Process for preparing optically active cyclopentenones

A process for preparing 3-hydroxycyclopentenone [IX] and/or racemic 4-hydroxycyclopentenone of the formulae:

• ##STR27## wherein R is a C.sub.1 -C.sub.6 alkyl and the symbol .chi. means a double bond or triple bond, which comprises the steps of
• (a) reacting a diester of the formula:
• ##STR28## wherein R and the symbol .chi. are as defined above, with an alkaline earth metal hydroxide, followed by decomposing the product with an acid to give a half ester of the formula:
• ##STR29## wherein R and the symbol.chi. are as defined above, (b) reacting the half ester [VI] with furan in the presence of an acid anhydride of the formula:
• (XYCHCO).sub.2 O [XIII]
• wherein X and Y are the same or different and are each hydrogen atom, chlorine atom, or bromine atom, provided that both X and Y are not simultaneously hydrogen atom, in the presence of a boron trifluoride or boron trifluoride complex catalyst, or reacting the half ester [VI] with furan in the presence of trifluoroacetic acid anhydride to give a furfuryl ketone of the formula:
• ##STR30## wherein R and the symbol .chi. are as defined above, (c) treating the furfuryl ketone [VII] with a reducing agent to give a furancarbinol of the formula:
• ##STR31## (d) treating the furancarbinol [VIII] in an aqueous solvent at pH 3.5-6 in the presence or absence of a catalyst,
• e) in case that the starting diester [II] has a triple bond as the symbol.chi. and the desired 3-hydroxycyclopentenone [IX] and/or racemic 4-hydroxycyclopentenone have a double bond as the symbol .chi. subjecting the product before the step (a) or after any step of a) to d) to partial hydrogenation in the presence of a catalyst.

A process for preparing a racemic 4-hydroxycyclopentenone of the formula:

• ##STR35## wherein R is a C.sub.1 -C.sub.6 alkyl and the symbol .chi. means double bond or triple bond, which comprises the steps of
• (a) reacting a diester of the formula:
• ##STR36## wherein R and the symbol .chi. are as defined above, with an alkaline earth metal hydroxide, followed by decomposing the product with an acid to give a half ester of the formula:
• ##STR37## wherein R and the symbol .chi. are as defined above, (b) reacting the half ester [VI] with furan in the presence of an acid anhydride of the formula:
• (XYCHCO).sub.2 O [XIII]
• wherein X and Y are the same or different and are each hydrogen atom, chlorine atom, or bromine atom, provided that both X and Y are not simultaneously hydrogen atom, in the presence of a boron trifluoride or boron trifluoride complex catalyst, or reacting the half ester [VI] with furan in the presence of trifluoroacetic acid anhydride to give a furfuryl ketone of the formula:
• ##STR38## wherein R and the symbol .chi. are as defined above, (c) treating the furfuryl ketone [VII] with a reducing agent to give a furancarbinol of the formula:
• ##STR39## wherein R and the symbol .chi. are as defined above, (d) treating the furancarbinol [VIII] in an aqueous solvent at pH 3.5-6 in the presence or absence of a catalyst to give a 3-hydroxycyclopentenone [IX] and/or racemic 4-hydroxycyclopentenone of the formulae:
• ##STR40## wherein R and the symbol .chi. are as defined above, (e) subjecting the 3-hydroxycyclopentenone [IX] and/or racemic 4-hydroxycyclopentenone to
• 1) treatment in an aqueous solvent at pH 6-9, or treatment with chloral and an organic amine to convert into racemic 4-hydroxycyclopentenone, or
• 2-i) treatment with an aliphatic carboxylic acid of the formula:
• R.sub.1 'COOH [X']
• wherein R.sub.1 ' is a C.sub.1 -C.sub.5 alkyl having optionally a halogen substituent, an anhydride of the aliphatic carboxylic acid [X'] and a metal salt of the aliphatic carboxylic acid [X'] to give a cyclopentenone ester of the formula:
• ##STR41## wherein R, R.sub.1 ' and the symbol .chi. are as defined above, and 2-ii) treating the cyclopentenone ester [XI] with an alcohol of the formula:
• R--OH [XII]
• wherein R is as defined above, in the presence of an acid catalyst, and
• f) in case that the starting diester [II] has a triple bond as the symbol.chi. and the desired racemic 4-hydroxycyclopentenone has a double bond as the symbol.chi., subjecting the product before the step (a) or after any step of a) to e) to partial hydrogenation in the presence of a catalyst.