Kind of Random, but a famous Sonic game hacker by the name of Stealth made a hack to port a concept level of Sonic CD to the regular Genesis. It's only the first stage, with only one time zone, and no music. But the graphics, sound effects, and level design of Palmtree Panic present Act 1 is fully intact. It was pretty amazing actually. He did it for Sonic Retro (a Sonic community). I can't link you to the rom since it's illegal (and I don't know if it works anymore anyways) so I'm sorry. If you search, the site though you may find out where to get it.
Anyways, it was just a concept hack he released with his OTHER concept port of the original Sonic 1 to GBA. It was pretty cool for a concept though. Shame he never followed up on it as it would have been neat to have Sonic CD for the regular Genesis.