CN113698359B - Method for synthesizing 3,5-disubstituted isoxazole compound based on three-component reaction - Google Patents
Method for synthesizing 3,5-disubstituted isoxazole compound based on three-component reaction Download PDFInfo
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- C07D261/02—Heterocyclic compounds containing 1,2-oxazole or hydrogenated 1,2-oxazole rings not condensed with other rings
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- C07D261/08—Heterocyclic compounds containing 1,2-oxazole or hydrogenated 1,2-oxazole rings not condensed with other rings having two or more double bonds between ring members or between ring members and non-ring members with only hydrogen atoms, hydrocarbon or substituted hydrocarbon radicals, directly attached to ring carbon atoms
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Abstract
The invention provides a method for synthesizing 3,5-disubstituted isoxazole compounds based on three-component reaction, which comprises the step of mixing aldehyde, olefin and nitrite, heating and reacting to generate 3,5-disubstituted isoxazole compounds. The safety of the scheme of the invention is greatly improved; the raw materials can be purchased commercially, advanced preparation is not needed, the reaction is easier to implement, and the reaction operation is simpler and more convenient; the application range of the substrate is wider, and substrates such as aliphatic hydrocarbon, aromatic hydrocarbon, fused ring and the like can be suitable for the reaction system; the reaction can be carried out in both acidic and alkaline environments; the reaction can be carried out under the air condition without the protection of inert gas.
Description
Technical Field
The invention belongs to the technical field of organic synthesis, and particularly relates to a method for synthesizing 3,5-disubstituted isoxazole compounds based on three-component reaction.
Background
As early as 1888, claisen et al cyclized to form 3-hydroxyisoxazole using a reaction of beta-ketoester and hydroxylamine. Thereafter, a large number of researchers have been working on the synthesis methodology of isoxazoles by means of cycloaddition reaction [3+2], cycloisomerization reaction, condensation reaction, and the like (shown in FIG. 1). The isoxazole synthesis method is now summarized after classification by type as follows:
1. isoxazoles (Cycloaddition) were synthesized by the Cycloaddition reaction [3+2 ]: the most common method for the synthesis of isoxazoles is the 1,3-dipolar cycloaddition of chlorooxime acetate with an alkyne or alkene. Firstly, aromatic aldehyde reacts with hydroxylamine hydrochloride to obtain aldoxime, the aldoxime reacts with chlorosuccinimide (NCS) to obtain chlorooxime, the chlorooxime reacts with triethylamine to obtain nitrile oxide, and then reacts with alkyne or alkene in 1,3-dipolar cycloaddition reaction to obtain the target product isoxazole (shown in figure 2A). The synthesis conditions are mild, the prepared isoxazole compounds are various in types, the compounds containing active groups such as amino, hydroxyl, active halogen and the like can be directly prepared, and the method also has important application in synthesis methodology, such as development of methods of metal catalysis, catalyst loading and the like, but has the defect that a substrate needs a compound containing a terminal acetylene bond, and certain limitation and difficulty are added to synthesis. Zhu Min etc. adopts catalytic amount of organic high-valence iodine reagent to develop the [3+2] cyclization reaction of terminal alkyne and aldoxime, and synthesizes a series of 3,5-disubstituted isoxazole compounds. The reaction is simple and convenient, the regioselectivity is strong, and the isoxazole synthesis under the alkali-free condition is realized (as shown in figure 2B).
2. Isoxazoles (cycloisomenzation) were synthesized by Cycloisomerization: intramolecular cyclization of alkynyloxime as substrate is also a commonly used synthesis method of isoxazole. In 1970, sisido et al studied the cyclization of alkynylketoxime and found that the acid-base property of the reaction system had a significant determining effect on the ring formation (FIG. 3A). After the reaction of alkynyl ketoester and hydroxylamine hydrochloride to oxime, if ring closure is carried out under acidic condition, 5-substituted isoxazole-3-ethyl formate (I) is obtained, and if ring closure is carried out under weak alkaline condition, isoxazoline-3-ethyl formate (II) is mainly generated. The formation of isoxazoles with alkyne oximes is more reported, and the formation of isoxazole rings with alkene oximes is less common. In 2009, an inventory of Lanzhou university utilized α, β -unsaturated keto esters and TsNHOH one-pot synthesis of a series of 3,5-disubstituted isoxazole compounds, wherein ethyl 3-phenylisoxazole-5-carboxylate was synthesized in 65% yield (FIG. 3B). The possible ring mechanism is that TsNHOH first undergoes an addition reaction to the alpha-unsaturated ethylenic bond of the carbonyl group, followed by the elimination of benzenesulfinic acid to give an alpha-carbonyl oxime which is dehydrated to form an isoxazole ring.
Since then, in 2011, the Miyata group developed Ag using phenol as a proton source + Isoxazole was synthesized under catalysis (shown in FIG. 3C). The authors concluded that the mechanism of catalytic cyclization was Ag + Binds to the electron-deficient alkyne bond, activating the alkyne bond. The density of electron cloud is increased because of the connection of an electron donating group benzyl to the oxime oxygen atom, lone pair electrons of the oxime oxygen attack activated alkyne bonds, and then an addition reaction is carried out to form an isoxazole ring, and meanwhile, the oxime oxygen is benzyl and Ag + Detachment of Ag + The catalyst is circulated in the reaction. But the reaction yield is generally low and the reaction time is long.
The Zhu topic group reported a new method of palladium/silver co-catalysis in 2014 (shown in figure 3D). To demonstrate the applicability of the method, they successfully applied the method to the synthesis of the drugs Valdecenib and Oxacillin. However, the use of noble metals reduces the possibility of the process being used industrially.
Recently, the Chang group synthesized a series of mono-, di-, and tri-substituted (aryl, alkyl, and/or alkenyl) isoxazoles from readily available α, β -unsaturated oximes via iodine-mediated oxidative C-O bond formation (FIG. 3E). The synthesis method has the advantages of no use of transition metal, simple operation, mild reaction conditions, short reaction time, wide substrate application range and the like.
3. Synthesis of isoxazoles (Condensation) by Condensation reaction: in 1888, claisen et al cyclized using the reaction of beta-ketoester and hydroxylamine to form 3-hydroxyisoxazole (shown in FIG. 4A). The one-pot synthesis of isoxazole can be realized under nonmetal conditions, but a by-product 5-isoxazolidone is generated in the system, so that the yield of the main product is reduced. To clarify the mechanism of side reaction formation, cocievera et al, studied in 1976 by nuclear magnetic resonance, suggested that 5-isoxazolidone was converted from the thermodynamically unstable cis isomer. In 2000, larsen et al avoided the formation of the by-product 5-isoxazolidone by modifying the procedure (FIG. 4B). The 3-hydroxy 5-methylisoxazole derivative is synthesized by a three-step method through carrying out N, O protection on raw materials.
In conclusion, since the isoxazole synthesis method was first developed by Claisen et al in 1888, researchers enriched new isoxazole synthesis methods by means of new strategies such as [3+2] cycloaddition reaction, cyclization isomerization reaction, condensation reaction and the like.
In the (3+2) cycloaddition reaction strategy, the raw material aldoxime or ketoxime is not easy to be obtained commercially and needs to be prepared in advance; in addition, in the cyclization isomerization reaction and condensation reaction strategy, hydroxylamine hydrochloride reagent is required to be used, and the reagent has a restriction factor such as safety when used on a large scale. With the increasing prominence of environmental problems, the development of efficient, green and simple synthetic methodology will be the development direction of future synthetic chemistry.
Disclosure of Invention
Aiming at the problems, the invention provides a method for synthesizing 3,5-disubstituted isoxazole compounds based on three-component reaction.
In order to realize the purpose, the following technical scheme is adopted:
a method for synthesizing 3,5-disubstituted isoxazole compounds based on three-component reaction is characterized in that aldehyde, olefin and nitrite are mixed and heated to react to generate 3,5-disubstituted isoxazole compounds.
Preferably, the reaction is carried out in water.
Preferably, the reaction is carried out in an organic solvent.
Preferably, the organic solvent is any one of tetrahydrofuran, chlorobenzene, acetone, N-dimethylformamide, N-methylpyrrolidone, acetonitrile, dimethyl sulfoxide, methanol or ethanol.
Preferably, a persulfate is added to the reaction as an oxidizing agent.
Preferably, an acidic substance or a basic substance is added to the reaction.
Preferably, sodium sulfate is added to the reaction.
Preferably, the aldehyde is selected from an aliphatic aldehyde, an aromatic aldehyde or a fused ring aldehyde. The olefin is selected from aromatic olefin or fused ring olefin; the nitrite is selected from alkyl nitrites.
Preferably, the organic solvent contains water, and the volume ratio of the organic solvent to the water is 5:1.
Preferably, the persulfate is any one or more of sodium persulfate, potassium persulfate and ammonium persulfate.
Preferably, the acidic substance is formic acid, acetic acid, trifluoroacetic acid, hydrochloric acid, hydrofluoric acid, boron trifluoride diethyl etherate or fluoroboric acid; the alkaline substance is imidazole, potassium tert-butoxide, sodium carbonate, 4-dimethylaminopyridine, sodium acetate, piperazine, potassium phosphate, triethylamine, sodium bicarbonate, 1,4-diazabicyclo [2.2.2] octane, cesium carbonate or 1,8-diazabicycloundecen-7-ene.
Preferably, the molar ratio of the aldehyde, olefin and nitrite is: 1-5:1-10.
Preferably, the heating temperature of the reaction is 20-140 ℃, and the reaction time is 0.5-24h.
Preferably, the heating temperature of the reaction is 100 ℃ and the reaction time is 8h.
The invention has the following beneficial effects: 1. the nitrogen atom in the isoxazole molecule is derived from nitrite instead of hydroxylamine hydrochloride, so that the reaction safety is greatly improved; 2. the raw materials can be purchased commercially, advanced preparation is not needed, the reaction is easier to implement, and the reaction operation is simpler and more convenient; 3. the application range of the substrate is wider, and the substrates such as aliphatic hydrocarbon, aromatic hydrocarbon, fused ring and the like can be suitable for the reaction system; 4. the reaction can be carried out in both acidic environment and alkaline environment; 5. the reaction can be carried out under the air condition without the protection of inert gas.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and those skilled in the art can also obtain other drawings according to the drawings without creative efforts.
FIG. 1 is a schematic diagram of a method for synthesizing isoxazole in the prior art;
FIG. 2 is a schematic diagram of a process for the cycloaddition synthesis of isoxazole by [3+2 ];
FIG. 3 is a schematic diagram of a process for the synthesis of isoxazoles by a cycloisomerization reaction;
FIG. 4 is a schematic diagram of a condensation reaction process for the synthesis of isoxazoles;
FIG. 5 is a schematic diagram showing the reaction scheme of 3,5-diphenylisoxazole, a product obtained in example 1 of this invention;
FIG. 6 is a graph schematically showing the different products obtained by modifying a substrate according to the present invention;
FIG. 7 is a schematic diagram of the reaction mechanism of the present invention;
FIG. 8 is a graph showing reaction conditions and yield results of various examples of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Example 1:
a method for synthesizing 3,5-disubstituted isoxazole compounds based on three-component reaction adopts 0.5mmol of styrene, 0.25mmol of p-bromobenzaldehyde and 0.5mmol of tert-butyl nitrite (TBN) to react for 8 hours in 0.6mL of solvent water at 100 ℃ and the white transparent crystal 3aa is obtained by column chromatography separation with the yield of 5 percent.
Example 2:
a method for the synthesis of 3,5-disubstituted isoxazoles based on a three-component reaction differs from example 1 in that the solvent used is DMF and the yield is 15%.
Example 3:
a method for synthesizing 3,5-disubstituted isoxazoles based on a three-component reaction is different from example 1 in that the solvent used is a mixed solution of DMF and water, the ratio of DMF to water is 5:1, and the yield is 35%.
Example 4:
a method for synthesizing 3,5-disubstituted isoxazoles based on three-component reaction is different from example 3 in that 0.125mmol K is further added during the reaction 2 S 2 O 8 As the oxidizing agent, the yield was 47%.
Example 5:
a method for synthesizing 3,5-disubstituted isoxazoles based on a three-component reaction is distinguished from example 4 in that 0.625mmol of acetic acid is additionally added during the reaction, giving a yield of 51%.
Example 6:
a method for synthesizing 3,5-disubstituted isoxazoles based on a three-component reaction differs from example 5 in that 0.25mmol sodium sulfate is further added during the reaction, yielding 58%.
Example 7:
a method for synthesizing 3,5-disubstituted isoxazoles based on a three-component reaction is distinguished from example 6 in that 0.5mmol of sodium sulfate is added during the reaction, giving a yield of 61%.
Example 8:
a method for synthesizing 3,5-disubstituted isoxazoles based on a three-component reaction differs from example 6 in that the reaction temperature is 80 ℃ and the yield is 52%.
Example 9:
a process for the synthesis of 3,5-disubstituted isoxazoles based on a three component reaction differs from example 6 in that the reaction temperature is 110 ℃ and the yield is 61%.
Example 10:
a method for synthesizing 3,5-disubstituted isoxazoles based on a three-component reaction differs from example 6 in that the reaction temperature is 120 ℃ and the yield is 40%.
Example 11:
a method for synthesizing 3,5-disubstituted isoxazoles based on a three-component reaction is distinguished from example 6 in that 0.25mmol of styrene is used, in 22% yield.
Example 12:
a method for synthesizing 3,5-disubstituted isoxazoles based on a three-component reaction is distinguished from example 6 in that 0.75mmol of styrene is used, giving a yield of 71%.
Example 13:
a method for synthesizing 3,5-disubstituted isoxazole compounds based on three-component reaction comprises the steps of firstly adopting 2mmol of styrene, 1mmol of benzaldehyde and 2mmol of tert-butyl nitrite, reacting for 3 hours at 30 ℃ in 2mL of solvent DMF, and separating by column chromatography to obtain white transparent crystals 4a with the yield of 5%. The nuclear magnetic analysis of the prepared compound showed that 4a was 3,5-diphenylisoxazole, and the reaction formula is shown in FIG. 5. The reaction conditions and yield results of the above examples are shown in FIG. 8.
Further, the method of the present invention is not limited to the above reaction substrate, and the aldehyde substrates such as aliphatic aldehyde, aryl aldehyde group and fused ring aldehyde are all suitable for the reaction, as shown in fig. 6, and different substrates are used for reactant 1 and reactant 2 to obtain different products 4, such as compounds 4a, 4b.
The process used in the present invention proceeds through the following reaction scheme, as shown in FIG. 7: aldehyde A, olefin B and nitrite E are used as reactants, and in a reaction system, aldehyde free radicals C generated by the aldehyde A under the action of an oxidant are added to olefin to generate free radicals D. At this time, the free radical D and nitroso free radical F generated by heating nitrite E are subjected to free radical coupling reaction to generate compound G, which is rapidly isomerized into 1,3-dicarbonyl ketoxime intermediate H, and then subjected to intramolecular ring closure reaction to generate compound I, and the target isoxazole compound J is generated by losing 1 molecule of water. As shown in fig. 6, in the reaction system, aldehyde substrates such as aliphatic aldehyde cyclohexanecarboxaldehyde (product 4u after reaction), aromatic aldehyde benzaldehyde (product 4a after reaction), heterocyclic aldehyde 4-pyridineformaldehyde (product 4r after reaction), and the like are applicable, and olefin substrates such as aliphatic olefin 1-hexene (product 5f after reaction), aromatic olefin 4-bromostyrene (product 5a after reaction), condensed ring olefin 2-naphtalene (product 5d after reaction), and the like are applicable; nitrite substrates such as isobutyl nitrite, n-butyl nitrite, isoamyl nitrite and the like can be suitable; the reaction can be carried out in both acidic and basic environments.
In summary, the nitrogen atom in the isoxazole molecule is from a TBN molecule rather than hydroxylamine hydrochloride, hydroxylamine hydrochloride is used as a source, aldehyde oxime or ketoxime is usually prepared in advance through a substrate aldehyde or ketone reaction, the operation is complicated, and the hydroxylamine hydrochloride has a safety problem in large-scale reaction. When TBN is used as a raw material, the raw material does not need to be prepared in advance, and the method can be finished by a one-pot method, and has better safety compared with hydroxylamine hydrochloride.
Although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.
Claims (7)
1. A method for synthesizing 3,5-disubstituted isoxazole compounds based on three-component reaction is characterized in that aldehyde, olefin and nitrite are mixed and heated to react to generate 3,5-disubstituted isoxazole compounds;
wherein the aldehyde is an aromatic aldehyde; the olefin is aromatic olefin; the nitrite is tert-butyl nitrite; the molar ratio of the aldehyde, the olefin and the nitrite is 1-5:1-10;
the reaction is carried out in an organic solvent, wherein the organic solvent is N, N-dimethylformamide, the organic solvent contains water, and the volume ratio of the organic solvent to the water is 5:1.
2. The method for synthesizing 3,5-disubstituted isoxazoles based on the three-component reaction of claim 1 wherein persulfate is added to the reaction as oxidant.
3. The method for synthesizing 3,5-disubstituted isoxazoles based on three-component reaction according to claim 1, wherein an acidic substance or a basic substance is added to the reaction.
4. The method for synthesizing 3,5-disubstituted isoxazoles based on the three-component reaction of claim 1 wherein sodium sulfate is added to the reaction.
5. The method for synthesizing 3,5-disubstituted isoxazoles based on three-component reaction according to claim 2, wherein the persulfate is any one or more of sodium persulfate, potassium persulfate or ammonium persulfate.
6. The method for synthesizing 3,5-disubstituted isoxazoles based on three-component reaction according to claim 3 wherein the acidic substance is formic acid, acetic acid, trifluoroacetic acid, hydrochloric acid, hydrofluoric acid, boron trifluoride diethyl etherate or fluoroboric acid; the alkaline substance is imidazole, potassium tert-butoxide, sodium carbonate, 4-dimethylaminopyridine, sodium acetate, piperazine, potassium phosphate, triethylamine, sodium bicarbonate, 1,4-diazabicyclo [2.2.2] octane, cesium carbonate or 1,8-diazabicycloundecen-7-ene.
7. The method for synthesizing 3,5-disubstituted isoxazoles based on three-component reaction according to any of claims 1-6, wherein the heating temperature of the reaction is 20-140 ℃ and the reaction time is 0.5-24h.
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