(3S,11aR)-3-methyl-6-(methyloxy)-5,7-dioxo-2,3,5,7,11,11a- hexahydro[1,3]oxazolo [3,2-a]pyrido[1,2-d]pyrazine-8-carboxylic acid (100 gm) and carbonyl dimidazole (78.89 gm) was suspended in acetonitrile (1000 mL). The mixture was heated to 75°C and stirred for 1 hour. The resulting solution was cooled to a temperature of 20°C and treated with 2,4- difluorobenzyl amine solution (55.2 gm was dissolved in 200 mL of acetonitrile). The reaction mixture was maintained for 2 hours, concentrated, and the compound was extracted with ethyl acetate (1000 mL). Isopropyl alcohol (500 mL) was added at 40°C, stirred the reaction mass for 30 minutes at a temperature of 50°C, and cooled the reaction mass to 25°C. The reaction mixture was maintained for 8 hours at the same temperature. The product O-Methyl Dolutegravir was collected by filtration and dried under vacuum (85 gm).
