Intermediates for the preparation of pramipexole

A compound of formula (I) or of formula (II), as a single (R) or (S) enantiomer, or a salt thereof,

• wherein R is a protected amino group;
• R1 is straight or branched C1-C6 alkyl optionally substituted by phenyl;
• and the asterisk * indicates the stereogenic carbon atom;
• or a compound of formula (II), as a mixture of (R,S) enantiomers, or a salt thereof, wherein, R and the asterisk * being as defined above, R1 is straight or branched C1-C6 alkyl substituted by phenyl.

A compound as racemic (R,S) mixture, or a salt thereof, which is selected from:

• 2-acetylamino-4,5,6,7-tetrahydro-benzoth iazole-6-carboxylic acid;
• 2-propionylamino-4,5,6,7-tetrahydro-benzothiazole-6-carboxylic acid;
• 2-acetylamino-4,5,6,7-tetrahydro-benzothiazole-6-carboxylic acid methyl ester;
• 2-acetylamino-4,5,6,7-tetrahydro-benzothiazole-6-carboxylic acid ethyl ester;
• 2-acetylamino-4,5,6,7-tetrahydro-benzothiazole-6-carboxylic acid propyl ester;
• 2-propionylamino-4,5,6,7-tetrahydro-benzothiazole-6-carboxylic acid methyl ester;
• 2-propionylamino-4,5,6,7-tetrahydro-benzothiazole-6-carboxylic acid ethyl ester;
• and
• 2-propionylamino-4,5,6,7-tetrahydro-benzothiazole-6-carboxylic acid propyl ester.

A process for the preparation of pramipexole, or a pharmaceutically acceptable salt thereof, comprising the acylation of a compound of formula (VIl), either as the single (S) enantiomer or as mixture of (R,S) enantiomers

• wherein R3 is hydrogen and Ra is a free or protected amino group, by reaction with propionic anhydride, and subsequent reduction of the resulting compound of formula (IX)
• wherein Ra is as defined above, by treatment with an alkali metal borohydride and molecular iodine, to obtain a compound of formula (VII)
• wherein R3 is hydrogen and Ra is as defined above;
• followed, if necessary, by deprotection of the primary amino group and/or by resolution of the mixture of (R,S) enantiomers into the single (S) enantiomer and, if desired, by conversion of pramipexole to a pharmaceutically acceptable salt thereof.