What is the best chemical cleaning agent clean tough stains out of a microwave other than vinegar, baking soda and lemon juice?
Bar Keepers friend is a powdered cleaning agent that contains oxalic acid as its main active ingredient, along with abrasives. It's great for removing many kitchen stains, including the polymerized oils that get baked onto pots and stovetops. 

Acetone (the nail polish remover you have been using) is highly flammable, and toxic, so should never be used anywhere near food.