Two structures involved in the separation of the enantiomeric pair of 2,2'-spirobi[indan]-1,1'-dione

Abstract

R,2'S)-l'-Oxo-2,2'-spirobi(indan)-l-yl (1 S)-4, 7,7-trimethyl- 3 -oxo-2-oxabicyclo )hept- (1972). A stereoselective reduction of one of the carbonyl groups in the diketone was performed with lithium tri-tert-butoxylaluminium hydride. The resulting alcohol group in the racemic trans-hydroxy ketone was transformed into an ester by acylation with (-)-to-camphanic acid chloride conserving the geometry of the reduced carbon. The two diaster- eomeric esters formed, (1) and (2), were separated by fractional crystallization. (1) had lower solubility in acetone than (2) and was isolated as nice pure crys- tals in the first fractions. (2), with a lower melting point than (1), was more difficult to isolate, and had to be recrystallized several times to obtain a single crystal useful for X-ray analysis. Equidimensional single-crystal fragments of maxi- mum dimensions less than 0.5 mm were used for the crystallographic examinations. The space groups of both crystals were determined from precession photographs to be monoclinic with only systematic absences 0k0 for k odd indicating P21. The lattice constants of both compounds were refined from approximately 25 centred reflections in the range 20 30-(/) were used for structure determination and refinements. It was observed that intensities drop more quickly with sin0/a for (2) than for (1), and so for (2) data were collected for 20 _ 3o-(1). The intensities were corrected for Lorentz and polarization effects. /z(1) = 0.83 cm-i and /~(2) = 0.81 cm -~, thus no absorption corrections were applied. Positions of all C and O atoms in the structures were found by direct methods (Sheldrick, 1990). H-atom positions were found from difference Fourier maps. The structures were refined by full- matrix least-squares techniques using anisotropic thermal parameters for the non-H atoms and iso-