The structures of ethyl 1,4,5-exo-trimethyl-7-oxo-2,3-diphenylbicyclo[2.2.1]hept-2-ene-5-endo-carboxylate (A) and ethyl 1,4-dimethyl-7-oxo-2,3-diphenylbicyclo[2.2.1]hept-2-ene-5-endo-carboxylate (B)

Abstract

Crystals of C₂₅H₂₆O₃ are triclinic, space group Pï, with a=9.197(2), b=10.357 (2), c=11.086 (3) Å, α=94.07 (2), β=98.21 (3), γ=90.82(2) °, V=1042.2 ų, Z=2, D_obs=1.19, , D_calc=1.198 Mg m^-3 and μ (Cu Kα)=0.661 mm^-1; R=6.2% for 2525 significant reflections. Crystals of C₂₄H₂₄O₃ (B) are monoclinic, space group P21/a, with a=11.584 (2), b=11.315 (2), c=15.900 (4) Å, β=104.02 (2)°, V=2022.4 ų, Z=4, D_obs=1.199, D_calc=1.185 Mg m^-3and μ (Cu Kα=0.081 mm^-1; R=4.2% for 1990 significant reflections. The steric strain introduced by the bulky sbstituents on the norbornenone system is discussd. In addition, a possible relationshp between the orienation of the ester function and the anisochrony of O-methylene protons is brought out.