Like bash is trying to tell you: take out the parentheses.
convert front5.jpg -gravity north -pointsize 40 -fill '#ffffff' -background none label:'Hello World' -virtual-pixel transparent -distort Arc 320 -geometry +0+0 -composite front2.jpg
I grabbed a random jpg and tried this command on it and got a neat little text arc (that's a pretty cool effect by the way) on the result.
It also works if you escape the parens, but I can't find any noticeable difference in the result, so I'd just use the first one for simplicity.
convert front5.jpg \( -gravity north -pointsize 40 -fill '#ffffff' -background none label:'Hello World' -virtual-pixel transparent -distort Arc 320 \) -geometry +0+0 -composite front2.jpg