OPTICALLY ACTIVE PHOSPHINE CHALCOGENIDES. 22.¹ STEREOCHEMISTRY AND X-RAY STRUCTURE OF THE MAJOR ENDO CYCLOADDUCT OF (S)-METHYLPHENYLVINYLPHOSPHINE OXIDE TO CYCLOPENTADIENE

Abstract

The stereochemistry of the major endo adduct obtained in the thermal Diels-Alder reaction of (S)-methylphenylvinylphosphine oxide and cyclopentadiene was analyzed by a single-crystal X-ray diffraction technique C₁₄H₁₇OP, space group P2₁2₁2₁, a = 7.042(1) Å, b = 10.522(1) Å, c = 18.039(1) Å, V = 1336.6(3) Å 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 1 > 3[sgrave](1). In the crystal packing two intermolecular C—H…O contacts involving phosphoryl oxygen and α 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)-methylphenylvinyl-phosphine oxide preferred to enter the studied 4 + 2 cycloaddition in the s-trans conformation.

Key Words:

• Enantiomeric phosphine oxide
• X-ray analysis
• absolute configuration
• vinyl phosphine oxide
• 4 + 2 cycloaddition
• reactive conformation