A 2,3-disubstituted cyclopentanone is an important compound for the synthesis of useful chemical substances such as a jasmine fragrance and prostaglandins.  Among others, those having an alkoxycarbonylmethyl group at the 3-position are important for the synthesis of a jasmine fragrance, and many production processes have been disclosed so far. 
For example, there are disclosed a process using cyclopentanone as a raw material (Non-patent Document 1) and a process using adipic acid as a raw material (Non-patent Document 2).  These processes provide a thermodynamically stable stereoisomer, that is, a trans-2,3-disubstituted cyclopentanone in which substituents at the 2,3-positions are in the trans relationship with each other with respect to the five-membered ring.  The percentage of the cis-isomer is generally only 10% or less.  However, as a result of recent studies, it has been found that, in a jasmonate which occupies an important position in a jasmine fragrance, a cis-2,3-disubstituted cyclopentanone has a considerably stronger scent than a trans-2,3-disubstituted cyclopentanone (Non-patent Document 3).  Thus, development of industrial processes for producing a cis-2,3-disubstituted cyclopentanone is strongly desired.  However, as described above, many of conventional techniques provide a trans-2,3-disubstituted cyclopentanone as a main component. 
As a technique to compensate for such a difficulty, there is disclosed a process for producing a cis-2,3-disubstituted cyclopentanone by using a catalyst to isomerize the resulting trans-2,3-disubstituted cyclopentanone (patent Document 1).  However, in the case of this technique, not only a special apparatus and a special step are required for isomerization, but also a high temperature of 160 to 190° C. is required for isomerization, which inevitably causes thermal degradation.  There is a problem that a special apparatus and a special step are further required for removing high boiling impurities produced due to the degradation.  In addition, the concentration of the resulting cis-isomer (epimer) is only about 40%. 
On the other hand, as a process for selectively synthesizing a cis-2-substituted-3-alkoxycarbonylmethyl cyclopentanone, there is known a process for hydrogenating the double bond in a 2-substituted-3-alkoxycarbonylmethyl cyclopentenone. 
Patent Document 2 discloses a process of catalytic hydrogenation in the presence of aluminum alcoholate.  The process can provide a desired cis-2-substituted-3-alkoxycarbonylmethyl cyclopentanone at a selectivity of 90% or more.  However, in addition to restrictions on reaction operation and equipment that require pressurization of 3 to 10 kg/cm2, it is necessary to use an equivalent amount of aluminum alcoholate as a third component.  Moreover, since the aluminum alcoholate added is decomposed by an aqueous acetic acid solution or the like after the reaction, a large amount of aluminum-based wastes are generated, making post-processing difficult.  Further, the process also has a difficulty in that the catalyst is polluted with these wastes to make recycling of the catalyst difficult. 
Patent Document 3 discloses a process of hydrogenation in the presence of a ruthenium complex having a specific ligand.  This document describes that a desired cis-2-substituted-3-alkoxycarbonylmethyl cyclopentanone can be obtained at a high selectivity of 99% or more.  However, in addition to the necessity of using a very expensive catalyst of ruthenium, it is necessary to use a special and expensive compound also for the ligand.  A complicated pretreatment is also required for the catalyst beforehand.  Further, since the process requires a very high hydrogen pressure of 10 to 90 kg/cm2, restrictions on reaction operation and equipment are very large.  Furthermore, the technique has a serious difficulty in the industrial implementation thereof in that, since it uses a homogeneous catalyst (dissolved in a solvent), a special operation is required for the separation of the catalyst and the product after reaction.  Moreover, in the above technique, since a specific ligand, which is added as a third component, is dissociated from the ruthenium complex based on the dissociation equilibrium, part of the ligand may be transferred to the product.  As a result, there was a serious drawback that the composition of a catalyst composition was changed in the catalyst separation operation after reaction and the reproducibility of the catalyst performance was not obtained. 
Patent Document 4 discloses a process of hydrogenation in the presence of a rhodium-carbon catalyst in combination with a phosphate or the like.  This document describes that a desired cis-2-substituted-3-alkoxycarbonylmethyl cyclopentanone can be obtained at a high selectivity of 90% or more at ordinary pressure.  However, according to an experiment by the present inventors, the selectivity of a cis-2-substituted-3-alkoxycarbonylmethyl cyclopentanone showed a very low value of 30% or less.  Further, according to the above technique, it is necessary to add a salt such as phosphate as a third component.  However, since such a salt has a certain solubility in an organic solvent such as methanol, part of the salt transfers to the product in the catalyst separation operation (filtration of the catalyst) after reaction.  As a result, there was a serious drawback that the composition of a catalyst composition was changed and the reproducibility of the catalyst performance was not obtained.  As described above, a technique which can selectively synthesize a cis-2-substituted-3-alkoxycarbonylmethyl cyclopentanone and has proved satisfactory in terms of industrial implementation has not yet been reported. 
On the other hand, a family of 1,3-cyclopentanediones includes very useful compounds for organic synthesis and useful compounds also as precursors for producing a substituted cyclopentanone according to the present invention.  However, they are substances which are far more difficult to synthesize than expected from the apparently simple molecular structure thereof (Non-patent Document 4). 
Among others, 1,3-cyclopentanedione itself, which not only has a fundamental structure but also is very useful, is particularly difficult to synthesize.  Typical processes for synthesizing 1,3-cyclopentanediones reported so far are illustrated below.  A first process is a process for reacting succinic acid with acyl chloride in the presence of aluminum chloride (Non-patent Document 5).  According to this process, 1,3-cyclopentanediones can be synthesized in one step, but the yield shows a very low value of 50%.  Moreover, according to this process, it is necessary to use a large excess of aluminum chloride and acyl chloride, that is, 2.4 times by mole and 4 times by mole, respectively, relative to the amount of succinic acid as a raw material.  This causes production of a large amount of by-product.  In addition, it is necessary to use an explosive solvent such as nitrobenzene as a solvent.  Thus, it is difficult to consider the above process as a satisfactory process from the standpoint of industrial implementation.  Further, since it is known that 1,3-cyclopentanedione which not only has a fundamental structure but also is very useful, cannot be synthesized by the above process (Non-patent Document 4), the above process cannot be a universal process for synthesizing 1,3-cyclopentanediones.  A second process is a process for cyclizing a 4-oxoalkanoate with a base.  Although this process is also a process in which a 1,3-cyclopentanedione can be synthesized in one step, the yield of 1,3-cyclopentanedione which not only has a fundamental structure but also is very useful, is low.  1,3-cyclopentanedione cannot be produced at all by using a general base (Non-patent Document 6) and can be obtained in at most 60% yield (Non-patent Document 7) only when a special base (potassium triphenylmethoxide) is used.  Furthermore, even in the case of a long chain 4-oxoalkanoate which is considered to undergo cyclization relatively easily, the yield is as low as about 35 to 80% (Non-patent Document 4).  Thus, it is difficult to consider this technique as a technique that can be industrially implemented.  As described above, a technique for producing 1,3-cyclopentanediones which has proved satisfactory in terms of industrial implementation has not yet been reported owing to the difficulty in synthesizing 1,3-cyclopentanediones. 
On the other hand, a γ-ketoester is a useful compound for organic synthesis and is also useful as a precursor for producing a substituted cyclopentanone according to the present invention.  However, it is difficult to synthesize a γ-ketoester in a small number of steps because it has two types of highly reactive functional groups, that is, ketone and ester in the same molecule.  As an example of a few efficient synthetic processes, it is already known that a γ-ketoester can be synthesized at a stroke by treating furfuryl alcohol with hydrogen chloride in an alcohol.  For example, Non-patent Document 8 discloses an example of reacting furfuryl alcohol in methanol or ethanol.  However, a γ-ketoester can be obtained only in a very low yield of 29 to 36% by this technique.  In other words, synthesis of a γ-ketoester with high efficiency has not yet been achieved by conventional techniques. 
Further, a substituted cyclopentenone represented by the following formula (15) is a useful compound as a precursor for producing a substituted cyclopentanone according to the present invention.  Non-patent Document 5 is known as a process for producing this compound. 

This production process has a step in which succinic acid is reacted with an acid chloride using aluminum chloride as a catalyst and nitromethane as a solvent.  However, this step has a serious problem for the industrial implementation thereof.  First, the yield is as low as 50%.  In addition, this step requires a large amount of aluminum chloride and an acid chloride, which are difficult in handling due to fuming properties and corrosive properties, that is, 2.4 times by mole and 4 times by mole, respectively, relative to the amount of succinic acid as a raw material.  This is not only the problem of production such as a difficulty in operation at the time of charging these compounds and corrosion of reactor materials but also the problem of environmental protection in that a large amount of aluminum-based and chloride-based wastes are discharged after reaction.  Moreover, there is also a problem that since nitromethane which is used as a solvent is an explosive substance, a particular safety measure is required for using the same in an industrial scale.  As described above, in conventional techniques, there is no process for safely and efficiently producing a substituted cyclopentenone represented by the above formula (15) in an industrial scale. 
A 1,3-cyclopentanediones having a structure with a trans-double bond in a side chain, represented by the following formula (17), is a useful compound as an intermediate for producing a substituted cyclopentanone according to the present invention. 

For synthesizing this compound by conventional techniques, there can be mentioned, for example, a process in which a halide having an allyl group in which the double bond is in trans configuration, represented by the following formula (40):
(wherein R25 represents the meaning described below; and X represents a halogen atom) is allowed to react with 1,3-cyclopentanedione in the presence of a base.  However, according to this process, it is necessary to stereoselectively synthesize a halide represented by the above formula (40) beforehand.  This involved, for example, a problem that a complicated process is required such that the triple bond of a compound represented by the following formula (41):
(wherein R25 represents the meaning described below) is hydrogenated with sodium in liquid ammonia, followed by conversion of the alcohol to halogen.  In other words, simple production of a 1,3-cyclopentanedione having a trans-double bond in a side chain, represented by the above formula (17), has not yet been achieved by conventional techniques. 
If the trans-double bond in the side chain of a compound represented by the following formula (18) could be selectively converted to an oxirane (epoxidation) to synthesize a compound represented by the following formula (19), the double bond in the side chain would be protected.  Furthermore, if the oxirane ring could be converted to a diol by its cleavage to the anti-type, the technique may provide a clue to the introduction of a cis-double bond.  This could be very useful for the synthesis of a substituted cyclopentanone such as a jasmine fragrance.  However, such a technique has not yet been disclosed. 


Methylcyclopentenones such as cis-jasmone and dihydrojasmone occupy an important position among jasmine fragrances, and a large number of production processes have been reported.  Many of these processes are based on an intramolecular aldol reaction of a 1,4-diketone.  For example, a large number of examples such as Patent Documents 5 and 6 and Non-patent Document 9 are known.  According to these processes, specific methylcyclopentenones can be produced.  However, since these processes are uniquely specialized in the production of these specific methylcyclopentenones, it is difficult to produce other useful fragrances by using these processes.  In the fragrance industry, it is indispensable that many types of fragrance can be produced freely, and a production process specialized in one fragrance material as described above is very inefficient.  For example, it is practically impossible to derivatively obtain jasmonates which are especially useful and have a large demand in jasmine fragrance by using these processes, and a totally different production process must be adopted to produce these esters.  Therefore, there was a difficulty in that unreasonableness and disadvantageousness arise in supply of production equipment and raw materials and the like.  In other words, conventional techniques have not yet achieved derivative production of jasmonates and methylcyclopentenones, both of which occupy important positions in the field of jasmine fragrance, through the same synthetic route. 
There are many reports on the production process of γ-lactones, and many of them are on the production of γ-lactones from an alcohol and an acrylic acid derivative by radical addition with an organic peroxide and the like.  For example, there is known a process in which an acrylic acid derivative is allowed to react with an alcohol in the presence of di-t-butyl peroxide and zinc halide (Patent Document 7).  However, γ-lactones produced by this process generally had a serious drawback in that they had a plastic-like flavor and sourness and their original good fruity or floral fragrance was impaired.  Various purification processes to improve such a drawback had been disclosed, but none of them was perfect.  Further, there was also a difficulty in that an organic peroxide such as di-t-butyl peroxide was a dangerous substance having explosiveness and required special measures for the handling thereof.  Thus, development of a fundamentally different production process of γ-lactones has been strongly desired.     [Patent Document 1] Japanese Patent Laid-Open No.  2002-69477    [Patent Document 2] Japanese Patent Laid-Open No.  54-90155    [Patent Document 3] National Publication of International Patent Application No.  10-513402    [Patent Document 4] Japanese Patent Laid-Open No.  62-87555    [Patent Document 5] Japanese Patent Publication No.  45-24771    [Patent Document 6] Japanese Patent Laid-Open No.  49-75555    [Patent Document 7] Japanese Patent Laid-Open No.  4-54177    [Non-patent Document 1] Motoichi Indo, “Gosei Koryo (Synthetic Perfume)”, published by The Chemical Daily Co., Ltd., Mar. 22, 2005, amended and revised edition, p. 677    [Non-patent Document 2] Motoichi Indo, “Gosei Koryo (Synthetic Perfume)”, published by The Chemical Daily Co., Ltd., Mar. 22, 2005, amended and revised edition, p. 676    [Non-patent Document 3] Edited by The Chemical Society of Japan, “Aji-to Nioi-no Bunshi Ninshiki (Molecular Recognition of Taste and Odor)”, published by Japan Scientific Societies Press, Apr. 10, 2000, p. 168    [Non-patent Document 4] Synthesis, 479 (1989)    [Non-patent Document 5] Zhou Jingyao, Lin Guomei Sun Wei Sun Jing, “Youji Huaxue”, 1985, No.  6, p. 491    [Non-patent Document 6] Chem.  Pharm.  Bull.  13, 1359 (1965)    [Non-patent Document 7] Collect.  Czech.  Chem.  Commun.  42, 998 (1977)    [Non-patent Document 8] Studia Universitatis Babes-Bolyai, Chemia, 19 (2), 26 (1974)    [Non-patent Document 9] J. Org.  Chem.,  31, 977 (1966)