Facile Synthesis of Energetic Multi-Heterocyclic Compound via a Promising Intramolecular Integration Strategy

The design of energetic compounds generally pursues the plane effect in order to obtain energetic compounds with high density, high thermal stability, and low sensitivity. Multi-heterocyclic compounds have strong conjugation effect, which is conducive to the formation of coplanar, but their synthesis conditions are harsh and the synthesis route is long. Here, a four-ring energetic compound 5,5′-bis(1H-tetrazol-5-yl)-3,3′-bi(1,2,4-oxadiazole) (4) was designed and synthesized efficiently by a clever intramolecular cyclization strategy. In addition, the structures of compound 4 and its corresponding salts were confirmed. Compound 4 is insensitive to external stimuli because of its special three-dimensional crystal packing and has positive heat of formation (596.7 kJ·mol^-1) and moderated thermal stability (T_dec = 259.2 °C) owing to the special structure with a macrocyclic system. Its salts show good thermal stability (216.0-276.2 °C), good mechanical sensitivity (IS > 40 J, FS > 360 N), and positive heat of formation (449.0-530.7 kJ·mol^-1). Therefore, the multi-heterocyclic compound synthesized by intramolecular cyclization exhibits excellent performance, which presents a new avenue for the design and synthesis of energetic materials.