NOVELTY - Preparation (M1) of Raltegravir (I) involves: hydrogenating 2-(1-benzyloxycarbonylamino-1-methyl-ethyl)-5-(2,2-dimethyl-propionyloxy)-1-methyl-6-oxo-1,6-dihydro-pyrimidine-4-carboxylic acid methyl ester (II) to produce 2-(1-amino-1-methyl-ethyl)-5-(2,2-dimethyl-propionyloxy)-1-methyl-6-oxo-1,6-dihydro-pyrimidine-4-carboxylic acid methyl ester (III) or its salt, acetylating the compound (III) with 5-methyl-(1,3,4)oxadiazole-2-carboxylic acid (IV), or its reactive derivative to produce corresponding ester (V), hydrolyzing to ester, reacting the ester with 4-fluorobenzylamine.    USE - For preparation of Raltegravir (claimed) which is used as antiretroviral drug used to treat HIV infection.    ADVANTAGE - The method use reagents that are less expensive or easier to handle, consume smaller amounts of reagents, provide a higher yield of product, involve fewer steps, have smaller or more eco-friendly waste products, or provide a product of higher purity; is cost effective and commercially viable process for the preparation of Raltegravir; is a simple and cost effective for preparing N-substituted hydroxypyrimidinone carboxamide derivative with high purity and good yield on a commercial scale.    DETAILED DESCRIPTION - Preparation (M1) of Raltegravir of formula (I) involves: either i) hydrogenating 2-(1-benzyloxycarbonylamino-1-methyl-ethyl)-5-(2,2-dimethyl-propionyloxy)-1-methyl-6-oxo-1,6-dihydro-pyrimidine-4-carboxylic acid methyl ester of formula (II) to produce 2-(1-amino-1-methyl-ethyl)-5-(2,2-dimethyl-propionyloxy)-1-methyl-6-oxo-1,6-dihydro-pyrimidine-4-carboxylic acid methyl ester of formula (III) or its salt, ii) acetylating the compound (III) with 5-methyl-(1,3,4)oxadiazole-2-carboxylic acid of formula (IV), or its reactive derivative to produce 5-(2,2-dimethyl-propionyloxy)-1-methyl-2-(1-methyl-1-((5-methyl-(1,3,4)oxadiazole-2-carbonyl)-amino)-ethyl)-6-oxo-1,6-dihydro-pyrimidine-4-carboxylic acid methyl ester of formula (V), iii) hydrolyzing the compound (V) to 5-hydroxy-1-methyl-2-(1-methyl-1-((5-methyl-(1,3,4)oxadiazole-2-carbonyl)-amino)-ethyl)-6-oxo-1,6-dihydro-pyrimidine-4-carboxylic acid methyl ester of formula (VI), iv) reacting the compound (VI) with 4-fluorobenzylamine to produce Raltegravir (I); or ia) hydrogenating 2-(1-benzyloxycarbonylamino-1-methyl-ethyl)-5-hydroxy-1-methyl-6-oxo-1,6-dihydro-pyrimidine-4-carboxylic acid 4-fluoro-benzyl ester of formula (IIa), to produce 2-(1-amino-1-methyl-ethyl)-5-hydroxy-1-methyl-6-oxo-1,6-dihydro-pyrimidine-4-carboxylic acid 4-fluoro-benzylamidecompound of formula (IIIa), its hydrate or solvate, (iia) acetylating the compound (IIIa) with the compound (IV), or its reactive derivative to produce Raltegravir (I).