Iron-catalyzed diboration and carboboration of alkynes
Naohisa Nakagawa1, Takuji Hatakeyama, Masaharu Nakamura
1International Research Center for Elements Science, Institute for Chemical Research, Kyoto University, Uji, Kyoto, 611-0011 (Japan), Fax: (+81) 774-38-3186; Department of Energy and Hydrocarbon Chemistry, Graduate School of Engineering, Kyoto University, Nishikyo-ku, Kyoto 615-8510 (Japan); CREST (Japan) Science and Technology Agency (JST).
Abstract:
An iron-catalyzed diboration reaction of alkynes with bis(pinacolato)diboron (B2pin2) and external borating agents (MeOB(OR)2) affords diverse symmetrical or unsymmetrical cis-1,2-diborylalkenes. The simple protocol for the diboration reaction can be extended to the iron-catalyzed carboboration of alkynes with primary and, unprecedentedly, secondary alkyl halides, affording various tetrasubstituted monoborylalkenes in a highly stereoselective manner. DFT calculations indicate that a boryliron intermediate adds across the triple bond of an alkyne to afford an alkenyliron intermediate, which can react with the external trapping agents, borates and alkyl halides. In situ trapping experiments support the intermediacy of the alkenyl iron species using radical probe stubstrates.
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