Direct synthesis of hydroxamates from carboxylic acids using 2-mercaptopyridone-1-oxide-based thiouronium salts

Tetrafluoroborate and hexafluorophosphate thiouronium salts derived from 2-mercaptopyridone-1-oxide and tetramethylurea (TOTT and HOTT) or N,N′-dimethylpropyleneurea (TODT and HODT) convert carboxylic acids to Weinreb amides and N-methoxy or N-benzoxyamides in high yields by reaction with N,O-dimethylhydroxylamine and O-methyl- or O-benzyl-hydroxylamine hydrochlorides, respectively, in the presence of triethylamine or DIEA.