separated due to which the intermediate s 4 4 hydrazinobenzyl 1 3 oxazolidin 2 one of formula iii of desired purity could be isolated this helped in lowering the consumption of n n dimethylamino butyraldehyde diethyl acetal iv in the final step to give zolmitriptan i of high purity having impurity levels conforming to regulatory specifications in an embodiment s 4 4 aminobenzyl 1 3 oxazolidin 2 one of formula ii which was prepared using prior art methods was treated with an aqueous solution of sodium nitrite in concentrated hydrochloric acid at u2212 5 to 10 u00b0 c after completion of reaction based on hplc the resulting diazonium salt was treated with stannous chloride in hydrochloric acid at u2212 15 to 10 u00b0 c to give s 4 4 hydrazinobenzyl 1 3 oxazolidin 2 one of formula iii after completion of the reaction based on hplc the ph of the reaction mass was adjusted in the range of 2 0 to 6 0 using aqueous sodium hydroxide solution the resulting reaction mixture was stirred cooled and filtered to separate the impurities the filtrate was optionally washed with an organic solvent such as dichloromethane and further treated with aqueous sodium hydroxide solution till a ph range of 6 0 to 10 0 was attained the reaction mass was stirred cooled and filtered to give s 4 4 hydrazinobenzyl 1 3 oxazolidin 2 one iii of desired purity it is pertinent to note.