A method for preparing pyrrole and furan compounds from N-acetylglucosamine

Abstract

The application discloses a method for preparing pyrrole and furan compounds from marine waste biomass chitin monomer N-acetyl glucosamine. In the method, N-acetyl glucosamine is catalyzed by a composite valence molybdenum catalyst to perform reverse aldol reaction in a salt-containing water system, and then reacts with a beta-bisketone compound, so that the pyrrole and furan compounds are obtained. The introduction of inorganic salt can promote the dehydration process and improve the distribution ratio of the pyrrole compound in the organic phase, so that the pyrrole compound is prepared from N-acetyl glucosamine at a high yield. The application opens up a new way for efficiently preparing pyrrole and furan compounds from marine waste biomass renewable resources under mild conditions.

Description

Technical Field

[0001] This invention belongs to the field of chemical synthesis technology, specifically relating to a method for preparing pyrrole and furan compounds from N-acetylglucosamine. Background Technology

[0002] N-Acetyl-D-glucosamine (NAG) molecular formula C8H 15 NO6, with a molecular weight of 221.21, is an acetyl derivative of glucosamine and a building block of chitin, a polysaccharide found in marine crustaceans. Chitin is the second largest biopolymer in nature after lignocellulose and is an important component of the exoskeletons of many lower animals, such as shrimp (approximately 15%–30%) and crab (approximately 15%–20%). It is also a component of the cell membranes of lower plant fungi and is found in a range of organisms including fungi, green algae, yeast, squid, sponges, mollusks, nematodes, and arthropods.

[0003] In traditional industrial fields, there are well-established methods for extracting chitin from marine waste biomass. The main steps include demineralization, deproteinization, and decolorization. The obtained chitin can be further degraded to obtain NAG or glucosamine. For the utilization of NAG, the current focus is mainly on hydrogenation to prepare amino alcohols, oxidation to prepare aminoglycosides, bi-molecule cyclization to prepare deoxyfructosine, and pyrolysis to obtain a series of compounds such as pyrrole, pyrazine, or pyridine. Kerton developed a method for preparing 3-acetamido-5-acetylfuran (3A5AF) from NAG by dehydration, and derived a series of furanamine compounds for drug synthesis (ChemSusChem, 2012, 5(9): 1767-7); Cao Fei et al. obtained a new, unsubstituted 3-acetamidofuran (3AF) compound from NAG by reverse aldol-dehydration reaction, and applied it to the synthesis of dantrolene analogues (ChemSusChem 2023, e202300133). The preparation of these compounds all made full use of the nitrogen element contained in NAG.

[0004] Pyrrole is a five-membered nitrogen heterocyclic compound with unique electronic and steric hindrance properties, making it an important intermediate and precursor for various bioactive substances, natural products, pharmaceuticals, fragrances, and functional materials. For example, the pyrrole ring is a key structural unit in important biological molecules such as chlorophyll, heme, and porphyrin-like cofactors (e.g., heme b, chlorophyll a, vitamin B12). The pyrrole ring is also widely found in natural products and drug candidates, and its derivatives have applications in antifungal, analgesic, antitumor, and antiviral fields, as well as in the synthesis of pesticides and fragrances. Furthermore, polypyrrole is a highly efficient conductive polymer that can be used in electrode materials, electromagnetic shielding materials, and gas separation membrane materials, with broad application value in energy, optoelectronic devices, sensors, and molecular wires.

[0005]

[0006] Formula 1

[0007] To date, the main methods for preparing pyrrole compounds are cyclization reactions. Classical pyrrole ring synthesis methods include the Knorr method, the Paal-Knorr method, the Hantzsch method, the Van Leusen reaction, and the Barton-Zard reaction (Equation 1). These methods can be divided into two categories: one is the construction of pyrrole rings through the condensation reaction of carbonyl compounds (such as amino ketones, dicarbonyl compounds, or haloketones) and amines; the other is the formation of pyrrole rings through the condensation cyclization of enamine reactive intermediates or isocyanates with nitroolefins. Except for the relatively easy synthesis of 2,5-disubstituted pyrroles via the Paal-Knorr reaction of some readily available dicarbonyl compounds, other pyrrole ring synthesis methods suffer from limitations such as the difficulty in obtaining starting materials and demanding reaction conditions. In recent years, many methods using new catalysts and multi-component one-pot processes have been developed for pyrrole synthesis, but these methods still need further expansion. For example, the Van Leusen reaction has the advantage of directly obtaining unsubstituted pyrroles with very high yields, but high yields require low temperatures of -80°C, making operation difficult and energy-intensive. The choice of different synthetic routes mainly depends on factors such as the position and number of substituents on the pyrrole ring, the ease of synthesis of raw materials, and atom economy. There is still huge potential for further development of new and greener pyrrole ring synthesis technologies.

[0008] Considering that pyrrole is a nitrogen-containing heterocycle, its nitrogen element can be derived from the amino groups of nitrogen-containing biomass, such as chitin, glucosamine, and amino acids, thus solving the raw material problem for pyrrole preparation. As early as the 1980s, heterocyclic compounds such as pyrazines, pyrroles, and pyridines were discovered in the pyrolysis reaction of chitin. GAO et al. pyrolyzed chitin at 300℃ and indeed detected pyrrole, pyrazines, and pyridine compounds in the pyrolysis products. Chen et al. also used pyrolysis to generate furfural from cellulose glucose, and then exchanged furfural with ammonia to generate pyrrole (Equation 2). In this specific method, ammonia promoted the dealdehydeization of the cellulose pyrolysis product FF to generate furan, which then underwent a ring-opening reaction, allowing the amino group at C2 to connect with the C5 position to form a ring. The O atom was removed as a hydroxyl group through dehydration to form pyrrole. In 2011, Li et al. reported a possible mechanism involving a tandem reaction of carbocation intermediates under InCl3 catalysis. C-pyrrolidinyl glycosides were synthesized by one-pot tandem condensation of amino sugars (D-glucosamine and D-galactosamine) with 1,3-dicarbonyl compounds in water. Another example is the report by Professor David Milstein's research group at the Weizmann Institute of Science in Israel (Angew. Chem. Int. Ed., 2016, 55, 14373-14377), which used a simple method to obtain pyrrole compounds via enzymatic hydrolysis of lignocellulose, followed by Co-catalyzed dehydrogenation and coupling with amines. The reaction conditions were more favorable. However, the preparation conditions using their PNNH-Co chelate catalyst remained relatively difficult.

[0009]

[0010] Formula 2 Summary of the Invention

[0011] This invention provides a method for preparing pyrrole and furan compounds from N-acetylglucosamine. In this method, in a saline system, the intermediate N-acetylacetaldehyde amine, generated by the reverse aldol reaction catalyzed by a molybdenum catalyst in a complex valence state, reacts with erythrose / threose and then with β-diketone compounds under mild conditions, forming pyrrole (1) and furan (2) compounds through a condensation-dehydration reaction.

[0012]

[0013] In this invention, we have established a method for preparing pyrrole and furan compounds from N-acetylglucosamine. The method mainly utilizes the retro-aldol reaction of NAG to form active N-acetylglucosamine and erythrose, which then undergo in-situ condensation-dehydration reactions with dicarbonyl compounds to form pyrrole and furan compounds (Formula 3).

[0014]

[0015] Formula 3

[0016] The technical solution adopted in this invention is as follows:

[0017] A method for preparing pyrrole and furan compounds from N-acetylglucosamine involves using molybdenum in a complex valence state as a catalyst in a saline system, adding N-acetylglucosamine and β-diketone compounds, and reacting them under mild conditions to obtain pyrrole compounds (1). The reaction also co-produces furan compounds (2).

[0018] When acetylacetone is selected as the in-situ scavenging agent β-diketone, its pyrrole product is N-acetyl-2-methyl-3-acetylpyrrole (3), and its furan product is 5-(1,2-dihydroxyethyl)-2-methyl-3-acetylfuran (DMAF) (4).

[0019]

[0020] The composite molybdenum catalyst mainly refers to the IV, V, and VI valence composite catalyst obtained by reducing VI-valent molybdenum. VI-valent molybdenum raw materials include, but are not limited to, molybdic acid, molybdenum trioxide, magnesium molybdate, ammonium molybdate, and phosphomolybdic acid, with molybdic acid, molybdenum trioxide, or sodium molybdate being preferred. Among these, the composite molybdenum catalyst prepared using molybdic acid as a raw material exhibits the best performance. The optimal amount of N-acetylglucosamine in the composite molybdenum catalyst during the reaction is 0.5-1.0.

[0021] The β-diketone compounds mentioned include, but are not limited to, the following two categories: acetylacetones (I) and ethyl acetoacetate compounds (II). The former includes acetylacetone, 2,4-hexanedione, benzoylacetone, dibenzoylmethane, 1,3-indanedione, 1,3-cycloheptanedione, 2,4-piperidinedione, 1,3-cyclopentanedione, methyl acetylacetate, etc.; the latter includes ethyl acetoacetate, ethyl formylate, ethyl aminoacetoacetate, ethyl chloroacetoacetate, ethyl benzoylacetate, etc. The present invention preferably uses acetylacetone, ethyl acetoacetate, ethyl 4-chloroacetoacetate, ethyl carbamoylacetate, 2,5-hexanedione, 2,4-piperidinedione, and 1,3-cyclopentanedione, among which acetylacetone is the most effective.

[0022]

[0023]

[0024] The saline system includes, but is not limited to, salts such as sodium chloride, calcium chloride, sodium bromide, potassium chloride, lithium chloride, lithium bromide, magnesium chloride, sodium carbonate, sodium bicarbonate, and calcium sulfate. Chloride or bromide salts are preferred, with sodium chloride, magnesium chloride, and lithium bromide being the most suitable.

[0025] The reaction conditions are as follows: reaction temperature 60-120℃, reaction time 1-4h, preferably 80-100℃, reaction time 1-3.5h. The concentration of the molybdenum-containing catalyst is 0.5-1.5mmol. The salt solution system is preferred, with chloride and bromide salts at a concentration of 5wt.%-30wt.%. More preferably, a 15% LiBr brine system is selected.

[0026] The molar ratio of the reaction substrate N-acetylglucosamine to β-diketone compounds is 1:1 to 1:20, preferably 1:3 to 1:8.

[0027] The raw material for this invention, N-acetylglucosamine, is derived from marine waste biomass.

[0028] In one embodiment of the present invention: 2.5 mL of water, 2.5 mL of acetylacetone, 220 mg of N-acetylglucosamine, 60 mg of composite molybdenum catalyst, and 15 wt.% of lithium bromide were used. After the reaction, the organic phase was separated to obtain pyrrole compound, and the aqueous phase was separated to obtain furan compound. Under optimal conditions, when the reaction temperature was 90 °C and the reaction time was 3 h, the yields of pyrrole compound and furan compound were 95% and 74%, respectively.

[0029] Beneficial effects: Compared with the problems of difficult-to-obtain raw materials and harsh reaction conditions in existing pyrrole synthesis methods, the raw material source of this invention, N-acetylglucosamine, comes from marine waste biomass; the whole reaction process is simple and has a high yield; and two heterocyclic compounds, pyrrole and furan, are obtained at the same time, which is a preferred process route for the high-value utilization of marine waste biomass. Attached Figure Description

[0030] Figure 1 The effect of molybdate type on the yield of pyrrole compounds;

[0031] Figure 2 The effect of salt type on the yield of pyrrole compounds;

[0032] Figure 3 The effect of salt concentration on the yield of pyrrole compounds;

[0033] Figure 4 The effect of molybdic acid content on the yield of pyrrole compounds;

[0034] Figure 5 Effect of reaction temperature on the yield of p-pyrrole and furan compounds;

[0035] Figure 6 Single crystal of N-acetyl-2-methyl-3-acetylpyrrole, a pyrrole product;

[0036] Figure 7The pyrrole product N-acetyl-2-methyl-3-acetylpyrrole 1 H NMR;

[0037] Figure 8 The pyrrole product N-acetyl-2-methyl-3-acetylpyrrole 13 C NMR;

[0038] Figure 9 MS of the pyrrole product N-acetyl-2-methyl-3-acetylpyrrole;

[0039] Figure 10 The furan product 5-(1,2-dihydroxyethyl)-2-methyl-3-acetylfuran (DMAF) 1 H NMR;

[0040] Figure 11 The furan product 5-(1,2-dihydroxyethyl)-2-methyl-3-acetylfuran (DMAF) 13 C NMR;

[0041] Figure 12 Furan product 5-(1,2-dihydroxyethyl)-2-methyl-3-acetylfuran (DMAF) MS;

[0042] Figure 13 pyrrole product MS of the reaction of N-acetylglucosamine with 1,3-cyclohexanedione;

[0043] Figure 14 pyrrole product MS of the reaction of N-acetylglucosamine with 1,3-indanedione;

[0044] Figure 15 MS, a pyrrole product of the reaction of N-acetylglucosamine with 1,3-cyclopentanedione;

[0045] Figure 16 pyrrole product MS of the reaction of N-acetylglucosamine with 2,4-hexanedione;

[0046] Figure 17 pyrrole product MS from the reaction of N-acetylglucosamine with methyl acetylacetate;

[0047] Figure 18 pyrrole product MS from the reaction of N-acetylglucosamine with ethyl acetoacetate;

[0048] Figure 19 pyrrole product MS from the reaction of N-acetylglucosamine with ethyl 4-chloroacetoacetate;

[0049] Figure 20 MS is a pyrrole product resulting from the reaction of N-acetylglucosamine with ethyl carbamoyl. Detailed Implementation

[0050] The present invention can be better understood from the following embodiments. However, the descriptions of the embodiments are for illustrative purposes only and should not, and will not, limit the invention as described in detail in the claims.

[0051] General experimental methods:

[0052] 1) Preparation of composite valence state molybdenum catalysts:

[0053] Water, VI-valent molybdenum raw materials (such as molybdic acid, molybdenum trioxide, magnesium molybdate, ammonium molybdate, or phosphomolybdic acid), and reducing agent vitamin C were added to a pressure-resistant tube. The ratio of VI-valent molybdenum raw materials to reducing agent was 1:5. The reaction was carried out at 60-80℃ for 1-2 hours. Acetylacetone was added dropwise and stirred for 30 minutes. The organic phase was separated, and acetylacetone was removed by vacuum distillation to obtain a gray-green composite molybdenum catalyst. The composite molybdenum catalyst was characterized by XPS, showing that it was a mixture of IV, V, and VI valence states.

[0054] 2) Preparation of pyrrole and furan compounds from N-acetylglucosamine:

[0055] In a saline system, a complex molybdenum catalyst catalyzes the reverse aldol reaction of N-acetylglucosamine. The generated reactive intermediates, N-acetylacetaldehyde amine and erythrose, are captured in situ by the β-diketone compound acetylacetone. Under mild conditions, they react to yield pyrrole and furan compounds. Specifically:

[0056] Add 2.5 mL of water, 2.5 mL of acetylacetone, 220 mg of N-acetylglucosamine, 60 mg of a composite molybdenum catalyst, and 15 wt.% lithium bromide to a pressure-resistant tube, and react at 120 °C for 2 h. After the reaction, rapidly cool the tube in ice water. Determine the content of pyrrole compounds by gas chromatography on the organic phase, and determine the content of furan compounds by high-performance liquid chromatography on the aqueous phase.

[0057] 3) Separation of pyrrole compounds: After the reaction, separate the organic phase (using 10 mL of reagent), add 150 mL of 10% copper acetate solution, stir well and react for 3-5 h, filter to precipitate (blue-green, copper acetylacetonate); extract the aqueous phase with ethyl acetate 2-3 times, add anhydrous sodium sulfate and dry overnight, evaporate the ethyl acetate to obtain crude pyrrole compounds. If further purification is required, column chromatography can be used to further separate the target product.

[0058] 4) Separation of furan compounds: After the reaction is complete, separate the aqueous phase (with 10 mL of reagent), add 10 mL of 10% copper acetate solution, stir well and react for 3-5 h, filter to precipitate (blue-green, copper acetylacetonate); further concentrate the aqueous phase to dryness to obtain crude furan compounds. If further purification is required, column chromatography is used to further separate the target product.

[0059] Product characterization and detection methods:

[0060] Characterization of pyrrole compounds: The product N-acetyl-2-methyl-3-acetylpyrrole was subjected to HRMS in DMSO-d6 or methanol. 1 H and 13 C10 NMR characterization: HRMS (ESI, C10) 13 NH) m / z: 166.1 (M+H) + (See attached document for details) Figure 1-4 .

[0061] Characterization of furan compounds: The product 5-(1,2-dihydroxyethyl)-2-methyl-3-acetylfuran (DMAF) was characterized by HRMS in DMSO-d6 or methanol. 1 H and 13 C10 NMR characterization, HRMS (ESI, C10) 13 NH) m / z: 185 (M+H) + See attached for details. Figure 5-7 .

[0062] The pyrrole product N-acetyl-2-methyl-3-acetylpyrrole was detected by GC. The reaction product sample in the organic phase was analyzed using a Shimadzu gas chromatograph (GC-2010Plus) equipped with a Restek Rtx-VMS capillary. Specific conditions were as follows: 1 μL of sample was injected into the gas chromatograph column at a split ratio of 49:1. Helium was used as the carrier gas at a flow rate of 1 mL / min⁻¹. The initial oven temperature was 40 °C and held for 5 minutes. The temperature was then increased to 240 °C at a rate of 7.5 °C / min and held at 240 °C for 15 minutes.

[0063] The furan product 5-(1,2-dihydroxyethyl)-2-methyl-3-acetylfuran was detected by HPLC (Dionex, Sunnyvale, CA). Specific conditions included a Sinochrom ODS-BP 5µm C18 column and a 254 nm UV detector; the mobile phase was 17% CH3CN / H2O; the flow rate was 0.6 mL min⁻¹; and the column temperature was 30 ºC.

[0064] Detection of N-acetylglucosamine: The lower aqueous phase of the reaction solution was analyzed using HPLC (Dionex ICS-3000, Sunnyvale, CA). Specific conditions included the use of an integrated amperometric detector and a CarboPac PA1 guard and analytical column (Dionex, Sunnyvale, CA) for quantification of acetylglucosamine to determine the completeness of the reaction. The mobile phase was 0.005 mmol H₂SO₄, and the flow rate was 0.6 mL / min. The column oven was set to 30 ºC.

[0065] Product yield calculation method:

[0066] The yield of pyrrole compounds is calculated according to the following equation.

[0067]

[0068] The yield of furan compounds is calculated according to the following equation.

[0069]

[0070] Example 1: The effect of catalyst type on reaction process

[0071] We chose acetylacetone as a diketone compound to explore the optimal reaction conditions for its in-situ scavenging effect in the preparation of pyrrole and furan compounds. In this invention, a catalyst is added to catalyze the reverse aldol reaction of N-acetylglucosamine, yielding the reactive N-acetylacetaldehyde amine and erythrose, which then undergoes an in-situ condensation reaction with acetylacetone, followed by dehydration to produce pyrrole and furan compounds. Therefore, the reverse aldol reaction of N-acetylglucosamine is crucial for the preparation of pyrrole and furan compounds, making the selection of highly efficient reverse aldol catalysts extremely important.

[0072] This example uses a single-factor analysis method, selecting four VI-valent molybdenum raw materials—molybdic acid, molybdenum trioxide, sodium molybdate, phosphomolybdic acid, and vitamin C—as reducing agents to prepare a composite valence molybdenum catalyst. The reaction conditions are: 70℃ for 1.5 h. The specific conditions for preparing pyrrole and furan compounds from N-acetylglucosamine are: 2.5 mL water (pressure-resistant tube); 2.5 mL acetylacetone (pressure-resistant tube); reaction temperature 100℃; reaction time 1 h; N-acetylglucosamine dosage 220 mg; composite valence molybdenum catalyst dosage 60 mg. Simultaneously, we selected no catalyst and IV-valent molybdenum dioxide as catalysts for comparative experiments. Since the reverse aldol reaction produces N-acetylacetaldehyde amine and erythrose in equal proportions, which undergo a condensation reaction with acetylacetone, theoretically, pyrrole and furan compounds are produced in equal proportions. Therefore, after the reaction, we took the upper organic phase and determined the content of pyrrole compounds by gas chromatography to judge the catalyst efficiency.

[0073] Depend on Figure 1 It was found that the reverse aldol reaction did not occur when the composite molybdenum catalyst was used as a blank control. Although N-acetylglucosamine was consumed during the reaction, no pyrrole compounds were detected in the organic phase. However, the addition of the four composite molybdenum catalysts all showed some reverse aldol catalytic effect, with pyrrole compound yields ranging from 7% to 39%. Among them, the composite molybdenum catalyst prepared using molybdic acid as a VI-valent molybdenum raw material exhibited significantly better catalytic performance than the other catalysts, achieving a pyrrole compound yield of 39% under the reaction conditions. When using IV-valent molybdenum dioxide as a catalyst, a small amount of pyrrole compounds could be detected, with a yield of less than 3%. Further research will focus on composite molybdenum catalysts derived from molybdic acid.

[0074] Example 2: The promoting effect of salt type on the reaction

[0075] During the reaction, we observed poor partitioning between the water and organic phases. Therefore, we considered introducing inorganic salts into the aqueous phase. On one hand, the addition of inorganic salts can promote the dehydration reaction and reduce the formation of the byproduct dihydropyrrole compounds; on the other hand, the addition of inorganic salts can increase the partition ratio of pyrrole compounds in the organic phase, promoting rapid phase separation between the water and organic phases.

[0076] This example employs a single-factor analysis method, using a control group without added salt. Five typical chloride and bromide salts were selected, including sodium chloride, lithium bromide, magnesium chloride, calcium chloride, and potassium chloride. The reaction conditions were: 2.5 ml water (pressure-resistant tube); 2.5 ml acetylacetone (pressure-resistant tube); reaction temperature 120℃; reaction time 2 h; acetylglucosamine dosage 220 mg; molybdate-derived composite molybdenum catalyst dosage 60 mg; and salt concentration 10 wt.%. Similarly, the promoting effect of inorganic salts was determined by gas chromatography to measure the content of pyrrole compounds in the upper organic phase.

[0077] Depend on Figure 2 It can be seen that the addition of inorganic salts slightly increased the yield of some pyrrole compounds in the reaction. Among them, lithium bromide had the best promoting effect, with a pyrrole product yield of 48%. This indicates that lithium bromide does indeed promote the formation of pyrrole compounds.

[0078] Example 3: The promoting effect of salt concentration on the reaction

[0079] Example 2 introduced inorganic salts, revealing their promoting effect on the reaction. Further consideration was given to the influence of salt concentration to further improve the yield. Therefore, we selected two salts with relatively good effects—lithium bromide and magnesium chloride—for comparative research.

[0080] Single-factor analysis was used to select lithium bromide and magnesium chloride to react under the same reaction conditions. The reaction conditions were: 2.5 ml water (pressure-resistant tube); 2.5 ml acetylacetone (pressure-resistant tube); reaction temperature 120℃; reaction time 2 h; acetylglucosamine dosage 220 mg; composite molybdenum catalyst dosage 60 mg; salt concentration 5-30 wt.%. Similarly, the promoting effect of inorganic salts was determined by gas chromatography to determine the content of pyrrole compounds in the upper organic phase.

[0081] Depend on Figure 3 It can be seen that, regardless of the concentration, lithium bromide as an inorganic salt has a better promoting effect than magnesium chloride. The promoting effect on pyrrole compounds becomes more pronounced with increasing inorganic salt concentration. However, the promoting effect decreases above 15 wt.%. Considering both the type and concentration of salt, 15% LiBr yields the best results, achieving a pyrrole compound yield as high as 65%.

[0082] Example 4: Investigating the effect of molybdic acid concentration on yield

[0083] After completing Examples 1-3, we determined that the molybdenum catalyst with a composite valence state derived from molybdic acid was the optimal catalyst and 15wt% LiBr was the optimal salt. We then continued to consider the effect of catalyst dosage and optimized the reaction.

[0084] Single-factor analysis was used to vary the amount of molybdate-derived composite molybdenum catalyst. The reaction conditions were as follows: 2.5 ml water (pressure-resistant tube); 2.5 ml acetylacetone (pressure-resistant tube); reaction temperature 120℃; reaction time 2 h; acetylglucosamine dosage 220 mg; lithium bromide concentration 15 wt.%; and the amount of molybdate-derived composite molybdenum catalyst 30-90 mg. Similarly, the catalyst's effect was determined by gas chromatography to analyze the content of pyrrole compounds in the upper organic phase.

[0085] Depend on Figure 4 It can be seen that the increase in the amount of molybdenum catalyst of composite valence state derived from molybdic acid does not show a certain regularity in the effect on the formation of pyrrole compounds. When the amount of molybdenum acid is 60 mg, the pyrrole compounds are obtained with the highest yield of 65%.

[0086] Example 5: Effect of reaction temperature and time on the yield of pyrrole compounds

[0087] After determining the optimal raw materials, raw material ratios, and catalyst concentrations, we investigated the effects of temperature and time in this example. First, using single-factor analysis, we selected different temperatures under the same 2-hour reaction conditions. The reaction conditions were: 2.5 ml water (pressure-resistant tube); 2.5 ml acetylacetone (pressure-resistant tube); reaction time 2 hours; acetylglucosamine dosage 220 mg; molybdate-derived composite molybdenum catalyst dosage 60 mg; lithium bromide 15 wt.%; and reaction temperature between 80-120℃. Considering that the formation of both pyrrole and furan compounds is correlated with temperature, after the reaction, we determined the pyrrole content in the organic phase using gas chromatography and the furan content in the aqueous phase using high-performance liquid chromatography. The yields of both products were calculated, as shown in Table 1.

[0088] Table 1: Yields of pyrrole and furan compounds at different temperatures

[0089] pyrrole compound yield % 28 66 65 74 65 Furan compound yield % 12 55 45 27 7

[0090] Table 1 shows that the yields of both pyrrole and furan compounds were low at both lower reaction temperatures (80℃) and higher reaction temperatures (120℃); however, the yields of both products were acceptable at temperatures of 90℃, 100℃, and 110℃. Since the yields of the two compounds may vary at different reaction times, we selected 90℃, 100℃, and 110℃ to investigate the product yields at different times. Specific results are shown in [Table 1]. Figure 5 .

[0091] Depend on Figure 5 The data shows that the yields of both pyrrole and furan compounds increase with increasing reaction time; however, the growth trends differ at different temperatures. Under optimal conditions (reaction temperature 90℃, reaction time 3h), the yields of pyrrole and furan compounds are 95% and 74%, respectively.

[0092] Example 6: Reactivity of diketone compounds

[0093] Under the aforementioned reaction conditions, we expanded the range of diketone compounds. Different diketone compounds were used to replace acetylacetone as in-situ trapping agents, and condensed with N-acetylacetaldehyde amine / erythrose obtained from the reverse aldol reaction of N-acetylglucosamine catalyzed by a molybdate-derived composite molybdenum catalyst, forming different pyrrole and furan compounds.

[0094] This example employs a single-factor analysis method, selecting eight dicarbonyl compounds, including 5-methyl-1,3-cyclohexanedione, 1,3-indanedione, 1,3-cyclopentanedione, 2,4-hexanedione, methyl acetylacetonate, ethyl acetoacetate, ethyl 4-chloroacetoacetate, and ethyl carbamoyl. The specific reaction conditions were as follows: 220 mg of N-acetylglucosamine; 60 mg of molybdate-derived composite molybdenum catalyst; 2.5 ml of water (pressure-resistant tube); the dicarbonyl compounds were added at a molar ratio of 3:1 to N-acetylglucosamine; the reaction temperature was 120℃; and the reaction time was 2 hours. After the reaction was completed, samples were taken for mass spectrometry analysis.

[0095] Table 2 shows that different diketone compounds exhibit varying reaction results with N-acetylglucosamine. Here, some reactions in which the target pyrrole compounds can be detected by mass spectrometry are listed. The structures of the pyrrole compounds are shown in Table 2, and their mass spectrometry detection details can be found in [link to table]. Figure 13-20 .

[0096] Table 2: Preparation of pyrrole compounds from different β-diketones

[0097]

Claims

1. A method for preparing pyrrole and furan compounds from N-acetylglucosamine, characterized in that, In a saline system, using molybdenum in a complex valence state as a catalyst, N-acetylglucosamine and β-diketone compounds were added and reacted under mild conditions to obtain pyrrole compounds (1). The reaction also produced furan compounds (2). The composite molybdenum catalyst refers to a composite catalyst with IV, V and VI valence states obtained by reducing VI-valent molybdenum; the VI-valent molybdenum raw materials include molybdic acid, molybdenum trioxide, magnesium molybdate, ammonium molybdate, and phosphomolybdic acid; The mild conditions are a reaction temperature of 80-120℃ and a reaction time of 1-3.5h. 。 2. The method for preparing pyrrole and furan compounds from N-acetylglucosamine according to claim 1, characterized in that, The β-diketone compounds include the following two categories: acetylacetone compounds and ethyl acetoacetate compounds. The acetylacetone compounds include acetylacetone, 2,4-hexanedione, benzoylacetone, dibenzoylmethane, 1,3-indanedione, 1,3-cycloheptanedione, 2,4-piperidinedione, 1,3-cyclopentanedione, and methyl acetylacetate. The ethyl acetoacetate compounds include ethyl acetoacetate, ethyl formylate, ethyl aminoacetoacetate, ethyl chloroacetoacetate, and ethyl benzoylacetate.

3. The method for preparing pyrrole and furan compounds from N-acetylglucosamine according to claim 1, characterized in that, The saline system includes salts such as sodium chloride, calcium chloride, sodium bromide, potassium chloride, lithium chloride, lithium bromide, magnesium chloride, sodium carbonate, sodium bicarbonate, and calcium sulfate.

4. The method for preparing pyrrole and furan compounds from N-acetylglucosamine according to claim 1, characterized in that, The molar ratio of N-acetylglucosamine to β-diketones is 1:1 to 1:

20.

5. The method for preparing pyrrole and furan compounds from N-acetylglucosamine according to claim 1, characterized in that, Composite molybdenum catalyst: The amount of N-acetylglucosamine used is 0.5-1.

0.

6. The method for preparing pyrrole and furan compounds from N-acetylglucosamine according to claim 1, characterized in that, The β-diketone is acetylacetone, its pyrrole product is N-acetyl-2-methyl-3-acetylpyrrole (3), and its furan product is 5-(1,2-dihydroxyethyl)-2-methyl-3-acetylfuran (4). 。 7. The method for preparing pyrrole and furan compounds from N-acetylglucosamine according to claim 2, characterized in that, The β-diketone compounds are acetylacetone, ethyl acetoacetate, 2,5-hexanedione, 2,4-piperidinedione, and 1,3-cyclopentanedione.

8. The method for preparing pyrrole and furan compounds from N-acetylglucosamine according to claim 3, characterized in that, The salt in the saline system is a chloride or bromide salt, and the salt concentration is 5 wt.%-30 wt.%.

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