| EP0271834A2 | 1988-06-22 |
| 1. | A process for the preparation of 2,4 or 2,4,5substituted 6hydroxypyrimidines of the general formula I R3 R 1 wherein R1 represents alkyl . [preferably CH3, C2H5, nC3H7, CH(CH3)2 or nC4Hg] or R7 M , \R8 R2 represents alkyl, aryl or aralkyl [preferably CH3, C2H5, nC3H7, CH(CH3)2, nC4H9, C(CH3)3, C6H5 or CH2CH2C6H5], and R3, R7 and R° each independently represents hydrogen, alkyl or aralkyl [preferably H, CH3, C H5, nC3H7 , CH(CH3)2, nC4H9, C(CH3)3, CH2C6H5 or CH2CH2C6H5] , or salts thereof with a saltforming cation, characterized by reacting a 3 or 2,3substituted 3aminoacrylic acid derivative of the general formula II wherein R2 and R3 are as defined above, and X repre sents OR4 or R5 N/ \R6 wherein R4 represents alkyl, aryl or aralkyl [prefera _ _ 5^bly CH3, C2H5,_ nC3H7, CH(CH3)2, nC4Hg, C(CH3)3, . C6H5 or CH2C6H5], and R5 and R6 each independently represents hydrogen, alkyl or aralkyl [preferably H, CH3, C2H5, nC3H7, CH(CH3)2, nC4H9, C(CH3)3, CH2C6H5 or CH2CH2C6H5], 10 with a nitrile of the general formula III R1C=N III wherein R1 is as defined above, in the presence of a base and a solvent, and then, if desired, converting the salt formed to the free pyrimi 15 dine of formula I by adding an acid. |
| 2. | The process according to claim 1, character¬ ized in that the base used is an alkali metal or alkaline earth metal, or an alkali metal hydride, alkali metal amide or a alkali metal alkoxide or a 20 corresponding alkaline earth metal compound. |
| 3. | The process according to claim l, character¬ ized in that the base used is an alkali metal phenol ate, alkali metal hydroxide, alkali metal carbonate or alkali metal carboxylate or a corresponding alkaline 25 earth metal compound. |
| 4. | The process according to any of the preceding claims, characterized in that the solvent used is an alcohol, ether, ethylene glycol ether, ketone or carbonic ester or an aliphatic or aromatic hydrocarbon. |
| 5. | 30 5. |
| 6. | The process according to any one of the pre¬ ceding claims, characterized in that the reaction 0 0 temperature is between 20 C and 180 C, preferably between 80 C and 140 C. |
| 7. | The process according to any one of the pre 35 ceding claims, characterized in that the reaction mixture is treated with a mineral acid or an organic acid. |
| 8. | The process according to any one of the pre¬ ceding claims, characterized in that the nitrile of *5 formula III used is isobutyronitrile, ethylcyanamide, dimethylcyanamide or diethylcyanamide. [ . |
| 9. | The process according to any one of claims 1 to 7, characterized in that the acrylic acid deriva¬ tive of formula II used is 3aminocrotonamide or a 0 3aminocrotonic ester. |
| 10. | The process according to any one of claims 1 to 7, characterized in that the acrylic acid deri¬ vative of for ule II used is 2methyl3aminocroton amide or a 2methyl3aminocrotonic ester. 5. |
| 11. | The process according to any one of claims 1 to 7, characterized in that the acrylic acid deriva¬ tive of formula II used is 2nbutyl3^aminocrotonamide or a 2nbutyl3amiήocrotonic ester. |
5 The present invention relates to a novel process for the preparation of 2,4- or 2,4,5-substit ted 6-hy- droxypyrimidines of the general formula I
R
15 wherein R 1 represents alkyl [preferably CH 3 , C 2 H 5 , n-C 3 H 7 , CH(CH 3 ) 2 or n-C 4 Hg] or
R 7 \ R 8
20
R 2 represents alkyl, aryl or aralkyl [preferably CH 3 , C 2 H 5 , n-C 3 H , CH(CH 3 ) 2 , n-C 4 H 9 , C(CH 3 ) 3 , CgH 5 or CH 2 CH 2 C 6 H 5 ], and R 3 , R 7 and R 8 each independently represents hydrogen. 5 alkyl or aralkyl [preferably H, CH 3 , C 2 H 5 , n-C 3 H 7 , CH(CH 3 ) 2 , n-C 4 H 9 , C(CH 3 ) 3 , CH 2 C 6 H 5 or CH 2 CH 2 C 6 H 5 ] , or salts thereof with a salt-forming cation, and said process is characterized by reacting a 3- or 2,3-substituted 3-aminoacrylic acid derivative of the 0 general formula II
wherein R~ and R- are as defined above, and X repre¬ sents OR 4 or
» \ R 6
wherein R 4 represents alkyl, aryl or aralkyl [prefera¬ bly CH 3 , C 2 H 5 , n-C 3 H 7 , CH( ' CH 3 ) 2 , n-C 4 Hg, ' C(CH 3 )3, CgH 5 or CH 2 CgH 5 }, and
R 5 and R 6 each independently represents hydrogen, alkyl or aralkyl [preferably H, CH 3 , C 2 H 5 , n-C 3 H 7 , CH(CH 3 ) 2 , n-C 4 H 9 , C(CH 3 ) 3 , CH 2 C 6 H 5 or CH 2 CH 2 C 5 H 5 ], with a nitrile of the general formula III R 1 -C≡N III wherein R 1 is as defined above, in the presence of a base and a solvent, and then, if desired, converting the salt formed -to the free pyrimi- dine of formula I by adding an acid. This process can be represented by the following reaction scheme:
wherein the various symbols have the meanings defined above. The process can be described as the reaction between a 3-aminoacrylic ester or a 3-aminoacrylamide and a nitrile while splitting off an alcohol or a monia/amine, respectively. The reaction is general for the above-mentioned starting materials as well
as for the tauto eric forms in which the starting materials may exist.
By way of example, the starting materials occur as follows: a. Ethylcyanamide as
EtNH-C=N ^=i EtN=C=NH
b. 3-aminocrotonamide as
Likewise, the pyrimidine occurs in various tautomeric forms:
Use can be made of various expedient embodi¬ ments of the process of the invention as stated in claims 2 to 10.
The reaction proceeds in the presence of a base which can be a free alkali metal or alkaline earth metal, or an alkali metal hydride, alkali metal amide, alkali metal alkoxide, alkali metal phenolate, alkali metal hydroxide, alkali metal carbonate or alkali metal carboxylate or a corresponding alkaline earth metal compound. In the reaction a salt results, e.g., an alkali metal salt of the pyrimidine. The free pyrimidine may
be released therefrom by treatment with an acid such as a mineral acid or an organic acid.
The reaction proceeds in the presence of a sol¬ vent which by way of example may be an alcohol, ether, ethylene glycol ether, ketone or carbonic ester or an aliphatic or aromatic hydrocarbon.
The reaction generally proceeds at a temperature of between 20 C and 180 C, preferably between 80 C and 140°C. A number of processes for the preparation of industrially interesting pyrimidines is known as described below.
A. 2-Isopropyl-4-methyl-6-hydroxypyrimidine
U.S. Patent No. 4,014,879, U.S. Patent No. 4,496,728 and GB Patent No. 2,083,814 deal with the preparation of 2-isopropyl-4-methyl-6-hydroxypyrimi- dine from isobutyronitrile. Isobutyronitrile is converted to isopropylimino- ether by reaction with alcohol and dry hydrogen chlo¬ ride. Isopropyliminoether is converted to isopropyl- amidine by reaction with ammonia. Isopropylamidine is reacted with methyl acetoacetate to form 2-isopropyl- 4-methyl-6-hydroxypyrimidine.
JP Patent Abstract No. 48/39943 describes a similar reaction from isopropylamidine and diketene, whereas GB Patent No. 2,027,710 describes the reaction between isopropyliminoether and diketene, followed by reaction with ammonia.
U.S. Patent No. 4,052,397, DE Published Speci¬ fications Nos. 2,065,698 and 3,344,429 and JP Patent Abstracts Nos. 48/26020 and 48/39942 deal with the preparation of 2-isopropyl-4-methyl-6-hydroxypyrimidine by reaction between 3-aminocrotonamide and isobutyric acid salt, isobutyric ester or isobutyric anhydride.
B. 2-Dimethylamino-4-methyl-6-hydroxypyrimidine
GB Patent No. 1,182,584 deals with the prepara¬ tion of 2-dimethylamino-4-methyl-6-hydroxypyrimidine from dimethylguanidine and ethyl acetoacetate.
C. 2-Diethylamino-4-metyl-6-hydroxypyrimidine
DE Published Specification No . 2 , 520 , 832 deals with the preparation of 2-diethylamino-4-methyl-6- hydroxypyrimidine from diethylguanidine and diketene .
D. 2-Ethylamino-4-methyl-5-butyl-6-hydroxypyrimidine
DE Published Specifications Nos. 2,109,880 and 2,308,858 deal with the preparation of 2-ethylamino- 4-methyl-5-butyl-6-hydroxypyrimidine from ethylguani- dine and ethyl butylacetoacetate.
DE Published Specification No. 2,008,875 deals with the preparation of 2-methoxy-4-methyl-5-butyl-6- hydroxypyrimidine from O-methyl-isourea and ethyl butylacetoacetate. Exchange of the 2-methoxy group by a 2-ethylamino group takes place by reaction with ethylamine.
E. 2-(Di)alkylamino-4-methyl-5-substituted-6-hydroxy- pyrimidine
DE Published Specifications Nos. 2,239,213 and 2,533,710 deal with the preparation of 2-(di)alkyl- amino-4-methyl-5-substituted-6-hydroxypyrimidine from nitroguanidine or thiourea and substituted acetoaceta¬ te. Exchange of the nitroamino group takes place by reaction with amine. Exchange of the ercapto group takes place by methylation and reaction with amine.
The process of the invention differs from the processes thus known for the preparation of 2,4- or 2,4,5-substituted 6-hydroxypyrimidines in that use is made of already known starting materials, but in a combination not previously known, and in this connec¬ tion it is surprising that nitriles react with, the 3- or 2,3-substituted 3-aminoacrylic acid derivatives of formula II as used according to the invention. As compared to already known reactions wherein nitriles are used, it is not necessary in the process of the invention to convert the nitrile to the corresponding iminoether or amidine prior to the coupling reaction and thereby fewer reaction steps become involved than in the known processes. The process of the invention differs also from the known processes in that the reaction is more general, and therefore the process of the invention is applicable for the preparation of a wide range of substituted pyrimidines, the utility of which will be known or obvious to a person skilled in the art.
The process of the invention is further illu¬ strated by the following Examples with reference to the drawing which shows 13 C NMR spectra of the products prepared according to the Examples.
Example 1
In 300 ml of isobutanol 23 g of sodium is dis¬ solved under reflux. When all of the sodium has been dissolved, the mixture is slightly cooled and added with 157 g of 3-aminocrotonic acid -isobutylester and 69 g of isobutyronitrile. Hereafter the mixture is heated at reflux for 3 hours. The reaction mixture is worked up as described in Example 7. The 2-iso- propyl-4-methyl-6-hydroxypyrimidine formed appears as a white to pale yellow product which after drying has a purity >95% determined by HPLC.
On the drawing the 13 C NMR spectrum of the product in deuterated D SO [Product 1] is shown.
Example 2 -: -' .. .
To a mixture of 100 g "of 3-aminocrotonamide dissolved in about 100 ml of liquid ammonia, 23 g of sodium is added in small portions while cooling. When all of the sodium has been dissolved, the reaction mixture is heated slowly while distilling off ammonia.
0 When the temperature reaches 20 C, 200 ml of toluene is added and the mixture heated to reflux. At the reflux temperature 69 g of isobutyronitrile is added dropwise during 1 to 2 hours. Upon completion of the dropwise addition the temperature is maintained for a further 3 hours at reflux. .. The reaction" mixture is worked up as described in Example 7. The 2-isopropyl-4-methyl-6- hydroxypyrimidine ^formed appears as a white to pale yellow product which after drying has a purity >95% de¬ termined by HPLC. On the drawing the 13 C NMR spectrum of the product in deuterated DMSO [Product 1] is shown.
Example 3
To a mixture of 143 g of 2-methyl-3-aminocro- tonic acid ethylester and 70 g of dimethylcyanamide and about 200 ml of tetrahydrofuran, heated to reflux, a total of 23 g of sodium is added in small portions. The reaction mixture is kept at reflux for 3 hours. The reaction mixture is worked up as described in Example 7. The 2-dimethylamino-4,5-dimethyl-6-hydroxy- pyrimidine formed appears as a white to pale yellow product which after drying has a purity >95% determined by HPLC. On the drawing the 13 C NMR spectrum of the product in deuterated DMSO [Product 2] is shown.
Example 4
To a slurry of 24 g of sodium hydride in 100 g of monoethyleneglycoldimethylether, heated to reflux, a mixture of 98 g of diethylcyanamide and 100 g of 3-aminocrotonamide dissolved in 100 g of- monoethylene- glycoldimethylether is added dropwise. The reaction mixture is maintained at reflux for 3 hours. The reac¬ tion mixture is worked up as described in Example 7. The 2-diethylamino-4-methyl-6-hydroxypyrimidine formed appears as a white to pale yellow product which after drying has a purity >95% determined by HPLC.
On the drawing the 13 C NMR spectrum of the product in deuterated DMSO [Product 3] is shown.
Example 5
A mixture of 157 g of 3-aminocrotonic acid iso- butylester and 112 g of potassium tert.-butoxide in about 200 ml of dioxane is heated to reflux and 98 g of diethylcyanamide is added dropwise during 1 to 2 hours. Upon completion of the dropwise addition the temperature is maintained for a further 3 hours at re¬ flux. The reaction mixture is worked up as described in Example 7. The 2-diethylamino-4-methyl-6-hydroxypyrimi- dine formed appears as a white to pale yellow product which after drying has a purity >95% determined by HPLC.
On the drawing the 13 C NMR spectrum of - the product in deuterated DMSO [Product 3] is shown.
Example 6
A mixture of 100 g of 3-aminocrotonamide, 98 g of diethylcyanamide and 56 g of potassium hydroxide in about 200 ml of tetrahydrofuran is heated at reflux for
3 hours. The reaction mixture is worked up as described in Example 7. The 2-diethylamino-4-methyl-6-hydroxy- pyrimidine formed appears as a white to pale yellow product which after drying has a purity >95% determined by HPLC.
On the drawing the 13 C NMR spectrum of the product in deuterated DMSO [Product 3] is shown.
Example 7
A mixture of 143 g of 2-methyl-3-aminocrotonic acid ethylester, 70 g of ethylcyanamide and 138 g of potassium carbonate in 300 ml of diethyl carbonate is heated at reflux for 6 hours. The reaction mixture is worked up by one of the following methods:
a. The reaction mixture is neutralized with a mineral acid (e.g., dry hydrogen chloride or cone, sulphuric acid) or an organic acid (e.g. acetic acid), heated at reflux for half an hour and evaporated to dryness on a rotary evapo¬ rator, and then 200 ml of water is added. The product precipitates in the aqueous phase and can be filtered therefrom. b. The reaction mixture is evaporated to dryness on a rotary evaporator, and then 200 ml of water is added. The aqueous phase is neutralized with mineral acid whereby the product is precipitated and can be filtered therefrom.
The 2-ethylamino-4,5-dimethyl-6-hydroxypyrimi- dine formed appears as a white to pale yellow product which after drying has a purity >95% determined by HPLC.. On the drawing the 13 C NMR spectrum of the product in deuterated DMSO [Product 4] is shown.
By a similar process 2-ethylamino-4-methyl-5- n-butyl-6-hydroxypyrimidine can be prepared by using 2-n-butyl-3-aminocrotonic acid ethylester instead of 2-methyl-3-aminocrotonic acid ethylester.