Regular expression to remove the file extension

I have a simple workflow to rename the file and populate the Title field. When I am using the Name column when creating the Title it also adds the file extension. How can I get rid of it? Can you please provide a regular expression that could do it?  For example:

Convert This is some sample name.pdf TO This is some sample name

Convert MyFileName.040616.final.xlsx TO MyFileName.040616.final

Convert This is a test.doc.pdf TO This is a test.doc

Thanks!