The structures of different diastereomers of bicyclo[2.2.1]hept-5-en-2-yl phenyl sulfoxide

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 separated 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, Mr = 218.31, orthorhombic, P2(1)2(1)2(1), a = 10.517 (2), b = 10.914 (2), c = 9.642 (3) A, V = 1106.7 A3, Z = 4, Dx = 1.31 g cm-3, Cu K alpha, lambda = 1.54178 A, mu = 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, Mr = 218.31, triclinic, P1, a = 8.775 (4), b = 16.353 (8), c = 7.804 (3) A, alpha = 90.67 (3), beta = 101.08 (4), gamma = 85.64 (5) degrees, V = 1095.8 A3, Z = 4, Dx = 1.32 g cm-3, Mo K alpha, lambda = 0.71069 A, mu = 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.(ABSTRACT TRUNCATED AT 250 WORDS)