Crystal and molecular structure of anhydroerythromycinA cyclic carbonateN-methyl iodide

The crystal and molecular structure of C₃₉H₆₆INO₁₃ · CH₃OH has been determined by single-crystal x-ray diffraction analysis. The compound crystallizes in the monoclinic space, groupP2₁, witha =14.35(1),b=14.38(1),c =10.91(1) Å, = 96.10(5) °, andZ = 2. Three-dimensional intensity data were collected on a four-circle fully automated diffractometer. The structure was solved by the heavy-atom method. The positions of all atoms have been refined by block-diagonal and full-matrix least squares, using anisotropic temperature factors. The finalR value was 0.109 for 2194 independent reflections. The analysis does not confirm the hypothetical structure proposed by the Eli Lilly group, as far as a position of a cyclic carbonate moiety is concerned. They postulated that the cyclic carbonate moiety was attached to C(9) and C(11) of the erythronolide. The results obtained by us show that the cyclic carbonate moiety is attached to C(11) and C(12). The absolute configuration of the asymmetric centers agrees fully with that established for erythromycinA.     

The Thermal Isomerizations of Bicyclo[2.1.0]pent-5-yl Methyl Ketones: endo-exo stereomutation and cyclopropyl-allylic rearrangement to cyclopent-2-enyl methyl ketones

Bicyclo[2.1.0]pent-5-yl methyl ketones undergo two thermal isomerization reactions. The endo-exo stereomutation follows the ring-flip path in better than 90%, with inversion of the configuration of the angular carbon atoms by cleavage and reclosure of the central bond. Stereomutation and cyclopropyl-allylic rearrangement to cyclopent-2-enyl methyl ketone do not involve a common intermediate and proceed on separate potential energy surfaces. The activation parameters of the rearrangement suggest an allowed concerted cycloreversion process.