(2S,7R,11S,16R)-1,8,10,17-Tetraazapentacyclo[8.8.1.1^8,17.0 ^2,7.0^11,16]icosane and its enantiomer. Synthesis, NMR analysis and X-ray crystal structure

(2S,7R,11S,16R)-1,8,10,17-tetraazapentacyclo[8.8.1.1^8,17.0 ^2,7.0^11,16]icosane (7) has been synthesized by reaction of commercial 1,2-cyclohexanediamine with formaldehyde in dimethylformamide solution. The crystal structure of 7 has been determined by single crystal X-ray diffraction analysis. The crystal structure of 7 shows that the geometry of the N-atoms is the less likely cis-configuration, the precise configuration that was claimed by previous investigators to be unlikely to exist! The C-C-C bond angles within the cyclohexane rings of 7 are in the range 113.9(7)-124.6(8) °, indicating that the cyclohexane rings are more planar than chair-like. The N-C-N bond angles around the bridging methylene groups are similarly distorted from tetrahedral geometry. The crystal structure of 7 is compared with the previously reported structures of 1,3,6,8-tetraazatricyclo[4.4.1.1 ^3,8]dodecane(1) and 1,4-dimethano-dibenzo[d,i]-1,3,6,8-tetrazecine(2) . The title compound (7) {C₁₆H₂₈N₄}, crystallizes in the orthorhombic, space group Fdd2, with lattice constants: a=11.9733(17) Å, b=12.8485(18) Å, c=19.095(3) Å, α=90°, β=90°, γ=90°, V=2937.5(7) ų, Z=8, D_c=1.250 mg m^-3, F(000)=1216, R₁=0.0834, wR₂=0.2255.