The Minimum Connection Time between flights landing in Terminal 2 (Lufthansa) and flights departing from Terminal 1 (Vueling) is 45 minutes. Thus technically this is a valid connection.
However valid connection does not mean that you will make your flight - it just means that the airlines will let you book such a connection when booked on the same ticket.
If you are planning to book these two flights on the same ticket, then it's potentially worth the risk. If you miss the outbound flight then it will be up to the airlines (most likely Lufthansa) to get you to your destination, either by moving you to a later Vueling flight, or more likely by putting you on one of their own flights to your destination.
However, if you are considering booking these flights on separate tickets then your chances of something going wrong are very high. One of the reasons that MUC has such a low Minimum Connection Time is that they will make arrangements for getting people directly from inbound gate to outbound gate - especially in cases of delayed inbound flights (eg, using vehicles that drive across the airport itself). If you are on multiple tickets then they will not know that you are connecting, and thus will not make any such arrangements for you.
On separate tickets it is still possible that you will make your connecting flight, but personally I would never consider such a short connection. Your odds of missing the flight are too high, and if you do miss it you'll likely have to purchase a new ticket to get yourself to your destination.