Discoveries during the last two years have revealed the existence of a vast region of star formation close to the base of the Scutum Arm, where at least five clusters of red supergiants have been found. In order to understand the nature of this region, we need to determine accurate distances to the clusters. So far, only indirect estimates, based on kinematics of the red supergiants have been derived. We have managed to identify the population of blue stars in Stephenson 2, the most massive and less obscured of all the clusters. In this talk we highlight the results of an OSIRIS campaign in 2011A, in which we perform spectroscopy of a sample of stars close to the main-sequence turn-off, allowing us to derive a more accurate distance and age for Stephenson 2.