7-Bromo-4-methyl-3,4-dihydro-2h-1,4-benzoxazine is useful reactant in the preparation of a purine-based Hsp90 Inhibitor known as (2S)-1-[4-(2-{6-Amino-8-[(6-bromo-1,3-benzodioxol-5-yl)sulfanyl]-9H-purin-9-yl}ethyl)piperidin-1-yl]-2-hydroxypropan-1-one (MPC-3100).