A New Bis(8-hydroxyquinolinylmethyl) Perhydrobenzimidazole Obtained from a Cyclic Aminal Derived from trans-1,2-Diaminocyclohexane and 8-Hydroxyquinoline

The reaction of 8-hydroxyquinoline and (2R,7R,11S,16S)-1,8,10,17-tetraazapentacyclo [8.8.1.1.8,170.2,70.11,16]icosane under Mannich-type conditions afforded a new quinoline-functionalized diazabicyclic derivative in 27% yield. The structure of the product was established by FT-IR, 1H and 13C NMR, HSQC, HMBC, and ESI-MS analyses, which confirmed the connectivity between the two quinoline units and the perhydrobenzimidazole heterocyclic fragment. The conformational strain of the perhydroimidazolidine fragment prevents the rearrangement pathway previously reported for related systems, such as cyclic aminal 1,3,6,8-tetraazatricyclo [4.4.1.13,8]dodecane (TATD), leading to a different reaction outcome. The results demonstrate that the conformationally constrained aminal exhibits reactivity distinct from that reported for TATD-derived systems, providing new insight into the behavior of cyclic aminals in Mannich-type reactions.