Preheat the oven to 350°. In a heavy 14-inch skillet, combine the sugar, light corn syrup, water and vanilla bean and seeds and bring to a boil, stirring to dissolve the sugar. Cook over moderate heat without stirring, gently swirling the syrup in the skillet occasionally and washing down the side of the skillet with a wet pastry brush, until a medium-light amber caramel forms, about 10 minutes. Off the heat, stir in the butter. Add the sliced quince and cook over moderately low heat, stirring occasionally with a nonstick rubber spatula, until softened, about 5 minutes. Let the quince cool slightly. Evenly distribute the quince slices over the bottom of the skillet or, for a neater appearance, carefully arrange them in concentric circles.