A process for producing an alpha,beta-unsaturated carbonyl compound

Abstract: There is disclosed a process for producing an α,β-unsaturated carbonyl compound which comprises contacting an alkenyl ester represented by the formula [I]: with a carbonic ester represented by the formula [III]: in the presence of a catalyst.

Description: This invention relates to a novel process for producing an α,β-unsaturated carbonyl compound. RELATED ART STATEMENT α,β-unsaturated carbonyl compounds such as 2-cyclopentenone, 2-cyclohexenone, 2-cyclododecenone, etc. are useful chemical substances in the fields of perfumes, medicines, chemicals, etc. As a process for synthesizing such an unsaturated carbonyl compound, there has been reported a process which comprises treating an alkenyl ester and an allyl type carbonic ester with a platinum group metal compound catalyst in the presence of an organotin alkoxide (Jap. Pat. Appln. Kokai (Laid-Open) No. 60-36435, and Chemistry Letters 1133-1136 (1984)). However, the organotin alkoxide used as indispensable component in this process is difficult to handle and it is insufficient in safety from the viewpoint of industrial hygiene and contamination of the organotin alkoxide to a final product. SUMMARY OF THE INVENTION In order to solve the above-stated problem, the present inventors have earnestly investigated. Consequently they unexpectedly found that the above reaction can be allowed to proceed by the use of a platinum group metal compound catalyst alone without using an organotin alkoxide which is used as an indispensable component in the above report. On the basis of the above finding, the present invention has been accomplished. Thus, according to the present invention, there is provided a process for producing an α,β-unsaturated carbonyl compound of the general formula [II] shown below, comprising bringing an alkenyl ester of the general formula [I] shown below into contact with an allyl type carbonic ester in the presence of a platinum group metal compound catalyst, which process is superior to that of the prior art in operations and safety and can give an α,β-unsaturated carbonyl compound in high yield. (wherein R₁, R₂, R₃ and R₄ are independently hydrogen atoms or hydrocarbon residues, and R₁, R₂, R₃ and R₄ may be linear or may form one or more rings when taken together in arbitrary combinations; and X is an acyl group.) DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS In the present invention, an alkenyl ester of the above general formula [I] is used as a first starting material. In the general formula [I], R₁ is a hydrogen atom or a hydrocarbon residue. The hydrocarbon residue includes an alkyl group such as a methyl, ethyl, propyl, pentyl group, etc.; an alkylene group which are bonded to R₂, R₃ or R₄ to form a ring such as a cyclopentane, cyclohexane, cyclododecane ring or the like; and an aryl group such as a phenyl, trityl group, etc. R₂, R₃ and R₄ are independently hydrogen atoms or the same alkyl, alkylene or aryl group as R₁. X is an acyl group. The above substituents R₁, R₂, R₃ and R₄ may be taken together in arbitrary combinations to form one or more rings. Specific examples of such a compound are 1-cyclopentenyl acetate, 1-cyclohexenyl acetate, 6-methyl-1-cyclopentenyl acetate, 6-ethyl-1-cyclopentenyl acetate, 1-cycloheptenyl acetate, 1-cyclododecenyl acetate, 1-cyclopentenyl propionate, 1-cyclopentenyl butylate, 1-cyclopentenyl benzoate, 1-phenyl-1-butenyl acetate, 1-propenyl acetate, 1-hexenyl acetate, 3-methyl-1-butenyl acetate, 3-phenyl-1-propenyl acetate, etc. Of these, cycloalkenyl esters are preferable. Of esters, cyclopentenyl esters are particularly preferable because they permit progress of the reaction with ease and can give a desired product in high yield. These compounds may be synthesized by a conventional method. For example, 1-cyclopentenyl acetate can easily be synthesized by such a method that comprises reacting cyclopentanone with isopropenyl acetate in the presence of an acid, or reacting cyclopentanone with acetic anhydride. The allyl type carbonic ester used as a second starting material is a carbonic ester having at least one allyl or its allied residue and it is usually a compound of the general formula [III]: wherein R₅ is a hydrocarbon residue, and R₆, R₇, R₈ and R₉ are independently hydrogen atoms or hydrocarbon residues. The hydrocarbon residues include, for example, alkyl groups having 1 to 8 carbon atoms (e.g. methyl, ethyl group, etc.) and alkenyl groups having 2 to 8 carbon atoms. Specific examples of such a compound are allyl methyl carbonate, allyl ethyl carbonate, allyl propyl carbonate, allyl butyl carbonate, allyl pentyl carbonate, crotyl methyl carbonate, ethyl methallyl carbonate, diallyl carbonate, etc. Of these, there are preferably used allyl esters, crotyl esters and methallyl esters, in which R₅ is a lower alkyl group having 4 or less carbon atoms. In the present invention, a platinum group metal compound catalyst is used in the reaction. The platinum group metal compound catalyst is a platinum group metal compound per se or it is composed of a platinum group metal compound and a ligand. The platinum group metal compound used is a salt or complex of palladium, platinum, rhodium, iridium or ruthenium. Specific examples thereof are tris(dibenzylideneacetone)dipalladium (0), tris(tribenzylideneacetylacetone)tripalladium (0), palladium acetate, palladium propionate, palladium butyrate, palladium benzoate, palladium acetylacetonate, palladium nitrate, palladium sulfate, palladium chloride platinum [II] acetate, platinum acetylacetonate, etc. In the case where an inorganic strong acid salt of these compounds is used, it is preferable to place together therewith a base such as potassium acetate, sodium alkoxides, tertiary amines or the like. Of platinum group metals, palladium is particularly preferable from the viewpoint of reactivity, and employment of a zerovalent olefin complex or a divalent organic compound is particularly preferable. The ligand used is a monodentate or multidentate electron donor compound having, as a ligand atom, an element of Group V of the periodic table, i.e., nitrogen, phosphorus, arsenic or antimony. Specific examples of the ligand are nitrogen-containing compounds such as pyridine, quinoline, trimethylamine, triethylamine, tributylamine, α,α-dipyridine, 1,10-phenanthroline, N,N,N′,N′-tetramethylethylenediamine, etc.; phosphorus-containing compounds such as triethylphosphine, tri-n-butylphosphine, tri-n-dodecylphosphine, triphenylphosphine, tri-o-tolylphosphine, tri-p-biphenylphosphine, tri-o-methoxyphenylphosphine, phenyldiphenoxyphosphine, triethyl phosphite, tri-n-butyl phosphite, tri-n-hexyl phosphite, triphenyl phosphite, tri-o-tolyl phosphite, triphenyl thiophopshite, α,β-ethylenedi(diphenyl)phosphine, α,β-ethylenedi(dibutyl)phosphine, α,γ-propylenedi(diphenyl)phosphine, etc.; arsenic-containing compounds such as triethylarsine, tributylarsine, triphenylarsine, etc.; and antimony-containing compounds such as tripropylstibine, triphenylstibine, etc. Of these, the nitrogen-containing compounds and the phosphorus-containing compounds are preferable from the viewpoint of, for example, the activity, selectivity and economical benefit of reaction. Although such a ligand is not always indispensable as a constituent of the catalyst, it can greatly improve the stability of the catalyst when used in a suitable amount. The amount of the ligand used is varied depending on the kind thereof, but it is usually 2.5 moles or less, preferably 0.1 to 2 moles, per mole of the metal compound. The amount of the catalyst in the present invention is properly chosen. Said amount is usually in such a proportion that the amount of the platinum group metal compound is 0.01 to 10 moles, preferably 0.1 to 5 moles, per 100 moles of the alkenyl ester. Although the platinum group metal compound and the ligand may be previously reacted with each other, the catalyst is usually prepared by bringing these components into contact with each other in a reaction system. The reaction of the present invention is carried out by heating the above two starting materials in the presence of the catalyst. For example, a reaction formula in the case of using 1-cyclopentenyl acetate and allyl methyl carbonate is as follows: As to the proportions of the starting materials to be used, the allyl type carbonic ester is usually used in an amount of 0.8 to 5 moles, preferably 1 to 3 moles, per mole of the alkenyl ester. The reaction temperature is usually 50°C or higher, preferably 55°C to 150°C, and the reaction time is usually 10 minutes to 20 hours. A diluent can be present in the reaction. Specific examples of the diluent are nitriles such as acetonitrile, propionitrile, butyronitrile, benzonitrile, etc.; sulfoxides such as dimethyl sulfoxide, diethyl sulfoxide, etc.; amides such as dimethylformamide, diethylformamide, dimethylacetamide, dimethylpropioamide, N-methylpyrrolidone, etc.; ethers such as tetrahydrofuran, dioxane, dibutyl ether, ethylene glycol dimethyl ether, etc.; ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, etc.; esters such as methyl acetate, ethyl acetate, propyl acetate, ethyl propionate, etc.; alcohols such as ethanol, propanol, tert-butanol, ethylene glycol, diethylene glycol monoethyl ether, etc.; and hydrocarbons such as n-hexane, cyclohexane, benzene, toluene, xylene, etc. Of these, aprotic polar solvents, in particular, the nitriles and the sulfoxides are preferable. The above-exemplified diluents are usually used in such a proportion that the concentration of the starting materials becomes 1 to 50% by weight. The diluent can improve an activity and selectivity of the reaction and the stability of the catalyst. After completion of the reaction, a desired product is separated from the reaction mixture by a conventional method, whereby there can be obtained an α,β-unsaturated carbonyl compound (i.e. an α,β-unsaturated ketone or an α,β-unsaturated aldehyde) of high purity. Such an unsaturated carbonyl compound is used as an intermediate for synthesis of various useful compounds, in particular, as an intermediate for perfumes, medicines, etc. The present invention is more specifically illustrated with the following examples. Example 1 Into a reactor were charged 0.1 mole of 1-cyclopentenyl acetate, 0.12 mole of allyl methyl carbonate ad 50 ml of acetonitrile, and the mixture heated up to the boiling point of the solvent with stirring; and 0.001 mole of palladium acetate was added. Then, the reaction was carried out with refluxing under nitrogen for 2 hours. The reaction mixture was analyzed by gas chromatography to find tat 2-cyclopenten-1-one (hereinafter abbreviated to CPE) had been produced in 93% yield. Such a compound was identified by IR, NMR and MS spectroscopy. Example 2 Reaction was carried out in the same manner as in Example 1, except for adding 0.001 mole of triphenylphosphine in addition to palladium acetate. Consequently, the yield of CPE was 94%. Example 3 Reaction was carried out in the same manner as in Example 1, except for using 0.001 mole of tris(dibenzylideneacetone)dipalladium (0) in place of palladium acetate. Consequently, the yield of CPE was 92%. Example 4 Reaction was carried out according to Example 1, except for using 50 ml of dimethyl sulfoxide in place of acetonitrile. Consequently, the yield of CPE was 93%. Example 5 Reaction was carried out according to Example 4, except for using 1-cyclohexenyl acetate as a starting material. Consequently, 2-cyclohexen-1-one was obtained in 42% yield. Example 6 Reaction was carried out according to Example 4, except for using 4-heptenyl acetate as a starting material. Consequently, 2-hepten-4-one was obtained in 26% yield.

Claims: A process for producing an α,β-unsaturated carbonyl compound represented by the general formula [II]: wherein R₁, R₂, R₃ and R₄ are independently hydrogen atoms or chain hydrocarbon residues, and R₁, R₂, R₃ and R₄ may be linear or may form one or more rings when taken together in arbitrary combination which comprises bringing an alkenyl ester represented by the general formula [I]: wherein R₁, R₂, R₃ and R₄ have the same meanings as those defined above, and X is an acyl group in the presence of a platinum group metal compound catalyst into contact with a carbonic ester of the general formula [III]: wherein R₅ is a hydrocarbon residue, and R₆, R₇, R₈ and R₉ are independently hydrogen atoms or hydrocarbon residues and wherein the reaction is carried out in the absence of an organotin alkoxide. The process according to Claim 1, wherein R₁, R₂, R₃ and R₄ are independently hydrogen atoms or hydrocarbon groups selected from alkyl groups, alkenyl groups or aryl groups. The process according to Claim 1, wherein the alkenyl ester represented by the general formula [I] is a cycloalkenyl ester. The process according to Claim 3, wherein the cycloalkenyl ester is a cyclopentenyl ester. The process according to Claim 1, wherein the carbonic ester is a lower alkyl ester of allyl carbonate, crotyl carbonate or methally carbonate. The process according to claim 1, wherein the catalyst is a platinum group metal compound or a catalyst composed of a platinum group metal compound and a ligand. The process according to Claim 6 wherein the platinum group metal compound is a salt or a complex of a platinum group metal selected from palladium, platinum, rhodium, iridium or ruthenium. The process according to Claim 7 wherein the platinum group metal is palladium. The process according to Claim 7 wherein the platinum group metal compound is a zerovalent olefin complex or a divalent organic compound of palladium. The process according to Claim 6 wherein the ligand is a monodentate or multidentate electron donor compound having, as a ligand atom, an element of Group V of the periodic table. The process according to Claim 10 wherein said element is N, P, As or Sb. The process according to Claim 6 wherein the ligand is used in amount of 2.5 moles or less per mole of the metal compound. The process according to Claim 1 wherein the catalyst is used in amount selected from 0.01 to 10 moles per 100 moles of the alkenyl ester. The process according to Claim 1 wherein the carbonic ester is used in amount of from 0.8 to 5 moles per mole of the alkenyl ester. The process according to Claim 1 wherein the contact between the alkenyl ester with the carbonic ester is carried out at a temperature of 50°C or more for a period of from 10 minutes to 20 hours. The process according to Claim 1 wherein the contact is carried out in the presence of a diluent. The process according to Claim 16 wherein the diluent is one selected from nitriles, sulfoxides, amides, ethers, ketones, esters, alcohols and hydrocarbons. The process according to Claim 16 wherein the diluent is an aprotic polar solvent. The process according to Claim 16 wherein the diluent is used in such an amount that the concentration of the esters becomes 1 to 50% by weight.

Inventors: MATSUOKA RIKITARO, WATANABE KIYOSHI, MATSUOKA, RIKITARO, WATANABE, KIYOSHI
Applicants: NIPPON ZEON CO, NIPPON ZEON CO., LTD.
Application year: 1990
Main classification: C07C45
IPC codes: C07C47, C07C49, B01J31, C07C45, C07B61