1-Hy­droxy-1H-benzo[d][1,2,6]oxaza­borinin-4(3H)-one

The structure of the title compound, C₇H₆BNO₃, a new boron heterocycle, prepared by the condensation of (2-eth­oxy­carbonyl­phen­yl)boronic acid and hydroxyl­amine, reveals the specific mode of intra­molecular condensation between a phenyl­boronic acid and an ortho hydroxamic acid substituent. The crystal structure shows that dehydration occurs to form a planar oxaza­borinine ring possessing both phenol-like B-O-H and lactam functional groups. In the extended structure, inter­molecular hydrogen bonding generates a 14-membered ring. To our knowledge, this is the first crystal structure determination involving a six-membered ring that exhibits consecutive B-OH, O, NH, and C=O functional groups.