Urazole synthesis. Part 2: facilitating N4 substitution

Abstract The di- tert -butyl-di- p -nitrophenyl ester of hydrazinetetracarboxylic acid was prepared and shown to be useful in the preparation of urazoles (i.e., 1,2,4-triazolidine-3,5-diones), by reaction with a primary amine using either n -BuLi or pyridine as base, depending on the desired N 4 substituent. With more electronegative N 4 substituents, pyridine is the preferred base. This work complements our reported urazole synthesis, which introduced the N 4 substituent early in the sequence and thus did not facilitate variation at N 4 for library synthesis.