Enantioselective organocatalytic cyclopropanations. The identification of a new class of iminium catalyst based upon directed electrostatic activation |
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Authors: | Kunz Roxanne K MacMillan David W C |
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Institution: | Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, USA. |
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Abstract: | A new method for enantioselective organocatalytic cyclopropanation is described. This study outlines the identification of a new class of iminium catalyst based on the concept of directed electrostatic activation (DEA). This novel organocatalytic mechanism exploits dual activation of ylide and enal substrates through a proposed electrostatic activation and stereodirected protocol. Formation of trisubstituted cyclopropanes with high levels of enantio- and diastereoinduction is accomplished for a variety of alpha,beta-unsaturated aldehydes and sulfonium ylides. In addition, mechanistic studies have found that this cyclopropanation reaction exhibits enantioselectivity and reactivity profiles that are in accord with the proposed DEA step. |
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