257. all-Heteroatom-Substituted Carbon Spiro Stereocenters: Synthesis, Resolution, Enantiomeric Stability, and Absolute Configuration
     Olivier Viudes, Céline Besnard, Alexander F. Siegle, Oliver Trapp, Thomas Bürgi, Gennaro Pescitelli, Jérôme Lacour
     J. Am. Chem. Soc. 2025, 147, 21121-21130

Chiral tetra heterosubstituted methanes, i.e. tetraoxa and azatrioxa carbon spiro stereocenters, are synthesized under CpRu catalysis, using cyclic carbonates and carbamates as substrates and α-diazo-β-ketoesters as reagents. Single enantiomers, isolated by chiral stationary phase chromatography, display chiroptical properties, from g_abs ~10^–5 to ~10^–4, which, together with TD-DFT calculations, provide robust absolute configuration assignments. Crystalline spiro diastereomers were also obtained, confirming further the structural and configurational assignments. Using enantioselective dynamic chromatography, remarkable enantiomerization barriers were determined for the ortho-carbonates and ortho-carbamates, with values up to 27.6 and 34.6 kcal/mol (half-lives 227 days and >84’000 years at 25 °C, respectively). DFT further elucidates the origin of this large difference pointing towards preferred C–O or C–N bond cleavages in the rate-determining step of the S_N1-like mechanism.

DOI : 10.1021/jacs.5c06394 

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