The Development of a Practical and Reliable Large-Scale Synthesis of 2,6-Diamino-4-bromopyridine

A novel, safer, and efficient synthetic route to 2,6-diamino-4-bromopyridine has been developed. In discovery research a five-step synthesis afforded 2,6-diamino-4-bromopyridine in 56% yield with a double Curtius rearrangement as a key transformation. Due to potential safety concerns on larger scale an alternative synthetic strategy was necessary. Starting from 2,4-dibromopyridine- N- oxide two complementary procedures have been developed to access 2,6-diamino-4-bromopyridine. The four-step procedure yielded in 28% overall, and the five-step procedure, in 33% overall 2,6-diamino-4-bromopyridine in a safe and straightforward manner using a regioselective 2,6-diamination reaction as key step. Additionally, a general route to unsymmetrical substituted pyridine N -oxide derivatives is disclosed.