Urazole synthesis. Part 2: facilitating N4 substitution

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 N4 substituent. With more electronegative N4 substituents, pyridine is the preferred base. This work complements our reported urazole synthesis, which introduced the N4 substituent early in the sequence and thus did not facilitate variation at N4 for library synthesis.