Process for producing alpha, beta-unsaturated ketones

A process for producing alpha,beta-unsaturated ketones represented by the following general formula ##STR1## wherein R.sub.1 represents a hydrocarbon radical, R.sub.2 represents an organic radical bonded through a carbon-carbon bond, R.sub.3 and R.sub.4 represent a hydrogen atom or a hydrocarbon radical, and R.sub.1, R.sub.2, R.sub.3 and R.sub.4 may be straight-chained or form a ring in arbitrary combinations, which comprises contacting an alpha-disubstituted-beta-keto acid ester represented by the general formula ##STR2## wherein R.sub.1, R.sub.2, R.sub.3 and R.sub.4 are as defined, and R.sub.5, R.sub.6, R.sub.7 and R.sub.8 represent a hydrogen atom or a hydrocarbon radical, with a catalyst consisting essentially of (a) a compound of a platinum-group metal and optionally (b) a monodentate ligand (b).

BACKGROUND OF THE INVENTION 
This invention relates to a novel process for producing 
alpha,beta-unsaturated ketones. More specifically, it relates to a process 
for producing alpha,beta-unsaturated ketones starting from 
alpha-disubstituted-beta-keto acid esters. 
Unsaturated ketones such as cyclopentenone derivatives, cyclohexenone 
derivatives and cyclododecenone derivatives are useful chemical substances 
in the fields of perfumes, medicines and chemicals. 
Recently, a new process for synthesizing such an unsaturated ketone was 
reported which comprises treating an alpha-disubstituted-beta-keto acid 
ester with a catalyst consisting essentially of a palladium compound and 
an alpha,omega-alkylenedi(disubstituted)phosphine (Journal of Chemical 
Society, 1982, 104, 5844-5846). This document states that the above 
reaction is a specific reaction which takes place only when the 
alpha,omega-alkylenedi(disubstituted)phosphine is used as a ligand, and 
the use of an ordinary ligand such as triphenyl phosphine leads to a 
different reaction. 
Accordingly, in such a prior technique, the ligands that can be used are 
limited to expensive compounds having a special structure. Moreover, this 
technique does not prove to be entirely satisfactory in regard to the 
activity of the catalyst, the selectivity of the reaction and the 
stability of the catalyst in the reaction system. 
SUMMARY OF THE INVENTION 
We made extensive investigations in order to remove the defects of the 
prior technique, and have found that this reaction does not always require 
the alpha,omega-alkylenedi(disubstituted)phosphine regarded as an 
essential catalyst ingredient in the above report; that a monodentate 
ligand such as triphenyl phosphine when used in a specific proportion is 
more effective than the alpha,omega-alkylenedi(disubstituted)phosphine; 
and that when the reaction is carried out in the presence of a certain 
compound, the activity and stability of the catalyst are further improved. 
According to this invention, there is provided a process for producing an 
alpha,beta-unsaturated ketone represented by the following general formula 
[II], which comprises contacting an alpha-disubstituted-beta-keto acid 
ester represented by the following general formula [I] optionally in the 
presence of an allyl compound with a catalyst consisting essentially of 
(a) a compound of a platinum-group metal and as required, (b) a 
monodendate ligand in an amount of not more than 2.5 moles per mole of 
said compound (a). 
##STR3## 
In the above formulae, R.sub.1 represents a hydrocarbon radical, R.sub.2 
represents an organic radical bonded through a carbon-carbon bond, 
R.sub.3, R.sub.4, R.sub.5, R.sub.6, R.sub.7 and R.sub.8 represent a 
hydrogen atom or a hydrocarbon radical, and R.sub.1, R.sub.2, R.sub.3 and 
R.sub.4 may be straight-chained or form a ring in arbitrary combinations. 
DETAILED DESCRIPTION OF THE INVENTION 
In the process of this invention, the allylic ester of the 
alpha-disubstituted-beta-keto acid represented by general formula [I] is 
used as a starting material. In the formula, R.sub.1 is preferably an 
alkyl radical such as a methyl, ethyl, propyl, butyl or pentyl radical, or 
an alkylene radical which forms a ring such as a cyclopentane, cyclohexane 
or cyclododecane ring together with R.sub.2, R.sub.3 or R.sub.4. R.sub.2 
is preferably the same alkyl or alkylene radical as R.sub.1, or an organic 
radical having a polar radical such as an alkoxycarbonyl, 
alkenoxycarbonyl, alkoxyalkyl or alkoxycarbonylalkyl radical and being 
bonded to the adjacent carbon atom through a carbon-carbon bond. R.sub.3 
and R.sub.4 are preferably hydrogen or the same alkyl or alkylene radical 
as R.sub.1. R.sub.5, R.sub.6, R.sub.7 and R.sub.8 are preferably hydrogen 
or alkyl radicals. R.sub.1, R.sub.2, R.sub.3 and R.sub.4 may form a ring 
in arbitrary combinations. 
Specific examples of the compound [I] include esters formed between 
alpha-disubstituted-beta-keto acids such as 
1-alkyl-2-oxocyclopentanecarboxylic acids, 
1-alkenyl-2-oxocyclopentanecarboxylic acids, 
1-alkynyl-2-oxocyclopentanecarboxylic acids, 
1-alkyl-2-oxocyclohexanecarboxylic acids, 
1-alkenyl-2-oxocyclohexanecarboxylic acids, 
1-alkoxycarbonylalkyl-2-oxocyclohexanecarboxylic acids, 
1-alkenoxycarbonyl-2-oxocyclohexanecarboxylic acids, 
1-alkoxyalkyl-2-oxocyclohexanecarboxylic acids, 
1-alkyl-2-oxocyclododecanecarboxylic acid, 
1-acetyl-1-cyclopentanecarboxylic acid, alpha-dialkylacetoacetic acids and 
alpha-dialkyl-beta-oxononanoic acids and allylic alcohols such as allyl 
alcohol, methallyl alcohol, crotyl alcohol, 2-pentenyl alcohol and 
2-ethyl-2-butenol. The keto acids preferably have not more than 20 carbon 
atoms, and the allylic alcohols preferably have not more than 6 carbon 
atoms. 
The compounds of formula [I] may be synthesized in a customary manner. For 
example, allyl 1-pentyl-2-oxocyclopentanecarboxylate can be synthesized by 
cyclizing diallyl adipate to allyl 2-oxocyclopentanecarboxylate by 
Dieckmann condensation, and reacting the product with n-pentyl bromide in 
the presence of potassium carbonate, or by reacting 2-pentyl 
cyclopentanone with allyl chloroformate. 
The reaction in the process of this invention is catalyzed by a catalyst 
composed of (a) a compound of a platinum-group metal, or a catalyst 
composed of (a) a compound of a platinum-group metal and (b) a monodentate 
ligand. 
The compound (a) of a platinum-group metal used is a salt or complex of 
palladium, platinum, rhodium, iridium or ruthenium. Specific examples 
include tris(dibenzylideneacetone)dipalladium (0), tris(tribenzylidene 
acetylacetone)tripalladium (0), palladium acetate, palladium propionate, 
palladium butyrate, palladium benzoate, palladium acetylacetonate, 
palladium nitrate, palladium sulfate, palladium chloride, platinous 
acetate and platinum acetylacetonate. When inorganic strong acid salts of 
platinum-group metals are used, it is desirable to cause a base such as 
potassium acetate, sodium alcoholate or a tertiary amine to be present 
together. Of the platinum-group metals, palladium is preferred in view of 
its reactivity. It is particularly preferred to use 0-valent olefin 
complexes or divalent organic compounds. 
The monodentate ligand (b) used as the catalyst ingredient is an electron 
donating compound having an element of Group V of the periodic table, i.e. 
nitrogen, phosphorus, arsenic or antimony, as a coordinating atom. 
Specific examples include nitrogen-containing compounds such as pyridine, 
quinoline, trimethylamine, triethylamine and tributylamine; 
phosphorus-containing compounds such as triethyl phosphine, tri-n-butyl 
phosphine, tri-n-dodecyl phosphine, triphenyl phosphine, tri-o-tolyl 
phosphine, tri-p-biphenyl phosphine, tri-o-methoxyphenyl phosphine, 
phenyldiphenoxy phosphine, triethyl phosphite, tri-n-butyl phosphite, 
tri-n-hexyl phosphite, triphenyl phosphite, tri-o-tolyl phosphite and 
triphenyl thiophosphite; arsenic-containing compounds such as triethyl 
arsenic, tributyl arsenic and triphenyl arsenic; and antimony-containing 
compounds such as tripropyl antimony and triphenyl antimony. Of these, the 
nitrogen-containing compounds and phosphorus-containing compounds are 
preferred in respect of the activity, selectivity and economy of the 
reaction. 
The monodentate ligand is not essential as a catalyst ingredient. But its 
use in a suitable amount can greatly increase the stability of the 
catalyst and reduce the amount of the catalyst used. If its amount becomes 
excessively large, the known allylic reaction becomes a main reaction. The 
amount of the monodentate ligand (b) should therefore be limited to not 
more than 2.5 moles, preferably 0.1 to 2 moles, especially preferably 0.3 
to 1.8 moles, per mole of the metal compound. 
The amount of the catalyst used in this invention may be properly chosen. 
Usually, the platinum-group metal compound (a) is used in a proportion of 
0.01 to 10 moles, preferably 0.1 to 5 moles, per 100 moles of the starting 
compound [I]. The platinum-group metal compound (a) may be pre-reacted 
with the ligand (b). Usually, these ingredients are contacted in the 
reaction system to prepare the catalyst in situ. 
The reaction of this invention proceeds in accordance with the following 
reaction scheme by contacting the starting material with the catalyst. 
##STR4## 
In carrying out the reaction, an allylic compound may be present in the 
reaction system, and this leads to a further improvement in the activity 
and stability of the catalyst. The allylic compound is an ester or ether 
having at least one allylic radical in the molecule. Specific examples 
include allyl acetate, methallyl acetate, crotyl acetate, 2-pentenyl 
acetate, cinnamyl acetate, allyl propionate, allyl butyrate, allyl 
benzoate, diallyl carbonate, diallyl oxalate, diallyl malonate, diallyl 
succinate, diallyl adipate, diallyl phthalate, methyl allyl ether, methyl 
methallyl ether, methyl crotyl ether, ethyl allyl ether, propyl allyl 
ether, butyl allyl ether, diallyl ether and phenyl allyl ether. Those 
having not more than 10 carbon atoms are preferred. 
The amount of the allylic compound used may be selected properly. It is 
usually at least 0.5 mole, preferably 0.7 to 2.0 moles, per mole of the 
platinum-group metal compound. 
There is no particular limitation on the method of adding the allylic 
compound. It may be added, for example, during the step of preparing the 
catalyst, or at the start of the reaction, or during the progress of the 
reaction. As required, it may be added in two or more portions at 
different times. Preferably, the allylic compound is added in the step of 
preparing the catalyst. 
The reaction may be carried out in the presence of a diluent. Examples of 
the diluent are nitriles such as acetonitrile, propionitrile, 
butyronitrile and benzonitrile; amides such as dimethylformamide, 
diethylformamide, dimethylacetamide, dimethylpropionamide and 
N-methylpyrrolidone; ethers such as tetrahydrofuran, dioxane, dibutyl 
ether and ethylene glycol dimethyl ether; ketones such as acetone, methyl 
ethyl ketone and methyl isobutyl ketone cyclohexanone; esters such as 
methyl acetate, ethyl acetate, propyl acetate and ethyl propionate; 
alcohols such as ethanol, propanol, tert-butanol, ethylene glycol and 
diethylene glycol monoethyl ether; sulfoxides such as dimethyl sulfoxide 
and diethyl sulfoxide; and hydrocarbons such as n-hexane, cyclohexane, 
benzene, toluene and xylene. Of these, aprotic polar solvents, especially 
nitriles, amides, ethers, ketones and esters, are preferred. 
The diluent is used normally in such a proportion that the concentration of 
the starting material in it becomes 1 to 50% by weight. The use of the 
diluent can increase the activity and selectivity of the reaction and the 
stability of the catalyst. 
Other reaction conditions may be properly chosen. The reaction temperature 
is usually at least 20.degree. C., preferably 50.degree. to 150.degree. 
C., and the reaction time is usually 5 minutes to 10 hours. 
After the reaction, the desired product is separated from the reaction 
mixture in a customary manner to give the alpha,beta-unsaturated ketone 
having a high purity. The unsaturated ketones are used as intermediates 
for synthesis of various useful compounds, especially perfumes and 
medicines. For example, by the Michael addition of dimethyl malonate to 
2-(2-cis-pentenyl)-2-cyclopenten-1-one and subsequent decarboxylation, 
methyl jasmonate useful as a perfume can be easily synthesized. 
According to this invention, easily available compounds can be used as the 
catalyst, and the desired alpha,beta-unsaturated ketones can be produced 
with higher activity and selectivity than the conventional methods. The 
present invention can also improve the stability of the catalyst in the 
reaction system. 
The following examples illustrate the present invention more specifically. 
The stability of the catalyst in these examples was determined by observing 
the state of precipitation of palladium in the reaction system and 
evaluating it on the scale of A, B, C, D and E as follows: 
A: No precipitation occurs after the lapse of 12 hours from the end of the 
reaction. 
E: Precipitation begins during the reaction. 
B to D: Varying degrees of precipitation between A and E.

EXAMPLE 1 
A vessel was charged with 1 mole of allyl 
1-(2-pentynyl)-2-oxocyclopentanecarboxylate of the following formula 
##STR5## 
20 moles of acetonitrile and 0.01 mole of palladium acetate. At room 
temperature, they were rapidly stirred. The mixture was then heated to the 
boiling point of the solvent, and the reaction was carried out under 
reflux for 30 minutes. After the reaction, the reaction mixture was 
distilled under reduced pressure in a customary manner to give 
2-(2-pentynyl)-2-cyclopenten-1-one (PCP for short) in a yield of 85%. This 
compound was identified by using its IR, NMR and mass spectra. 
The state of the reaction system during the reaction and after the reaction 
was observed. Palladium began to be precipitated during the reaction, and 
after the end of the reaction, palladium precipitated more vigorously. 
Thus, the stability of the catalyst was evaluated as D. 
EXAMPLE 2 
Example 1 was repeated except that palladium acetylacetonate was used 
instead of palladium acetate. The yield of PCP was 80%. The state of 
precipitation of palladium was the same as in Example 1. 
EXAMPLE 3 
Example 1 was repeated except that tris(dibenzylidenediacetone)dipalladium 
(0) was used instead of palladium acetate. The yield of PCP was 83%. The 
state of precipitation of palladium was the same as in Example 1. 
EXAMPLE 4 
Example 1 was repeated except that a amount of triphenyl phosphine was used 
in addition to palladium acetate. The results are shown in Table 1. In 
either case, scarcely any precipitation of palladium during the reaction 
was observed. The stability of the catalyst was evaluated as C. 
TABLE 1 
______________________________________ 
Invention Control 
Run No. 1 2 3 4 5 
______________________________________ 
Amount of triphenyl 
0.005 0.01 0.015 0.02 0.03 
phosphine (moles) 
Mole ratio of tri- 
0.5 1.0 1.5 2.0 3.0 
phenyl phosphine 
to palladium 
Yield of PCP (%) 
82 85 87 71 6 
______________________________________ 
It is seen from the results obtained above that when the amount of 
triphenyl phosphine used is within a certain range, good results can be 
obtained in respect of the stability of the catalyst and the yield of the 
desired product. 
EXAMPLE 5 
Run No. 3 of Example 4 was repeated except that each of the ligands 
indicated in Table 2 was used instead of triphenyl phosphine. The results 
are shown in Table 2. The results show that a monodentate ligand is 
preferred to a bidentate ligand. 
TABLE 2 
______________________________________ 
Run Invention Control 
No. 1 2 3 4 5(*2) 
______________________________________ 
Ligand 
Triphenyl Pyridine Triethyl- 
Triphenyl 
ADP(*1) 
phosphite amine arsenic 
Yield 81 82 77 75 60 
of PCP 
(%) 
______________________________________ 
(*1)alpha,beta-ethylenedi(diphenyl)phosphine 
(*2)The amount of ADP was 0.01 mole. 
EXAMPLE 6 
Run No. 3 of Example 4 was repeated except that 20 moles of each of the 
solvents indicated in Table 3 was used instead of acetonitrile. The 
results are also shown in Table 3. 
TABLE 3 
______________________________________ 
Run No. Solvent Yield of PCP (%) 
______________________________________ 
1 Propionitrile 85 
2 Benzonitrile 87 
3 Dimethylformamide 
87 
4 Dioxane 83 
5 t-Butanol 74 
6 Toluene 76 
______________________________________ 
EXAMPLE 7 
Run No. 3 of Example 4 was repeated except that each of the compounds 
indicated in Table 4 was used as a starting material. The results are 
shown in Table 4. 
TABLE 4 
__________________________________________________________________________ 
Run Yield 
No. 
Starting material Product (mole %) 
__________________________________________________________________________ 
##STR6## 
##STR7## 92 
2 
##STR8## 
##STR9## 95 
3 
##STR10## 
##STR11## 75 
__________________________________________________________________________ 
EXAMPLE 8 
A vessel was charged with 1 mole of allyl 
1-(2-pentynyl)-2-oxocyclopentanecarboxylate, 20 moles of acetonitrile, 
0.003 mole of palladium acetate, 0.0045 mole of triphenyl phosphine and 
0.003 mole of diallyl carbonate. They were rapidly stirred at room 
temperature, and the mixture was heated to the boiling point of the 
solvent. The reaction was carried out under reflux until the conversion of 
the starting material became nearly 100%. Since the reaction ended in 
about 3 hours, the product was distilled under reduced pressure in a 
customary manner. PCP was obtained in a yield of 88%. The stability of the 
catalyst was evaluated as A. 
EXAMPLE 9 
Example 8 was repeated until the conversion of the starting material became 
nearly 100% except that each of the allyl compounds indicated in Table 5 
was used instead of diallyl carbonate. The results are shown in Table 5. 
TABLE 5 
______________________________________ 
Invention 
Run No. 1 2 3 4 
______________________________________ 
Allyl compound 
-- Diallyl Allyl Phenyl 
adipate acetate 
allyl 
ether 
Yield of PCP (%) 
85 85 85 80 
Reaction time (hr) 
10 5 5 5 
Stability of the 
C B B B 
catalyst 
______________________________________ 
EXAMPLE 10 
A vessel was charged with 1 mole of allyl 
1-(2-pentynyl)-2-oxocyclopentanecarboxylate, 20 moles of acetonitrile, 
0.01 mole of palladium acetate, 0.015 mole of triphenyl phosphite and 0.01 
mole of allyl acetate, and they were rapidly stirred at room temperature. 
The mixture was heated to the boiling point of the solvent, and under 
reflux, the reaction was carried out for 30 minutes. PCP was obtained in a 
yield of 82%. The stability of the catalyst was evaluated as B. 
EXAMPLE 11 
Example 10 was repeated except that pyridine was used instead of triphenyl 
phosphite. The yield of PCP was 82%, and the stability of the catalyst was 
evaluated as B. 
EXAMPLE 12 
Example 8 was repeated except that palladium acetylacetonate was used 
instead of palladium acetate. Nearly the same results as in Example 8 were 
obtained. 
EXAMPLE 13 
Example 8 was repeated except that tris(dibenzylideneacetone)dipalladium 
was used instead of palladium acetate. Nearly the same results as in 
Example 8 were obtained.