The present invention provides a process for preparing 2-(1,5,5-trimethyl-2-cyclopentenyl)ethyl acetate of the following formula (3), wherein Ac represents an acetyl group, the process comprising: subjecting a haloacetaldehyde alkyl 3,4,4-trimethyl-2-cyclopentenyl acetal compound of the following general formula (1), wherein R represents a linear or branched alkyl group having 1 to 4 carbon atoms, and Y represents a halogen atom, to a dehydrohalogenation reaction in the presence of a base, followed by a rearrangement reaction to obtain a (1,5,5-trimethyl-2-cyclopentenyl)acetate compound of the following general formula (2), wherein R is as defined above, and subjecting the alkoxycarbonylmethyl group (i.e., —CH.sub.2C(═O)OR) of the (1,5,5-trimethyl-2-cyclopentenyl)acetate compound (2) to a multi-step conversion to be converted into a 2-acetoxyethyl group (i.e., —CH.sub.2CH.sub.2OAc) to obtain 2-(1,5,5-trimethyl-2-cyclopentenyl)ethyl acetate (3).

##STR00001##

The present invention provides a process for preparing 2-(1,5,5-trimethyl-2-cyclopentenyl)ethyl acetate of the following formula (3), wherein Ac represents an acetyl group, the process comprising: subjecting a haloacetaldehyde alkyl 3,4,4-trimethyl-2-cyclopentenyl acetal compound of the following general formula (1), wherein R represents a linear or branched alkyl group having 1 to 4 carbon atoms, and Y represents a halogen atom, to a dehydrohalogenation reaction in the presence of a base, followed by a rearrangement reaction to obtain a (1,5,5-trimethyl-2-cyclopentenyl)acetate compound of the following general formula (2), wherein R is as defined above, and subjecting the alkoxycarbonylmethyl group (i.e., —CH.sub.2C(═O)OR) of the (1,5,5-trimethyl-2-cyclopentenyl)acetate compound (2) to a multi-step conversion to be converted into a 2-acetoxyethyl group (i.e., —CH.sub.2CH.sub.2OAc) to obtain 2-(1,5,5-trimethyl-2-cyclopentenyl)ethyl acetate (3).

##STR00001##

The present invention provides a process for preparing a (1,2-dimethyl-3-methylenecyclopentyl)acetate compound of the following general formula (3), wherein R represents a linear or branched alkyl group having 1 to 4 carbon atoms, the process comprising subjecting a haloacetaldehyde alkyl 2,3-dimethyl-2-cyclopentenyl acetal compound of the following general formula (1), wherein R is as defined above, and Y represents a halogen atom, to a dehydrohalogenation reaction in the presence of a base, followed by a rearrangement reaction to obtain a (1,2-dimethyl-2-cyclopentenyl)acetate compound of the following general formula (2), wherein R is as defined above, and subjecting the (1,2-dimethyl-2-cyclopentenyl)acetate compound (2) to an epoxidation reaction, followed by an isomerization reaction and then a methylenation reaction to obtain the (1,2-dimethyl-3-methylenecyclopentyl)acetate compound of the following general formula (3). The present invention also provides a process for preparing (1,2-dimethyl-3-methylenecyclopentyl)acetaldehyde of the following formula (4), the process comprising the aforesaid process for preparing the (1,2-dimethyl-3-methylenecyclopentyl)acetate compound (3), and converting an alkoxycarbonylmethyl group (i.e., —CH.sub.2C(═O)OR) of the (1,2-dimethyl-3-methylenecyclopentyl)acetate compound (3) to a formylmethyl group (i.e., —CH.sub.2CHO) to obtain (1,2-dimethyl-3-methylenecyclopentyl)acetaldehyde (4).

##STR00001##

The present invention provides a process for preparing a (1,2-dimethyl-3-methylenecyclopentyl)acetate compound of the following general formula (3), wherein R represents a linear or branched alkyl group having 1 to 4 carbon atoms, the process comprising subjecting a haloacetaldehyde alkyl 2,3-dimethyl-2-cyclopentenyl acetal compound of the following general formula (1), wherein R is as defined above, and Y represents a halogen atom, to a dehydrohalogenation reaction in the presence of a base, followed by a rearrangement reaction to obtain a (1,2-dimethyl-2-cyclopentenyl)acetate compound of the following general formula (2), wherein R is as defined above, and subjecting the (1,2-dimethyl-2-cyclopentenyl)acetate compound (2) to an epoxidation reaction, followed by an isomerization reaction and then a methylenation reaction to obtain the (1,2-dimethyl-3-methylenecyclopentyl)acetate compound of the following general formula (3). The present invention also provides a process for preparing (1,2-dimethyl-3-methylenecyclopentyl)acetaldehyde of the following formula (4), the process comprising the aforesaid process for preparing the (1,2-dimethyl-3-methylenecyclopentyl)acetate compound (3), and converting an alkoxycarbonylmethyl group (i.e., —CH.sub.2C(═O)OR) of the (1,2-dimethyl-3-methylenecyclopentyl)acetate compound (3) to a formylmethyl group (i.e., —CH.sub.2CHO) to obtain (1,2-dimethyl-3-methylenecyclopentyl)acetaldehyde (4).

##STR00001##

The present invention relates to a process for preparing a (1S,2R)-(2-hydroxy-3,5,5-trimethyl-3-cyclopentenyl)methyl carboxylate compound of the following general formula (S,R)-(2), wherein R.sup.1 represents a monovalent hydrocarbon group having 1 to 6 carbon atoms, and a bold wedged bond represents the absolute configuration, and a (1R,2S)-(2-acetoxy-3,5,5-trimethyl-3-cyclopentenyl)methyl carboxylate compound of the following general formula (R,S)-(3), wherein R.sup.1 is as defined above, a hashed wedged bond represents the absolute configuration, and Ac represents an acetyl group, the process comprising: subjecting a (1RS,2SR)-(2-hydroxy-3,5,5-trimethyl-3-cyclopentenyl)methyl carboxylate compound of the following general formula (RS,SR)-(2), wherein R.sup.1 is as defined above, and a hashed unwedged bond represents a relative configuration, to a kinetic resolution reaction with a lipase in the presence of vinyl acetate to obtain the (1S,2R)-(2-hydroxy-3,5,5-trimethyl-3-cyclopentenyl)methyl carboxylate compound ((S,R)-(2)) and the (1R,2S)-(2-acetoxy-3,5,5-trimethyl-3-cyclopentenyl)methyl carboxylate compound ((R,S)-(3)).

##STR00001##

The present invention relates to a process for preparing a (1S,2R)-(2-hydroxy-3,5,5-trimethyl-3-cyclopentenyl)methyl carboxylate compound of the following general formula (S,R)-(2), wherein R.sup.1 represents a monovalent hydrocarbon group having 1 to 6 carbon atoms, and a bold wedged bond represents the absolute configuration, and a (1R,2S)-(2-acetoxy-3,5,5-trimethyl-3-cyclopentenyl)methyl carboxylate compound of the following general formula (R,S)-(3), wherein R.sup.1 is as defined above, a hashed wedged bond represents the absolute configuration, and Ac represents an acetyl group, the process comprising: subjecting a (1RS,2SR)-(2-hydroxy-3,5,5-trimethyl-3-cyclopentenyl)methyl carboxylate compound of the following general formula (RS,SR)-(2), wherein R.sup.1 is as defined above, and a hashed unwedged bond represents a relative configuration, to a kinetic resolution reaction with a lipase in the presence of vinyl acetate to obtain the (1S,2R)-(2-hydroxy-3,5,5-trimethyl-3-cyclopentenyl)methyl carboxylate compound ((S,R)-(2)) and the (1R,2S)-(2-acetoxy-3,5,5-trimethyl-3-cyclopentenyl)methyl carboxylate compound ((R,S)-(3)).

##STR00001##

The present invention provides processes for preparing an α-necrodyl compound of the following general formula (3): wherein R.sup.2 represents a monovalent hydrocarbon group having 1 to 9 carbon atoms, the process comprising: subjecting a 3, 5, 5-trimethyl-3-cyclopentene compound of the following general formula (1): wherein R.sup.2 is as defined above, and X represents a leaving group, to a nucleophilic substitution reaction with a methylating agent of the following general formula (2): wherein M represents Li, MgZ.sup.1, ZnZ.sup.1, Cu, CuZ.sup.1, or CuLiZ.sup.1, and Z.sup.1 represents a halogen atom or a methyl group, to form the α-necrodyl compound (3). The present invention further provides processes for preparing γ-necrodyl compounds of the following general formula (4): wherein R.sup.2 represents a monovalent hydrocarbon group having 1 to 9 carbon atoms, the process comprising: subjecting the α-necrodyl compound (3) thus obtained to a positional isomerization reaction at the double bond to form the γ-necrodyl compound (4). ##STR00001##

The present invention provides processes for preparing an α-necrodyl compound of the following general formula (3): wherein R.sup.2 represents a monovalent hydrocarbon group having 1 to 9 carbon atoms, the process comprising: subjecting a 3, 5, 5-trimethyl-3-cyclopentene compound of the following general formula (1): wherein R.sup.2 is as defined above, and X represents a leaving group, to a nucleophilic substitution reaction with a methylating agent of the following general formula (2): wherein M represents Li, MgZ.sup.1, ZnZ.sup.1, Cu, CuZ.sup.1, or CuLiZ.sup.1, and Z.sup.1 represents a halogen atom or a methyl group, to form the α-necrodyl compound (3). The present invention further provides processes for preparing γ-necrodyl compounds of the following general formula (4): wherein R.sup.2 represents a monovalent hydrocarbon group having 1 to 9 carbon atoms, the process comprising: subjecting the α-necrodyl compound (3) thus obtained to a positional isomerization reaction at the double bond to form the γ-necrodyl compound (4). ##STR00001##

The present invention provides a process for preparing a (1,2-dimethyl-3-methylenecyclopentyl)acetate compound of the following general formula (3), wherein R represents a linear or branched alkyl group having 1 to 4 carbon atoms, the process comprising subjecting a haloacetaldehyde alkyl 2,3-dimethyl-2-cyclopentenyl acetal compound of the following general formula (1), wherein R is as defined above, and Y represents a halogen atom, to a dehydrohalogenation reaction in the presence of a base, followed by a rearrangement reaction to obtain a (1,2-dimethyl-2-cyclopentenyl)acetate compound of the following general formula (2), wherein R is as defined above, and subjecting the (1,2-dimethyl-2-cyclopentenyl)acetate compound (2) to an epoxidation reaction, followed by an isomerization reaction and then a methylenation reaction to obtain the (1,2-dimethyl-3-methylenecyclopentyl)acetate compound of the following general formula (3). The present invention also provides a process for preparing (1,2-dimethyl-3-methylenecyclopentyl)acetaldehyde of the following formula (4), the process comprising the aforesaid process for preparing the (1,2-dimethyl-3-methylenecyclopentyl)acetate compound (3), and converting an alkoxycarbonylmethyl group (i.e., —CH.sub.2C(═O)OR) of the (1,2-dimethyl-3-methylenecyclopentyl)acetate compound (3) to a formylmethyl group (i.e., —CH.sub.2CHO) to obtain (1,2-dimethyl-3-methylenecyclopentyl)acetaldehyde (4). ##STR00001##

The present invention provides a process for preparing a (1,2-dimethyl-3-methylenecyclopentyl)acetate compound of the following general formula (3), wherein R represents a linear or branched alkyl group having 1 to 4 carbon atoms, the process comprising subjecting a haloacetaldehyde alkyl 2,3-dimethyl-2-cyclopentenyl acetal compound of the following general formula (1), wherein R is as defined above, and Y represents a halogen atom, to a dehydrohalogenation reaction in the presence of a base, followed by a rearrangement reaction to obtain a (1,2-dimethyl-2-cyclopentenyl)acetate compound of the following general formula (2), wherein R is as defined above, and subjecting the (1,2-dimethyl-2-cyclopentenyl)acetate compound (2) to an epoxidation reaction, followed by an isomerization reaction and then a methylenation reaction to obtain the (1,2-dimethyl-3-methylenecyclopentyl)acetate compound of the following general formula (3). The present invention also provides a process for preparing (1,2-dimethyl-3-methylenecyclopentyl)acetaldehyde of the following formula (4), the process comprising the aforesaid process for preparing the (1,2-dimethyl-3-methylenecyclopentyl)acetate compound (3), and converting an alkoxycarbonylmethyl group (i.e., —CH.sub.2C(═O)OR) of the (1,2-dimethyl-3-methylenecyclopentyl)acetate compound (3) to a formylmethyl group (i.e., —CH.sub.2CHO) to obtain (1,2-dimethyl-3-methylenecyclopentyl)acetaldehyde (4). ##STR00001##