-uan pinyin pronunciation
There are several cases in Mandarin of multiple sounds sharing the same symbols in Pinyin, such as -uan as you've noticed, as well as -i which has multiple sounds associated with it. In the case of -uan, this final behaves differently when prefaced with the initials y-, j-, q-, and x-. As a general rule, -u, -ue, -uan, and -un behave differently when prefaced with those 4 initials and you'll see them separated  out on any pinyin chart: 



The u in these cases is actually a ü which does not exist in English and is something I struggle with myself so I'll just redirect you here.