Imitation cinnamon is primarly pure cinnamaldehyde, or a related chemical. That's chemically identical to what's found in cinnamon sticks and ground cinnamon, so you're not consuming anything you wouldn't also be getting from real cinnamon. It's what produces the piquancy (burn) of cinnamon, as well as the scent and flavor.
It's actually probably derived by extracting it from cinnamon bark (likely poor quality cinnamon bark that wouldn't taste good added to baked goods), though that can be labeled "natural" rather than "imitation". "Imitation" may indicate that some of the other flavor chemicals in it are synthesized, or that they will include some synthesized cinnamaldehyde if that turns out to be cheaper.
Natural cinnamon is made by dissolving cinnamon bark in a solvent like ethanol. Imitation cinnamon will also come with a solvent, with the same concentration of cinnamyl. It also contains a few hundred other chemicals, some of which are known, some of which are unknown, that are also dissolved from the bark.
If you buy a bottle of "imitation cinnamon" it will have at least some of those chemicals added in as well. The imitation versions have a more one-dimensional version of the taste, while the natural versions are more well-rounded. Adding in other chemicals tries to give it a less one-note taste.
For commercial flavors, like those added to candies, they'll use different sets of additional chemicals depending on their desired flavor profile, and the cost. More complex mixtures are more expensive to develop and make. Cheap candies tend to have just a few: their goal is to hit you with the heat and with a really obvious "this is cinnamon" effect.