APPLICATION OF LITHIUM 4-METHOXYANILINE IN CATALYSIS OF HYDROBORATION REACTION OF IMINE AND BORANE

Abstract

The present invention relates to the application of lithium 4-methoxyaniline in catalysis of the hydroboration reaction of an imine and a borane. A catalyst, a borane and an imine are successively stirred and mixed until uniform, reacted for 1 to 2 hours, and then exposed to air so as to stop the reaction, and the reaction liquid is subjected to decompression to remove a solvent therein, so as to obtain a borate with different substituents. The lithium 4-methoxyaniline disclosed in the present invention can catalyze the hydroboration reaction of an imine and a borane in a high activity manner at room temperature, wherein the amount of the catalyst is merely 4-5 mol % of the molar amount of the imine, and the yield of the reaction can reach 90% or more. The yield of a borate with different substituents can reach 99% with mild reaction conditions under an optimized condition.

Claims

1. A method of preparing a borate ester comprising: reacting an imine with a borane in an organic solvent and in the presence of 4-methoxyaniline lithium as a catalyst at room temperature under anhydrous, oxygen-free, and inert gas conditions for 1-2 hours; and stirring in air to stop reaction and to obtain the borate ester.

2. The method of claim 1, wherein: the imine has the following structure: ##STR00004## the borane is pinacol borane; the borate ester has the following structure: ##STR00005## and R.sub.1 and R.sub.2 are independently selected from the group consisting of halogen, methyl and methoxy.

3. The method of claim 1, wherein the organic solvent is tetrahydrofuran.

4. The method of claim 1, wherein an amount of 4-methoxyaniline lithium is 4% to 5% of a molar amount of the imine.

5. The method of claim 1, wherein a molar ratio of the imine to the borane is 1:1 to 1:1.2.

6. The method of claim 5, wherein the molar ratio of the imine to the borane is 1:1.2.

Description

EMBODIMENTS OF THE INVENTION

[0021] The present invention will be further described in combination with the following embodiments:

Example 1 Catalytic Hydroboration Reaction of Biphenylaniline and Pinacol Borane by 4-Methoxyaniline Lithium

[0022] In a reaction flask, which was treated by dehydration and deoxidation, 0.5 mmol of biphenylaniline and 100 μl of THF were added under the protection of argon. 0.6 mmol (0.0871 mL) of borane was added with a pipette gun and mixed well. Finally, 69.9 μl of 4-methoxyaniline lithium in tetrahydrofuran (0.3577 M) (5 mol % amount) was added. The reaction was carried out for 1 hour. A drop of the reaction solution was taken and added to an NMR tube. CDCl.sub.3 was then added to the NMR tube. The conversion rate calculated based on .sup.1H is 96%. .sup.1H NMR data of the product is: .sup.1H NMR (CDCl.sub.3, 400 MHz) δ: 7.29-7.12 (m, 9H), 6.88-6.84 (t, 1H), 4.69 (s, 2H), 1.29 (s, 12H).

Example 2 Catalytic Hydroboration Reaction of Biphenylaniline and Pinacol Borane by 4-Methoxyaniline Lithium

[0023] In a reaction flask, which was treated by dehydration and deoxidation, 0.5 mmol of biphenylaniline and 100 μl of THF were added under the protection of argon. 0.6 mmol (0.0871 mL) of borane was added with a pipette gun and mixed well. Finally, 69.9 μl of 4-methoxyaniline lithium in tetrahydrofuran (0.3577 M) (5 mol % amount) was added. The reaction was carried out for 2 hours. A drop of the reaction solution was taken and added to an NMR tube. CDCl.sub.3 was then added to the NMR tube. The conversion rate calculated based on .sup.1H is 99%. .sup.1H NMR data of the product is: .sup.1H NMR (CDCl.sub.3, 400 MHz) δ: 7.29-7.12 (m, 9H), 6.88-6.84 (t, 1H), 4.69 (s, 2H), 1.29 (s, 12H).

[0024] If 4-methoxyaniline lithium was replaced with the lithium compound of formula I, a hydroboration product could not be obtained.

##STR00003##

Example 3 Catalytic Hydroboration Reaction of Biphenylaniline and Pinacol Borane by 4-Methoxyaniline Lithium

[0025] In a reaction flask, which was treated by dehydration and deoxidation, 0.5 mmol of biphenylaniline and 100 μl of THF were added under the protection of argon. 0.6 mmol (0.0871 mL) of borane was added with a pipette gun and mixed well. Finally, 55.9 μl of 4-methoxyaniline lithium in tetrahydrofuran (0.3577 M) (4 mol % amount) was added. The reaction was carried out for 2 hours. A drop of the reaction solution was taken and added to an NMR tube. CDCl.sub.3 was then added to the NMR tube. The conversion rate calculated based on .sup.1H is 96%. .sup.1H NMR data of the product is: .sup.1H NMR (CDCl.sub.3, 400 MHz) δ: 7.29-7.12 (m, 9H), 6.88-6.84 (t, 1H), 4.69 (s, 2H), 1.29 (s, 12H).

Example 4 Catalytic Hydroboration Reaction of Biphenylaniline and Pinacol Borane by 4-Methoxyaniline Lithium

[0026] In a reaction flask, which was treated by dehydration and deoxidation, 0.5 mmol of biphenylaniline and 100 μl of THF were added under the protection of argon. 0.5 mmol (0.0726 mL) of borane was added with a pipette gun and mixed well. Finally, 69.9 μl of 4-methoxyaniline lithium in tetrahydrofuran (0.3577 M) (5 mol % amount) was added. The reaction was carried out for 2 hours. A drop of the reaction solution was taken and added to an NMR tube. CDCl.sub.3 was then added to the NMR tube. The conversion rate calculated based on .sup.1H is 90%. .sup.1H NMR data of the product is: .sup.1H NMR (CDCl.sub.3, 400 MHz) δ: 7.29-7.12 (m, 9H), 6.88-6.84 (t, 1H), 4.69 (s, 2H), 1.29 (s, 12H).

Example 5 Catalytic Hydroboration Reaction of Biphenylaniline and Pinacol Borane by 4-Methoxyaniline Lithium

[0027] In a reaction flask, which was treated by dehydration and deoxidation, 0.5 mmol of biphenylaniline and 100 μl of THF were added under the protection of argon. 0.55 mmol (0.0798 mL) of borane was added with a pipette gun and mixed well. Finally, 69.9 μl of 4-methoxyaniline lithium in tetrahydrofuran (0.3577 M) (5 mol % amount) was added. The reaction was carried out for 2 hours. A drop of the reaction solution was taken and added to an NMR tube. CDCl.sub.3 was then added to the NMR tube. The conversion rate calculated based on .sup.1H is 95%. .sup.1H NMR data of the product is: .sup.1H NMR (CDCl.sub.3, 400 MHz) δ: 7.29-7.12 (m, 9H), 6.88-6.84 (t, 1H), 4.69 (s, 2H), 1.29 (s, 12H).

Example 6 Catalytic Hydroboration Reaction of N-(p-Methylbenzylidene)Aniline and Pinacol Borane by 4-Methoxyaniline Lithium

[0028] In a reaction flask, which was treated by dehydration and deoxidation, 0.5 mmol of N-(p-methylbenzylidene)aniline and 100 μl of THF were added under the protection of argon. 0.6 mmol (0.0871 mL) of borane was added with a pipette gun and mixed well. Finally, 69.9 μl of 4-methoxyaniline lithium in tetrahydrofuran (0.3577 M) (4 mol % amount) was added. The reaction was carried out for 2 hours. A drop of the reaction solution was taken and added to an NMR tube. CDCl.sub.3 was then added to the NMR tube. The conversion rate calculated based on .sup.1H is 99%. .sup.1H NMR data of the product is: .sup.1H NMR (CDCl.sub.3, 400 MHz) δ: 7.23-7.08 (m, 8H), 6.89-6.85 (t, 1H), 4.66 (s, 2H), 2.31 (s, 3H), 1.30 (s, 12H).

Example 7 Catalytic Hydroboration Reaction of N-(p-Methoxybenzylidene)Aniline and Pinacol Borane by 4-Methoxyaniline Lithium

[0029] In a reaction flask, which was treated by dehydration and deoxidation, 0.5 mmol of N-(p-methoxybenzylidene)aniline and 100 μl of THF were added under the protection of argon. 0.6 mmol (0.0871 mL) of borane was added with a pipette gun and mixed well. Finally, 69.9 μl of 4-methoxyaniline lithium in tetrahydrofuran (0.3577 M) (5 mol % amount) was added. The reaction was carried out for 2 hours. A drop of the reaction solution was taken and added to an NMR tube. CDCl.sub.3 was then added to the NMR tube. The conversion rate calculated based on .sup.1H is 99%. .sup.1H NMR data of the product is: .sup.1H NMR (CDCl.sub.3, 400 MHz) δ: 7.22-7.13 (d, 6H), 6.89-6.80 (d, 3H), 4.63 (s, 2H), 3.77 (s, 3H), 1.30 (s, 12H).

Example 8 Catalytic Hydroboration Reaction of N-(4-Fluorobenzylidene)Aniline and Pinacol Borane by 4-Methoxyaniline Lithium

[0030] In a reaction flask, which was treated by dehydration and deoxidation, 0.5 mmol of N-(4-fluorobenzylidene) aniline and 100 μl of THF were added under the protection of argon. 0.6 mmol (0.0871 mL) of borane was added with a pipette gun and mixed well. Finally, 69.9 μl of 4-methoxyaniline lithium in tetrahydrofuran (0.3577 M) (5 mol % amount) was added. The reaction was carried out for 2 hours. A drop of the reaction solution was taken and added to an NMR tube. CDCl.sub.3 was then added to the NMR tube. The conversion rate calculated based on .sup.1H is 99%. .sup.1H NMR data of the product is: .sup.1H NMR (CDCl.sub.3, 400 MHz) δ: 7.22-7.15 (d, 6H), 6.98-6.94 (d, 3H), 4.66 (s, 2H), 1.30 (s, 12H).

Example 9 Catalytic Hydroboration Reaction of N-(4-Chlorobenzylidene)Aniline and Pinacol Borane by 4-Methoxyaniline Lithium

[0031] In a reaction flask, which was treated by dehydration and deoxidation, 0.5 mmol of N-(4-chlorobenzylidene)aniline and 100 μl of THF were added under the protection of argon. 0.6 mmol (0.0871 mL) of borane was added with a pipette gun and mixed well. Finally, 69.9 μl of 4-methoxyaniline lithium in tetrahydrofuran (0.3577 M) (5 mol % amount) was added. The reaction was carried out for 2 hours. A drop of the reaction solution was taken and added to an NMR tube. CDCl.sub.3 was then added to the NMR tube. The conversion rate calculated based on .sup.1H is 99%. .sup.1H NMR data of the product is: .sup.1H NMR (CDCl.sub.3, 400 MHz) δ: 7.20-7.14 (d, 6H), 6.99-6.93 (d, 3H), 4.64 (s, 2H), 1.30 (s, 12H).

Example 10 Catalytic Hydroboration Reaction of N-(4-Bromobenzylidene)Aniline and Pinacol Borane by 4-Methoxyaniline Lithium

[0032] In a reaction flask, which was treated by dehydration and deoxidation, 0.5 mmol of N-(4-bromobenzylidene)aniline and 100 μl of THF were added under the protection of argon. 0.6 mmol (0.0871 mL) of borane was added with a pipette gun and mixed well. Finally, 69.9 μl of 4-methoxyaniline lithium in tetrahydrofuran (0.3577 M) (5 mol % amount) was added. The reaction was carried out for 2 hours. A drop of the reaction solution was taken and added to an NMR tube. CDCl.sub.3 was then added to the NMR tube. The conversion rate calculated based on .sup.1H is 99%. .sup.1H NMR data of the product is: .sup.1H NMR (CDCl.sub.3, 400 MHz) δ: 7.24-7.16 (d, 6H), 6.97-6.93 (d, 3H), 4.63 (s, 2H), 1.31 (s, 12H).

Example 11 Catalytic Hydroboration Reaction of Benzylidene-p-Toluidine and Pinacol Borane by 4-Methoxyaniline Lithium

[0033] In a reaction flask, which was treated by dehydration and deoxidation, 0.5 mmol of N benzylidene-p-toluidine and 100 μl of THF were added under the protection of argon. 0.6 mmol (0.0871 mL) of borane was added with a pipette gun and mixed well. Finally, 69.9 μl of 4-methoxyaniline lithium in tetrahydrofuran (0.3577 M) (5 mol % amount) was added. The reaction was carried out for 2 hours. A drop of the reaction solution was taken and added to an NMR tube. CDCl.sub.3 was then added to the NMR tube. The conversion rate calculated based on .sup.1H is 99%. .sup.1H NMR data of the product is: .sup.1H NMR (CDCl.sub.3, 400 MHz) δ: 7.32-7.28 (d, 5H), 7.10-7.08 (d, 2H), 6.64-6.60 (d, 2H), 4.62 (s, 2H), 1.31 (s, 12H).

Example 12 Catalytic Hydroboration Reaction of N-(Benzylidene)-4-Fluoroaniline and Pinacol Borane by 4-Methoxyaniline Lithium

[0034] In a reaction flask, which was treated by dehydration and deoxidation, 0.5 mmol of N-(benzylidene)-4-fluoroaniline and 100 μl of THF were added under the protection of argon. 0.6 mmol (0.0871 mL) of borane was added with a pipette gun and mixed well. Finally, 69.9 μl of 4-methoxyaniline lithium in tetrahydrofuran (0.3577 M) (5 mol % amount) was added. The reaction was carried out for 2 hours. A drop of the reaction solution was taken and added to an NMR tube. CDCl.sub.3 was then added to the NMR tube. The conversion rate calculated based on .sup.1H is 99%. .sup.1H NMR data of the product is: .sup.1H NMR (CDCl.sub.3, 400 MHz) δ: 7.24-7.02 (d, 7H), 6.75-6.70 (d, 2H), 4.66 (s, 2H), 1.32 (s, 12H).

Example 13 Catalytic Hydroboration Reaction of N-(Benzylidene)-4-Chloroaniline and Pinacol Borane by 4-Methoxyaniline Lithium

[0035] In a reaction flask, which was treated by dehydration and deoxidation, 0.5 mmol of N-(benzylidene)-4-chloroaniline and 100 μl of THF were added under the protection of argon. 0.6 mmol (0.0871 mL) of borane was added with a pipette gun and mixed well. Finally, 69.9 μl of 4-methoxyaniline lithium in tetrahydrofuran (0.3577 M) (5 mol % amount) was added. The reaction was carried out for 2 hours. A drop of the reaction solution was taken and added to an NMR tube. CDCl.sub.3 was then added to the NMR tube. The conversion rate calculated based on .sup.1H is 99%. .sup.1H NMR data of the product is: .sup.1H NMR (CDCl.sub.3, 400 MHz) δ: 7.26-7.05 (d, 7H), 6.74-6.69 (d, 2H), 4.61 (s, 2H), 1.30 (s, 12H).

Example 14 Catalytic Hydroboration Reaction of N-(Benzylidene)-4-Bromoaniline and Pinacol Borane by 4-Methoxyaniline Lithium

[0036] In a reaction flask, which was treated by dehydration and deoxidation, 0.5 mmol of N-(benzylidene)-4-bromoaniline and 100 μl of THF were added under the protection of argon. 0.6 mmol (0.0871 mL) of borane was added with a pipette gun and mixed well. Finally, 69.9 μl of 4-methoxyaniline lithium in tetrahydrofuran (0.3577 M) (5 mol % amount) was added. The reaction was carried out for 2 hours. A drop of the reaction solution was taken and added to an NMR tube. CDCl.sub.3 was then added to the NMR tube. The conversion rate calculated based on .sup.1H is 99%. .sup.1H NMR data of the product is: .sup.1H NMR (CDCl.sub.3, 400 MHz) δ: 7.27-7.03 (d, 7H), 6.76-6.71 (d, 2H), 4.62 (s, 2H), 1.30 (s, 12H).

[0037] The examples above were conducted at room temperature. The present invention discloses that the commercial reagent 4-methoxyaniline lithium can catalyze the borohydride reaction of imine under mild reaction conditions, with a high yield and a wide substrate. The scope of application, low price of the catalyst and mild catalytic conditions provide possibilities for industrial applications.