Thank you very much Mindlusion for bringing up that important point.

In fact I was thinking about utilising formaldehyde (Eschweiler-clark) as methylating agent in my last step. I assume the formation of reactive Schiff-base leads to an opportunity for side reactions to take place and create harmful side products.

Then again I'm thinking of utilising the Gabriel synthesis might be a way around the problem I face and have to change some other steps. Then again I don't want to talk much about this as then more harmful chemicals/procedures will be necessary.