Ring-fused hexahydro-1,2,4,5-tetrazines: synthesis, structure, and mechanistic studies on isolable rotational isomers.

We designed conformationally stable rotational isomers around the C(sp2)-C(sp3) axis at the C3-position of hexahydro-1,2,4,5-tetrazines. Isolation of each rotamer by silica gel column chromatography was successfully achieved at room temperature. The proposed isomerization mechanism of the rotamers was supported by NMR kinetic studies.