Abstract: A process for preparation of gabapentin comprising a step of obtaining 1,1-cyclohexane diacetic acid monoamide from 1,1-cyclohexane diacetic acid anhydride, wherein said reaction is characterized by the use of ammonia precursor or pre-generated ammonia-isopropanol solution. The invention further discloses preparation of gabapentin and isolation of gabapentin in polymorphic Form II with high yield and purity.

Abstract: A one-pot industrial process for preparing 1,2,3,9-tetrahydro-9-methyl-3-[(2-methyl-1H-imidazole-1-yl)methyl]-4H-carbazol-4-one of Formula-(I) from 1,2,3,9-tetrahydro-9-methyl-4H-carbazol-4-one of Formula-(IV) involves reaction of Formula (IV) with HNR1R2 salt and paraformaldehyde, where R1,R2 are independently alkyl groups or together forms a cyclic alkyl group, in a solvent system of acetic acid and hydrocarbon solvent to form a crude mixture of intermediate compounds of Formula (III) and (VIII), which is converted to ondansetron (Formula (I)) without isolation by reaction with 2methyimidazole in a suitable solvent system in the same pot.