Method for preparing 3-alkoxy quinoxaline-2 (1H)-ketone compound through photocatalysis

Abstract

The invention discloses a method for preparing a 3-alkoxy quinoxaline-2 (1H)-ketone compound through photocatalysis, and belongs to the field of organic synthesis.The method comprises the following steps that the quinoxaline-2 (1H)-ketone compound, an alcohol compound and a photocatalyst mpg-C3N4 (mesoporous graphite phase carbon nitride) are added into a reaction kettle and mixed to be uniform; carrying out illumination reaction at room temperature in an air atmosphere; and after the reaction is completed, treating and separating to obtain a 3-alkoxy quinoxaline-2 (1H)-ketone product. The method is mild in reaction condition, simple to operate and wide in application range, and the 3-alkoxy quinoxaline-2 (1H)-ketone compound can be synthesized in one step.

Description

Technical Field

[0001] The invention belongs to the field of organic synthesis, and in particular relates to a method for preparing 3-alkoxyquinoxaline-2(1H)-one compounds by photocatalysis. Background Art

[0002] Quinoxaline-2(1H)-one is an important bioactive skeleton with wide applications in medicinal chemistry and materials chemistry. In particular, 3-alkoxyquinoxaline derivatives have significant pharmacological activity and can be used as aldose reductase inhibitors, so the construction of such molecules is of great significance (Eur J Med Chem, 2014, 80: 383-392; Org Biomol Chem, 2020, 18: 6558-6563.).

[0003]

[0004] Given their significant biological activity and medicinal value, the synthesis of 3-alkoxyquinoxalin-2(1H)-ones has garnered widespread interest. 3-Alkoxyquinoxalin-2(1H)-ones are typically synthesized via direct CH / OH cross-dehydrogenative coupling of quinoxalin-2(1H)-one with alcohols or phenols, which is crucial for their atom and step economies. Research has focused on the selection and optimization of reaction conditions, including catalysts and oxidants.

[0005] For example, in 2019, the Li group (Adv Synth Catal, 2019, 361: 5363.) used acridinium salt as a photosensitizer, and in the same year, the Li Jianjun group (Adv Synth Catal, 2019, 361: 5371) used rhodamine photosensitizer to achieve the alkoxylation reaction of quinoxalinone with alcohol.

[0006]

[0007] However, in practice, especially in pharmaceutical synthesis, the application of these methods is limited by the need for expensive homogeneous photocatalysts or oxidants. Therefore, an efficient and catalyst-recyclable photocatalytic method is urgently needed to synthesize quinoxalinone alkoxy ethers. To this end, we used mpg-C3N4 as a photocatalyst and alcohols as alkoxylation agents to achieve the alkoxylation reaction of quinoxalinone with alcohols under transition metal-free and oxidant-free conditions via visible light catalysis.

[0008] Summary of the Invention

[0009] The present invention provides a method for photocatalytically preparing 3-alkoxyquinoxaline-2(1H)-one compounds. The method uses mpg-C3N4 (mesoporous graphitic carbon nitride) as a photocatalyst, sequentially adds a quinoxaline-2(1H)-one compound, an alcohol compound, and the photocatalyst to a reaction kettle (the alcohol serves as both a reactant and a solvent) and mixes them evenly. The reaction is then irradiated with light at room temperature in an air atmosphere. After the reaction is complete, the 3-alkoxyquinoxaline-2(1H)-one product is separated and processed. This method eliminates the use of metal reagents, additional oxidants, high temperatures, and cumbersome operating steps, and features low reaction energy consumption, safety, and high efficiency.

[0010] In order to achieve the above object, the technical solution adopted by the present invention is:

[0011] A method for photocatalytically preparing 3-alkoxyquinoxaline-2(1H)-one compounds comprises the following steps:

[0012] A quinoxaline-2(1H)-one compound represented by structural formula 1, an ether compound represented by structural formula 2, and a photocatalyst mpg-C3N4 are added to a Shrek tube with a magnetic stirrer, mixed evenly, and the tube is sealed with a rubber septum; the reaction is carried out at room temperature, in an air atmosphere, under irradiation with an LED lamp, and at 20-50° C. for 6-72 hours; after detection by TLC, the reaction solution is centrifuged to separate carbon nitride, a saturated saline solution is added to the reaction solution for washing, and then ethyl acetate is added for extraction. After the extract is dried over anhydrous sodium sulfate, the extract is concentrated until it is free of solvent to obtain a crude product, which is then subjected to rapid column chromatography to obtain a 3-alkoxyquinoxaline-2(1H)-one product.

[0013] The general reaction formula is as follows:

[0014]

[0015] wherein R1 and R2 in structural formula 1 are hydrogen, halogen, alkyl, alkoxy, aryl or aryloxy; wherein R3 in structural formula 2 is a C1-C6 straight chain or branched hydrocarbon group, aryl or substituted aryl group;

[0016] Further defined, the compound corresponding to structural formula 3 is:

[0017]

[0018]

[0019] It is further defined that the mass of the photocatalyst mesoporous graphitic carbon nitride is 10 mg to 30 mg;

[0020] It is further defined that in the reaction between the quinoxaline-2(1H)-one compound and the alcohol compound, the alcohol is both a reactant and a solvent;

[0021] It is further defined that the light source is a 450-455nm blue LED lamp or a 390-400nm purple LED lamp.

[0022] Beneficial effects: The present invention provides a method for photocatalytically preparing 3-alkoxyquinoxaline-2(1H)-one compounds, which has the following advantages over the prior art:

[0023] 1. The present invention does not require pre-functionalization of quinoxaline-2(1H)-one. Since the synthesis of 3-alkoxyquinoxaline-2(1H)-one compounds is carried out in a single step under visible light catalysis, the reaction conditions are mild, the energy is clean, no strong oxidant is required, the reaction is highly safe, and the functional group compatibility is good.

[0024] 2. The present invention adopts a non-metallic photocatalyst, which effectively avoids the use of metal reagents and reduces metal pollution. In addition, carbon nitride can be recycled and reused, saving reaction costs and being environmentally friendly. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a flow chart of the photocatalytic reaction in an embodiment of the present invention; DETAILED DESCRIPTION

[0026] The present invention is described in detail below in conjunction with specific embodiments:

[0027] Unless otherwise specified, the experimental methods used in the following examples are conventional methods; the reaction temperature is room temperature and can be set at any temperature between 20°C and 50°C depending on the ambient temperature under light; the materials and reagents used, unless otherwise specified, can be obtained from commercial sources or synthesized from commercially available raw materials.

[0028] Example 1

[0029]

[0030] Quinoxaline-2(1H)-one (1a, 0.20 mmol), methanol (2a, 5 mL), and 20 mg of the photocatalyst mpg-CN were added to a Shrek tube equipped with a magnetic stirrer, mixed thoroughly, and sealed with a rubber septum. The reaction was allowed to proceed at room temperature under air and irradiated with a blue LED light for 54 hours. HPLC analysis revealed a 78% yield. After centrifugation, extraction, and column chromatography, the product 3a, 3-methoxyquinoxaline-2(1H)-one, was obtained as a white solid (26.7 mg, 76% yield), with an mp of 243-244°C. 1H NMR (400MHz, DMSO-d6) δ12.35 (s, 1H), 7.53 (dd, J=8.0, 1.4Hz, 1H), 7.34 (ddd, J=8.4, 7.1, 1.4Hz, 1H), 7.27-7.19 (m, 2H), 3.95 (s, 3H). 13 C NMR (101MHz, DMSO-d6) δ155.58, 150.84, 130.83, 130.67, 127.23, 126.51, 123.69, 115.46, 54.51.HRMS (ESI): m / zcalcd for C9H8NaN2O2 + [M+Na] + :199.0478;found:199.0503..

[0031] Example 2

[0032] The reactant quinoxaline-2(1H)-one (1a, 0.20 mmol), the reactant methanol (2a, 5 mL), and 20 mg of the photocatalyst mpg-CN were added to a Shrek tube equipped with a magnetic stirrer, mixed thoroughly, and the tube was sealed with a rubber septum. The reaction was carried out at room temperature in an air atmosphere under blue LED light for 48 hours. HPLC analysis showed a yield of 61%.

[0033] Example 3

[0034] The reactant quinoxaline-2(1H)-one (1a, 0.20 mmol), the reactant methanol (2a, 5 mL), and 20 mg of the photocatalyst mpg-CN were added to a Shrek tube equipped with a magnetic stirrer, mixed thoroughly, and the tube was sealed with a rubber septum. The reaction was carried out at room temperature in an air atmosphere under blue LED light for 24 hours. HPLC analysis showed a yield of 52%.

[0035] Example 4

[0036] The reactant quinoxaline-2(1H)-one (1a, 0.20 mmol), the reactant methanol (2a, 5 mL), and the photocatalyst mpg-CN420 mg were added to a Shrek tube equipped with a magnetic stirrer, mixed uniformly, and the tube was sealed with a rubber septum. The reaction was carried out at room temperature in an air atmosphere under blue LED light for 60 hours. HPLC analysis showed a yield of 75%.

[0037] Example 5

[0038] The reactant quinoxaline-2(1H)-one (1a, 0.20 mmol), the reactant methanol (2a, 5 mL), and the photocatalyst mpg-CN 10 mg were added to a Shrek tube equipped with a magnetic stirrer, mixed thoroughly, and the tube was sealed with a rubber septum. The reaction was carried out at room temperature in an air atmosphere under blue LED light for 54 hours. HPLC analysis showed a yield of 72%.

[0039] Example 6

[0040] The reactant quinoxaline-2(1H)-one (1a, 0.20 mmol), the reactant methanol (2a, 5 mL), and the photocatalyst mpg-CN3N430 mg were added to a Shrek tube equipped with a magnetic stirrer, mixed thoroughly, and the tube was sealed with a rubber septum. The reaction was carried out at room temperature in an air atmosphere under blue LED light for 54 hours. HPLC analysis showed a yield of 71%.

[0041] Example 7

[0042] The reactant quinoxaline-2(1H)-one (1a, 0.20 mmol), the reactant methanol (2a, 5 mL), and 20 mg of the photocatalyst mpg-CN were added to a Shrek tube equipped with a magnetic stirrer, mixed thoroughly, and the tube was sealed with a rubber septum. The reaction was carried out at room temperature under a nitrogen atmosphere and irradiated with a blue LED light for 54 hours. HPLC analysis showed a yield of 42%.

[0043] Example 8

[0044] The reactant quinoxaline-2(1H)-one (1a, 0.20 mmol), the reactant methanol (2a, 5 mL), and 20 mg of the photocatalyst mpg-CN were added to a Shrek tube equipped with a magnetic stirrer, mixed thoroughly, and the tube was sealed with a rubber septum. The reaction was carried out at room temperature under an oxygen atmosphere and irradiation with a blue LED light for 54 hours. HPLC analysis showed a yield of 75%.

[0045] Example 9

[0046] The reactant quinoxaline-2(1H)-one (1a, 0.20 mmol), the reactant methanol (2a, 5 mL), and the photocatalyst mpg-CN420 mg were added to a Shrek tube equipped with a magnetic stirrer, mixed evenly, and the tube was sealed with a rubber septum. The reaction was carried out at room temperature in an air atmosphere under irradiation with a purple LED light for 54 hours. HPLC analysis showed a yield of 43%.

[0047] Example 10

[0048] The reactant quinoxaline-2(1H)-one (1a, 0.20 mmol), the reactant methanol (2a, 5 mL), and 20 mg of the photocatalyst mpg-CN were added to a Shrek tube equipped with a magnetic stirrer, mixed thoroughly, and the tube was sealed with a rubber septum. The reaction was incubated at 50°C in an air atmosphere under blue LED light for 54 hours. HPLC analysis revealed a yield of 74%.

[0049] Example 11

[0050]

[0051] The reactant, quinoxaline-2(1H)-one (1a, 0.20 mmol), the reactant, ethanol (2b, 5 mL), and 20 mg of the photocatalyst, mpg-CN, were added to a Shrek tube equipped with a magnetic stirrer, mixed thoroughly, and sealed with a rubber septum. The reaction was allowed to proceed at room temperature under air and irradiation with a blue LED light for 54 hours. After centrifugation, extraction, and column chromatography, the product 3b, 3-ethoxyquinoxaline-2(1H)-one, was obtained as a white solid, 23.0 mg, in a 60% yield, with an mp of 198-199°C. 1 H NMR (400MHz, DMSO-d6) δ12.34 (s, 1H), 7.50 (dd, J=8.0, 1.4Hz, 1H), 7.33 (ddd, J=8. 3, 7.1, 1.4Hz, 1H), 7.27-7.16 (m, 2H), 4.39 (q, J=7.1Hz, 2H), 1.37 (t, J=7.1Hz, 3H). 13 C NMR (101MHz, DMSO-d6) δ155.09, 150.88, 130.76, 130.73, 127.12, 126.48, 123.65, 115.41, 63.06, 14.50. HRMS (ESI): m / z calcd for C 10 H 10 NaN2O2 + [M+Na] + :213.0634; found:213.0659.

[0052] Example 12

[0053]

[0054] The reactant, quinoxalin-2(1H)-one (1a, 0.20 mmol), the reactant, n-pentanol (2c, 5 mL), and 20 mg of the photocatalyst, mpg-CN, were added to a Shrek tube equipped with a magnetic stirrer, mixed thoroughly, and sealed with a rubber septum. The reaction was allowed to proceed at room temperature under air and irradiation with a blue LED light for 54 hours. After centrifugation, extraction, and column chromatography, the product 3c, 3-n-pentyloxyquinoxalin-2(1H)-one, was obtained as a white solid, 31.3 mg, in a 67% yield, with an mp of 160-161°C. 1 H NMR (400MHz, DMSO-d6) δ12.42 (s, 1H), 7.78 (dd, J=8.0, 1.3Hz, 1H), 7.56-7.47 (m, 1H), 7.30 (t, J=8.1Hz, 2H), 5. 02-4.78 (m, 2H), 1.89-1.74 (m, 1H), 1.62 (tq, J=13.3, 7.5, 6.1Hz, 1H), 1.41-1.28 (m, 4H), 0.87 (q, J=6.7Hz, 3H). 13 C NMR (101MHz, DMSO-d6) δ162.81, 154.49, 132.33, 131.72, 130.37, 128.77, 123.72, 115.79, 68.98, 34.75, 27.98, 22.55, 14.42.HRMS (ESI): m / z calcd for C 13 H 16 NaN2O2 + [M+Na] + :255.1104; found:255.1132.

[0055] Example 13

[0056]

[0057] The reactant, quinoxalin-2(1H)-one (1a, 0.20 mmol), the reactant, 2-methylpropanol (2d, 5 mL), and 20 mg of the photocatalyst, mpg-CN, were added to a Shrek tube equipped with a magnetic stirrer, mixed thoroughly, and sealed with a rubber septum. The reaction was allowed to proceed at room temperature under air and irradiation with a blue LED light for 54 hours. After centrifugation, extraction, and column chromatography, the product, 3-(2-methyl)propoxyquinoxalin-2(1H)-one, was obtained as a white solid, 11.0 mg, in an isolated yield of 25%, with an mp of 148-150°C. 1H NMR (400MHz, DMSO-d6) δ12.40 (s, 1H), 7.50 (dd, J=7.9, 1.3Hz, 1H), 7.33 (ddd, J=8.3, 7.2, 1.4Hz , 1H), 7.27-7.15 (m, 2H), 4.11 (d, J=6.7Hz, 2H), 2.09 (hept, J=6.7Hz, 1H), 0.99 (d, J=6.7Hz, 6H). 13 C NMR (101MHz, DMSO-d6) δ155.24, 150.87, 130.74, 130.72, 127.13, 126.47, 123.66, 115.41, 73.11, 27.66, 19.49. HRMS (ESI): m / z calcd for C 12 H 14 NaN2O2 + [M+Na] + :241.0947; found:241.0956.

[0058] Example 14

[0059]

[0060] The reactant, quinoxaline-2(1H)-one (1a, 0.20 mmol), isopropanol (2e, 5 mL), and 20 mg of the photocatalyst, mpg-CN, were added to a Shrek tube equipped with a magnetic stirrer, mixed thoroughly, and sealed with a rubber septum. The reaction was allowed to proceed at room temperature under air and irradiated with a blue LED light for 54 hours. After centrifugation, extraction, and column chromatography, the product, 3-isopropoxyquinoxaline-2(1H)-one 3e, was obtained as a white solid, 11.0 mg, in a 27% yield, with an mp of 144-145°C. 1 H NMR (400MHz, Chloroform-d) δ12.15 (s, 1H), 7.62 (dd, J=7.9, 1.5Hz, 1H), 7.42 (dd, J=8.0, 1.6Hz, 1H), 7.36 (td, J=7 .6, 1.5Hz, 1H), 7.30 (ddd, J=8.7, 7.2, 1.5Hz, 1H), 5.55 (hept, J=6.2Hz, 1H), 1.52 (d, J=6.2Hz, 6H). HRMS (ESI): m / z calcd for C 11 H 12 NaN2O2 + [M+Na] + :227.0791; found:227.0817.

[0061] Example 15

[0062]

[0063] The reactants, quinoxalin-2(1H)-one (1a, 0.20 mmol), 2-butanol (2f, 5 mL), and 20 mg of the photocatalyst mpg-CN4 were added to a Shrek tube equipped with a magnetic stirrer, mixed thoroughly, and sealed with a rubber septum. The reaction was allowed to proceed at room temperature under air and irradiated with a blue LED light for 54 hours. After centrifugation, extraction, and column chromatography, the product 3f, 3-(2-butoxy)-quinoxalin-2(1H)-one, was obtained as a white solid, 4.4 mg, in a 10% yield, with an mp of 102-104°C. 1 H NMR (400MHz, DMSO-d6) δ12.35 (s, 1H), 7.49 (dd, J=8.0, 1.4Hz, 1H), 7.32 (ddd, J=8.4, 7.1, 1.5Hz, 1H), 7.25-7.17 (m, 2H), 5.18 (p, J=6.2Hz, 1H), 1.70 (qdd, J=13.5, 7.6, 6.3Hz, 2H), 1.31 (d, J=6.2Hz, 3H), 0.92 (t, J=7.4Hz, 3H). 13 C NMR (101MHz, DMSO-d6) δ154.68, 151.04, 130.77, 130.58, 127.00, 126.41, 123.62, 115.35, 74.29, 28.59, 19.28, 10.02. HRMS (ESI): m / z calcd for C 12 H 14 NaN2O2 + [M+Na] + :241.947; found:241.0956.

[0064] Example 16

[0065]

[0066] The reactant, quinoxaline-2(1H)-one (1b, 0.20 mmol), the reactant, methanol (2a, 5 mL), and 20 mg of the photocatalyst, mpg-CN, were added to a Shrek tube equipped with a magnetic stirrer, mixed thoroughly, and sealed with a rubber septum. The reaction was allowed to proceed at room temperature under air and irradiation with a blue LED light for 54 hours. After centrifugation, extraction, and column chromatography, 3 g of the product, 6-fluoro-3-methoxyquinoxaline-2(1H)-one, was obtained as a white solid (26 mg) in a 67% yield, mp 231-232°C.1 H NMR (400MHz, DMSO-d6) δ12.40 (s, 1H), 7.33 (d, J=9.6Hz, 1H), 7.23 (d, J=7.0Hz, 2H), 3.95 (s, 3H). 13 C NMR (101MHz, DMSO-d6) δ159.66, 157.30, 156.51, 150.45, 131.53, 131.41, 127.60, 116.67, 116.57, 114.88, 114.64, 112.17, 111.95, 54.75. 19 F NMR(376MHz, DMSO-d6) δ-119.55.HRMS(ESI): m / z calcd for C9H7FNaN2O2 + [M+Na] + :217.0384; found:217.0406.

[0067] Example 17

[0068]

[0069] The reactant, quinoxaline-2(1H)-one (1c, 0.20 mmol), the reactant, methanol (2a, 5 mL), and 20 mg of the photocatalyst, mpg-CN, were added to a Shrek tube equipped with a magnetic stirrer, mixed thoroughly, and sealed with a rubber septum. The reaction was allowed to proceed at room temperature under air and irradiated with a blue LED light for 54 hours. After centrifugation, extraction, and column chromatography, the product, 6-chloro-3-methoxyquinoxaline-2(1H)-one (3h), was obtained as a white solid, 14.2 mg, in a 34% isolated yield, with an mp of 250-251°C. 1 H NMR (400MHz, DMSO-d6) δ12.35 (s, 1H), 7.57-7.40 (m, 1H), 7.21 (dt, J=14.7, 5.0Hz, 2H), 4.09-3.83 (m, 3H). 13 C NMR (101MHz, DMSO-d6) δ155.77, 150.65, 131.92, 131.07, 129.64, 128.05, 123.59, 114.75, 54.66.HRMS (ESI): m / z calcd for C9H7ClNaN2O2 + [M+Na] + :233.0088; found:233.0094.

[0070] Example 18

[0071]

[0072] The reactant, quinoxalin-2(1H)-one (1d, 0.20 mmol), the reactant, methanol (2a, 5 mL), and 20 mg of the photocatalyst, mpg-CN, were added to a Shrek tube equipped with a magnetic stirrer, mixed thoroughly, and sealed with a rubber septum. The reaction was allowed to proceed at room temperature under air and irradiation with a blue LED light for 54 hours. After centrifugation, extraction, and column chromatography, the product, 6-bromo-3-methoxyquinoxalin-2(1H)-one 3i, was obtained as a white solid, 21.7 mg, in an isolated yield of 43%, with an mp of 228-230°C. 1 H NMR (400MHz, DMSO-d6) δ12.46 (s, 1H), 7.67 (s, 1H), 7.57-7.41 (m, 1H), 7.29-7.08 (m, 1H), 3.95 (s, 3H). 13 C NMR (101MHz, DMSO-d6) δ156.37, 150.68, 132.04, 130.25, 129.77, 128.52, 117.32, 115.00, 54.77.HRMS (ESI): m / z calcd for C9H7BrNaN2O2 + [M+Na] + :276.9583; found:276.9585.

[0073] Example 19

[0074]

[0075] The reactant, quinoxaline-2(1H)-one (1e, 0.20 mmol), the reactant, methanol (2a, 5 mL), and 20 mg of the photocatalyst, mpg-CN, were added to a Shrek tube equipped with a magnetic stirrer, mixed thoroughly, and sealed with a rubber septum. The reaction was allowed to proceed at room temperature under air and irradiated with a blue LED light for 54 hours. After centrifugation, extraction, and column chromatography, the product, 3,6-dimethoxyquinoxaline-2(1H)-one, was obtained as a white solid, 14.4 mg, in an isolated yield of 35%, with an mp of 250-251°C. 1 H NMR (400MHz, DMSO-d6) δ 12.25 (s, 1H), 7.16 (d, J = 8.8Hz, 1H), 7.04 (d, J = 2.8Hz, 1H), 6.98 (dd, J = 8.9, 2.8Hz, 1H), 3.95 (s, 3H), 3.78 (s, 3H). 13C NMR (101MHz, DMSO-d6) δ156.02, 155.95, 150.31, 131.45, 124.69, 116.22, 115.70, 109.11, 55.91, 54.54. HRMS (ESI): m / z calcdforC 10 H 14 N3O3 + [M+NH4] + :224.1030; found:224.1055.

[0076] Example 20

[0077]

[0078] The reactant, quinoxalin-2(1H)-one (1f, 0.20 mmol), the reactant, methanol (2a, 5 mL), and 20 mg of the photocatalyst, mpg-CN, were added to a Shrek tube equipped with a magnetic stirrer, mixed thoroughly, and sealed with a rubber septum. The reaction was allowed to proceed at room temperature under air and irradiation with a blue LED light for 54 hours. After centrifugation, extraction, and column chromatography, the product, 7-bromo-3-methoxyquinoxalin-2(1H)-one 3k, was obtained as a white solid, 31.2 mg, in an isolated yield of 61%, with an mp of 229-234°C. 1 H NMR (400MHz, DMSO-d6) δ12.40 (s, 1H), 7.42 (d, J=8.4Hz, 1H), 7.36-7.31 (m, 2H), 3.94 (s, 3H). 13 C NMR (101MHz, DMSO-d6) δ155.85, 150.60, 132.14, 129.91, 128.27, 126.38, 119.21, 117.65, 54.70.HRMS (ESI): m / z calcd for C9H7BrNaN2O2 + [M+Na] + :276.9583; found:276.9585.

[0079] Example 21

[0080]

[0081] The reactant, quinoxaline-2(1H)-one (1 g, 0.20 mmol), the reactant methanol (2a, 5 mL), and the photocatalyst mpg-CN (20 mg) were added to a Shrek tube equipped with a magnetic stirrer, mixed thoroughly, and sealed with a rubber septum. The reaction was allowed to proceed at room temperature under air and irradiated with a blue LED light for 54 hours. After centrifugation, extraction, and column chromatography, the product 31, 3,7-dimethoxyquinoxaline-2(1H)-one, was obtained as a white solid, 30.2 mg, in an isolated yield of 73%, with an mp of 285-287°C. 1 H NMR (400MHz, DMSO-d6) δ12.26 (s, 1H), 7.45 (d, J=8.8Hz, 1H), 6.87-6.80 (m, 1H), 6.77-6.71 (m, 1H), 3.91 (s, 3H), 3.78 (s, 3H) .13CNMR (101MHz, DMSO-d6) δ158.48, 153.75, 150.99, 131.88, 127.59, 124.83, 111.45, 98.81, 55.86, 54.29.HRMS (ESI): m / z calcd for C 10 H 14 N3O3 + [M+NH4] + :224.1030; found:224.1055.

[0082] Example 22

[0083]

[0084] The reactant, quinoxalin-2(1H)-one (1h, 0.20 mmol), the reactant, methanol (2a, 5 mL), and 20 mg of the photocatalyst, mpg-CN, were added to a Shrek tube equipped with a magnetic stirrer, mixed thoroughly, and sealed with a rubber septum. The reaction was allowed to proceed at room temperature under air and irradiated with a blue LED light for 54 hours. After centrifugation, extraction, and column chromatography, the product, 6,7-dichloro-3-methoxyquinoxalin-2(1H)-one 3m, was obtained as a white solid, 26.3 mg, in a 54% yield, with an mp of 254-255°C. 1 H NMR (400MHz, DMSO-d6) δ12.50 (s, 1H), 7.75 (s, 1H), 7.37 (s, 1H), 3.96 (s, 3H). 13C NMR (101MHz, DMSO-d6) δ156.60, 150.51, 130.84, 130.71, 128.91, 127.45, 125.31, 116.36, 54.94.HRMS (ESI): m / z calcd for C9H6NaCl2N2O2 + [M+Na] + :266.9699; found:266.9681.

[0085] Example 23

[0086]

[0087] The reactant, quinoxalin-2(1H)-one (1i, 0.20 mmol), the reactant, methanol (2a, 5 mL), and 20 mg of the photocatalyst, mpg-CN, were added to a Shrek tube equipped with a magnetic stirrer, mixed thoroughly, and sealed with a rubber septum. The reaction was allowed to proceed at room temperature under air and irradiated with a blue LED light for 54 hours. After centrifugation, extraction, and column chromatography, the product, 6,7-dibromo-3-methoxyquinoxalin-2(1H)-one 3n, was obtained as a white solid, 51.4 mg, in a 77% yield, with an mp of 280-281°C. 1 H NMR (400MHz, DMSO-d6) δ12.48 (s, 1H), 7.82 (s, 1H), 7.50 (s, 1H), 3.95 (s, 3H). 13 C NMR (101MHz, DMSO-d6) δ156.61, 150.50, 133.05, 131.35, 130.42, 121.26, 119.43, 117.18, 54.93.HRMS (ESI): m / z calcd for C9H6NaBr2N2O2 + [M+Na] + :356.8668; found:356.8655.

[0088] Example 24

[0089]

[0090] The reactant, quinoxalin-2(1H)-one (1j, 0.20 mmol), the reactant, methanol (2a, 5 mL), and 20 mg of the photocatalyst, mpg-CN, were added to a Shrek tube equipped with a magnetic stirrer, mixed thoroughly, and sealed with a rubber septum. The reaction was allowed to proceed at room temperature under air and irradiation with a blue LED light for 54 hours. After centrifugation, extraction, and column chromatography, the product, 6,7-dimethyl-3-methoxyquinoxalin-2(1H)-one 3o, was obtained as a white solid, 11.1 mg, in an isolated yield of 27%, with an mp of 248-250°C. 1 H NMR (400MHz, DMSO-d6) δ12.23 (s, 1H), 7.30 (s, 1H), 6.98 (s, 1H), 3.91 (s, 3H), 2.24 (d, J=3.9Hz, 6H). 13 C NMR (101MHz, DMSO-d6) δ155.02, 150.82, 136.03, 132.08, 128.75, 128.62, 126.73, 115.65, 54.33, 19.88, 19.40. HRMS (ESI): m / z calcd for C 11 H 12 NaN2O2 + [M+Na] + :227.0791; found:227.0801.

[0091] Example 25

[0092]

[0093] The reactant, quinoxaline-2(1H)-one (1k, 0.20 mmol), the reactant, methanol (2a, 5 mL), and 20 mg of the photocatalyst, mpg-CN, were added to a Shrek tube equipped with a magnetic stirrer, mixed thoroughly, and sealed with a rubber septum. The reaction was allowed to proceed at room temperature under air and irradiated with a blue LED light for 54 hours. After centrifugation, extraction, and column chromatography, the product, 3-methoxybenzoquinoxaline-2(1H)-one 3p, was obtained as a white solid, 10.9 mg, in an isolated yield of 24%, with an mp of 259-260°C. 1 H NMR (400MHz, DMSO-d6) δ12.41 (s, 1H), 8.10 (s, 1H), 7.96 (d, J=8.1Hz, 1H), 7.90 (d, J=8.2Hz, 1H), 7.62 (s, 1H), 7.45 (dddd, J=23.0, 8.0, 6.6, 1.2Hz, 2H), 4.00 (s, 3H). 13C NMR (101MHz, DMSO-d6) δ155.55, 151.09, 131.84, 130.86, 130.24, 130.09, 128.27, 127.12, 126.75, 125.00, 124.37, 110.86, 54.68. HRMS (ESI): m / z calcd for C 13 H 10 NaN2O2 + [M+Na] + :249.0634; found:249.0639.

[0094] Examples 1-10 optimize the conditions of the method, discuss the effects of factors such as reaction time, catalyst dosage, reaction atmosphere, temperature and lighting conditions on product yield, and obtain the optimal reaction conditions. Examples 11-25 expand the adaptability of the method to substrates, and all of them can obtain the target products with moderate to excellent yields, further illustrating the universality of this method.

[0095] There are other technical features that are the same or similar to the use of compounds represented by general formulas 1 and 2 as starting materials, and the use of carbon nitride to carry out a 3-alkoxylation reaction of quinoxaline-2(1H)-one under air and light reaction conditions to obtain the compound represented by general formula 3, which are all one embodiment of the present invention, and the various technical features of the above-mentioned embodiments can be combined arbitrarily. The above embodiment is only one implementation form of the method for preparing 3-alkoxyquinoxaline-2(1H)-one compounds based on carbon nitride photocatalysis provided by the present invention. According to other variations of the scheme provided by the present invention, adding or reducing components or steps therein, or applying the present invention to other technical fields close to the present invention, all fall within the scope of protection of the present invention.

Claims

1. A method for preparing 3-alkoxyquinoxaline-2(1H)-one compounds by photocatalysis, characterized in that: The following steps are involved: A quinoxaline-2(1H)-one compound, an alcohol compound and a photocatalyst mesoporous graphitic carbon nitride are added to a reaction kettle and mixed evenly; the reaction is irradiated with light at room temperature and air atmosphere; and after the reaction is completed, the 3-alkoxyquinoxaline-2(1H)-one product is separated and processed to obtain the product.

2. The method for photocatalytically preparing 3-alkoxyquinoxaline-2(1H)-one compounds according to claim 1, characterized in that: The general formula of the reaction is as follows: Wherein R1 and R2 in structural formula 1 are hydrogen, halogen, alkyl, alkoxy, aryl or aryloxy; wherein R3 in structural formula 2 and structural formula 3 is a C1-C6 straight chain or branched hydrocarbon group, aryl or substituted aryl group.

3. The method for photocatalytically preparing 3-alkoxyquinoxaline-2(1H)-one compounds according to claim 1 or 2, characterized in that: The compound corresponding to structural formula 3 is:

4. The method for photocatalytically preparing 3-alkoxyquinoxaline-2(1H)-one compounds according to claim 1 or 2, characterized in that: The mass of the photocatalyst mesoporous graphite phase carbon nitride is 10 mg to 30 mg.

5. The method for photocatalytically preparing 3-alkoxyquinoxaline-2(1H)-one compounds according to claim 1 or 2, characterized in that: The light source is a 450-455nm blue LED lamp or a 390-400nm purple LED lamp.

6. The method for photocatalytically preparing 3-alkoxyquinoxaline-2(1H)-one compounds according to claim 1 or 2, characterized in that: The reaction temperature is 20-50° C., and the reaction time is 6-72 hours.

7. The method for photocatalytically preparing 3-alkoxyquinoxaline-2(1H)-one compounds according to claim 1 or 2, characterized in that: In the reaction, the alcohols of formula 2 serve as both reactants and solvents.

8. The method for photocatalytically preparing 3-alkoxyquinoxaline-2(1H)-one compounds according to claim 1 or 2, characterized in that: After the reaction is completed, the reaction solution is centrifuged to separate the catalyst, and a saturated saline solution is added to the reaction solution for washing, followed by extraction with ethyl acetate. The extract is dried over anhydrous sodium sulfate, concentrated to a solvent-free state, and then subjected to rapid column chromatography to obtain the 3-alkoxyquinoxaline-2(1H)-one product.

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