convert accented character to base character

I want to convert accented characters to the according base character, e.g. "Ü" or "Ú" to "U".

Is there a way to do this with pgsql functions?

  postgres=# select convert('Ü', 'UTF8', 'SQL_ASCII');

   convert

  ----------

   \303\234

did not work as I had hoped.

Any help would be appreciated -

Cheers, Joachim