Phosphine-Catalyzed Enantioselective Synthesis of Oxygen Heterocycles

摘要

Although phosphines serve as nucleophilic catalysts for an array of useful transformations,comparatively few highly enantioselective variants in the presence of chiral phosphines have been described.In 1994,Trost discovered a novel dppp-catalyzed(dppp = 1,3-bis(diphenylphosphino)propane)cyclization of hydroxy-2-alkynoates that generates saturated oxygen heterocycles.Despite the importance of such structures,owing to their presence in a wide range of bioactive molecules,'41 there has been no progress toward the development of an asymmetric version of the Trost cyclization.Herein,we establish that chiral spiro phosphepine 1 can achieve this objective with a variety of hydroxy-2-alkynoates with good enantiomeric excess [Eq.(1)].