JP3788525B2 - Scandium-perfluoroalkanesulfonylimide complex and method for producing the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention is a compound represented by the general formula [I] used as a useful catalyst in a reaction such as an acylation reaction of an alcohol with a carboxylic acid anhydride.
[0002]
[Chemical formula 5]
[Sc [N (Tf ¹ ) Tf ² ] _p ]. (H ₂ O) _m. (RCOOH) _n [I]
[Wherein, Tf ¹ represents —SO ₂ Rf ¹ , and Tf ² represents —SO ₂ Rf ² (Rf ¹ and Rf ² each independently have a fluorine atom, or a linear or branched chain having 1 to 10 carbon atoms. represents a perfluoroalkyl group.) represents, R represents an alkyl group having a straight chain or branched chain of 1 to 10, a 1 ≦ p ≦ 3, a 0 ≦ m ≦ 9, 0 < n ≦ 2 And 3 ≦ p + m + n ≦ 12. ]
The scandium-perfluoroalkanesulfonylimide complex shown by these, and its manufacturing method.
[0003]
[Problems to be solved by the invention]
Conventionally, in the acylation reaction of alcohols with carboxylic acid anhydrides, various catalysts have been developed. For example, tributylphosphine, 4- (dimethylamino) pyridine (DMAP) and the like are known [(a). J. et al. Am. Chem. Soc. 1993, 115, 3358, (b) J. et al. Org. Chem. 1993, 58, 7286, (c) Angew. Chem. , Int. Ed. Engl. 1978, 17, 569].
[0004]
However, the catalytic activity of these conventional catalysts is not sufficient, and in order to solve such problems, the present inventors have intensively studied and, as a result, have already developed a method using scandium triflate as a catalyst. [J. Am. Chem. Soc. 1995, 117, 4413].
[0005]
[Means for Solving the Problems]
Based on the above findings, the inventors of the present invention have further intensively studied. As a result, the scandium-perfluoroalkanesulfonylimide complex is more effective than scandium triflate in reactions such as acylation reactions with carboxylic anhydrides of alcohols. The inventors have found that the catalyst has a higher catalytic activity, and have reached the present invention.
[0006]
That is, the first of the present invention is the general formula [I].
[0007]
[Chemical 6]
[Sc [N (Tf ¹ ) Tf ² ] _p ]. (H ₂ O) _m. (RCOOH) _n [I]
[Wherein, Tf ¹ represents —SO ₂ Rf ¹ , and Tf ² represents —SO ₂ Rf ² (Rf ¹ and Rf ² each independently have a fluorine atom, or a linear or branched chain having 1 to 10 carbon atoms. represents a perfluoroalkyl group.) represents, R represents an alkyl group having a straight chain or branched chain of 1 to 10, a 1 ≦ p ≦ 3, a 0 ≦ m ≦ 9, 0 < n ≦ 2 And 3 ≦ p + m + n ≦ 12. ]
Is a scandium-perfluoroalkanesulfonylimide complex represented by the formula:
[0008]
The second of the present invention is the general formula [II].
[0009]
[Chemical 7]
Sc (OCOR) ₃ [II]
[Wherein, R represents an alkyl group having 1 to 10 linear or branched chains . ]
And a scandium-carboxylate represented by the general formula [III]
[0010]
[Chemical 8]
HN (Tf ¹ ) Tf ² [III]
[Wherein, Tf ¹ represents —SO ₂ Rf ¹ , and Tf ² represents —SO ₂ Rf ² (Rf ¹ and Rf ²
Each independently represents a fluorine atom or a perfluoroalkyl group having a straight or branched chain having 1 to 10 carbon atoms. ). ]
And a perfluoroalkanesulfonylimide acid represented by the general formula [I]:
[0011]
[Chemical 9]
[Sc [N (Tf ¹ ) Tf ² ] _p ]. (H ₂ O) _m. (RCOOH) _n [I]
[Wherein, Tf ¹ represents —SO ₂ Rf ¹ , and Tf ² represents —SO ₂ Rf ² (Rf ¹ and Rf ² each independently have a fluorine atom, or a linear or branched chain having 1 to 10 carbon atoms. represents a perfluoroalkyl group.) represents, R represents an alkyl group having a straight chain or branched chain of 1 to 10, a 1 ≦ p ≦ 3, a 0 ≦ m ≦ 9, 0 < n ≦ 2 And 3 ≦ p + m + n ≦ 12. ]
It is a manufacturing method of the scandium-perfluoro alkane sulfonylimide complex shown by these.
[0012]
Hereinafter, the present invention will be described in detail.
In the scandium-perfluoroalkanesulfonylimide complex represented by the general formula [I] of the present invention, one scandium atom and p perfluoroalkanesulfonylimide groups: —N (Tf ¹ ) Tf ² [Tf ¹ is represents -SO ^₂ Rf ^1, Tf ₂ are each -SO ₂ Rf ² (Rf ¹ and Rf ² are independently a fluorine atom or represents a perfluoroalkyl group having a linear or branched chain of 1 to 10 carbon atoms. ). ] For scandium-perfluoroalkanesulfonylimide complex: Sc [N (Tf ¹ ) Tf ² ] _p , m water: H ₂ O and n carboxylic acids: RCOOH [R is 1-10 An alkyl group having a straight chain or a branched chain is represented. ] Is coordinated.
[0013]
In the present invention, the perfluoroalkyl group having a linear or branched chain having 1 to 10 carbon atoms specifically includes, for example, a trifluoromethyl group, a pentafluoroethyl group, an n-heptafluoropropyl group, iso-heptafluoropropyl group, n-nonafluorobutyl group, iso-nonafluorobutyl group, sec-nonafluorobutyl group, tert-nonafluorobutyl group, n-undecafluoropentyl group, n-tridecafluorohexyl group N-pentadecafluoroheptyl group, n-heptadecafluorooctyl group and the like. In addition, the alkyl group having 1 to 10 linear or branched chains in the present invention specifically includes, for example, a methyl group, an ethyl group, an n-propyl group, an iso-propyl group, an n-butyl group, an iso group. -Butyl group, sec-butyl group, tert-butyl group, n-pentyl group, n-hexyl group, n-heptyl group, n-octyl group and the like can be mentioned.
[0014]
The above p, m and n are numerical values in the range of 1 ≦ p ≦ 3, 0 ≦ m ≦ 9 and 0 <n ≦ 2, respectively, and the sum of p, m and n is 3 ≦ p + m + n ≦ The numerical value is 12.
[0015]
The scandium-perfluoroalkanesulfonylimide complex represented by the general formula [I] of the present invention is represented by the general formula [II].
[0016]
[Chemical Formula 10]
Sc (OCOR) ₃ [II]
[Wherein, R represents an alkyl group having 1 to 10 linear or branched chains . ]
And a scandium-carboxylate represented by the general formula [III]
[0017]
Embedded image
HN (Tf ¹ ) Tf ² [III]
[Wherein, Tf ¹ represents —SO ₂ Rf ¹ , and Tf ² represents —SO ₂ Rf ² (Rf ¹ and Rf ² each independently have a fluorine atom, or a linear or branched chain having 1 to 10 carbon atoms. Represents a perfluoroalkyl group ). ]
The perfluoroalkanesulfonylimide acid represented by can be easily produced by reacting with water as a solvent.
[0018]
In the method for producing a scandium-perfluoroalkanesulfonylimide complex represented by the general formula [I] of the present invention, 1 mole of scandium-carboxylate represented by the general formula [II] and the general formula [III] are used. Pmol of perfluoroalkanesulfonylimide acid dissolved in water and reacted.
[0019]
The reaction temperature in the above reaction is usually 90 ° C to 150 ° C, preferably 90 ° C to 130 ° C, more preferably 90 ° C to 110 ° C. If the temperature is lower than this range, the reaction may not proceed sufficiently, which may cause a decrease in yield, or may cause problems such as a decrease in reaction rate and a long time to complete the reaction. It is not preferable. Moreover, when the temperature is higher than this range, decomposition or the like may occur during the reaction, which causes a decrease in yield, which is not preferable.
[0020]
In the method for producing a scandium-perfluoroalkanesulfonylimide complex represented by the general formula [I] of the present invention, after completion of the reaction, the reaction solution is cooled to room temperature, filtered, and excess water is distilled from the filtrate under reduced pressure conditions. The target scandium-perfluoroalkanesulfonylimide complex represented by the general formula [I] can be obtained by leaving and further drying under high vacuum.
[0021]
The scandium-perfluoroalkanesulfonylimide complex represented by the general formula [I] of the present invention as described above has very high catalytic activity in reactions such as acylation reactions of alcohols with carboxylic acid anhydrides. The reaction proceeds rapidly even at a low temperature of about room temperature or lower, and the desired reaction product can be obtained with a very high yield and selectivity. Can do. Therefore, the scandium-perfluoroalkanesulfonylimide complex represented by the general formula [I] of the present invention is a very useful compound.
[0022]
DETAILED DESCRIPTION OF THE INVENTION
EXAMPLES Hereinafter, although an Example demonstrates embodiment of this invention concretely, this invention is not limited to these Examples.
[0023]
【Example】
Example 1
Scandium acetate (222.1 mg, 1 mmol) and trifluoromethanesulfonylimidic acid (843.5 mg, 3 mmol) were dissolved in water (0.5 mL). This aqueous solution was reacted under reflux conditions for 3 hours. Then, it cooled to room temperature and filtered. The solvent was distilled off from the filtrate under reduced pressure, dried under high vacuum (10 ⁻³ to 10 ⁻⁵ Torr, 120 ° C.) for 12 hours, and scandium-trifluoromethanesulfonylimide complex [Sc (NTf ₂ ) ₃ ]. (H ₂ O) _m · (CH ₃ COOH) _1.5 was quantitatively obtained as colorless glassy crystals. [Tf is —SO ₂ CF ₃ , and 0 ≦ m ≦ 7.5. ]
[Sc (NTf ₂ ) ₃ ]. (H ₂ O) _m. (CH ₃ COOH) _1.5
¹ H-NMR [D ₂ O, standard (δ 3.32 (s, CH ₃ OH)
)] Δ 2.05 (s, CH ₃ COOH)
¹³ C-NMR [D ₂ O, standard (δ 48.92 (CH ₃ OH))
] Δ 21.71 (CH ₃ COOH), 119.3 (q, J _C
F = 317.8 Hz, CF ₃ ), 186.82 (CH ₃ CO
OH)
IR (KBr) 3270 (br), 1350 (s), 1333 (s),
1240 (s), 1202 (s), 1146 (s),
1059, 797, 745 cm ^-1
HNTf ₂
¹³ C-NMR [D ₂ O, standard (δ 48.92 (CH ₃ OH))]
δ 119.3 (q, J _CF = 317.6 Hz, CF ₃ )
IR (CH ₂ Cl ₂ ) 3227 (br), 1447 (s), 1350,
1333, 1229 (s), 1202 (s), 1132
(S), 1057, 860 cm ^-1
Sc (OCOCH ₃ ) ₃
¹ H-NMR [D ₂ O, standard (δ 3.32 (s, CH ₃ OH))] δ 1.99 (s, CH ₃ COO)
Example 2
Menthol (1 mmol) and acetic anhydride (1.2 mmol) were dissolved in acetonitrile (4.5 mL), and an acetonitrile solution of the scandium-trifluoromethanesulfonylimide complex obtained in Example 1 (500 μL, 0.01 mmol, 0 mmol) was dissolved therein. .02M) was added at 0 ° C. After stirring at 0 ° C. for 1 hour, an aqueous NaHCO ₃ solution was added, and the mixture was extracted with ether. The organic layer was dried over anhydrous magnesium sulfate and filtered, and the solvent was distilled off under reduced pressure. Purification by silica gel column chromatography gave the corresponding acetylated compound quantitatively.
[0024]
Example 3
2-Methyl-2-undecanol (1 mmol) and acetic anhydride (5 mmol) were dissolved in acetonitrile (4.5 mL), and an acetonitrile solution of the scandium-trifluoromethanesulfonylimide complex obtained in Example 1 (500 μL, 0 mL) was dissolved therein. 0.01 mmol, 0.02 M) was added at -20 ° C. After stirring at −20 ° C. for 2.5 hours, an aqueous NaHCO ₃ solution was added, and the mixture was extracted with ether. The organic layer was dried over anhydrous magnesium sulfate and filtered, and the solvent was distilled off under reduced pressure. Purification by silica gel column chromatography gave the corresponding acetylated compound in 77% yield.
[0025]
Comparative Example 1
The target acetylated compound was obtained in a yield of 38% in the same manner as in Example 3 except that scandium triflate was used in place of the scandium-trifluoromethanesulfonylimide complex.
[0026]
Example 4
Menthol (1 mmol) and benzoic anhydride (1.5 mmol) were dissolved in acetonitrile (4.5 mL), and an acetonitrile solution of the scandium-trifluoromethanesulfonylimide complex obtained in Example 1 (500 μL, 0.01 mmol, 0.02M) was added at 18 ° C. After stirring at 18 ° C. for 6 hours, an aqueous NaHCO ₃ solution was added, and the mixture was extracted with ether. The organic layer was dried over anhydrous magnesium sulfate and filtered, and the solvent was distilled off under reduced pressure. Purification by silica gel column chromatography gave the corresponding benzoylated compound in 69% yield.
[0027]
Comparative Example 2
The target benzoylated compound was obtained in a yield of 3% in exactly the same manner as in Example 4 except that scandium triflate was used in place of the scandium-trifluoromethanesulfonylimide complex.
[0028]
Example 5
Phenol (1 mmol) and benzoic anhydride (1.5 mmol) were dissolved in acetonitrile (4.5 mL), and an acetonitrile solution of the scandium-trifluoromethanesulfonylimide complex obtained in Example 1 (50 μL, 0.001 mmol, 0.02M) was added at 25 ° C. After stirring at 25 ° C. for 30 minutes, an aqueous NaHCO ₃ solution was added, and the mixture was extracted with ether. The organic layer was dried over anhydrous magnesium sulfate and filtered, and the solvent was distilled off under reduced pressure. Purification by silica gel column chromatography gave the corresponding benzoylated compound in 21% yield.
[0029]
Comparative Example 3
The target benzoylated compound was obtained in a yield of 6% in the same manner as in Example 5 except that scandium triflate was used instead of the scandium-trifluoromethanesulfonylimide complex.
[0030]
Example 6
3-phenyl-1-propanol (1 mmol) and benzoic anhydride (1.5 mmol) were dissolved in acetonitrile (4.5 mL), and an acetonitrile solution of the scandium-trifluoromethanesulfonylimide complex obtained in Example 1 ( 1 mL, 0.02 mmol, 0.02 M) was added at 25 ° C. After stirring at 25 ° C. for 1.5 hours, an aqueous NaHCO ₃ solution was added, and the mixture was extracted with ether. The organic layer was dried over anhydrous magnesium sulfate and filtered, and the solvent was distilled off under reduced pressure. Purification by silica gel column chromatography gave the corresponding benzoylated compound in 95% yield.
[0031]
Example 7
Menthol (1 mmol) and benzoic anhydride (1.5 mmol) were dissolved in acetonitrile (4.5 mL), and an acetonitrile solution of the scandium-trifluoromethanesulfonylimide complex obtained in Example 1 (1 mL, 0.02 mmol, 0.02M) was added at 25 ° C. After stirring at 25 ° C. for 3 hours, an aqueous NaHCO ₃ solution was added, and the mixture was extracted with ether. The organic layer was dried over anhydrous magnesium sulfate and filtered, and the solvent was distilled off under reduced pressure. Purification by silica gel column chromatography gave the corresponding benzoylated compound in 98% yield.
[0032]
Comparative Example 4
The target benzoylated compound was obtained in a yield of 45% in the same manner as in Example 7, except that trifluoromethanesulfonylimide acid was used instead of the scandium-trifluoromethanesulfonylimide complex.
[0033]
Example 8
Phenol (1 mmol) and benzoic anhydride (1.5 mmol) were dissolved in acetonitrile (4.5 mL), and an acetonitrile solution of the scandium-trifluoromethanesulfonylimide complex obtained in Example 1 (250 μL, 0.005 mmol, 0.02M) was added at 25 ° C. After stirring at 25 ° C. for 45 minutes, an aqueous NaHCO ₃ solution was added, and the mixture was extracted with ether. The organic layer was dried over anhydrous magnesium sulfate and filtered, and the solvent was distilled off under reduced pressure. Purification by silica gel column chromatography gave the corresponding benzoylated compound in 95% yield.
[0034]
Example 9
2,4,6-Trimethylphenol (1 mmol) and benzoic anhydride (1.5 mmol) were dissolved in acetonitrile (4.5 mL), and an acetonitrile solution of the scandium-trifluoromethanesulfonylimide complex obtained in Example 1 was added thereto. (250 μL, 0.005 mmol, 0.02 M) was added at 25 ° C. After stirring at 25 ° C. for 1.5 hours, an aqueous NaHCO ₃ solution was added, and the mixture was extracted with ether. The organic layer was dried over anhydrous magnesium sulfate and filtered, and the solvent was distilled off under reduced pressure. Purification by silica gel column chromatography gave the corresponding benzoylated compound in 90% yield.
[0035]
Example 10
2-Methyl-2-undecanol (1 mmol) and acetic anhydride (5 mmol) were dissolved in acetonitrile (4.5 mL), and an acetonitrile solution of the scandium-trifluoromethanesulfonylimide complex obtained in Example 1 (500 μL, 0 mL) was dissolved therein. 0.01 mmol, 0.02 M) was added at -20 ° C. After stirring at −20 ° C. for 4 hours, an aqueous NaHCO ₃ solution was added, and the mixture was extracted with ether. The organic layer was dried over anhydrous magnesium sulfate and filtered, and the solvent was distilled off under reduced pressure. Purification by silica gel column chromatography gave the corresponding acetylated compound in 93% yield.
[0036]
Example 11
Menthol (1 mmol), propionic acid (1.5 mmol) and -p-nitrobenzoic anhydride (632.4 mg, 2 mmol) were dissolved in nitromethane (3.5 mL), and the scandium-trifluoro obtained in Example 1 was added thereto. A solution of lomethanesulfonylimide complex in nitromethane (500 μL, 0.01 mmol, 0.02 M) was added at 25 ° C. After stirring at 25 ° C. for 2 hours, an aqueous NaHCO ₃ solution was added, and the mixture was extracted with ether. The organic layer was dried over anhydrous magnesium sulfate and filtered, and the solvent was distilled off under reduced pressure. Purification by silica gel column chromatography gave the corresponding esterified compound in 96% yield.
[0037]
Example 12
Menthol (1 mmol), benzoic acid (1.5 mmol) and -p-nitrobenzoic anhydride (1.5 mmol) were dissolved in nitromethane (3.5 mL), and scandium-trifluoromethanesulfonyl obtained in Example 1 was added thereto. A solution of the imide complex in nitromethane (1 mL, 0.02 mmol, 0.02 M) was added at 25 ° C. After stirring at 25 ° C. for 8 hours, an aqueous NaHCO ₃ solution was added, and the mixture was extracted with ether. The organic layer was dried over anhydrous magnesium sulfate and filtered, and the solvent was distilled off under reduced pressure. Purification by silica gel column chromatography gave the corresponding esterified compound in 63% yield.
[0038]
Comparative Example 5
The target esterified compound was obtained in a yield of 11% in the same manner as in Example 12 except that scandium triflate was used instead of the scandium-trifluoromethanesulfonylimide complex.
[0039]
Example 13
Menthol (1 mmol), 2,4,6-trimethylbenzoic acid (1.5 mmol) and -p-nitrobenzoic anhydride (632.4 mg, 2 mmol) were dissolved in nitromethane (3.5 mL). A nitromethane solution (1 mL, 0.02 mmol, 0.02 M) of the scandium-trifluoromethanesulfonylimide complex obtained in 1 above was added at 25 ° C. After stirring at 25 ° C. for 3 hours, an aqueous NaHCO ₃ solution was added, and the mixture was extracted with ether. The organic layer was dried over anhydrous magnesium sulfate and filtered, and the solvent was distilled off under reduced pressure. Purification by silica gel column chromatography gave the corresponding esterified compound in 99% yield.
[0040]
Example 14
Menthol (1 mmol), benzoic acid (1.5 mmol) and -p-nitrobenzoic anhydride (632.4 mg, 2 mmol) were dissolved in nitromethane (3.5 mL), and the scandium-trifluoro obtained in Example 1 was added thereto. A solution of lomethanesulfonylimide complex in nitromethane (1 mL, 0.02 mmol, 0.02 M) was added at 25 ° C. After stirring at 25 ° C. for 3 hours, an aqueous NaHCO ₃ solution was added, and the mixture was extracted with ether. The organic layer was dried over anhydrous magnesium sulfate and filtered, and the solvent was distilled off under reduced pressure. Purification by silica gel column chromatography gave the corresponding esterified compound in 98% yield.
[0041]
Example 15
Phenol (1 mmol), benzoic acid (1.5 mmol) and -p-nitrobenzoic anhydride (632.4 mg, 2 mmol) were dissolved in nitromethane (3.5 mL), and the scandium-trifluoro obtained in Example 1 was added thereto. A solution of lomethanesulfonylimide complex in nitromethane (250 μL, 0.005 mmol, 0.02 M) was added at 25 ° C. After stirring at 25 ° C. for 1 hour, an aqueous NaHCO ₃ solution was added, and the mixture was extracted with ether. The organic layer was dried over anhydrous magnesium sulfate and filtered, and the solvent was distilled off under reduced pressure. Purification by silica gel column chromatography gave the corresponding esterified compound in 93% yield.
[0042]
Example 16
2,4,6-Trimethylphenol (1 mmol), benzoic acid (1.5 mmol) and -p-nitrobenzoic anhydride (632.4 mg, 2 mmol) were dissolved in nitromethane (3.5 mL). A nitromethane solution (250 μL, 0.005 mmol, 0.02 M) of the scandium-trifluoromethanesulfonylimide complex obtained in 1 above was added at 25 ° C. After stirring at 25 ° C. for 1.5 hours, an aqueous NaHCO ₃ solution was added, and the mixture was extracted with ether. The organic layer was dried over anhydrous magnesium sulfate and filtered, and the solvent was distilled off under reduced pressure. Purification by silica gel column chromatography gave the corresponding esterified compound in 98% yield.
[0043]
【The invention's effect】
The scandium-perfluoroalkanesulfonylimide complex represented by the general formula [I] of the present invention has a very high catalytic activity in a reaction such as an acylation reaction of an alcohol with a carboxylic acid anhydride and is very useful. A compound.

Claims (6)

Formula [I]

[Wherein, Tf ¹ represents —SO ₂ Rf ¹ , and Tf ² represents —SO ₂ Rf ² (Rf ¹ and Rf ² each independently have a fluorine atom, or a linear or branched chain having 1 to 10 carbon atoms. represents a perfluoroalkyl group.) represents, R represents an alkyl group having a straight chain or branched chain of 1 to 10, a 1 ≦ p ≦ 3, a 0 ≦ m ≦ 9, 0 < n ≦ 2 And 3 ≦ p + m + n ≦ 12. ]
A scandium-perfluoroalkanesulfonylimide complex represented by the formula: Scandium as claimed in claim 1, wherein Tf ¹ and Tf ² is -SO ₂ CF ₃ - perfluoroalkanesulfonyl imido complexes.   The scandium-perfluoroalkanesulfonylimide complex according to claim 1 or 2, wherein R is a methyl group. Formula [II]

[Wherein, R represents an alkyl group having 1 to 10 linear or branched chains . ]
And a scandium-carboxylate represented by the general formula [III]

[Wherein, Tf ¹ represents —SO ₂ Rf ¹ , and Tf ² represents —SO ₂ Rf ² (Rf ¹ and Rf ² each independently have a fluorine atom, or a linear or branched chain having 1 to 10 carbon atoms. Represents a perfluoroalkyl group ). ]
And a perfluoroalkanesulfonylimide acid represented by the general formula [I], wherein water is used as a solvent for the reaction.

[Wherein, Tf ¹ represents —SO ₂ Rf ¹ , and Tf ² represents —SO ₂ Rf ² (Rf ¹ and Rf ² each independently have a fluorine atom, or a linear or branched chain having 1 to 10 carbon atoms. represents a perfluoroalkyl group.) represents, R represents an alkyl group having a straight chain or branched chain of 1 to 10, a 1 ≦ p ≦ 3, a 0 ≦ m ≦ 9, 0 < n ≦ 2 And 3 ≦ p + m + n ≦ 12. ]
The manufacturing method of the scandium perfluoro alkane sulfonylimide complex shown by these. Claim 4, wherein the scandium Tf ¹ and Tf ² is -SO ₂ CF ₃ - perfluoroalkanesulfonyl imide method for producing a complex.   The method for producing a scandium-perfluoroalkanesulfonylimide complex according to claim 4 or 5, wherein R is a methyl group.