Preparation of Zopiclone and its enantiomerically enriched isomer
Present invention relates to an improved process for the preparation of Zopiclone and its enantiomerically enriched isomer (Eszopiclone). 6-(5-Chloropyridin-2-yl)-5-hydroxy-7-oxo-5,6-dihydropyrrolo[3,4-b]pyrazine is reacted with 1-chloro-carbonyl-4-methylpiperazine in the presence of alkali earth metal carbonates, hydroxides or oxides in a solvent medium to give Zopiclone. It is reacted with optically active acid in a mixture of water and water miscible organic solvent followed by work up to give Eszopiclone. The present invention also relates to process for the conversion of (R) or (S) Zopiclone to 6-(5-chloropyrid-2-yl)-5-hydroxy-7-oxo-5,6-dihydro-pyrrolo-[3,4-b]-pyrazine of the intermediate which can be converted to racemic Zopiclone.
1. A process for the preparation of racemic Zopiclone, comprising the step of condensing 6-(5-chloropyrid-2-yl)-5-hydroxy-7-oxo-5,6-dihydropyrrolo[3,4-b]pyrazine with 1-chlorocarbonyl-4-methylpiperazine in the presence of dimethylaminopyridine, and at least one alkaline earth metal carbonate, hydroxide or oxide in a solvent medium to give racemic Zopiclone.
2. A process for the preparation of racemic Zopiclone according to claim 1 , wherein the alkaline earth metal carbonate is selected from the, group consisting of magnesium carbonate and calcium carbonate; the alkaline earth metal hydroxide is selected from the group consisting of magnesium hydroxide and calcium hydroxide; and the alka inc earth metal oxide is selected from the group consisting of magnesium oxide calcium oxide.
3. A process for the preparation of racemic Zopiclone according to claim 1 , wherein the solvent is selected from the group consisting of toluene, dichloromethane, dichloroethane, ethyl acetate, tetrahydrofuran, N,N′-dimethylformamide, N,N′-dimethylacetamide, dimethyl sulfoxide and mixtures thereof.
4. A process for the preparation of enantiomerically enriched Zopiclone, comprising the steps of:
(a) condensing 6-(5-chloropyrid-2-yl)-5-hydroxy-7-oxo-5,6-dihydropyrrolo[3,4-b]pyrazine with 1-chlorocarbonyl-4-methylpiperazine in the presence of dimethylaminopyridine and at least one alkaline earth metal carbonate, hydroxide or oxide in a solvent medium to give racemic Zopiclone, and
(b) reacting the obtained racemic Zopiclone with an optically active acid in a mixture of water and at least one water miscible organic solvent and recovering (R)-Zopiclone or (S)-Zopiclone.
5. A process for the preparation of (S)-Zopiclone according to claim 4 , wherein the at least one water miscible organic solvent is selected from the group consisting of ketones, nitriles and aprotic polar solvents.
6. A process for the preparation of (S)-Zopiclone according to claim 5 , wherein the ketone solvent is acetone, the nitrile solvent is selected from the group consisting of acetonitrile and propionitrile, and the aprotic polar solvent is selected from the group consisting of N,N′-dimethylformamide, N,N′-dimethylacetamide, and dimethyl sulfoxide.
7. A process for the preparation of (S)-Zopiclone according to claim 4 , wherein the optically active acid is selected from the group consisting of D-(+)-O,O′-dibenzoyltartaric acid, D-(+)-O,O′-p-toluyldibenzoyltartaric acid, and D-(+)-mandelic acid.