DOI: 10.1002/chem.201406595
Communication
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Iron Catalysis
Iron-Catalyzed Diboration and Carboboration of Alkynes
[a, b, c]
[a, b, d]
[a, b]
Naohisa Nakagawa,
Takuji Hatakeyama,
and Masaharu Nakamura*
Abstract: An iron-catalyzed diboration reaction of alkynes
with bis(pinacolato)diboron (B pin ) and external borating
2
2
agents (MeOB(OR) ) affords diverse symmetrical or unsym-
2
metrical cis-1,2-diborylalkenes. The simple protocol for the
diboration reaction can be extended to the iron-catalyzed
carboboration of alkynes with primary and, unprecedent-
edly, secondary alkyl halides, affording various tetrasubsti-
tuted monoborylalkenes in
a highly stereoselective
manner. DFT calculations indicate that a boryliron inter-
mediate adds across the triple bond of an alkyne to afford
an alkenyliron intermediate, which can react with the ex-
ternal trapping agents, borates and alkyl halides. In situ
trapping experiments support the intermediacy of the al-
kenyl iron species using radical probe stubstrates.
With the development of Suzuki–Miyaura cross-coupling reac-
tions, alkenylboron compounds have attracted attention as key
intermediates for the synthesis of diverse functional molecules
[1]
for use as electronic materials and bioactive natural products.
Diborylalkenes are particularly attractive building blocks for
Scheme 1. Transition metal-catalyzed diboration and carboboration of al-
kynes. a) Previous works: Transition metal-catalyzed diboration of alkynes
and copper-catalyzed carboboration of alkynes; b) this work: Iron-catalyzed
diboration and carboboration of alkynes.
[
2]
[3]
substituted alkenes and p-extended polyarenes, and their
expedient synthesis has attracted much attention from syn-
thetic chemists. The transition metal-catalyzed diboration of al-
[
4]
kynes has been investigated intensively since its discovery by
[5a]
[5]
Suzuki and Miyaura, and diverse transition metals such as
platinum, cobalt, iridium, copper, and gold have proven to be
effective catalysts (Scheme 1a, upper reaction). Recently,
copper-catalyzed diboration of alkynes has been extended to
[
6,7]
a novel carboboration reaction,
furnishing diverse tetrasub-
[7d–h]
+
stituted borylalkenes,
which are valuable synthetic inter-
[
a] N. Nakagawa, Prof. Dr. T. Hatakeyama, Prof. Dr. M. Nakamura
International Research Center for Elements Science
Institute for Chemical Research, Kyoto University
Uji, Kyoto, 611-0011 (Japan)
mediates (Scheme 1a, lower reaction). The discovery of a new
diboration and carboboration catalyst has enhanced the syn-
thetic efficacy of the reaction. Herein we report that simple
iron salts, which are among the most promising practical cata-
lysts, can catalyze the diboration and carboboration of internal
alkynes (Scheme 1b). Trapping experiments and DFT calcula-
tions suggest that the diboration and carboboration reactions
occur through the formation of alkenyliron species, which
react with borating agents and unactivated alkyl halides, re-
spectively, to provide the above two reactions, which have, to
our knowledge, not been achieved by the existing methods.
Based on our previous studies on iron-catalyzed cross-cou-
Fax: (+81)774-38-3186
E-mail: masaharu@scl.kyoto-u.ac.jp
+
[
b] N. Nakagawa, Prof. Dr. T. Hatakeyama, Prof. Dr. M. Nakamura
Department of Energy and Hydrocarbon Chemistry
Graduate School of Engineering, Kyoto University
Nishikyo-ku, Kyoto 615-8510 (Japan)
[c] N. Nakagawa
CREST (Japan) Science and Technology Agency (JST)
+
[d] Prof. Dr. T. Hatakeyama
Elements Strategy Initiative for Catalysts and Batteries (ESICB)
Kyoto University, Katsura, Kyoto 615-8520 (Japan)
PRESTO (Japan) Science and Technology Agency (JST)
[8,9]
[10]
pling
and carbometalation reactions,
we screened iron
+
[
] Current address:
catalysts and reaction conditions and found that a simple iron
School of Science & Technology, Department of Chemistry
Kwansei Gakuin University
[11]
salt can catalyze the diboration of alkynes under particular
conditions: In the presence of 10 mol% FeBr , 10 mol% LiOMe,
2
-1 Gakuen, Sanda, Hyogo, 669-1337 (Japan)
2
and 1.5 equivalents of 2-methoxy-4,4,5,5-tetramethyl-1,3,2-di-
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201406595.
oxaborolane (MeOBpin) 3a, the diboration of 4-octyne 1 with
Chem. Eur. J. 2015, 21, 1 – 6
1
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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