US9012650B2 - Substituted (3s, 11ar)-N-[(2,4-Difluorophenyl)methyl]-6-Oxy-3-Methyl-5,7-Dioxo-2,3,5,7,11,11a-Hexahydro[1,3]oxazolo[3,2-A]pyrido[1,2-D]pyrazine-8-Carboxamides of Formula (i) Useful as HIV Agents