Divergent Synthesis of Isoxazolo[5,4‐b]pyridines.

Isoxazolopyridines are highly significant for the development of pharmaceuticals and new materials. In continuation of our ongoing research on transformations of 5‐aminoisoxazoles, we report herein a divergent synthesis of two kinds of novel isoxazolo[5,4‐b] pyridines through condensation of 5‐aminoisoxazoles with β,γ‐alkynyl‐α‐imino esters. By using two different silver salts and a phosphoric acid as catalysts, isoxazolo[5,4‐b] pyridine‐α‐carboxylates and isoxazolo[5,4‐b] pyridine‐γ‐carboxylates were constructed as major isomers in moderate to good yields, respectively. The structures of the two kinds of the isoxazolo[5,4‐b] pyridines were confirmed by X‐ray crystal structural analysis. Furthermore, control experiments were conducted to elucidate the reaction mechanism. [ABSTRACT FROM AUTHOR]