Enantioselective Ring Opening of meso-Epoxides with Silicon Tetrachloride Catalyzed by Pyridine N-Oxides Fused with the Bicyclo[3.3.1] nonane Framework

摘要

The synthesis of new chiral Lewis basic organocatalysts that contain pyridine N-oxide moieties fused with the bicyclo[3.3.1] nonane framework is reported. The obtained pyridine N-oxides were employed as catalysts in the enantioselective ring opening of meso-epoxides with silicon tetrachloride. Derivative 1b endowed with two 2,4-diaryl-substituted pyridine N-oxide moieties proved to be a particularly effective catalyst for desymmetrization of norbornene oxide 16i to furnish Wagner-Meerwein rearrangement product 20i in unprecedented 96% ee. Difunctional congener 3, which is striped of the 4-aryl substituents, exhibited moderate to high levels of asymmetric induction (47-88% ee) with alicyclic epoxide substrates.