ASSIGNMENT OF THE ABSOLUTE-CONFIGURATION TO ENANTIOMERIC 2,3-DIHYDRO-1-PHENYL-1H-PHOSPHOLE 1-SULFIDES - X-RAY STRUCTURE OF YLOCTAHYDRO-1H-PYRROLO[1,2-B]-1H-PHOSPHOLO[2,3-D]- ISOXAZOLE 1-SULFIDE())

The structure and absolute configuration of the predominant of the two diastereomeric tahydro-1H-pyrrolo[1,2-b]phospholo[2,3-d]isoxazole 1-s ulfides obtained in the kinetic resolution experiment involving cycloa ddition reaction of (S,S)-3,4-di-tert-butoxy-3,4-dihydro-2H-pyrrole 1- oxide (I) with an excess of racemic 2,3-dihydro-1-phenyl-1H-phosphole I-sulfide (2), was determined by a single-crystal X-ray diffraction te chnique. C22H34O3NPS, trigonal, space group P3(1), a = b = 11.831(1), c = 14.761(2) Angstrom, alpha = beta = 90 degrees, gamma = 120 degrees , V = 1789(4) Angstrom(3), Z = 3. The structure was solved by direct m ethods and was refined by full matrix least-squares calculations to R = 0.031 and R(w) = 0.036 using 3737 unique reflections with I > 3 sigm a(I). The absolute configuration of the studied molecule was determine d by calculation of the ETA (eta) parameter and was found to be 1S, 3a R, 7S, 8S, 8aR, 8bR. This finding assigns unequivocally the S configur ation to the faster reacting enantiomer of 2 and correspondingly the R configuration to the isolated slower reacting (-)-2. It also confirms fully the notion that in the cycloaddition transition state 1 and 2 p refer to approach each other in the exo mode and from the ring faces o pposite to P-Ph and C3-O-t-Bu substituents, respectively.