CN117342907A - Method for preparing phenol by hydroxylation reaction of boric acid derivatives in air without photocatalyst and alkali-free conditions - Google Patents

Abstract

The present invention relates to the technical field of organic synthesis, and more specifically to a method for preparing phenol through the hydroxylation reaction of boric acid derivatives in air without a photocatalyst and under alkali-free conditions. The method includes the following steps: using oxygen in the air as an oxidizing agent at room temperature, an oxidative hydroxylation reaction occurs between arylboronic acid and an ether solvent under light, and after the reaction is completed, post-processing is performed to obtain the phenolic compound. During the preparation process of the present invention, there is no need to add transition metals as catalysts, no need to add photocatalysts, no need to add oxidants, no need to add alkali, no need to add heating, and phenolic compounds are prepared with high yield under photocatalytic conditions.

Description

Preparation of boric acid derivatives through hydroxylation reaction in air without photocatalyst and alkali-free conditions Phenol method

Technical field

The present invention relates to the technical field of organic synthesis, and more specifically to a method for preparing phenol through the hydroxylation reaction of boric acid derivatives in air without a photocatalyst and under alkali-free conditions.

Background technique

Phenolic compounds are important organic chemical raw materials and are widely used in medicine, organic synthesis and industry. In recent years, with the rapid development of industry, electronics and other industries, the demand for phenolic compounds has increased significantly. Therefore, scientific researchers are constantly exploring more superior synthesis methods of phenolic compounds. Hydroxylation of arylboronic acids is one of the most effective methods for the synthesis of phenolic compounds. However, this method still has certain shortcomings. For example, pioneering research on the hydroxylation of arylboronic acids focused on the use of metal photocatalysts (ACS Sustainable Chem. Eng. 2020, 8, 2682-2687) while requiring strong bases in some cases (Green Chem., 2019, 21, 4614-4618), or using stoichiometric amounts of strong oxidants in the absence of metal catalysts (Org. Lett., 2012, 14, 3494-3497; Tetrahedron Lett., 2015, 56, 1524-1527) , or need to use microwave reaction equipment (Green Chem., 2019, 21, 4614-4618).

In recent years, research on the photocatalytic oxidative hydroxylation of arylboronic acids to generate phenols has received widespread attention. However, these photocatalytic reactions require photocatalysts, and most photocatalysts have problems such as tedious synthesis and high cost. Although patent CN110668921 A reports a method for preparing phenol through the aerobic hydroxylation of boric acid derivatives under photocatalyst-free conditions, this method The method still requires the addition of an organic base, requires a long reaction time (24 hours), and uses an ultraviolet light source.

Therefore, it is of great significance to develop a green, efficient, mild, and simple oxidation method for the synthesis of phenolic compounds.

Contents of the invention

In view of the above problems, the present invention provides a method for preparing phenol through the hydroxylation reaction of boric acid derivatives in air under no photocatalyst and no alkali conditions. During the preparation process, there is no need to add transition metals as catalysts, no need to add oxidants, and no need to add acids and bases. , phenolic compounds can be prepared by efficiently oxidizing arylboronic acid in air without heating and under photocatalytic conditions.

The object of the present invention is to provide a method for preparing phenol through the hydroxylation reaction of boric acid derivatives in air under no photocatalyst and alkali-free conditions, including the following steps:

Under room temperature conditions, oxygen in the air is used as the oxidant, and an oxidative hydroxylation reaction occurs between arylboronic acid and ether solvents under light. After the reaction is completed, post-processing is performed to obtain phenolic compounds.

Preferably, the reaction time is 5-60 minutes.

Preferably, the reaction time is 5 minutes.

Preferably, the ratio of arylboronic acid to ether solvent is 1 mmol: 1-10 mL.

Preferably, the ratio of arylboronic acid to ether solvent is 1 mmol:3 mL.

Preferably, the light source used for illumination is an ultraviolet lamp, a xenon lamp, an LED lamp or an incandescent lamp.

Preferably, the light source used for illumination is a xenon lamp.

Preferably, the ether solvent is one or both of tetrahydrofuran and 2-methyl-tetrahydrofuran.

Preferably, the arylboronic acid is phenylboronic acid, o-tolueneboronic acid, m-tolueneboronic acid, p-tolueneboronic acid, 4-methoxyphenylboronic acid, 2-fluorophenylboronic acid, 4-fluorophenylboronic acid, 4- Chlorobenzeneboronic acid, 2,4-dichlorophenylboronic acid, 2-chloro-5-methylphenylboronic acid, 2,6-di-tert-butyl-4-methylphenylboronic acid, α-naphthaleneboronic acid, β-naphthaleneboronic acid, 4-aldehyde benzene boronic acid, 2-carboxamido benzene boronic acid, 4-(benzyloxycarbonyl) benzene boronic acid, m-trifluoromethylbenzene boronic acid, p-nitrobenzene boronic acid, 4-methyl-3-nitrobenzene boronic acid one of them.

Compared with the prior art, the present invention has the following beneficial effects:

The present invention discloses for the first time a new method for preparing phenolic compounds. At room temperature and under light, _O2 in the air is used as the oxidant, tetrahydrofuran and/or 2-methyltetrahydrofuran is used as the solvent, and arylboronic acid is oxidized. Hydroxylation reaction produces phenolic compounds. This method does not require the addition of photocatalysts or bases, and the reaction can be completed quickly in 5 minutes at room temperature under a xenon lamp. It has the advantages of mild reaction conditions, simple operation, high safety, few side reactions, and short reaction time.

Detailed ways

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention.

As shown in Table 1, the present invention uses arylboronic acid as raw material, in tetrahydrofuran or 2-methyltetrahydrofuran solvent, and uses air as the oxidant. Under the irradiation of a light source, the boronic acid group in the arylboronic acid is converted into a hydroxyl group. The method does not require heating, no need to add photocatalysts and alkali, and has the advantages of simple operation, green, efficient, less by-products, and short reaction time. The reaction conditions of the present invention are shown in Table 1.

Table 1 ^Optimization of reaction conditionsa

Example Solvent Alkali addition light source Yield(%) 1 Tetrahydrofuran none UV lamp 90 2 Tetrahydrofuran none Blue/green LED light 85/88 3 Tetrahydrofuran none incandescent lamp 92 4 Tetrahydrofuran none xenon lamp 98 ^5b Tetrahydrofuran none xenon lamp 0 6 Tetrahydrofuran none Avoid light 0 7c Tetrahydrofuran Triethylamine xenon lamp 51 8 2-Methyltetrahydrofuran none xenon lamp 91 9 N,N-dimethylformamide none xenon lamp 12 10 ethanol none xenon lamp 15 11 Toluene none xenon lamp 16 12 2-Methyltetrahydrofuran none xenon lamp 93

^aReaction conditions: phenylboronic acid (1.0mmol), air (1atm), light source (15W), solvent (3.0mL), room temperature, 5min, isolated yield. ^bUnder nitrogen conditions. c base (1.5mmol),

We selected phenylboronic acid as the template substrate and screened out the optimal reaction conditions (Table 1). The experimental results show that under the conditions without photocatalyst, using tetrahydrofuran as the solvent, air atmosphere and room temperature, using ultraviolet lamp, blue/green LED lamp, incandescent lamp and xenon lamp as the light source respectively, it was found that the expected products can be obtained with high yields. Products (Example 1-Example 4). Among them, the yield of irradiation with a xenon lamp source close to sunlight was 98%. The control experiment under dark conditions did not achieve the expected results, confirming the necessity of continuous irradiation with the light source (Example 6). When the air was replaced with nitrogen, the reaction was terminated (Example 5), indicating that air plays an important role in the reaction. The present invention attempts to add organic base Et ₃ N as an additive on the basis of Example 4, but the yield is significantly reduced (Example 7), indicating that the addition of alkali will inhibit the progress of the reaction. Research on solvents (Example 9 to Example 12) shows that 2-methyltetrahydrofuran and tetrahydrofuran are the best solvents, with yields of 93% and 98% respectively (Example 4, Example 12). Therefore, 4 is the optimal reaction condition.

On the basis of optimizing the reaction conditions, we expanded the substrate range of boronic acid (Table 2). Arylboronic acids containing different functional groups on the aromatic ring have been shown to be compatible under standard conditions and provide corresponding hydroxylation products. Arylboronic acids with different substituents on the para position of the aromatic ring, including electron donating groups such as alkyl (Example 15), alkoxy (Example 16), electron withdrawing groups such as halogen (Example 18, 19), aldehyde group (Example 25), nitro group (Example 29), the reaction is good, and the required product can be provided under standard conditions. It is worth noting that the tert-butyl group with large steric hindrance on the aromatic ring (Example 26) can also adapt to the reaction conditions. Therefore, it can be inferred from these results that the electronic properties of the substituents have little influence on the reaction efficiency. In addition, the optimal reaction conditions are also applicable to fused rings. The fused ring substrates can smoothly undergo aerobic hydroxylation without photocatalyst, providing the corresponding products with yields of 92% and 94% (Example 23, Example 24) .

Table 2 Implementations of different embodiments and yields of target productsa

^aReaction conditions: boric acid (1.0mmol), air (1atm), light source (15W), solvent (3.0mL), room temperature, 5min, isolated yield.

The following is a detailed description of Embodiment 4 and Embodiment 13 to Embodiment 30:

Example 4

Add 1.0 mmol phenylboronic acid and 3 mL tetrahydrofuran to the reaction bottle in sequence, irradiate with a xenon lamp, react at room temperature and air for 5 min, and use thin layer chromatography to track the reaction progress. After the reaction is completed, add 5.0 mL HCl (2.0 M), extracted with ethyl acetate (3 × 10 mL), combined the organic phases, then washed the organic phase with water twice, dried over Na ₂ SO ₄ , filtered, concentrated, and then separated by column chromatography to obtain the target The product phenol was obtained in a yield of 98%, and the product structure was identified by ¹ H NMR and ¹³ C NMR. ¹ H NMR (400MHz, DMSO-d ₆ ) δ (ppm): 9.37 (s, 1H), 7.16-7.21 (m, 2H), 6.76-6.87 (m, 3H). ¹³ C NMR (100MHz, DMSO-d ₆ )δ(ppm):157.36,129.35,118.82,115.26.

Example 13

Add 1.0 mmol o-tolylboronic acid and 3 mL tetrahydrofuran to the reaction bottle in sequence, irradiate with a xenon lamp, react at room temperature and air for 5 minutes, and use thin layer chromatography to track the reaction progress. After the reaction is completed, add 5.0 mL HCl to the reaction bottle. (2.0M), extracted with ethyl acetate (3×10mL), combined the organic phases, then washed the organic phase with water twice, dried over _{Na2SO4 -} free, filtered, concentrated, and then separated by column chromatography. The target product o-methylphenol was obtained with a yield of 95%, and the product structure was identified by ¹ H NMR and ¹³ C NMR. ¹ H NMR (400MHz, CDCl ₃ ) δ (ppm): 7.09-7.16 (m, 2H), 6.88 (t, J = 7.4Hz, 1H), 6.79 (d, J = 8.0Hz, 1H), 4.89 (s ,1H),2.28(s,3H). ¹³ C NMR (100MHz, CDCl ₃ )δ(ppm):153.75,131.07,127.15,123.80,120.80,114.94,15.74

Example 14

Add 1.0 mmol m-tolylboronic acid and 3 mL tetrahydrofuran to the reaction bottle in sequence, irradiate with a xenon lamp, react at room temperature and air for 5 minutes, and use thin layer chromatography to track the reaction progress. After the reaction is completed, add 5.0 mL HCl to the reaction bottle. (2.0M), extracted with ethyl acetate (3×10mL), combined the organic phases, then washed the organic phase with water twice, dried over _{Na2SO4 -} free, filtered, concentrated, and then separated by column chromatography. The target product m-cresol was obtained with a yield of 96%, and the product structure was identified by ¹ H NMR and ¹³ C NMR. ¹ H NMR (400MHz, CDCl ₃ ) δ (ppm): 7.21 (t, J = 7.6 Hz, 1H), 6.86 (d, J = 7.6 Hz, 1H), 6.77 (d, J = 7.9 Hz, 2H), 6.50 (s, 1H), 2.38 (s, 3H). ¹³ CNMR (100MHz, CDCl ₃ ) δ (ppm): 155.28, 140.01, 129.59, 121.86, 116.31, 112.56, 21.39.

Example 15

Add 1.0 mmol p-methylbenzene boric acid and 3 mL tetrahydrofuran to the reaction bottle in sequence, irradiate with a xenon lamp, react at room temperature and air for 5 minutes, and use thin layer chromatography to track the reaction progress. After the reaction is completed, add 5.0 mL HCl to the reaction bottle. (2.0M), extracted with ethyl acetate (3×10mL), combined the organic phases, then washed the organic phase with water twice, dried over _{Na2SO4 -} free, filtered, concentrated, and then separated by column chromatography. The target product p-methylphenol was obtained with a yield of 98%, and the product structure was identified by ¹ H NMR and ¹³ C NMR. ¹ H NMR (400MHz, CDCl ₃ ) δ (ppm): 7.07 (d, J = 8.3 Hz, 2H), 6.78 (d, J = 8.4 Hz, 2H), 5.70 (s, 1H), 2.31 (s, 3H) ). ¹³ C NMR (100MHz, CDCl ₃ ) δ (ppm): 153.09, 130.16, 130.11, 115.24, 20.50

Example 16

Add 1.0 mmol 4-methoxyphenylboronic acid and 3 mL tetrahydrofuran to the reaction bottle in sequence, irradiate with a xenon lamp, react at room temperature and air for 5 minutes, and use thin layer chromatography to track the reaction progress. After the reaction is completed, add 5.0 mL HCl (2.0 M), extracted with ethyl acetate (3 × 10 mL), combined the organic phases, then washed the organic phase with water twice, dried over Na ₂ SO ₄ , filtered, concentrated, and then used column chromatography. After separation, the target product 4-methoxyphenol was obtained with a yield of 99%. The product structure was identified by ¹ H NMR and ¹³ C NMR. ¹ H NMR (400MHz, CDCl ₃ ) δ (ppm): 6.77-6.81 (m, 4H), 5.08 (s, 1H), 3.77 (s, 3H). ¹³ C NMR (100MHz, CDCl ₃ ) δ (ppm) :153.59,149.58,116.17,115.01,55.94

Example 17

Add 1.0 mmol 2-fluorophenylboronic acid and 3 mL tetrahydrofuran to the reaction bottle in sequence, irradiate with a xenon lamp, and react at room temperature and air for 5 minutes. Use thin layer chromatography to track the reaction progress. After the reaction is completed, add 5.0 mL HCl to the reaction bottle. (2.0M), extracted with ethyl acetate (3×10mL), combined the organic phases, then washed the organic phase with water twice, dried over _{Na2SO4 -} free, filtered, concentrated, and then separated by column chromatography. The target product 2-fluorophenol was obtained with a yield of 93%. The product structure was identified by ¹ H NMR and ¹³ C NMR. ¹ H NMR (400MHz, CDCl ₃ ) δ (ppm): 7.02-7.11 (m, 3H), 6.85-6.89 (m, 1H), 5.88 (s, 1H). ¹³ C NMR (100MHz, CDCl ₃ ) δ ( ppm):152.19,150.30,143.55,143.44,124.89,124.86,120.94,120.88,117.47,117.45,115.70,115.55.

Example 18

Add 1.0 mmol 4-fluorophenylboronic acid and 3 mL tetrahydrofuran to the reaction bottle in sequence, irradiate with a xenon lamp, react at room temperature and air for 5 minutes, and use thin layer chromatography to track the reaction progress. After the reaction is completed, add 5.0 mL HCl to the reaction bottle. (2.0M), extracted with ethyl acetate (3×10mL), combined the organic phases, then washed the organic phase with water twice, dried over _{Na2SO4 -} free, filtered, concentrated, and then separated by column chromatography. The target product 4-fluorophenol was obtained with a yield of 95%. The product structure was identified by ¹ H NMR and ¹³ C NMR. ¹ H NMR (400MHz, CDCl ₃ ) δ (ppm): 6.91-6.95 (m, 2H), 6.78-6.81 (m, 2H). ¹³ C NMR (100MHz, CDCl ₃ ) δ (ppm): 158.39, 156.50, 151.13,151.12,116.44,116.38,116.21,116.03

Example 19

Add 1.0 mmol 4-chlorophenylboronic acid and 3 mL tetrahydrofuran to the reaction bottle in sequence, irradiate with a xenon lamp, react at room temperature and air for 5 minutes, and use thin layer chromatography to track the reaction progress. After the reaction is completed, add 5.0 mL HCl to the reaction bottle. (2.0M), extracted with ethyl acetate (3×10mL), combined the organic phases, then washed the organic phase with water twice, dried over _{Na2SO4 -} free, filtered, concentrated, and then separated by column chromatography. The target product 4-chlorophenol was obtained with a yield of 92%, and the product structure was identified by ¹ H NMR and ¹³ C NMR. ¹ H NMR (400MHz, CDCl ₃ ) δ (ppm): 7.16-7.13 (m, 2H), 6.72-6.75 (m, 2H), 5.08 (s, 1H). ¹³ C NMR (100MHz, CDCl ₃ ) δ ( ppm):153.94,129.62,125.75,116.80

Example 20

Add 1.0 mmol 2,4-dichlorophenylboronic acid and 3 mL tetrahydrofuran to the reaction bottle in sequence, irradiate with a xenon lamp, react at room temperature and air for 5 minutes, and follow the reaction process with thin layer chromatography. After the reaction is completed, pour into the reaction bottle Add 5.0 mL HCl (2.0 M), extract with ethyl acetate (3 × 10 mL), combine the organic phases, then wash the organic phases with water twice, dry over Na ₂ SO ₄ , filter, concentrate, and then use column chromatography Separate by chromatography to obtain the target product 2,4-dichlorophenol with a yield of 91%. The product structure was identified by ¹ H NMR and ¹³ C NMR. ¹ H NMR (400MHz, DMSO-d6) δ (ppm): 10.42 (s, 1H), 7.38 (d, J = 1.9 Hz, 1H), 7.15-7.17 (m, 1H), 6.96 (d, J = 8.7 Hz, 1H). ¹³ C NMR (100MHz, DMSO-d6) δ (ppm): 152.27, 129.03, 127.80, 122.62, 120.60, 117.64.

Example 21

Add 1.0 mmol 2-chloro-5-methylphenylboronic acid and 3 mL tetrahydrofuran into the reaction bottle in sequence, irradiate with a xenon lamp, react at room temperature and air for 5 minutes, and use thin layer chromatography to track the reaction progress. After the reaction is completed, proceed to the reaction bottle. Add 5.0 mL HCl (2.0 M) to the bottle, extract with ethyl acetate (3 × 10 mL), combine the organic phases, then wash the organic phases with water twice, dry with Na ₂ SO ₄ , filter, concentrate, and then use a column Separate by chromatography to obtain the target product 2-chloro-5-methylphenol with a yield of 93%. The product structure was identified by ¹ H NMR and ¹³ C NMR. ¹ H NMR (400MHz, DMSO-d ₆ ) δ (ppm): 9.94 (s, 1H), 7.13-7.16 (m, 1H), 6.80 (s, 1H), 6.57 (d, J = 8.0Hz, 1H) ,2.34(s,3H). ¹³ C NMR (100MHz, DMSO-d ₆ )δ(ppm):152.71,137.49,129.33,120.65,117.18,116.68,20.49

Example 22

Add 1.0mmol 2,6-di-tert-butyl-4-methylphenylboronic acid and 3mL tetrahydrofuran into the reaction bottle in sequence, irradiate with a xenon lamp, react at room temperature and air for 5 minutes, and use thin layer chromatography to track the reaction progress. After completion, add 5.0 mL HCl (2.0 M) to the reaction flask, extract with ethyl acetate (3×10 mL), combine the organic phases, then wash the organic phases with water twice, dry with Na ₂ SO ₄ , filter, and concentrate. , and then separated by column chromatography to obtain the target product 2,6-di-tert-butyl-4-methylphenol with a yield of 94%. The product structure was identified by ¹ H NMR and ¹³ C NMR. ¹ H NMR (400MHz, DMSO-d ₆ ) δ (ppm): 6.88 (s, 2H), 6.62 (s, 1H), 2.35 (s, 3H), 1.38 (s, 18H). ¹³ C NMR (100MHz, DMSO-d ₆ )δ(ppm):151.48,139.10,127.94,124.84,21.01

Example 23

Add 1.0 mmol α-naphthalene boric acid and 3 mL tetrahydrofuran to the reaction bottle in sequence, irradiate with a xenon lamp, react at room temperature and air for 5 minutes, and follow the reaction process with thin layer chromatography. After the reaction is completed, add 5.0 mL HCl ( 2.0M), extracted with ethyl acetate (3×10mL), combined the organic phases, then washed the organic phase with water twice, dried over _{Na2SO4 -} free, filtered, concentrated, and then separated by column chromatography to obtain The target product α-naphthol has a yield of 92%, and the product structure was identified by ¹ H NMR and ¹³ C NMR. ¹ H NMR (400MHz, CDCl ₃ ) δ (ppm): 8.19-822 (m, 1H), 7.82-7.85 (m, 1H), 7.46-7.52 (m, 3H), 7.31-7.34 (m, 1H), 6.82 (dd, J=7.4, 0.5Hz, 1H), 4.58 (s, 1H). ¹³ CNMR (100MHz, CDCl ₃ ) δ (ppm): 151.38, 134.80, 127.71, 126.47, 125.86, 125.29, 124.39, 121.55, 120.73,108.68.

Example 24

Add 1.0 mmol β-naphthalene boric acid and 3 mL tetrahydrofuran to the reaction bottle in sequence, irradiate with a xenon lamp, react at room temperature and air for 5 minutes, and follow the reaction process with thin layer chromatography. After the reaction is completed, add 5.0 mL HCl ( 2.0M), extracted with ethyl acetate (3×10mL), combined the organic phases, then washed the organic phase with water twice, dried over _{Na2SO4 -} free, filtered, concentrated, and then separated by column chromatography to obtain The target product β-naphthol has a yield of 94%, and the product structure was identified by ¹ H NMR and ¹³ C NMR. ¹ H NMR (400MHz, CDCl ₃ ) δ (ppm): 7.75-7.79 (m, 2H), 7.68 (d, J = 8.2Hz, 1H), 7.42-7.46 (m, 1H), 7.34-7.36 (m, 1H), 7.16 (d, J=2.4Hz, 1H), 7.12 (dd, J=8.8, 2.5Hz, 1H). ¹³ C NMR (100MHz, CDCl ₃ ) δ (ppm): 153.35, 134.61, 129.87, 128.96 ,127.78,126.54,126.39,123.64,117.77,109.54

Example 25

Add 1.0 mmol 4-aldehyde phenylboronic acid and 3 mL tetrahydrofuran to the reaction bottle in sequence, irradiate with a xenon lamp, react at room temperature and air for 5 minutes, and follow the reaction process with thin layer chromatography. After the reaction is completed, add 5.0 mLHCl (2.0M), extracted with ethyl acetate (3×10mL), combined the organic phases, then washed the organic phase with water twice, dried over _{Na2SO4 -} free, filtered, concentrated, and then separated by column chromatography. , the target product 4-aldehyde phenol was obtained with a yield of 90%, and the product structure was identified by ¹ H NMR and ¹³ C NMR. ¹ H NMR (400MHz, DMSO-d ₆ ) δ (ppm): 10.57 (s, 1H), 9.77 (s, 1H), 7.74 (d, J = 8.1Hz, 2H), 6.93 (d, J = 8.2Hz ,2H). ¹³ C NMR (100MHz, DMSO-d ₆ ) δ (ppm): 190.75, 163.29, 132.02, 128.40, 115.80

Example 26

Add 1.0 mmol 2-carboxamidophenylboronic acid and 3 mL tetrahydrofuran to the reaction bottle in sequence, irradiate with a xenon lamp, react at room temperature and air for 5 minutes, and follow the reaction progress with thin layer chromatography. After the reaction is completed, add 5.0 mL HCl (2.0 M), extracted with ethyl acetate (3 × 10 mL), combined the organic phases, then washed the organic phase with water twice, dried over Na ₂ SO ₄ , filtered, concentrated, and then used column chromatography. After separation, the target product 2-carboxamidophenol was obtained with a yield of 89%. The product structure was identified by ¹ H NMR and ¹³ C NMR. ¹ H NMR (400MHz, DMSO-d ₆ ) δ (ppm): 13.03 (s, 1H), 8.40 (s, 1H), 7.86 (d, J = 8.0Hz, 2H), 7.38 (t, J = 7.7Hz ,1H),6.82-6.89(m,2H). ¹³ C NMR (100MHz, DMSO-d ₆ )δ(ppm):172.14,161.10,134.02,128.08,118.31,117.39,114.36

Example 27

Add 1.0 mmol 4-(benzyloxycarbonyl)phenylboronic acid and 3 mL tetrahydrofuran to the reaction bottle in sequence, irradiate with a xenon lamp, react at room temperature and air for 5 minutes, and use thin layer chromatography to track the reaction progress. After the reaction is completed, proceed to the reaction bottle. Add 5.0 mL HCl (2.0 M) to the bottle, extract with ethyl acetate (3 × 10 mL), combine the organic phases, then wash the organic phases with water twice, dry with Na ₂ SO ₄ , filter, concentrate, and then use a column Separate by chromatography to obtain the target product 4-(benzyloxycarbonyl)phenol with a yield of 87%. The product structure was identified by ¹ H NMR and ¹³ C NMR. ¹ H NMR (400MHz, DMSO-d ₆ ) δ (ppm): 10.49 (s, 1H), 7.87 (d, J＝7.2Hz, 2H), 7.33-7.45 (m, 5H), 6.88 (d, J＝ 7.2Hz, 2H), 5.29 (s, 2H). ¹³ C NMR (100MHz, DMSO-d ₆ ) δ (ppm): 165.39, 162.17, 136.47, 131.51, 128.44, 127.93, 127.81, 120.15, 115.39, 65.55

Example 28

Add 1.0 mmol m-trifluoromethylbenzene boric acid and 3 mL tetrahydrofuran to the reaction bottle in sequence, irradiate with a xenon lamp, react at room temperature and air for 5 minutes, and use thin layer chromatography to track the reaction progress. After the reaction is completed, add 5.0 mL HCl (2.0 M), extracted with ethyl acetate (3 × 10 mL), combined the organic phases, then washed the organic phase with water twice, dried over Na ₂ SO ₄ , filtered, concentrated, and then used column chromatography. After separation, the target product m-trifluoromethylphenol was obtained with a yield of 82%. The product structure was identified by ¹ H NMR and ¹³ C NMR. ¹ H NMR (400MHz, CDCl ₃ ) δ (ppm): 7.35 (t, J = 8.0 Hz, 1H), 7.22 (t, J = 7.8 Hz, 1H), 7.02-7.04 (m, 1H), 6.14 (s , 1H). ¹³ C NMR (100MHz, CDCl ₃ ) δ (ppm): 155.4, 132.5, 132.25, 131.99, 131.73, 130.35, 118.87, 118.86, 117.85, 117.82, 112.36, 112.33.

Example 29

Add 1.0 mmol p-nitrobenzene boric acid and 3 mL tetrahydrofuran to the reaction bottle in sequence, irradiate with a xenon lamp, and react at room temperature and air for 5 minutes. Use thin layer chromatography to track the reaction progress. After the reaction is completed, add 5.0 mL HCl to the reaction bottle. (2.0M), extracted with ethyl acetate (3×10mL), combined the organic phases, then washed the organic phase with water twice, dried over _{Na2SO4 -} free, filtered, concentrated, and then separated by column chromatography. The target product p-nitrophenol was obtained with a yield of 77%, and the product structure was identified by ¹ H NMR and ¹³ C NMR. ¹ H NMR (400MHz, DMSO-d ₆ )δ (ppm): 10.96 (s, 1H), 8.03 (s, 2H), 6.87 (s, 2H). ¹³ C NMR (100MHz, DMSO-d ₆ ) δ ( ppm):163.82,139.55,125.93,115.57

Example 30

Add 1.0 mmol 4-methyl-3-nitrobenzene boric acid and 3 mL tetrahydrofuran to the reaction bottle in sequence, irradiate with a xenon lamp, react at room temperature and air for 5 minutes, and follow the reaction process with thin layer chromatography. After the reaction is completed, proceed to the reaction bottle. Add 5.0 mL HCl (2.0 M) to the bottle, extract with ethyl acetate (3 × 10 mL), combine the organic phases, then wash the organic phases with water twice, dry with Na ₂ SO ₄ , filter, concentrate, and then use a column Separate by chromatography to obtain the target product 4-methyl-3-nitrophenol with a yield of 80%. The product structure was identified by ¹ H NMR and ¹³ C NMR. ¹ H NMR (400MHz, DMSO-d ₆ ) δ (ppm): 10.11 (s, 1H), 7.33 (s, 1H), 7.22 (d, J = 8.2Hz, 1H), 7.01 (d, J = 8.3Hz ,1H),2,36(s,3H). ¹³ CNMR(100MHz,DMSO-d ₆ )δ(ppm):156.02,148.98,133.44,122.58,120.81,110.44,18.71

Example 31

Add 1.0 mmol phenylboronic acid and 1 mL tetrahydrofuran to the reaction bottle in sequence, irradiate with a xenon lamp, react at room temperature and air for 60 min, and use thin layer chromatography to track the reaction progress. After the reaction is completed, add 5.0 mL HCl (2.0 M), extracted with ethyl acetate (3 × 10 mL), combined the organic phases, then washed the organic phases with water twice, dried over Na ₂ SO ₄ , filtered, concentrated, and then separated by column chromatography, 98 The target product phenol was obtained in % yield.

Example 32

Add 1.0 mmol phenylboronic acid and 10 mL solution (equal amounts of tetrahydrofuran and 2-methyl-tetrahydrofuran) into the reaction bottle in sequence, irradiate with a xenon lamp, react at room temperature and air for 30 minutes, and use thin layer chromatography to track the reaction progress. After completion, add 5.0 mL HCl (2.0 M) to the reaction flask, extract with ethyl acetate (3 × 10 mL), combine the organic phases, then wash the organic phases with water twice, dry with Na ₂ SO ₄ , filter, and concentrate. , and then separated by column chromatography to obtain the target product phenol with a yield of 98%.

Although the preferred embodiments of the present invention have been described, those skilled in the art will be able to make additional changes and modifications to these embodiments once the basic inventive concepts are apparent. Therefore, it is intended that the appended claims be construed to include the preferred embodiments and all changes and modifications that fall within the scope of the invention.

Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the invention. In this way, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and equivalent technologies, the present invention is also intended to include these modifications and variations.

Claims (9)

1. A method for preparing phenol through the hydroxylation reaction of boric acid derivatives in air under no photocatalyst and alkali-free conditions, which is characterized in that it includes the following steps: Under room temperature conditions, oxygen in the air is used as the oxidant, and an oxidative hydroxylation reaction occurs between arylboronic acid and ether solvents under light. After the reaction is completed, post-processing is performed to obtain phenolic compounds. 2. A method for preparing phenol through the hydroxylation reaction of boric acid derivatives in air under no photocatalyst and alkali-free conditions according to claim 1, characterized in that the reaction time is 5-60 min. 3. A method for preparing phenol through the hydroxylation reaction of boric acid derivatives in air under no photocatalyst and alkali-free conditions according to claim 2, characterized in that the reaction time is 5 min. 4. A method for preparing phenol through the hydroxylation reaction of boric acid derivatives in air under no photocatalyst and alkali-free conditions according to claim 1, characterized in that the ratio of arylboronic acid to ether solvent is 1 mmol: 1- 10mL. 5. A method for preparing phenol through the hydroxylation reaction of boric acid derivatives in air under photocatalyst-free and alkali-free conditions according to claim 4, characterized in that the ratio of arylboronic acid to ether solvent is 1 mmol: 3 mL. 6. A method for preparing phenol through the hydroxylation reaction of boric acid derivatives in air under no photocatalyst and alkali-free conditions according to claim 1, characterized in that the light source used for illumination is an ultraviolet lamp, a xenon lamp, an LED lamp or an incandescent lamp . 7. A method for preparing phenol through the hydroxylation reaction of boric acid derivatives in air under no photocatalyst and alkali-free conditions according to claim 6, characterized in that the light source used for illumination is a xenon lamp. 8. A method for preparing phenol by hydroxylation reaction of boric acid derivatives in air under no photocatalyst and alkali-free conditions according to claim 1, characterized in that the ether solvent is one of tetrahydrofuran and 2-methyl-tetrahydrofuran. One or two species. 9. A method for preparing phenol through the hydroxylation reaction of boric acid derivatives in air under no photocatalyst and alkali-free conditions according to claim 1, characterized in that the arylboronic acid is phenylboric acid, o-methylphenylboric acid, m- Methylboric acid, p-methylbenzeneboric acid, 4-methoxybenzeneboric acid, 2-fluorobenzeneboric acid, 4-fluorobenzeneboric acid, 4-chlorophenylboric acid, 2,4-dichlorophenylboronic acid, 2-chloro- 5-methylphenylboronic acid, 2,6-di-tert-butyl-4-methylphenylboronic acid, α-naphthaleneboronic acid, β-naphthaleneboronic acid, 4-aldehydebenzeneboronic acid, 2-carboxamidophenylboronic acid, 4- One of (benzyloxycarbonyl)phenylboronic acid, m-trifluoromethylbenzeneboronic acid, p-nitrobenzeneboronic acid, and 4-methyl-3nitrobenzeneboronic acid.