Preheat the oven to 350 degrees F. In a bowl, blend vinegar, chili sauce, Worcestershire sauce, and tomato paste. Mix in the onion, brown sugar, and cayenne pepper.
Spray a skillet with nonstick cooking spray and heat over medium heat. Saute the chicken thighs on both sides until browned.
Remove from heat, drain, and arrange in a medium baking dish. Cover with cider vinegar mixture.
Bake 40 minutes or until the internal cooking temperature measures 165 degrees F.