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 of 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 toward preferred C–O or C–N bond cleavages in the rate-determining step of the S_N1-like mechanism.

中文翻译：

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全杂原子取代的碳螺体立体中心：合成、分辨率、对映体稳定性和绝对构型

手性四异杂取代甲烷（即四氧杂取代的碳氧杂氧杂和氮杂氧杂氧碳螺体立体中心）是在 CpRu 催化下合成的，使用环状碳酸盐和氨基甲酸酯作为底物，α-重氮-β-酮酯作为试剂。通过手性固定相色谱分离的单个对映异构体显示出从 g_abs ∼10^–5 到 ∼10^–4 的手性特性，这与 TD-DFT 计算一起提供了稳定的绝对构型分配。还获得了结晶螺状非对映异构体，进一步证实了结构和构型分配。使用对映选择性动态色谱法，确定了邻碳酸盐和邻氨基甲酸酯的显著对映体化屏障，其值高达 27.6 和 34.6 kcal/mol（在 25 °C 下的半衰期分别为 227 天和 >84,000 年）。DFT 进一步阐明了这种巨大差异的起源，指向 S_N1 样机制的速率确定步骤中首选的 C-O 或 C-N 键裂解。