It is doable, but pretty tough.

I don't know MUC so well as to comment how doable it is there, but in FRA you will land in Terminal A. Depending on what your gate is, it will already take up to 20 minutes to get to passport control and security checks. Depending on the time of your arrival, that may not be enough, especially if you factor in things like a 5-10 minute delay in landing (which can always happen) or a late start in MUC.

Long story short: I would not advise to make such a booking.