Melt butter in a saucepan over medium heat; stir ketchup and brown sugar into melted butter, stirring to dissolve brown sugar. Whisk cornstarch into vinegar until smooth; pour into pan. Whisk constantly and add salt, soy sauce, and Worcestershire sauce to mixture; bring to a simmer. Cook until thickened, about 2 minutes. Stir pineapple into sauce.
Arrange chicken pieces in a 9x13-inch baking dish; pour pineapple sauce over chicken.
Bake until sauce is bubbling, chicken is browned, and the juices run clear, about 45 minutes. An instant-read meat thermometer inserted into the thickest part of a thigh should read at least 160 degrees F (70 degrees C).
