Abstract: A process for preparation of montelukast or a salt thereof is provided, the process including reacting a late intermediate compound which is 2-[1-[1-R-3-[2-(7 chloro quinolin-2-yl) vinyl [phenyl]-3-[2-methoxy carbonyl phenyl]propyl sulfonyl methyl]cyclo propyl]acetic acid or a salt thereof with methyl magnesium chloride or methyl magnesium bromide in an organic solvent. In one embodiment, the process includes reacting an earlier intermediate compound which is methyl 2-(3-R-(3-(2-(7-chloro 2-quinolinyl)-ethenyl)-3 hydroxy propyl) benzoate with methane sulfonyl chloride or toluene sulfonyl chloride to obtain a mesylated or tosylated derivative of the earlier intermediate compound; followed by a reaction of the mesylated or tosylated derivative with 1-mercapto methyl cyclopropane acetic acid in a polar solvent in a presence of a base to obtain the late intermediate compound.

Abstract: A process for preparation of montelukast or a salt thereof is provided, the process including reacting a late intermediate compound which is 2-[1-[1-R-3-[2-(7 chloro quinolin-2-yl) vinyl [phenyl]-3-[2-methoxy carbonyl phenyl] propyl sulfonyl methyl] cyclo propyl] acetic acid or a salt thereof with methyl magnesium chloride or methyl magnesium bromide in an organic solvent. In one embodiment, the process includes reacting an earlier intermediate compound which is methyl 2-(3-R-(3-(2-(7-chloro 2-quinolinyl)-ethenyl)-3 hydroxy propyl) benzoate with methane sulfonyl chloride or toluene sulfonyl chloride to obtain a mesylated or tosylated derivative of the earlier intermediate compound; followed by a reaction of the mesylated or tosylated derivative with 1-mercapto methyl cyclopropane acetic acid in a polar solvent in a presence of a base to obtain the late intermediate compound.