Control of Λ- and Δ-Isomerization of the Atrane Cages in Group XIV Metallatranes by Chiral Axial Substituents.

The syntheses of the novel stannatranes N(CHCMeO)Sn-(1 S)-(-)-OC(O)C(OMe)(CF)(CH), 1( S, Δ), and N(CHCMeO)Sn-(1 R)-(+)-OC(O)C(OMe)(CF)(CH), 2( R, Λ), and germatranes N(CHCMeO)Ge-(1 S)-(-)-OC(O)C(OMe)(CF)(CH), 3( S, Δ), and N(CHCMeO)Ge-(1 R)-(+)-OC(O)C(OMe)(CF)(CH), 4( R, Λ) (with 1, S, Δ-configured/2, R, Λ-configured and 3, S, Δ-configured/4, R, Λ-configured being pairs of enantiomers) are reported. The compounds were characterized by NMR and IR spectroscopy, electrospray ionization mass spectrometry, and single crystal X-ray diffraction analysis. The epimerization via Λ ⇌ Δ ring flip of the enantiomeric stannatrane pair 1( S, Δ)/2( R, Λ) was investigated by NMR experiments at variable temperatures and density functional theory (DFT) calculations.