OPTICALLY-ACTIVE PHOSPHINE CHALCOGENIDES .22. STEREOCHEMISTRY AND X-RAY STRUCTURE OF THE MAJOR ENDO CYCLOADDUCT OF (S)-METHYLPHENYLVINYLPHOSPHINE OXIDE TO CYCLOPENTADIENE

The stereochemistry of the major endo adduct obtained in the thermal D iels-Alder reaction of (S)-methylphenylvinylphosphine oxide and cyclop entadiene was analyzed by a single-crystal X-ray diffraction technique C14H17OP, space group P2(1)2(1)2(1), a = 7.042(1) Angstrom, b = 10.52 2(1) Angstrom, c = 18.039(1) Angstrom, V = 1336.6(3) Angstrom(3), Z = 4. The structure was solved by direct methods and was refined by full matrix least-square calculations to R = 0.043 and S = 1.033 using 2635 unique reflections with I > 3 sigma(I). In the crystal packing two in termolecular C-H ... O contacts involving phosphoryl oxygen and alpha and ortho hydrogens were revealed. The studied compound was identified as the endo adduct of the S configuration at C2. On the basis of this finding it could be concluded that (S)-methylphenylvinylphosphine oxi de preferred to enter the studied 4 + 2 cycloaddition in the s-trans c onformation.