Pat chicken dry and sprinkle with pepper and 1 teaspoon salt. Heat butter in a 12-inch heavy skillet or a wide heavy pot over moderately high heat until foam subsides, then brown chicken in 2 batches, turning with tongs, about 5 minutes per batch. Transfer chicken as browned to a plate.
Return chicken, skin sides up, to skillet along with any juices accumulated on plate. Add wine and boil until reduced by half, about 4 minutes. Add water, tomatoes, cinnamon stick, remaining 3/4 teaspoon salt, and a large pinch of pepper and bring to a boil. Reduce heat to moderately low and cover skillet, then simmer 20 minutes.
Stir in prunes, vinegar, and sugar and simmer, covered, until chicken is cooked through, about 10 minutes. Transfer chicken with tongs to a shallow serving dish and keep warm, covered with foil. Boil pan juices, stirring occasionally, until thickened and reduced to about 1 1/2 cups, 8 to 10 minutes. Discard cinnamon stick and spoon sauce over chicken.
Cooks' nte: Chicken can be made 1 day ahead and cooled, uncovered, then chilled, covered. Reheat before serving.