"I did not want you would know about it." I can say that is definitely wrong because "you would know about it" doesn't contain a direct object noun for the verb want. However, the sentence "I did not think you would know about it" is correct, because "you would know about it" itself forms a noun phrase as the direct object of think.
I'm a bit torn on exactly why "you would know about it" is a valid noun phrase for think and an invalid noun phrase for want, aside from it sounding completely wrong. The reason is almost certainly some intrinsic quality of the verbs themselves, but I'm not sur…