Place oven rack in upper-middle position, about 5 inches from heating element and heat to 325 degrees.
Whisk ketchup, onion, Worcestershire, mustard, molasses, maple syrup, vinegar, chili powder, and cayenne in small bowl. Set aside.
Heat oil in an oven-proof skillet over high heat and season chicken with salt and pepper. Once pan begins to smoke, add chicken and cook 1 to 2 minutes per side, until lightly browned on each side. Transfer to a plate.
Add sauce mixture to skillet and simmer over medium heat for about 5 minutes, stirring frequently.
Take pan off heat and add chicken back to pan. Turn to coat well with sauce. Place in oven and cook 10 to 14 minutes. Set oven to broil and keep cooking until thickest part of chicken registers 160 degrees, 5 to 10 minutes. Watch chicken carefully during this portion. The sauce will burn if it is too close to the heating element.