Maybe try British Airways, Aer Lingus, KLM, Sabena or Air France. None of the ibearian airlines have direct service from Europe to Boston. The 5 airlines listed all go to both cities and you wouldn't be flying out of your way (connecting in a european city further east than Barcelona). You could take Iberia (I don't know if Spanair or Air Europa flies it aswell) to London, and then take AA,UA,BA, or VS to BOS. If you don't mind backtracking you could also go Lufthansa, Alitalia and Swissair.
Have a nice flight!