Crystal structure and DFT calculations of 3,8-diphenyl-3a,4,5,5a,8a,8b-hexahydro-benzo[1,2-d: 3,4-d′]diisoxazole, C20H18N2O2

The molecular and crystal structures of 3,8-diphenyl-3a,4,5,5a,8a,8b-hexahydro-benzo[1,2-d: 3,4-d′]diisoxazole have been XRD determined. The compound crystallizes in the monoclinic system (space group P21/c) with cell dimensions a=15.278(1), b=9.839(1), c=10.912(2) Å, β=92.15(1)°. The structure was solved from 2193 reflections with I≥2σ(I). The final R was 0.039 for 289 variables. DFT calculations at the B3LYP/6-31G* level afforded a twist-boat conformer almost identical with the X-ray structure as well as a less stable half-chair conformer which lies 9.7 kJ/mole higher in enthalpy. The near planarity of the two fused isoxazoline rings destabilizes the staggered cyclohexane chair and forces the cyclohexane ring to adopt uncommon conformations.