Synfacts 2011(3): 0325-0325  
DOI: 10.1055/s-0030-1259449
Organo- and Biocatalysis
© Georg Thieme Verlag Stuttgart ˙ New York

Silicon-Catalyzed Mannich Reaction of Unactivated Amides

Contributor(s): Benjamin List, Olga Lifchits
S. Kobayashi*, H. Kiyohara, M. Yamaguchi
The University of Tokyo and Japan Science Technology Agency, Tokyo, Japan
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16. Februar 2011 (online)


Kobayashi and colleagues report an unusual Mannich reaction between unactivated amides 1 and tosylimines 2, catalyzed by triisopropylsilyl triflate and triethylamine. The authors propose that the reaction proceeds via a catalytic formation of a silyl enol ether A from amide 1, which reacts with imine 2 to form intermediate B. The ammonium triflate salt then regenerates the silicon catalyst, affording product 3 and completing the cycle. Although the proposed silyl intermediate A was elusive by NMR spectroscopy, several indirect experiments provide support for the suggested catalytic cycle. For less reactive substrates, a metal co-catalyst (CuOTf) was found necessary, which presumably provides Lewis acid activation of imines 2 rather than forming a copper enolate from 1.