Asymmetric Desymmetrization Based on an Intramolecular Haloetherification:A Highly Effective and Recyclable Chiral Nonracemic Auxiliary,2-exo-Methyl-3-endo-phenyl-5-norbornene-2-carboxaldehyde,for meso-1,3- and meso-l,4-Diols

摘要

A new chiral auxiliary,a 3-endo-phenyl norbornene aldehyde derivative,which is a crystalline,very stable,and easily handled,was developed for the desymmetrization of meso-1,3- and meso-1 ,4-diols.The key step of the method,an intramolecular bromoetherification,proceeded in a highly diastereoselective manner.A four-step sequence,1) acetalization,2) intramolecular bromoetherification followed by acid hydrolysis,3) protection of the alcohol,and 4) retrobro-moetherification,transformed the meso-diols into optically active derivalives.The 3-endo-phenyl norbornene aldehyde derivative was simultaneously reformed and could be used repeatedly.This is the first chemical example of a single auxiliary that is applicable for highly enantioselective desymmetrization of meso-1,3- and meso-l,4-diols;to the best of our knowledge,this is the best chemical method available for the desymmetrization of meso-1,4-diols.