Preparation of cyclopropylamines via enantioselective cyclopropanation of enecarbamates

by Masri, Nabih; Zheng, Nan

Taking care of the environment is very important. To preserve the environment, it is critically important to use renewable resources such as visible light to minimize the depletion of natural resources. As chemists it is our duty to learn how to harvest solar energy and use it in the form of chem. fuels in the labs. In Zheng's group, intermol. [3+2] cycloaddn. of cyclopropyl amines with olefins via visible light Photocatalysis was recently developed. One of the bottlenecks for this method is access to substituted cyclopropylamines whose synthesis is non-trivial. Buchwald-Hartwig Cross Coupling of aryl bromides with cyclopropylamines and the Kulinkovich-de Meijere reaction with amides are often the method of choice for the prepn. of cyclopropylamines. Both have limitations. The former depends on the access to cyclopropylamines, while in the latter reaction: the synthesis of the amides is often lengthy. Moreover, cyclopropylamines can't be obtained in enantiomeric pure form by either reaction. To address these issues, enantioselective cyclopropanation of enamides will be explored. Studies on cyclopropanation of the enamides are rare and limited. One notable example is Hsung's work on stereoselective cyclopropanation of chiral enamides. The enamides will be prepd. by Cu- or Pd-catalyzed N-vinylation of BOC protected anilines.