthesizing lignin-based carbazole derivatives according to claim 5, characterized in that: In the method: In the first step, the base is NaOH; In the second step, the solvent is toluene; In the second step, the Fe-based catalyst is Fe(NO3)3·9H2O.

7. The one-pot two-step method for synthesizing lignin-based carbazole derivatives according to claim 1, characterized in that: The reaction temperature of the first step is 110-130° C., and the reaction time is 0.5-4 h.

8. The one-pot two-step method for synthesizing lignin-based carbazole derivatives according to claim 1, characterized in that: The reaction temperature of the second step is 80-150° C., and the reaction time is 0.5-14 h.

9. The one-pot two-step method for synthesizing lignin-based carbazole derivatives according to claim 1, characterized in that: The reaction temperature of the second step is preferably 120° C., and the reaction time is preferably 8 h.

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