Most-bookable ways to fly BOS → FRA (business)

FRA likely needs 3+ stops from BOS

Frankfurt, Germany is a smaller airport with no nonstop or one-stop service from BOS. Award programs almost never have space on every segment of a 3+ stop itinerary, so trying to book end-to-end on points here usually fails.

Try this instead: search from BOS to a major international hub near Germany (think Singapore, Tokyo, Hong Kong, Doha, Dubai, Frankfurt — whichever is closest), book that long-haul leg with miles, then handle the final hop separately with cash or a regional program. You'll almost always come out ahead.