Angewandte
Communications
Chemie
Metathesis
FeCl -Catalyzed Ring-Closing Carbonyl–Olefin Metathesis
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Lina Ma , Wenjuan Li , Hui Xi, Xiaohui Bai, Enlu Ma, Xiaoyu Yan, and Zhiping Li*
Abstract: Exploiting catalytic carbonyl–olefin metathesis is an
eration of this M=O reagent precludes the development of
ongoing challenge in organic synthesis. Reported herein is an
a catalytic version of RCCOM, as it would dramatically
increase the cost of synthesis because of the high prices of the
molybdenum and ruthenium reagents. To circumvent this
shortcoming, chemists developed the photochemical [2+2]/
FeCl -catalyzed ring-closing carbonyl–olefin metathesis. The
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protocol allows access to a range of carbo-/heterocyclic alkenes
with good efficiency and excellent trans diastereoselectivity.
The methodology presents one of the rare examples of catalytic
ring-closing carbonyl–olefin metathesis. This process is pro-
[
4]
retro[2+2] cycloaddition to facilitate the RCCOM. Stoi-
chiometric Lewis-acid-promoted reactions of RCCOM have
also been disclosed, but only a few of carbocycles could be
posed to take place by FeCl -catalyzed oxetane formation
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[5]
followed by retro-ring-opening to deliver metathesis products.
achieved. Importantly, organocatalyzed ring-opening meta-
thesis (ROM) of cyclopropenes with aldehydes was first
[6]
R
ing-closing metathesis (RCM) of two carbon–carbon
realized by the group of Lambert. In 2015, the group of
Franzꢀn reported the trityl-catalyzed metathesis of aromatic
double bonds is one of the most significant reactions for the
[1]
[7]
synthesis of various-sized rings (Figure 1a). The impact of
RCM can be appreciated from its use in the synthesis of
materials, drugs, natural products, etc. Inspired by the power
aldehydes and alkenes. Very recently, Schindler and co-
workers reported an iron-catalyzed carbonyl–olefin meta-
thesis for the construction of functionalized carbocycles and
the method demonstrated a broader range of substrates, thus
[
8]
representing a breakthrough in this area. Considering the
limited success in the past and the urgent development of
green synthetic methodologies, developing
a catalytic
RCCOM is challenging but worthy of further exploration.
It was envisioned that if the olefin bears an aryl group and
is exposed to a Lewis acid, it could give an oxetane
intermediate, which then undergoes retro [2+2], and thus
a RCCOM reaction can be realized (Figure 1c). Toward this
end, we report an approach for the catalytic RCCOM
reaction using an earth-abundant and inexpensive iron
[
9]
catalyst.
We commenced our investigation by studying the carbon-
yl–olefin metathesis of 1a to give the cyclopentene 2a
(
Table 1). Efforts to address a catalytic RCCOM centered
Figure 1. Overview of ring-closing double-bond metathesis.
on suitable catalysts. With extensive screening of a variety of
Lewis acids and Brønsted acids, to our delight, the desired
cyclopentene product 2a was obtained in 73% yield by using
of RCM, chemists are also interested in developing ring-
closing carbonyl–olefin metathesis (RCCOM) of carbonyl-
FeCl as the catalyst in DCE (1,2-dichloroethane; entry 1),
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[
2]
enes to synthesize ring compounds (Figure 1b). First, the
carbonyl group in carbonyl-enes are either readily available
or easily prepared, while di-alkenes for RCM need more steps
to be synthesized. Second, carbonyl–olefin metathesis is
a powerful means to synthesize highly substituted and
otherwise difficult-to-obtain alkenes. However, the reported
RCCOM is realized by using a stoichiometric amount of an
RCM catalyst, such as titanium, molybdenum, or rhuthenium
while other Lewis acids and Brønsted acids either failed to
deliver 2a (entries 2–7) or showed lower efficiency (entries 8
and 9). Carrying out the reaction in a dilute solution resulted
in 87% yield of 2a (entry 10). Interestingly, DCM (dichloro-
methane) and PhCl are also applicable solvents for the
reaction (entries 11 and 12). However, 2a was not observed in
THF or acetonitrile (entries 13 and 14). Notably, only the
trans-product 2a was obtained in the reactions shown in
entries 1 and 10–12. We hypothesized that the steric bulk of
the phenyl and benzoyl group play a key role in the formation
of the oxabicyclo[3.2.0]heptane derivative, which is proposed
as an intermediate of this reaction.
[
3]
catalysts. The mechanism of these reported RCCOM
reactions involve the formation of the M=O reagent. Gen-
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[
*] L. Ma, W. Li, H. Xi, X. Bai, E. Ma, Dr. X. Yan, Prof. Dr. Z. Li
Department of Chemistry, Renmin University of China
Beijing 100872 (China)
Under optimal reaction conditions, we initially examined
the scope of the FeCl -catalyzed ring-closing carbonyl–olefin
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E-mail: zhipingli@ruc.edu.cn
metathesis for the formation of five-membered carbocycles
(Table 2). The 1,3-dicarbonyl-derived substrates 1a–g
afforded the corresponding metathesis products 2a–g in 62–
84% yields. In these cases, only the trans-configured products
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[
] These authors contributed equally to this work.
Angew. Chem. Int. Ed. 2016, 55, 1 – 5
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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