Do whatever you want. You will be more productive if you do what you want to do rather than what someone else thinks you should do.
It might be easier to get a non-synthesis project (as your advisor seems to think), but if you´re going to take something you´re not committed to you will not do well, and you might end up hating it. It is so important to be enthusiastic about the work you do, and the best chemists on paper are not necessarily the best chemists in practice - it´s a different world believe me.