Hello there, may I help you?
Is your son like this when doing work at school or just with you? If it is only with you it may be worth investing in a tutor or a short term basis which comes to complete homework with him. This way you are stepping away from the battle with your son and he is more likely to complete work if it is with someone else.
Once he realises he doesn't have to have a tutor if he completes his work with you, it should allow him to make the decision himself that he will complete the work without a tutor.
Here are some useful books and articles I have found which may be of interest to you.