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

Abstract

The invention discloses a method for preparing a 3-alkyl 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 ether compound and a photocatalyst mpg-C3N4 (mesoporous graphite phase carbon nitride) are added into an organic solvent 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-alkyl quinoxaline-2 (1H)-ketone product. The method is mild in reaction condition, simple to operate and wide in application range, and the 3-alkyl quinoxaline-2 (1H)-ketone compound can be synthesized in one step.

Description

Technical Field

[0001] The present invention belongs to the field of organic synthesis, and particularly relates to a method for photocatalytic preparation of 3-alkylquinoxalin-2(1H)-one compounds. Background Art

[0002] Quinoxalin-2(1H)-one is an important bioactive skeleton and has extensive applications in medicinal chemistry and materials chemistry. In particular, 3-alkylquinoxalinone derivatives have significant pharmacological activities and have been proven to be MDR antagonists. MDR refers to the phenomenon that tumor cells develop resistance to one anti-tumor drug and simultaneously show cross-resistance to other anti-tumor drugs with different structures and mechanisms of action. In addition, it can also be used as an anti-tumor agent and an aldose reductase inhibitor and other multi-drug resistance regulators. Therefore, the construction of such molecules is of great significance (J Org Chem, 2023, 88, 2344~2357; Org Biomol Chem, 2020, 18: 6558~6563.).

[0003]

[0004] In view of the important biological activities and medicinal values of 3-alkylquinoxalin-2(1H)-one, its synthetic methods have attracted extensive attention. 3-alkylquinoxalin-2(1H)-one is usually prepared by the direct C-H / C-H cross-dehydrogenative coupling method of quinoxalin-2(1H)-one with ethers, which is of great significance for its atom economy and step economy. The research focuses on the selection and optimization of reaction conditions such as catalysts and oxidants.

[0005] In 2019, Xue (Org Biomol Chem, 2019, 17: 6654~6661.) and Xie (ACS Sustainable Chem Eng, 2019, 7: 14153~14160.) et al. both used transition metal ruthenium as a photosensitizer to achieve visible light-mediated decarboxylative alkylation reaction of quinoxalinone with iodobenzene diacetate to generate 3-alkylquinoxalin-2(1H)-one. Both of these methods use iodobenzene diacetate as an alkylating agent. The difference is that the former reacts in dimethyl sulfoxide solvent under white light irradiation, while the latter reacts in PEG-200 solvent under blue light irradiation. In 2023, Zhao et al. (J Org Chem, 2023, 88: 6218~6226.) achieved photo-redox catalytic C-H direct alkylation reaction of quinoxalinone with alkyl borates through a ruthenium transition metal photosensitizer, and successfully prepared various 3-alkylquinoxalinones.

[0006] All of the above methods require the use of expensive metal catalysts. The recovery and reuse of the catalysts are relatively complex, and there are also disadvantages such as large environmental pollution and poor atom economy.

[0007] To overcome the disadvantages of expensive metal catalysts and large environmental pollution, the Wei research group in 2018 (ACS Sustainable Chem Eng, 2018, 6: 17252 - 17257) and the Gurunath research group in 2019 (New J Chem, 2019, 43: 7403.) respectively attempted to use rhodamine and eosin as photosensitizers, and through optimization, the alkylation reaction of quinoxalinone and ether was achieved. Ma Chunhua et al. reported (Chinese Invention Patent 2023104324070) a method for the synthesis of 3-alkylquinoxalin-2(1H)-one compounds mediated by visible light. This method uses 3,4-dihydro-1H-2-quinoxalinone compounds and alkyl NHPI esters as raw materials, and under the action of the catalyst 4CzIPN and the base DABCO, it is obtained through blue light irradiation under air conditions. Song Haiyang reported a method for the functionalization reaction of the C3 position of quinoxalin-2(1H)-one (Master's Thesis of Nanhua University, 2024.05). Using quinoxalin-2(1H)-one as the substrate and NHPI ester as the alkyl source, without adding an additional photosensitizer, Na2S is used as an electron donor to form an EDA complex with NHPI ester (electron acceptor), and under light irradiation conditions, the decarboxylation of carboxylic acid is catalyzed to form alkyl radicals, thereby realizing the alkylation of the C3 position of quinoxalin-2(1H)-one.

[0008] Although these methods do not use expensive metal catalysts, they need to use homogeneous photosensitizers that are costly, difficult to recycle, and prone to decomposition under long-term light irradiation conditions, or they need to use expensive NHPI esters as alkyl sources and raw materials Na2S with relatively large environmental pollution.

[0009] Therefore, it is highly desirable and necessary to develop a recyclable catalyst to construct complex heteroaromatic-containing ethers through direct C-H bond functionalization (Org Chem Front, 2018, 5: 2820.). For this purpose, based on the visible light-driven catalytic strategy, using mpg-C3N4 as a photocatalyst and ethers as alkylating reagents, in a green reaction system without transition metals and without the need for external oxidants, the direct coupling alkylation of the C-C bond between quinoxalinone and ether compounds was achieved to prepare 3-alkylquinoxalin-2(1H)-one.

[0010] Summary of the Invention

[0011] The present invention provides a method for photocatalytic preparation of 3-alkylquinoxalin-2(1H)-one compounds. Using mpg-C3N4 (mesoporous graphitic carbon nitride) as a photocatalyst, quinoxalin-2(1H)-one compounds, ether compounds and the photocatalyst are successively added into an organic solvent and mixed evenly; under room temperature and in an air atmosphere, a light reaction is carried out; after the reaction is completed, separation and treatment are carried out to obtain 3-alkylquinoxalin-2(1H)-one products. Without using metal reagents, additional oxidants, high temperature and cumbersome operation steps, it has the characteristics of low reaction energy consumption, high reaction safety and efficiency.

[0012] To achieve the above object, the technical solution adopted by the present invention is:

[0013] A method for photocatalytic preparation of 3-alkylquinoxalin-2(1H)-one compounds, comprising the following steps:

[0014] The quinoxalin-2(1H)-one compound shown in Structural Formula 1, the ether compound shown in Structural Formula 2 and the photocatalyst mpg-C3N4 are added into a Schlenk tube with a magnetic stir bar, and the tube is sealed with a rubber septum. An organic solvent is added and mixed evenly; the reaction is carried out under room temperature and in an air atmosphere, irradiated with an LED lamp, and reacted at 20-50 °C for 12-48 hours; after detecting the completion of the reaction by TLC, the reaction solution is centrifuged to separate the carbon nitride, the reaction solution is washed with a saturated sodium chloride solution, then extracted with ethyl acetate, the extract is dried over anhydrous sodium sulfate, and then the extract is concentrated to no solvent to obtain a crude product, and then flash column chromatography is carried out to obtain 3-alkylquinoxalin-2(1H)-one products.

[0015] The reaction general formula is as follows:

[0016]

[0017] Wherein in Structural Formula 1, R1 and R2 are hydrogen, halogen, alkyl, alkoxy, aryl or aryloxy; wherein Structural Formula 2 is oxolane, oxane, 1,4-dioxane, 1,3-dioxane, 1,3-dioxolane, ethylene glycol dialkyl ether and alkyl-substituted products of the foregoing compounds;

[0018] The mass of the photocatalyst mesoporous graphitic carbon nitride is 10 mg - 30 mg;

[0019] The molar ratio of the quinoxalin-2(1H)-one compound to the ether compound is 1:1 - 1:10;

[0020] The organic solvent is oxolane, N, N-dimethylformamide, dimethyl sulfoxide, acetonitrile, toluene, halogenated benzene, nitrobenzene, oxane, 1,4-dioxane, 1,3-dioxane, 1,3-dioxolane, ethylene glycol dimethyl ether;

[0021] The light source is a blue LED lamp with a wavelength of 450 - 455 nm or a purple LED lamp with a wavelength of 390 - 400 nm.

[0022] Advantages: The present invention provides a method for photocatalytic preparation of 3-alkylquinoxalin-2(1H)-one compounds, which has the following advantages compared with the prior art:

[0023] 1. The present invention does not require pre-functionalization of quinoxalin-2(1H)-one. Since 3-alkylquinoxalin-2(1H)-one compounds are synthesized in one step under visible light catalysis, the reaction conditions are mild, the energy is clean, no strong oxidant is required, the reaction has high safety, and good functional group compatibility;

[0024] 2. Since the present invention uses a non-metallic photocatalyst, the use of metal reagents is effectively avoided, metal pollution is reduced, and carbon nitride can be recycled, saving the reaction cost and being environmentally friendly; Description of the Drawings

[0025] Figure 1 It is the reaction flow chart of photocatalysis in the embodiment of the present invention; Detailed Description of the Invention

[0026] The present invention will be described in detail below with reference to specific embodiments:

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

[0028] Example 1

[0029]

[0030] The reactants quinoxalin-2(1H)-one (1a, 0.20 mmol), oxolane (2a, 0.60 mmol) and the photocatalyst mpg-C3N4 (20 mg) were added to a Schlenk tube equipped with a magnetic stir bar, and the tube was sealed with a rubber septum. 5 mL of the solvent oxolane was added and mixed evenly; the reaction was carried out at room temperature under an air atmosphere and irradiated with a blue LED lamp for 48 hours; after HPLC detection, the HPLC yield was 80%. After centrifugation, extraction and column chromatography, the 3-alkylquinoxalin-2(1H)-one product 3a was obtained. White solid, 34.2 mg, isolation yield 78%, m.p. 142-144 °C. 1 H NMR (400 MHz, DMSO-d6) δ 12.40 (s, 1H), 7.75 (dd, J = 8.0, 1.4 Hz, 1H), 7.50 (ddd, J = 8.4, 7.1, 1.4 Hz, 1H), 7.33 - 7.25 (m, 2H), 5.21 (dd, J = 7.9, 5.7 Hz, 1H), 4.01 (q, J = 7.1 Hz, 1H), 3.84 (td, J = 7.5, 5.7 Hz, 1H), 2.24 (dtd, J = 11.6, 8.1, 5.8 Hz, 1H), 2.10 - 1.87 (m, 3H). 13 C NMR (101 MHz, DMSO-d6) δ 161.03, 154.44, 132.44, 131.77, 130.46, 129.04, 123.65, 115.74, 76.66, 68.65, 30.06, 25.82. HRMS (ESI): m / z calcd for C 12 H 12 NaN2O2 + [M+Na] + : 239.0791; found: 239.0799.

[0031] Example 2

[0032] The reactants quinoxalin-2(1H)-one (1a, 0.20 mmol), oxolane (2a, 0.60 mmol) and the photocatalyst mpg-C3N4 (20 mg) were added to a Schlenk tube equipped with a magnetic stir bar, and the tube was sealed with a rubber septum. 5 mL of the solvent oxolane was added and mixed evenly; the reaction was carried out at room temperature under an air atmosphere and irradiated with a blue LED lamp for 24 hours; after HPLC detection, the HPLC yield was 34%.

[0033] Example 3

[0034] The reactants quinoxalin-2(1H)-one (1a, 0.20 mmol), oxolane (2a, 0.60 mmol) and the photocatalyst mpg-C3N4 20 mg were added to a Schlenk tube equipped with a magnetic stir bar, and the tube was sealed with a rubber septum. 5 mL of the solvent oxolane was added and mixed evenly; the reaction was carried out at room temperature under an air atmosphere and irradiated with a blue LED lamp for 54 hours; detected by HPLC, the HPLC yield was 79%.

[0035] Example 4

[0036] The reactants quinoxalin-2(1H)-one (1a, 0.20 mmol), oxolane (2a, 0.60 mmol) and the photocatalyst mpg-C3N4 10 mg were added to a Schlenk tube equipped with a magnetic stir bar, and the tube was sealed with a rubber septum. 5 mL of the solvent oxolane was added and mixed evenly; the reaction was carried out at room temperature under an air atmosphere and irradiated with a blue LED lamp for 48 hours; detected by HPLC, the HPLC yield was 39%.

[0037] Example 5

[0038] The reactants quinoxalin-2(1H)-one (1a, 0.20 mmol), oxolane (2a, 0.60 mmol) and the photocatalyst mpg-C3N4 30 mg were added to a Schlenk tube equipped with a magnetic stir bar, and the tube was sealed with a rubber septum. 5 mL of the solvent oxolane was added and mixed evenly; the reaction was carried out at room temperature under an air atmosphere and irradiated with a blue LED lamp for 48 hours; detected by HPLC, the HPLC yield was 70%.

[0039] Example 6

[0040] The reactants quinoxalin-2(1H)-one (1a, 0.20 mmol), oxolane (2a, 0.60 mmol) and the photocatalyst mpg-C3N4 20 mg were added to a Schlenk tube equipped with a magnetic stir bar, and the tube was sealed with a rubber septum. 5 mL of the solvent oxolane was added and mixed evenly; the reaction was carried out at room temperature under an oxygen atmosphere and irradiated with a blue LED lamp for 48 hours; detected by HPLC, the HPLC yield was 51%.

[0041] Example 7

[0042] The reactants quinoxalin-2(1H)-one (1a, 0.20 mmol), oxolane (2a, 0.60 mmol) and the photocatalyst mpg-C3N4 (20 mg) were added to a Schlenk tube equipped with a magnetic stir bar, and the tube was sealed with a rubber septum. 5 mL of the solvent oxolane was added and mixed evenly; the reaction was carried out at room temperature under a nitrogen atmosphere and irradiated with a blue LED lamp for 48 hours; detected by HPLC, the HPLC yield was 25%.

[0043] Example 8

[0044] The reactants quinoxalin-2(1H)-one (1a, 0.20 mmol), oxolane (2a, 0.60 mmol) and the photocatalyst mpg-C3N4 (20 mg) were added to a Schlenk tube equipped with a magnetic stir bar, and the tube was sealed with a rubber septum. 5 mL of the solvent oxolane was added and mixed evenly; the reaction was carried out at room temperature under an air atmosphere and irradiated with a purple LED lamp for 48 hours; detected by HPLC, the HPLC yield was 43%.

[0045] Example 9

[0046] The reactants quinoxalin-2(1H)-one (1a, 0.20 mmol), oxolane (2a, 0.60 mmol) and the photocatalyst mpg-C3N4 (20 mg) were added to a Schlenk tube equipped with a magnetic stir bar, and the tube was sealed with a rubber septum. 5 mL of the solvent acetonitrile was added and mixed evenly; the reaction was carried out at room temperature under an air atmosphere and irradiated with a blue LED lamp for 48 hours; detected by HPLC, the HPLC yield was 53%.

[0047] Example 10

[0048] The reactants quinoxalin-2(1H)-one (1a, 0.20 mmol), oxolane (2a, 0.60 mmol) and the photocatalyst mpg-C3N4 (20 mg) were added to a Schlenk tube equipped with a magnetic stir bar, and the tube was sealed with a rubber septum. 5 mL of the solvent dimethyl sulfoxide was added and mixed evenly; the reaction was carried out at room temperature under an air atmosphere and irradiated with a blue LED lamp for 48 hours; detected by HPLC, the HPLC yield was 38%.

[0049] Example 11

[0050] The reactants quinoxalin-2(1H)-one (1a, 0.20 mmol), oxolane (2a, 0.60 mmol) and the photocatalyst mpg-C3N4 (20 mg) were added to a Schlenk tube equipped with a magnetic stir bar, and the tube was sealed with a rubber septum. 5 mL of the solvent oxolane was added and mixed evenly; the reaction was carried out at 50 °C under an air atmosphere and irradiated with a blue LED lamp for 48 hours; detected by HPLC, the HPLC yield was 76%.

[0051] Example 12

[0052] The reactants quinoxalin-2(1H)-one (1a, 0.20 mmol), oxolane (2a, 6 mmol) and the photocatalyst mpg-C3N4 (20 mg) were added to a Schlenk tube equipped with a magnetic stir bar, and the tube was sealed with a rubber septum. 5 mL of the solvent acetonitrile was added and mixed evenly; the reaction was carried out at room temperature under an air atmosphere and irradiated with a blue LED lamp for 48 hours; detected by HPLC, the HPLC yield was 62%.

[0053] Example 13

[0054]

[0055] The reactants quinoxalin-2(1H)-one (1a, 0.20 mmol), 1,3-dioxolane (2b, 0.60 mmol) and the photocatalyst mpg-C3N4 (20 mg) were added to a Schlenk tube equipped with a magnetic stir bar, and the tube was sealed with a rubber septum. 5 mL of the solvent 1,3-dioxolane was added and mixed evenly; the reaction was carried out at room temperature under an air atmosphere and irradiated with a blue LED lamp for 48 hours, and then after centrifugation, extraction and column chromatography, the 3-alkylquinoxalin-2(1H)-one product 3b, a yellow solid, 74.4 mg, was obtained, and the isolated yield was 85%, and the melting point was 180 - 182 °C. 1 HNMR(400MHz, DMSO-d6)δ12.51(s, 1H), 7.79(dd, J = 8.3, 1.4Hz, 1H), 7.56(td, J = 7.6, 1.5Hz, 1H), 7.32(ddd, J = 8.2, 3.1, 1.4Hz, 2H), 6.11(s, 1H), 4.20 - 4.16(m, 2H), 4.02 - 3.98(m, 2H). 13 CNMR(101MHz, DMSO-d6)δ155.93, 154.14, 132.94, 131.53, 131.39, 129.50, 123.89, 115.88, 100.28, 65.68.HRMS(ESI): m / z calcd forC 11 H 10NaN2O3 + [M + Na] + :241.0584;found:241.0539.

[0056] Example 14

[0057]

[0058] The reactants quinoxalin - 2(1H)-one (1a, 0.20 mmol), 2 - methyl - 1,3 - dioxolane (2c, 0.60 mmol) and the photocatalyst mpg - C3N4 20 mg were added to a Schlenk tube equipped with a magnetic stir bar and the tube was sealed with a rubber septum. 5 mL of the solvent 2 - methyl - 1,3 - dioxolane was added and mixed evenly; the reaction was carried out at room temperature under an air atmosphere and irradiated with a blue LED lamp for 48 hours. After centrifugation, extraction and column chromatography, the 3 - alkylquinoxalin - 2(1H)-one product 3c, a white solid, 17.3 mg, was obtained with a separation yield of 37%, m.p. 231 - 233 °C. 1 1H NMR (400 MHz, DMSO - d6) δ 12.41 (s, 1H), 7.77 (d, J = 8.2 Hz, 1H), 7.54 (t, J = 7.7 Hz, 1H), 7.30 (q, J = 7.5, 6.3 Hz, 2H), 4.07 - 3.98 (m, 2H), 3.96 (d, J = 5.6 Hz, 2H), 1.76 (s, 3H). 13 13C NMR (101 MHz, DMSO - d6) δ 157.06, 153.54, 133.17, 131.20, 130.83, 129.49, 123.63, 115.49, 107.81, 65.31, 23.44. HRMS (ESI): m / z calcd for C 12 H 12 NaN2O3 + [M + Na] + :255.0741;found:255.0767.

[0059] Example 15

[0060]

[0061] The reactant quinoxalin-2(1H)-one (1a, 0.20 mmol), the reactant 1,4-dioxane (2d, 0.60 mmol), and 20 mg of the photocatalyst mpg-C3N4 were added to a Schlenk tube equipped with a magnetic stir bar, and the tube was sealed with a rubber septum. 5 mL of the solvent 1,4-dioxane was added and mixed evenly; the reaction was carried out at room temperature under an air atmosphere under irradiation with a blue LED lamp for 48 hours. After centrifugation, extraction, and column chromatography, the 3-alkylquinoxalin-2(1H)-one product 3d, a white solid, 34.1 mg, was obtained with a separation yield of 74%, m.p. 217 - 218 °C. 1 HNMR(400 MHz, DMSO-d6) δ 12.47 (s, 1H), 7.78 (d, J = 8.1 Hz, 1H), 7.52 (t, J = 7.7 Hz, 1H), 7.30 (dd, J = 8.1, 5.8 Hz, 2H), 4.88 - 4.75 (m, 1H), 4.01 (d, J = 11.3 Hz, 1H), 3.53 (td, J = 10.9, 3.8 Hz, 1H), 1.96 - 1.79 (m, 2H), 1.71 - 1.49 (m, 4H). 13 CNMR(101 MHz, DMSO-d6) δ 159.69, 154.20, 132.31, 131.89, 130.70, 129.12, 123.74, 115.76, 74.83, 68.47, 29.45, 25.93, 23.46. HRMS(ESI): m / z calcd for C 13 H 14 NaN2O2 + [M+Na] + : 253.0947; found: 253.0956.

[0062] Example 16

[0063]

[0064] The reactant quinoxalin-2(1H)-one (1a, 0.20 mmol), the reactant 1,4-dioxane (2e, 0.60 mmol), and 20 mg of the photocatalyst mpg-C3N4 were added to a Schlenk tube equipped with a magnetic stir bar, and the tube was sealed with a rubber septum. 5 mL of the solvent 1,4-dioxane was added and mixed evenly; the reaction was carried out at room temperature under an air atmosphere under irradiation with a blue LED lamp for 48 hours. After centrifugation, extraction, and column chromatography, the 3-alkylquinoxalin-2(1H)-one product 3e, a yellow solid, 26.5 mg, was obtained with a separation yield of 57%, m.p. 187 - 188 °C. 1HNMR (400 MHz, DMSO-d6) δ 12.50 (s, 1H), 7.79 (dd, J = 8.3, 1.5 Hz, 1H), 7.54 (td, J = 7.6, 7.1, 1.5 Hz, 1H), 7.31 (ddd, J = 8.3, 6.0, 1.6 Hz, 2H), 5.04 (dd, J = 9.6, 2.7 Hz, 1H), 3.96 (ddd, J = 29.8, 11.3, 2.7 Hz, 2H), 3.80 - 3.71 (m, 2H), 3.65 - 3.57 (m, 2H). 13 CNMR (101 MHz, DMSO-d6) δ 156.72, 154.21, 132.37, 131.89, 131.06, 129.22, 123.85, 115.88, 73.18, 69.00, 66.78, 66.25. HRMS (ESI): m / z calcd for C 12 H 12 NaN2O3 + [M + Na] + : 255.0741; found: 255.0747.

[0065] Example 17

[0066]

[0067] The reactants quinoxalin-2(1H)-one (1a, 0.20 mmol), ethylene glycol dimethyl ether (2f, 0.60 mmol) and 20 mg of the photocatalyst mpg-C3N4 were added to a Schlenk tube equipped with a magnetic stir bar, and the tube was sealed with a rubber septum. 5 mL of the solvent ethylene glycol dimethyl ether was added and mixed evenly; the reaction was carried out at room temperature under an air atmosphere and irradiated with a blue LED lamp for 48 hours. After centrifugation, extraction and column chromatography, the 3-alkylquinoxalin-2(1H)-one product 3f, a white solid of 11.3 mg, was obtained with a separation yield of 24% and a melting point of 150 - 151 °C. 1 HNMR (400 MHz, DMSO-d6) δ 12.49 (s, 1H), 7.79 (d, J = 8.0 Hz, 1H), 7.54 (t, J = 7.7 Hz, 1H), 7.32 (d, J = 8.7 Hz, 2H), 4.89 (t, J = 5.4 Hz, 1H), 3.69 (d, J = 5.4 Hz, 2H), 3.30 (d, J = 16.6 Hz, 6H). 13CNMR (101 MHz, DMSO-d6) δ 158.07, 154.79, 132.42, 131.92, 130.92, 129.19, 123.78, 115.85, 77.78, 73.51, 58.86, 57.91. HRMS (ESI): m / z calcd for C 12 H 14 NaN2O3 + [M + Na] + : 257.0897; found: 257.0922.

[0068] Example 18

[0069]

[0070] The reactants quinoxalin-2(1H)-one (1b, 0.20 mmol), oxolane (2a, 0.60 mmol), and the photocatalyst mpg-C3N4 20 mg were added to a Schlenk tube equipped with a magnetic stir bar, and the tube was sealed with a rubber septum. 5 mL of the solvent oxolane was added and mixed evenly; the reaction was carried out at room temperature under an air atmosphere and irradiated with a blue LED lamp for 48 hours. After centrifugation, extraction, and column chromatography, 3 g of the 3-alkylquinoxalin-2(1H)-one product, a yellow solid, 43.4 mg, was obtained with a separation yield of 73%, m.p. 210 - 212 °C. 1 1H NMR (400 MHz, DMSO-d6) δ 12.48 (s, 1H), 7.68 (d, J = 9.1 Hz, 1H), 7.46 - 7.40 (m, 2H), 5.18 (dd, J = 8.0, 5.7 Hz, 1H), 3.99 (q, J = 7.1 Hz, 1H), 3.83 (td, J = 7.5, 5.7 Hz, 1H), 2.24 (dtd, J = 13.7, 7.8, 6.9, 3.8 Hz, 1H), 1.98 (ddt, J = 36.4, 14.2, 6.5 Hz, 3H). 13 CNMR (101 MHz, DMSO-d6) δ 161.74, 154.16, 133.72, 130.88, 130.80, 126.54, 123.01, 117.99, 76.68, 68.70, 30.05, 25.78. HRMS (ESI): m / z calcd for C 12 H 11 NaN2O2 + [M + Na] + : 316.9896; found: 316.9872.

[0071] Example 19

[0072]

[0073] The reactants quinoxalin-2(1H)-one (1c, 0.20 mmol), oxolane (2a, 0.60 mmol) and the photocatalyst mpg-C3N4 (20 mg) were added to a Schlenk tube equipped with a magnetic stir bar, and the tube was sealed with a rubber septum. 5 mL of the solvent oxolane was added and mixed evenly. The reaction was carried out at room temperature under an air atmosphere and irradiated with a blue LED lamp for 48 hours. After centrifugation, extraction and column chromatography, the 3-alkylquinoxalin-2(1H)-one product 3h, a yellow solid, 40.9 mg, was obtained with a separation yield of 83%, m.p. 221 - 224 °C. 1 1H NMR (400 MHz, DMSO-d6) δ 12.31 (s, 1H), 7.65 (d, J = 8.9 Hz, 1H), 6.89 (dd, J = 8.9, 2.7 Hz, 1H), 6.74 (d, J = 2.7 Hz, 1H), 5.15 (dd, J = 7.7, 6.0 Hz, 1H), 3.97 (q, J = 7.1 Hz, 1H), 3.82 (s, 4H), 2.19 (dtd, J = 13.4, 7.8, 7.0, 3.8 Hz, 1H), 2.11 - 1.86 (m, 3H). 13 13C NMR (101 MHz, DMSO-d6) δ 160.89, 157.18, 154.71, 134.02, 130.38, 126.65, 112.20, 98.14, 76.57, 68.55, 56.03, 29.90, 25.93. HRMS (ESI): m / z calcd for C13H14NaN2O3+ [M + Na]+: 269.0897; found: 269.0927.

[0074] Example 20

[0075]

[0076] The reactants quinoxalin-2(1H)-one (1d, 0.20 mmol), oxolane (2a, 0.60 mmol) and the photocatalyst mpg-C3N4 (20 mg) were added to a Schlenk tube equipped with a magnetic stir bar, and the tube was sealed with a rubber septum. 5 mL of the solvent oxolane was added and mixed evenly. The reaction was carried out at room temperature under an air atmosphere and irradiated with a blue LED lamp for 48 hours. After centrifugation, extraction and column chromatography, the 3-alkylquinoxalin-2(1H)-one product 3i, a white solid, 38.1 mg, was obtained with a separation yield of 78%, m.p. 186 - 187 °C. 1HNMR (400 MHz, DMSO-d6) δ 12.25 (s, 1H), 7.52 (s, 1H), 7.04 (s, 1H), 5.19 (t, J = 6.9 Hz, 1H), 3.98 (q, J = 7.4 Hz, 1H), 3.82 (q, J = 7.1 Hz, 1H), 2.28 (d, J = 8.4 Hz, 6H), 2.16 - 1.81 (m, 4H). 13 CNMR (101 MHz, DMSO-d6) δ 159.58, 154.55, 139.94, 132.27, 130.44, 130.28, 128.95, 115.73, 76.57, 68.56, 29.95, 25.86, 20.18, 19.33. HRMS (ESI): m / z calcd for C 14 H 16 NaN2O2 + [M + Na] + : 267.1104; found: 267.1113.

[0077] Example 21

[0078]

[0079] The reactant quinoxalin-2(1H)-one (1e, 0.20 mmol), the reactant oxolane (2a, 0.60 mmol), and 20 mg of the photocatalyst mpg-C3N4 were added to a Schlenk tube equipped with a magnetic stir bar, and the tube was sealed with a rubber septum. 5 mL of the solvent oxolane was added and mixed evenly; the reaction was carried out at room temperature under an air atmosphere and irradiated with a blue LED lamp for 48 hours. After centrifugation, extraction, and column chromatography, the 3-alkylquinoxalin-2(1H)-one product 3j was obtained as a white solid, 16.5 mg, with a separation yield of 31%, m.p. 193-195 °C. 1H NMR (400 MHz, DMSO-d6) δ 12.37 (s, 1H), 8.41 (d, J = 9.9 Hz, 1H), 8.05 (d, J = 8.2 Hz, 1H), 7.94 (d, J = 8.3 Hz, 1H), 7.66 (s, 1H), 7.55 (t, J = 7.6 Hz, 1H), 7.52 - 7.41 (m, 1H), 5.40 - 5.18 (m, 1H), 4.04 (q, J = 7.3 Hz, 1H), 3.87 (q, J = 7.0 Hz, 1H), 2.37 - 1.85 (m, 4H). 13C NMR (101 MHz, DMSO-d6) δ 161.94, 154.47, 133.61, 131.63, 130.84, 129.85, 129.05, 128.18, 128.04, 127.14, 125.10, 110.91, 76.65, 68.70, 30.13, 25.81. HRMS (ESI): m / z calcd for C 16 H 14 NaN2O2 + [M + Na] + : 289.0947; found: 289.0977.

[0080] Examples 1-12 optimized the conditions of the method, discussed the effects of factors such as reaction temperature, solvent, catalyst dosage, light irradiation conditions, and reactant ratio on the product yield, and obtained the optimal reaction conditions. Examples 13-21 extended the applicable substrates of this method, and all could obtain the target products in moderate to excellent yields, further demonstrating the universality of this method.

[0081] There are also other technical features that are the same as or similar to those of using the compounds shown in General Formulas 1 and 2 as starting materials, and carrying out the 3-alkylation reaction of quinoxalin-2(1H)-one using carbon nitride under air and light reaction conditions to obtain the compounds shown in General Formula 3, which are all one of the embodiments of the present invention. Moreover, the technical features of the above-mentioned embodiments can be combined arbitrarily. The above-mentioned embodiments are only one implementation form of the method for preparing 3-alkylquinoxalin-2(1H)-one compounds based on carbon nitride photocatalysis provided by the present invention. According to other variations of the solution 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 protection scope of the present invention.

Claims

1. A method for photocatalytic preparation of 3-alkylquinoxalin-2(1H)-one compounds, characterized in that, It includes the following steps: Add quinoxalin-2(1H)-one compounds, ether compounds and the photocatalyst mesoporous graphitic carbon nitride into an organic solvent, and mix them evenly; carry out a photocatalytic reaction at room temperature under an air atmosphere; after the reaction is completed, carry out post-treatment and separation to obtain 3-alkylquinoxalin-2(1H)-one products.

2. The method for photocatalytic preparation of 3-alkylquinoxalin-2(1H)-one compounds according to claim 1, wherein The general formula of the reaction is as follows: In structural formula 1, R1 and R2 are hydrogen, halogen, alkyl, alkoxy, aryl or aryloxy; in structural formula 2, it is oxolane, oxane, 1,4-dioxane, 1,3-dioxane, 1,3-dioxolane, ethylene glycol dialkyl ether and alkyl-substituted products of the aforementioned compounds.

3. The method for preparing 3-alkylquinoxalin-2(1H)-one compounds by photocatalysis according to claim 1 or 2, characterized in that, The mass of the photocatalyst mesoporous graphitic carbon nitride is 10 mg - 30 mg.

4. The method for preparing 3-alkylquinoxalin-2(1H)-one compounds by photocatalysis according to claim 1 or 2, characterized in that, The molar ratio of the quinoxalin-2(1H)-one compounds to the ether compounds is 1:1 - 1:

10.

5. The method for preparing 3-alkylquinoxalin-2(1H)-one compounds by photocatalysis according to claim 1 or 2, characterized in that, The organic solvent is oxolane, N,N-dimethylformamide, dimethyl sulfoxide, acetonitrile, toluene, halogenated benzene, nitrobenzene, oxane, 1,4-dioxane, 1,3-dioxane, 1,3-dioxolane, ethylene glycol dimethyl ether.

6. The method for photocatalytic preparation of 3-alkylquinoxalin-2(1H)-one compounds according to claim 1 or 2, characterized in that, The light source is a blue LED lamp with a wavelength of 450 - 455 nm or a UV LED lamp with a wavelength of 390 - 400 nm.

7. The method for preparing 3-alkylquinoxalin-2(1H)-one compounds by photocatalysis according to claim 1 or 2, characterized in that, The reaction temperature is 20 - 50 °C.

8. The method for photocatalytic preparation of 3-alkylquinoxalin-2(1H)-one compounds according to claim 1 or 2, characterized in that, After the reaction is completed, centrifuge the reaction solution to separate the catalyst, wash the reaction solution with a saturated sodium chloride aqueous solution, then extract with ethyl acetate. After the extract is dried over anhydrous sodium sulfate, concentrate the extract until there is no solvent, and then obtain 3-alkylquinoxalin-2(1H)-one products through flash column chromatography.

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