The Roles of 2- and 3-Axial Methoxy Groups in Determining the Stereochemistry of the Complex Metal Hydride Reduction of Cyclohexanones: Examination of the Cieplak Model

Article abstract of DOI:10.1246/bcsj.69.3297

The 2- and 3-axially substituted methoxy groups in cyclohexanones exhibit steric hindrance similar to that of the methyl group in LiAlH₄ and NaBH₄ reductions. The chelate complex formation between the zinc ion and the two oxygens in the molecule was suggested in the zinc borohydride reduction. The relative reactivities of cyclohexanones in which the 2-axial position is substituted by the methyl or the methoxy group in the LiAlH₄ reduction strongly support Cieplak's proposal, which focuses on the importance of the stabilization of the transition state by anti-periplanar allylic bonds.