6-Amino-7-fluoro-2H-benzo[b][1,4]oxazin-3(4H)-one, a crucial intermediate in the synthesis of herbicides, flumioxazin and thidiazimin

An efficient synthesis of 6-amino-7-fluoro-2H-benzo[b][1,4]oxazin-3(4H)-one, a key intermediate in the preparation of the herbicides flumioxazin and thidiazimin, is accomplished in three steps from readily available 1,3-difluorobenzene. The key steps of nitration, condensation, and reductive cyclization were optimized to obtain the product in 78% overall yield with 99.4% purity.