Ethyl (3S)-3-[(3aR,5R,6S,6aR)-6-hydroxy-2,2-dimethyltetrahydrofuro[4,5-d][1,3]dioxol-5-yl]-3-{(3S)-3-[(3aR,5R,6S,6aR)-6-hydroxy-2,2-dimethyltetrahydrofuro[4,5-d][1,3]dioxol-5-yl]-5-oxoisoxazolidin-2-yl}propanoate chloroform monosolvate

Abstract

<jats:p>The title compound, C<jats:sub>22</jats:sub>H<jats:sub>33</jats:sub>NO<jats:sub>12</jats:sub>·CHCl<jats:sub>3</jats:sub>, was obtained as a product of a double aza-Michael addition of hydroxylamine on a Chiron with a known absolute configuration. The enantiopure compound crystallized as a chloroform solvate, in space group <jats:italic>P</jats:italic>1, and diffraction data were collected at room temperature with Ag <jats:italic>K</jats:italic>α radiation. The Flack parameter refined to <jats:italic>x</jats:italic> = −0.01 (16); however, the Flack and Watkin 2<jats:italic>AD</jats:italic> plot clearly shows that differences between Friedel opposites (the <jats:italic>D</jats:italic> component of the plot) do not carry any reliable information about resonant scattering of Cl atoms, and are rather dominated by random and systematic errors. The <jats:italic>R<jats:sub>D</jats:sub> </jats:italic> factor calculated using 1941 acentric Friedel pairs is <jats:italic>R<jats:sub>D</jats:sub> </jats:italic> = 0.995. On the other hand, the 2<jats:italic>A</jats:italic> component of the plot, related to average intensities of Friedel pairs, shows that data are of good quality (<jats:italic>R<jats:sub>A</jats:sub> </jats:italic> = 0.069). This example illustrates that while using Ag <jats:italic>K</jats:italic>α radiation (λ = 0.56083 Å), scatterers heavier than Cl should be present in a chiral crystal in order to determine confidently the absolute structure of the crystal.</jats:p>