A new family of fused-ring heat-resistant energetic compounds has been developed through rational molecular design and efficient synthetic strategies. Starting from 4-amino-6-chloropyrimidine-5-carbonitrile, three distinct reaction pathways were established, enabling the one-step cyclization to construct a polycyclic fused compound 1 and a series of fused-ring compounds 2 – 5 incorporating a 1,2,3-triazine N-oxide moiety. Notably, the formation of compound 1 proceeds via a new reaction mechanism. The molecular structures and packing features were elucidated by single-crystal X-ray diffraction. These compounds exhibit a favorable balance of detonation performance, high thermal stability, and low mechanical sensitivity. This work provides an efficient synthetic approach to heat-resistant energetic materials and highlights the potential of fused heterocyclic frameworks for advanced energetic applications.