The behavior of o-formylbenzeneboronic acid towards various aldehyde reagents is described. Reaction with secondary diamines, malononitrile, sodium bisulfite, and Girard's reagent T provides the usual products, while the 2, 4-dinitrophenylhydrazone is isolated as the diethyl boronate ester. The boronic acid function participates in condensation reactions with semicarbazide and p-carboxyphenylhydrataine hydrochlorides to give the ...