If your name is on the contract the seller should be compelled to put your name on the deed. Easy answer, have your son sign the contract if he is the intended grantee in any case.
Your question raises several issues. First, yes you can pay for property that is deed in your son's name. You can contract to do this either by putting the contract in your son's name or by putting it in your name putting a provision in the contract that you have the right to assign your contractual interest. However, in either event, if you are putting your cash in property titled in your son's name to hide it from your creditors, the deed can be set aside and your creditors can take the house from your son. While your situation seems simple on its face, there may be hidden issues. You should consult an experienced real estate lawyer in your area to make sure that what you are planning to do is actually accomplished.
Disclaimer: This answer is provided for informational purposes only, does not constitute legal advice, and does not create an attorney-client relationship. Actual legal advice can only be provided after completing a comprehensive consultation in which all of the relevant facts are discussed and reviewed.
In addition to everything Attorney Deason has mentioned, you may also want to run that by your accountant to see if there are any gift tax issues in the transaction.
Carol Johnson Law Firm, P.A. : (727) 647-6645 : email@example.com : Wills, Trusts, Real Property, Probate, Special Needs: Information provided here is anecdotal and should not be relied upon or considered legal advice. Every matter is different and answers given here are general in nature and may not reflect current Florida law at the time you are reading this posting. Please contact me if you feel you need additional assistance with your matter.