It's going to be very difficult to extract yourself from this contract without at least some impact on your reputation with this boss/company as it's almost inevitably going to impact upon delivery/meeting deadlines.
I would suggest at least giving your boss a chance to resolve the issues (even if you don't really believe it is possible).
The best approach would be to have a 1-1 meeting with your manager as soon as you can and just be honest - explain the issues you're facing and that you don't feel that you can continue in this way. Your boss might be able to take some actions or have some suggestions that will make the situation tolerable for you and if they do I'd suggest at least giving them a shot - it may work and if it doesn't then at least you've shown a willingness to try which should count for a lot. And if they don't work out (or if they don't even try to change it themselves) then you can explain that you are sorry but that it's just not working out and you can discuss an exit plan that would be inline with your contractual obligations (I'm assuming there must be some kind of break clause) and would minimize impact on the project and company.