A PROCESS FOR SYNTHESIZING DIOL (VIII)-AN INTERMEDIATE OF MONTELUKAST SODIUM

摘要

A process comprises preparing benzaldehyde of formula I in a conventional manner, reacting the said benzaldehyde I with Grignard reagent in water miscible etheral solvent to precipitate the alcohol of formula (II) by addition of ammonium salt and water followed by isolating the alcohol thus precipitated by any known methods and then oxidizing directly under 'Swern's conditions' to get a ketone of formula m, enolizing the said ketone in presence of a mild base such as alkali metal alkoxide and then reacting it with dialkyl carbonate under conditions effective to yield a β- ketoester of formula IV, benzylating the said β-ketoester so obtained in the preceding step to form the benzoate of formula V in presence of mild inorganic base followed by decarboxylating the said benzoate to a mixture of a ketoester of formula VI and its corresponding acid of formula VIA in the presence of acidic conditions, alkylating the acid VIA present in the mixture in the preceding step to obtain ketoester of formula VI and purifying it if so desired, asymmetrically reducing the ketoester of formula VI, to a chiral alcohol of formula VII using (-) diisopinocamphenylchloroborane (-DIPC1) in presence of less than 4 times v/w aprotic solvent and optionally in presence of Lewis base with respect to the said ketoester of formula VI, treating the said chiral alcohol VII with cerium halo salt, and alkylmagnesium halide followed by isolating the title compound using hyflow supercel and ammonium chloride to get the intermediate diol of formula VIII. Atemately, the said alcohol to Heck coupling with methyl-2-iodobenzoate in presence of Lewis base, acetonitrile, and palladium acetate to yield ketoester (VI), which is converted to diol (VIII) as described herein above.