bash aliases and command chaining with ; (semi-colon)

What am I doing wrong here? Or is this not possible?
A bug?

alias f='find . >found 2>/dev/null &'

f ; sleep 20 ; ls -l
-bash: syntax error near unexpected token `;'

Just use parenthesis, if you want to run a command in the background:

alias f='(find . >found 2>/dev/null &)'
f ; sleep 20 ; ls -l

That did it, thanks.