The Structures of Different Diastereomers of Bicyclohept-5-en-2-yl Phenyl Sulfoxide

Article abstract of DOI:10.1107/S0108768188009103

Three diastereomers of bicyclo<2.2.1>hept-5-en-2-yl phenyl sulfoxide were prepared by Diels-Alder <4+2> cycloadditions between phenyl vinyl sulfoxide and cyclopentadiene.The isomers were separeted by column chromatography on silica gel and repeated recrystallizations gave the pure racemates of three of the four possible diastereomers.It proved to be impossible to assign the stereochemistry of the products from low-resolution NMR spectra.The X-ray diffraction studies of the three diastereomers showed the relative configuration at the two chiral centers and these stereochemical assignments were, subsequently, correlated with the two-dimensional NMR spectroscopic results.Compound (I), exo-(2R^*,8S^*)-bicyclo<2.2.1>hept-5-en-2-yl phenyl sulfoxide < or the exo-(2S^*,8R^*)-isomer>, C13H14OS, M_r=218.31, orthorhombic, P2₁2₁2₁, a=10.517(2), b=10.914(2), c=9.642(3) Angstroem, V=1106.7 Angstroem³, Z=4, D_x=1.31 gcm^-3, Cu Kα, λ=1.54178 Angstroem, μ=22.14 cm^-1, F(000)=464, T=138(2) K, R=0.042 for 1151 data.Compound (II), exo-(2RS,8RS)-bicyclo<2.2.1>hept-5-en-2-yl phenyl sulfoxide, C13H14OS, M_r=218.31, triclinic, P1<*>, a=8.775(4), b=16.353(8), c=7.804(3) Angstroem, α=90.67(3), β=101.08(4), γ=85.64 (5) deg, V=1095.8 Angstroem³, Z=4, D_x=1.32 gcm^-1, Mo Kα, λ=0.71069 Angstroem, μ=2.18 cm^-1, F(000)=464, T=138(2) K, R=0.062 for 3264 data.The two molecules in the asymmetric unit are crystallographically independent, but their conformations are similar.Compound (III), endo-(2SR,8SR)-bicyclo<2.2.1>hept-5-en-2-yl phenyl sulfoxide, C13H14OS, M_r=218.31, orthorhombic, P2₁2₁2₁, a=14.454(2), b=14.800(2), c=10.388(1) Angstroem, V=2222.2 Angstroem₃, Z=8, D_x=1.31 gcm^-1, Mo Kα, λ=0.71069 Angstroem, μ=2.15 cm^-1, F(000)=928, T=138(2) K, R=0.029 for 2385 data.The two molecules in the asymmetric unit are enantiomeric with respect to both chiral atoms C(2) and S(8) and their conformations show small differences.For both the exo-(2RS,8RS) and endo-(2SR,8SR) conformers, the two molecules in the asymmetric unit have closely similar molecular dimensions.The results show an appreciable distortion from mirror symmetry for the norbornene ring system.The distortion is similar in size for the compounds but in opposite directions for the 2-exo- and the 2-endo-substituted norbornene system.