Tetrahedron
Letters
Tetrahedron Letters 46 (2005) 5961–5964
Heteroaryl manganese reagents: direct preparation and
reactivity studies
a
b
Reuben D. Rieke,a,b, YoungSung Suh and Seung-Hoi Kim
*
aDepartment of Chemistry, University of Nebraska-Lincoln, Lincoln, NE 68588-0304, USA
bRieke Metals Inc., 1001 Kingbird Rd, Lincoln, NE 68521, USA
Received 27 May 2005; accepted 9 June 2005
Abstract—Direct preparation of various heteroaryl manganese reagents was performed by using highly active manganese (Mn ) and
*
heteroaryl halides. The resulting organomanganese reagents were coupled with electrophiles such as aryl halides, vinyl halides, and
benzoyl chlorides under mild reaction conditions. The corresponding coupling products were obtained in good yields.
ꢀ 2005 Published by Elsevier Ltd.
Current interest in the synthesis of natural products con-
taining heteroaromatic moieties as building blocks for
pharmaceutical industries, material science, and supra-
molecular chemistry has resulted in considerable effort
in developing new synthetic methods.1
philes in excellent yields.5 In spite of the importance of
p-deficient heteroaryl manganese halides, few results
have been reported about the preparation and applica-
tion of heteroaromatic manganese reagents.6
Here, we wish to report the direct formation of hetero-
aryl manganese halides and the results of several cross-
coupling reactions. In addition, palladium-catalyzed
cross-coupling reaction of heteroaryl manganese
reagents is also described.
Among the extensive studies for the preparation of
heteroaryl compounds, organometallic reagents are
frequently used and mainly prepared from metal–halogen
exchange reactions or the methathesis of the corres-
ponding organolithium and organomagnesium deriva-
tives.2 However, this approach limits the number of
functional groups that can be tolerated. The same dis-
advantage was observed when organozinc reagents were
prepared by transmetalation of organolithium and
organomagnesium reagents.3 To alleviate the difficulty,
direct preparation of heteroaryl zinc reagents by using
Rieke zinc has been reported.4
In general, heteroaryl manganese halides are easily pre-
pared by the reaction of highly active manganese with
various heteroaryl halides under mild reaction condi-
tions. And, it is of interest that cross-coupling reaction
of these reagents with acid chlorides was accomplished
without using any transition metal catalyst which is
required for the reaction of organozinc reagents. The cor-
responding ketones were obtained in good isolated yield
(Scheme 1). The results of the cross-coupling reactions
are summarized in Tables 1 and 2.
In our continuing studies on the utility of active manga-
nese, we examined the range of oxidative addition and
cross-coupling reactions with a broad range of hetero-
cyclic halides. Until now, active manganese prepared
by the Rieke method has been shown to exhibit superior
activity to organic halides under mild reaction condi-
tions. The resulting organomanganese reagents have
also shown a great reactivity toward several electro-
The oxidative addition of Mn was completed using
*
3 equiv of Mn and 1 equiv of the corresponding halides
*
in a few hours at room temperature except with 3-bromo-
furan (Table 1, entries 6 and 11). The following coupling
reactions were performed in an hour at room tempera-
ture as well. It is noteworthy that the acylation reaction
of N-containing p-deficient heteroaryl compound such
as pyridine becomes readily feasible through direct prep-
aration and reaction of pyridinylmanganese reagents
(Table 1, entries 1, 4, 8, and 9). This is particularly
*
Corresponding author. Tel.: +1 402 434 2775; fax: +1 402 434
0040-4039/$ - see front matter ꢀ 2005 Published by Elsevier Ltd.
doi:10.1016/j.tetlet.2005.06.092