| abstract |
A process for the preparation of an enantiomerically pure compound of the formula is given wherein R and R 'represent C1-C10alkyl, C2-C10alkenyl or C3-C10cycloalkyl, and the wedge marks represent (S) - or (R) -serochemistry, while the substituents are in compound (II) in a trans position. Conjugated addition is performed between an organometallic nucleophile giving the group R as defined above and (R) -4-acetoxycyclopent-2-o-1-one, (S) -4-acetoxycyclopent-2-1-one, or a similar compound wherein has been replaced by acetoxy with another leaving group, giving e.g. in the case of acetoxy compounds, the trans-3,4-disubstituted addition product of formula III or IV; The acetyl group is eliminated from the addition product to give (R) - or (S) -4-alkyl or 4-alkenyl cyclopent-2-1-one compound, which is then hydrogenated to give cyclopentanone of formula (I) or conjugated addition of another organometallic nucleophile to give the group R 'as defined above to the compound of the above formula can be carried out to give the trans-3,4-disubstituted addition product of formula (II). One of the above compounds can be converted, e.g. via intermediates (XV) - (XVIII) (where the substituents R and R 'and the wedge marks have the meanings given above) to the gabapentin analog, one of the formulas shown, wherein R and R' and the wedge marks have the meanings given above. |