Take a look at the output from this tar command which just lists the contents of the archive.

Code:

tar tzf filename.tar.gz
# Or possilbly with the verbose switch
tar tvzf filename.tar.gz

If you run this and save the output, before running the tar xzf you have a file containing the name of the directory.
This is a general answer because we don't know anything about your Operating System or your Shell. All I can say is that the code posted is a syntax error in every Bourne-type Shell. There is much variation in the tar command.