Method for preparing nitrogen-containing fused ring compound through quantum dot catalysis [4 +2] cycloaddition

Abstract

The invention belongs to the technical field of catalytic synthesis, particularly relates to a method for preparing a nitrogen-containing fused ring compound through quantum dot catalyzed [4 + 2] cycloaddition, and aims to solve the problems of limited product structure and complex reaction system in the existing synthesis method. The synthesis method disclosed by the invention comprises the following steps: in an inert atmosphere, adding 1-phenylpyrrole and fumarate as reaction raw materials, quantum dots as a photocatalyst and an organic solvent into a reaction container, carrying out [4 + 2] cycloaddition reaction under visible light irradiation, and then filtering, concentrating, separating and purifying to obtain the nitrogen-containing fused ring compound. The reaction condition is mild, and the method can be realized by irradiating the quantum dot catalyst with a visible light source at normal temperature and pressure; a reaction system is simple, strong oxidants and additives are not needed, operation steps are convenient, and atom economy is achieved.

Description

Technical Field

[0001] This invention belongs to the field of catalytic synthesis technology, specifically relating to a method for preparing nitrogen-containing fused ring compounds by quantum dot catalytic [4+2] cycloaddition. Background Technology

[0002] Nitrogen-containing fused-ring compounds form the core structure of living organisms, and this type of skeleton is widely found in natural products, drug molecules, agrochemicals, and functional materials. Visible light photocatalysis has emerged as a revolutionary synthetic tool, offering significant advantages such as mild conditions, low energy consumption, environmental friendliness, and strong controllability. Traditional photocatalysts mainly include transition metal complexes and organic dyes; however, the former suffers from noble metal dependence and biotoxicity, while the latter generally exhibits poor photostability. Semiconductor quantum dots, as a novel type of nano-photocatalyst, demonstrate unparalleled advantages over traditional photocatalysts due to their unique "quantum confinement effect": such as ultra-high light absorption efficiency, excellent photochemical stability, abundant reactive sites, and easy modulation of catalytic selectivity through surface ligand modification.

[0003] Given the aforementioned advantages of quantum dots, researchers have begun exploring their application in visible-light catalytic cycloaddition reactions. Weiss et al. used CdSe quantum dots as a photocatalyst to catalyze the intermolecular [2+2] cycloaddition reaction of aromatic olefins via van der Waals forces, constructing a four-membered ring structure (Jiang et al., J. Am. Chem. Soc. 2022, 144,3782). Prato and Filippini used carbon quantum dot photocatalysts to complete the [3+2] cycloaddition reaction of arylcyclopropyl ketones with alkenes or alkynes for the synthesis of five-membered rings (Mamone et al., 2022, 144,3782). ChemSusChem (2025, 18, e202500521). It can be seen that most visible light photocatalytic cycloaddition reactions based on quantum dots are currently limited to [2+2] cycloaddition and [3+2] cycloaddition, which restricts the substrate range and the types of molecular skeletons that can be synthesized, making it difficult to meet the needs of synthesizing complex polycyclic structures.

[0004] As of the date of this application, there are few reports on the synthesis of nitrogen-containing fused-ring compounds by visible-light photocatalysis based on quantum dots using [4+2] cycloaddition. There is an urgent need in the field to develop a new technology to overcome the limitations of existing quantum dot catalysis, which is limited to [2+2] or [3+2] cycloaddition, and to realize visible-light photocatalysis based on quantum dots using [4+2] cycloaddition technology, providing a new solution for the efficient and green synthesis of nitrogen-containing fused-ring compounds. Summary of the Invention

[0005] This invention provides a method for preparing nitrogen-containing fused-ring compounds by quantum dot-catalyzed [4+2] cycloaddition, which aims to solve the problems of limited product structure and complex reaction system in existing synthetic methods.

[0006] In an inert atmosphere, 1-phenylpyrrole and fumarate were used as reactants, and quantum dots were used as photocatalysts. They were added to the reaction vessel along with an organic solvent and subjected to a [4+2] cycloaddition reaction under visible light irradiation. After filtration, concentration and separation purification, nitrogen-containing fused ring compounds were obtained.

[0007] Preferably, the photocatalyst is selected from one or more of the following quantum dots: CdSe, CdS, CdTe, ZnSe, ZnS, CdSe / ZnS, CdSe / ZnO, CdSe / CdS, CdTe / CdSe, CdS / ZnSe, CdS / ZnTe, and ZnSe / CdS heterojunction;

[0008] Preferably, the fumarate is selected from one of the following:

[0009] ;

[0010] In the formula, R1 and R2 are independent and are represented by Me; or

[0011] R1 and R2 are independent and can be represented by Et; or

[0012] R1 and R2 are independent. n Pr; or

[0013] R1 and R2 are independent. i Pr; or

[0014] R1 and R2 are independent. n Bu; or

[0015] R1 and R2 are independent. s Bu; or

[0016] R1 and R2 are independent. i Bu; or

[0017] R1 and R2 are independent. t Bu.

[0018] Preferably, the solvent is selected from one or more of acetone, DMSO, CHCl3, CH3OH, DMF, or CH3CN.

[0019] Preferably, the solubility of the photocatalyst is from zero to a saturated molar concentration, excluding zero.

[0020] Preferably, the molar ratio of 1-phenylpyrrole to fumarate is 1:(0.1~10).

[0021] Preferably, the molar concentration of 1-phenylpyrrole is 0.001 M to 10 M.

[0022] Preferably, the visible light source is selected from sunlight, LED lamps, medium-pressure mercury lamps, high-pressure mercury lamps, or xenon lamps.

[0023] Compared with the prior art, the advantages and positive effects of the present invention are as follows: (1) For the first time, nitrogen-containing fused ring compounds were prepared by the [4+2] cycloaddition of 1-phenylpyrrolidine and fumarate through visible light-driven quantum dot catalysis; (2) The reaction conditions are mild and can be achieved by irradiating the quantum dot catalyst with a visible light source at room temperature and pressure; (3) The reaction system is simple, requires no strong oxidants or additives, and is convenient to operate. It is atom-economical and demonstrates the potential value of this method in large-scale production. Attached Figure Description

[0024] Figure 1 The product of Example 1, 1,2,3,3a,4,5-hexahydropyrrolo[1,2-a]quinoline-4,5-dicarboxylate, is... 1 H NMR spectrum.

[0025] Figure 2 The product of Example 1, 1,2,3,3a,4,5-hexahydropyrrolo[1,2-a]quinoline-4,5-dicarboxylate, is... 13 C10 NMR spectrum. Detailed Implementation

[0026] To better understand the above-described objects, features, and advantages of the present invention, the present invention will be further described below with reference to embodiments. Many specific details are set forth in the following description to provide a thorough understanding of the present invention; however, the present invention may be practiced in other ways than those described herein, and therefore, the present invention is not limited to the specific embodiments disclosed in the following specification.

[0027] Example 1: CdSe quantum dot photocatalyst and 0.1 mmol of 1-phenylpyrrolidine were added to 2 mL of CH3CN. Air was replaced with Ar gas using a bubbling method, followed by the addition of 0.1 mmol of dimethyl fumarate. The mixture was irradiated with a 450 nm LED at room temperature for 6 hours. After the reaction was complete, the reaction mixture was concentrated under reduced pressure and then separated by column chromatography. 1H NMR, 1C NMR, and mass spectrometry identified the product as dimethyl 1,2,3,3a,4,5-hexahydropyrrolo[1,2-a]quinoline-4,5-dicarboxylate, with a yield of 81%.

[0028] Comparative Example 1: The reaction process in Comparative Example 1 is different from that in Example 1, except that the reaction process is carried out in the dark. The result shows that the reaction cannot occur, indicating that the cycloaddition reaction described in this invention can only occur under light conditions.

[0029] Comparative Example 2: The reaction process in Comparative Example 2 is different from that in Example 1, except that the reaction process is carried out in air. The result shows that the reaction cannot occur, indicating that the cycloaddition reaction described in this invention can only occur in an inert atmosphere.

[0030] Examples 2-8: In Examples 2-8, the reaction process is exactly the same as in Example 1, except that the fumarate compounds shown in Table 1 are used instead of dimethyl fumarate in Example 1. The specific products are shown in Table 1.

[0031] Table 1. Different fumarate esters and their corresponding products in Examples 2-8

[0032] Example number Fumarate compounds Yield (%) product 2 diethyl fumarate 75 1,2,3,3a,4,5-Hexahydropyrrolo[1,2-a]quinoline-4,5-dicarboxylic acid diethyl ester 3 dipropyl fumarate 73 1,2,3,3a,4,5-Hexahydropyrrolo[1,2-a]quinoline-4,5-dipropylcarboxylate 4 diisopropyl fumarate 71 1,2,3,3a,4,5-Hexahydropyrrolo[1,2-a]quinoline-4,5-dicarboxylic acid diisopropyl ester 5 dibutyl fumarate 71 1,2,3,3a,4,5-Hexahydropyrrolo[1,2-a]quinoline-4,5-dibutyl dicarboxylate 6 di-sec-butyl fumarate 63 1,2,3,3a,4,5-Hexahydropyrrolo[1,2-a]quinoline-4,5-dibutyl dimethyl ester 7 diisobutyl fumarate 65 1,2,3,3a,4,5-Hexahydropyrrolo[1,2-a]quinoline-4,5-dicarboxylic acid diisobutyl ester 8 di-tert-butyl fumarate 61 1,2,3,3a,4,5-Hexahydropyrrolo[1,2-a]quinoline-4,5-ditert-butyl ester

[0033] Examples 9-12: In Examples 9-12, the reaction process is exactly the same as in Example 1, except that the quantum dots shown in Table 2 are used instead of the CdSe quantum dots in Example 1. The specific yields are shown in Table 2.

[0034] Table 2 Different quantum dots in Examples 9-12 and their corresponding yields

[0035] Example number quantum dots Yield (%) 9 CdS 72 10 ZnSe 56 11 CdSe / CdS 53 12 ZnSe / CdS heterojunction 51

[0036] Examples 13-15: In Examples 13-15, the reaction process is exactly the same as in Example 1, except that the solvent shown in Table 3 is used instead of CH3CN in Example 1. The specific yields are shown in Table 3.

[0037] Table 3. Different solvents and their corresponding yields in Examples 13-15

[0038] Example number solvent Yield (%) 13 DMSO 53 14 <![CDATA[CH3OH]]> 61 15 DMF 48

[0039] Example 16: In Example 16, the reaction process was exactly the same as in Example 1, except that sunlight was used instead of the 450 nm LED in Example 1, and the yield was 32%.

[0040] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments that can be applied to other fields. However, any simple modifications or equivalent changes made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method for preparing nitrogen-containing fused-ring compounds by quantum dot-catalyzed [4+2] cycloaddition, characterized in that, Includes the following steps: In an inert atmosphere, 1-phenylpyrrole and fumarate were used as reactants, and quantum dots were used as photocatalysts. They were added to the reaction vessel along with an organic solvent and subjected to a [4+2] cycloaddition reaction under visible light irradiation. After filtration, concentration and separation purification, nitrogen-containing fused ring compounds were obtained. The photocatalyst is selected from one or more of the following quantum dots: CdSe, CdS, CdTe, ZnSe, ZnS, CdSe / ZnS, CdSe / ZnO, CdSe / CdS, CdTe / CdSe, CdS / ZnSe, CdS / ZnTe, and ZnSe / CdS heterojunction. The fumarate is selected from one of the following: ； In the formula, R1 and R2 are independent and are represented by Me; or R1 and R2 are independent and can be represented by Et; or R1 and R2 are independent. n Pr; or R1 and R2 are independent. i Pr; or R1 and R2 are independent. n Bu; or R1 and R2 are independent. s Bu; or R1 and R2 are independent. i Bu; or R1 and R2 are independent. t Bu.

2. The method according to claim 1, characterized in that, The solvent is selected from one or more of acetone, DMSO, CHCl3, CH3OH, DMF or CH3CN.

3. The method according to claim 1, characterized in that, The solubility of the photocatalyst is from zero to a saturated molar concentration, excluding zero.

4. The method according to claim 1, characterized in that, The molar ratio of 1-phenylpyrrole to fumarate is 1:(0.1~10).

5. The method according to claim 1, characterized in that, The molar concentration of the 1-phenylpyrrole is 0.001 M to 10 M.

6. The method according to claim 1, characterized in that, The visible light source is selected from sunlight, LED lamps, medium-pressure mercury lamps, high-pressure mercury lamps, or xenon lamps.

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