The problem lies in that you're assuming that the \1 is going to contain the contents of the first set of parentheses. It won't.
In a character class, metacharacters etc take on a different meaning. I believe in this case the second set of parantheses is attempting to match 'any character that doesn't have octal code 001'
Remember, metacharacters take on a different meaning inside character classes.
I'm just off now to see if I can figure out an elegant solution to this one.
Update: 4 seconds later -- as ever, others have answered before me. japhy's solution is classier than I can attempt
/me wonders off to look up lookahead assertions properly.