How can I convert an AI file to a CDR file?
What version of CorelDRAW? What's the workflow? 

.CDR is a proprietary format, so I'm not aware of any proper supported exporters. The sK1 project reverse-engineered the format, and claims to have the best support. But since recent versions of CorelDRAW can import Adobe Illustrator CS4 files, I think you would get the best results to just save it as .ai and import it into CorelDRAW.