4-Oxy-cyclopent-2-en-1-one derivative, a prostaglandin intermediate, and the process for its preparation

A process for the preparation of compounds of the general formula:

• ##STR21## wherein R.sup.x represents hydrogen or a removable alcohol protecting group selected from the group consisting of substituted silyl, alkoxyalkyl, tetrahydrofuran-2-yl and tetrahydropyran-2-yl;
• and R.sup.y represents halogen, an alkyl thio group, a dialkyl amino group, or a group of the formula R.sup.2, and R.sup.2 represents a straight- or branched-chain alkyl, alkenyl or alkynyl group which may optionally be substituted by one or more carboxyl, carboxylic acid ester, or free or protected hydroxy, thiol, aldehyde or keto groups, wherein the protected groups are selected from lower alkyl ethers and thio ethers, hydroxyl groups protected with substituted silyl, alkoxyalkyl, tetrahydrofuran-2-yl or tetrahydropyran-2-yl, non-cyclic or cyclic acetals and ketals and their thio analogues;
• with the proviso that R.sup.x is not hydrogen when R.sup.y is R.sup.2, said process comprising:
• (a) partial dehalogenation of a compound of the general formula II ##STR22## wherein Hal represents halogen, and R.sup.x is as defined above, to produce a compound of the general formula Ia:
• ##STR23## wherein Hal and R.sup.x are as defined above;
• (b) protection of the hydroxyl substituent of a compound of the general formula Ia as defined above, in which R.sup.x represents hydrogen to produce a compound of the general formula Ib;
• ##STR24## wherein Hal is as defined above and R.sup.1 represents a protective group;
• (c) replacement of the halogen substituent of a compound of the general formula Ib as defined above, to produce a compound of the general formula Ic:
• ##STR25## wherein R.sup.4 represents a substituted thio group or a disubstituted amino group and R.sup.1 represents a protecting group;
• and
• (d) reaction of a compound of the general formula Ib as defined above or of a compound of the general formula Ic as defined above in a conjugate addition-elimination reaction to produce a compound of the general formula Id:
• ##STR26## wherein R.sup.1 represents a protecting group and R.sup.2 is as defined above.

Compounds of the general formula I:

• ##STR28## wherein A represents O;
• R.sup.x represents hydrogen or a removable alcohol protecting group selected from the group consisting of substituted silyl, alkoxyalkyl, tetrahydrofuran-2-yl and tetrahydropyran-2-yl;
• and R.sup.y represents halogen, an alkyl thio group, a dialkyl amino group, or a group of the formula R.sup.2, and R.sup.2 represents a straight-or branched-chain alkynyl group which may optionally be substituted by one or more carboxyl, carboxylic acid ester, or free or protected hydroxy, thiol, aldehyde or keto groups wherein the protected groups are selected from lower alkyl ethers and thio ethers, hydroxyl groups protected with substituted silyl, alkoxyalkyl, tetrahydrofuran-2-yl or tetrahydropyran-2-yl, non-cyclic or cyclic acetals and ketals and their thio analogues;
• with the proviso that R.sup.x is not hydrogen when A is O and R.sup.y is R.sup.2.