JPH07106990B2 - Method for producing pinacols - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION a. Field of Industrial Application The present invention relates to a method for producing pinacols.
More specifically, it relates to a method for directly producing a pinacol by coupling an aromatic carbonyl compound or an aliphatic carbonyl compound with the aromatic carbonyl compound.

b. Prior art Pinacol is a general term for compounds having two hydroxyl groups of 1,2-glycol and the carbon atoms to which the hydroxyl groups are bonded are all tertiary carbon atoms. In general, this pinacol can be directly synthesized by reducing ketones, using magnesium amalgam, sodium amalgam, aluminum amalgam, a mixture of magnesium and magnesium iodide, a mixture of magnesium and ether as a reducing agent. It is known to be possible.

These known methods have problems to be solved, such as limiting the ketones to be used depending on the type of the reducing agent, complicating the separation of the target pinacol from the reaction mixture, and sometimes lowering the yield. there were.

c. Object of the present invention It is therefore an object of the present invention to provide a method capable of producing pinacols in high yield using an aromatic carbonyl compound which is an aromatic ketone or aldehyde.

Another object of the present invention is to provide the aromatic carbonyl compound,
An object of the present invention is to provide a method capable of producing asymmetrical pinacols from other carbonyl compounds in high yield.

Still another object of the present invention is to provide a versatile method for producing pinacols in which the type of the starting aromatic carbonyl compound is relatively unrestricted.

Still other objects of the present invention will be apparent from the following description.

d. Structure of the present invention According to the study by the present inventor, the object of the present invention is to couple an aromatic carbonyl compound or an aliphatic carbonyl compound with an aromatic carbonyl compound in the presence of a metal selected from Sm, Eu, and Yb. It was found that this can be achieved by a method for producing pinalols by densification.

An example of the reaction of the present invention is represented by the following formula (I).

[Wherein Ar represents an aromatic hydrocarbon group, R ₁ represents a hydrogen atom, an aliphatic hydrocarbon group or an aromatic hydrocarbon group. ] Another example of the reaction of the present invention is represented by the following formula (II) when represented by a reaction formula.

[In the formula, the definitions of Ar and R ₁ mean the same as those in the formula (I).

R ₂ is an aliphatic hydrocarbon group, R ₃ is a hydrogen atom or an aliphatic hydrocarbon group, and R ₂ and R ₃ may be bonded to each other to form a cyclic ketone. In the present invention, symmetrical pinacols can be obtained by the above formula (I) and asymmetric pinacols can be obtained by the above formula (II) in a high yield.

The aromatic carbonyl compound used as a raw material in the present invention is represented by the above formula (I). It is represented by. Here, Ar represents an aromatic hydrocarbon group,
Examples thereof include those having 20 or less, preferably 15 or less carbon atoms such as phenyl group, naphthyl group and diphenyl group, and the aromatic nucleus carbon of these groups has a substituent that does not inhibit the reaction. May be. Examples of such a substituent include a lower alkyl group, a halogen, a halo lower alkyl group, a cyano group and a lower alkoxy group.

Further, R ₁ represents a hydrogen atom, an aliphatic hydrocarbon group or an aromatic hydrocarbon group, and the aromatic hydrocarbon group is as described above.
The same thing as Ar can be illustrated. The aliphatic hydrocarbon group may be saturated or unsaturated, may be linear, and may be branched. The aliphatic hydrocarbon group has oxygen in its main chain,
It may contain atoms other than carbon such as nitrogen and sulfur. Examples of the aliphatic hydrocarbon group include methyl group, ethyl group, n-
Lower alkyl groups such as propyl group, iso-propyl group, n-butyl group, iso-butyl group and ter-butyl group are preferred. These aliphatic hydrocarbon groups may further have a substituent that does not hinder the reaction, and examples thereof include those mentioned as the substituent of Ar.

Specific examples of such aromatic carbonyl compounds include benzophenone, acetophenone, p-cyanoacetophenone, p-methoxyacetophenone, p-anisaldehyde, and 2-acetylnaphthalene.

In the reaction of the present invention, when only one kind of aromatic carbonyl compound is used as a raw material, symmetrical pinacols are obtained as shown in the above reaction formula (I).

However, aromatic carbonyl compounds And aliphatic carbonyl compounds When two kinds of the above are used as raw materials, the above reaction formula (II)
As shown in (1), asymmetrical pinacols can be obtained with high selectivity.

However, when the same reaction as in the present invention is carried out using only the aliphatic carbonyl compound as a raw material, the corresponding pinacols can be obtained only in a small yield.

In the present invention, the aliphatic carbonyl compound used together with the aromatic carbonyl compound, as described above, Where R ₂ is an aliphatic hydrocarbon group,
R ₃ is a hydrogen atom or an aliphatic hydrocarbon group, and R ₂ and R ₃
And may combine with each other to form a cyclic ketone. R ₂
The aliphatic hydrocarbon groups in and R ₃ may be the same or different and may be saturated or unsaturated. Further, it may be linear or branched. Preferred aliphatic hydrocarbon groups have 20 or less carbon atoms, more preferably 15 or less carbon atoms, and particularly preferably 10 or less carbon atoms. The main chain of these aliphatic hydrocarbon groups may contain atoms other than carbon such as oxygen, nitrogen and sulfur as long as the intended reaction is not hindered. Further, a substituent such as a halogen or a cyano group may be contained as long as the intended reaction is not hindered.

Examples of such aliphatic hydrocarbon group include, for example, methyl group, ethyl group, n-propyl group, iso-propyl group, n-butyl group, iso-butyl group, ter-butyl group, n-pentyl group, n-
A lower alkyl group such as a hexyl group; an alkenyl group such as an allyl group and a vinyl group.

Specific examples of the aliphatic carbonyl compound that may be used as a raw material in the present invention include acetone, methyl ethyl ketone, methyl propyl ketone, methyl-n-butyl ketone, methyl-t-butyl ketone, methyl isobutyl ketone, ethyl ethyl ketone, n-hexanone, n-octanone, n-decanone, cyclobutanone, cyclopentanone, cyclohexanone, cyclopentenone, cyclohexenone, 2-cyclohexen-1-one,
Examples include cyclooctanone.

In the present invention, when an aromatic carbonyl compound and an aliphatic carbonyl compound are used as raw materials, the ratio of the two is 1:10 to 10: 1 by mole, preferably 1: 5 to 5: 1, and particularly 1: 3 to 3. : 1
The range of is desirable.

In the method of the present invention, the metal used as a catalyst is Sm.
(62, Samarium), Eu (63, Europium), and Yb (70, Ytte
rbium), of which Sm and Yb are preferred.

These metals are 0.
1 to 10 atoms, preferably 0.2 to 5 atoms, particularly preferably 0.
It is preferably used in the range of 3 to 3 atoms.

The reaction of the present invention can be carried out without solvent, but it is generally desirable to carry out in an ether or amide polar solvent. In that case, as the ether, dimethyl ether,
Examples thereof include linear or cyclic aliphatic ethers such as diethyl ether, dioxane and tetrahydrofuran; aromatic ethers such as diphenyl ether and anisole. Examples of the amide-based polar solvent include dimethylformamide, dimethylacetamide, N-methylpyrrolidone and hexamethylphosphoramide.

It is desirable to use these solvents in a proportion of 1 to 20 parts by weight, preferably 2 to 10 parts by weight, relative to 1 part by weight of the carbonyl compound as a raw material.

The reaction of the present invention is advantageously carried out at a temperature in the range of -10 ° C to 100 ° C, preferably in the range of 0 ° C to 50 ° C.

As described above, according to the present invention, the corresponding pinacols can be obtained in high yield from the aromatic carbonyl compound or the aliphatic carbonyl compound.

Hereinafter, the method of the present invention will be described in detail with reference to examples.

Example 1 173 mg (1 mmol) of yttrium metal was added to 2 μm of methyl iodide under a nitrogen atmosphere using a syringe. Then, it was gradually heated with a dryer to activate the ytterbium metal. Additional 2 cm ^{3 of} tetrahydrofuran (THF) formed a pale yellow slurry, followed by 2 cm ^{3 of} hexamethylphosphoramide (HMPA).

Benzophenone 364 in 2 cm ^{3 of} tetravitrofuran (THF)
mg (2 mmol) was dissolved and this was further added using a syringe. The color of the solution immediately turned dark blue. The reaction mixture was stirred at room temperature for 10 minutes, finally giving an opaque purple solution.

By carrying out chromatographic purification on silica gel, the reductive dimerization product, benzopinacol 177.
5 mg (97% of yield, mp185-187 degreeC) were obtained.

Example 2 In Example 1, benzophenone 182 mg (1 mmol)
The reaction was performed in the same manner except that was used. The results are shown in Table 1 below.

Example 3 The reaction was performed in the same manner as in Example 1 except that 2 mmol of methyl phenyl ketone was used instead of benzophenone. The results are shown in Table 1 below.

Example 4 Methyl-p-cyanophenyl ketone The reaction was carried out in the same manner as in Example 1 except that 1 mmol was used instead of benzophenone. The results are shown in Table 1 below.

Example 5 Methyl-p-methoxyphenyl ketone The reaction was carried out in the same manner as in Example 1 except that 1 mmol was used instead of benzophenone. The results are shown in Table 1 below.

Example 6 p-anisaldehyde The reaction was carried out in the same manner as in Example 1 except that 1 mmol was used instead of benzophenone. The results are shown in Table 1 below.

Example 7 Methyl-2-naphthyl ketone The reaction was carried out in the same manner as in Example 1 except that 1 mmol was used instead of benzophenone. The results are shown in Table 1 below.

Comparative Example 1 2-octanone The reaction was carried out in the same manner as in Example 1 except that 1 mmol was used instead of benzophenone. The results are shown in Table 1 below.

Example 8 173 mg (1 mmol) of yttrium metal was added to 2μ of methyl iodide under a nitrogen atmosphere using a syringe. Then, it was gradually heated with a dryer to activate the ytterbium metal. Additional 2 cm ^{3 of} tetrahydrofuran (THF) formed a pale yellow slurry, followed by 2 cm ^{3 of} hexamethylphosphoramide (HMPA).

Benzophenone 182 in 2 cm ^{3 of} tetravitrofuran (THF)
mg (1 mmol) was dissolved and this was further added using a syringe. The color of the solution immediately turned dark blue. The reaction mixture was stirred at room temperature for 10 minutes, finally giving an opaque purple solution.

Next, after adding 58 mg (1 mmol) of acetone and reacting at room temperature for 20 minutes, 10 cm ³ of 2N HCl was added. The organic phase was extracted 4 times with ether (25 cm ³ ). After removing the ether by distillation, the reaction product is subjected to chromatographic purification using silica gel to obtain the coupling product, that is, Was obtained in a yield of 56%. This was confirmed by NMR and IR analyses.

Example 9 The reaction was performed in the same manner as in Example 8 except that 113 mg (1 mmol) of 2-octanone was used instead of acetone. The results are shown in Table 2 below.

Example 10 The reaction was performed in the same manner as in Example 8 except that 98 mg (1 mmol) of cyclohexanone was used instead of acetone. The results are shown in Table 2 below.

Example 11 96 mg of 2-cyclohexen-1-one instead of acetone
The reaction was performed in the same manner as in Example 8 except that (1 mmol) was used. The results are shown in Table 2 below.

Examples 12 to 15 The same reaction as in Example 1 was carried out, except that the metal of Table 3 below was used instead of the yttrium metal and the ketone compound was changed as shown in Table 3. The results are shown in Table 3 below.

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Claims (1)

[Claims] 1. A process for producing pinacols, which comprises coupling an aromatic carbonyl compound or an aliphatic carbonyl compound with an aromatic carbonyl compound in the presence of a metal selected from Sm, Eu, and Yb.