In a 12-inch skillet, combine the sugar and water. Cook over moderately high heat, swirling the pan occasionally, until a light-amber caramel forms, about 5 minutes. Remove from the heat. Add the red wine syrup along with the butter and liqueur and cook to dissolve the hardened caramel, about 1 minute. Add the pear halves to the skillet and cook over low heat, turning occasionally, until the pears are tender and the pan juices are syrupy, about 20 minutes. Arrange the pears cut side up in the skillet with the thin ends pointing toward the center. Let cool for 30 minutes.