Nickel-catalyzed decarboxylative cycloaddition of isatoic anhydrides with alkenes

Article abstract of DOI:10.1016/j.tetlet.2013.07.043

A new method for the synthesis of tricyclic 2,3-dihydro-4-quinolones by the NiCl₂(PMe₃)₂-catalyzed carboamination of alkenes by intermolecular decarboxylative cycloaddition reaction is reported here. Isatoic anhydrides were reacted with various norbornenes to afford the novel structure of quinolones. This protocol is simple and easy to handle.

Full text of DOI:10.1016/j.tetlet.2013.07.043

Accepted Manuscript
Nickel-Catalyzed Decarboxylative Cycloaddition of Isatoic Anhydrides with
Alkenes
Meng Sun, Yan-Na Ma, Ya-Min Li, Qiu-Ping Tian, Shang-Dong Yang
PII:
S0040-4039(13)01182-9
DOI:
http://dx.doi.org/10.1016/j.tetlet.2013.07.043
TETL 43241
Reference:
To appear in:
Tetrahedron Letters
Received Date:
Revised Date:
Accepted Date:
24 April 2013
1 July 2013
8 July 2013
Please cite this article as: Sun, M., Ma, Y-N., Li, Y-M., Tian, Q-P., Yang, S-D., Nickel-Catalyzed Decarboxylative
Cycloaddition of Isatoic Anhydrides with Alkenes, Tetrahedron Letters (2013), doi: http://dx.doi.org/10.1016/
j.tetlet.2013.07.043
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1
Tetrahedron Letters
journal homepage: www.elsevier.com
Nickel-Catalyzed Decarboxylative Cycloaddition of Isatoic Anhydrides with Alkenes
Meng Sun, Yan-Na Ma, Ya-Min Li, Qiu-Ping Tian, Shang-Dong Yanga, 
aState Key Laboratory of Applied Organic Chemistry, Lanzhou University Lanzhou 730000, P. R. China.
ARTICLE INFO
ABSTRACT
Article history:
Received
Received in revised form
Accepted
A new method for the synthesis of tricyclic 2, 3-dihydro-4-quinolones by the NiCl2(PMe3)2-
catalyzed carboamination of alkenes by intermolecular decarboxylative cycloaddition reaction is
reported here. Isatoic anhydrides were reacted with various norbornenes to afford the novel
structure of quinolones. This protocol is simple and easy to handle.
Available online
© 2013 Elsevier Ltd. All rights reserved .
Keywords:
Nickel-catalyzed
Decarboxylative
Cycloaddition
Isatoic anhydrides
Norbornene
Tricyclic 2,3-dihydro-4-quinolones are found in a number of
bioactive small molecules, including the acronycine family of
alkaloids that possess potent anticancer properties.1 As a result,
strategies have been developed in order to synthesize this
framework. The [4+2] cycloadditions reaction is one of the most
straightforward methods of synthesis.2 Another popular synthetic
route is the intermolecular Diels–Alder reaction.3 Moreover,
decarboxylative reactions is also to be a powerful method. 4 Other
methods also involve palladinum-catalyzed enolate arylation.5
However, despite a number of innovative synthetic approaches to
such N,O-polyheterocycles have been reported, existing
compound collections occupy only a small fraction of biogenic
chemical space. Thus, in order to enable the discovery of
bioactive chemotypes, the development of new and more
efficient methods for synthesis of novel heterocyclic molecules is
crucial. Recently, a nickel(0)-catalyzed direct insertion of an
unsaturated carbon-carbon bond into a carbon-nitrogen bond has
offered a useful transformation. This process takes into account
an atom and step economy which undertakes to prepare more
complicated azacytclic compounds in a single step, namely the
addition of C and N fragments to form C-C and C-N bonds
simultaneously (Scheme 1).6-10 It has been shown that
heterocyclic compounds such as triazoles, phthalimides, phthalic
anhydride, and isatoic anhydrides can work with Ni(0) through
oxidative addition and then extrusion of gaseous molecules such
as CO, CO2 and N2 to generate an active species (C-Ni-N). This
process leads to the carboamination of alkynes or allenes and can
be applied to the synthesis of different new heterocyclic
compounds (Scheme 1, A and B).11-13 However, only two
precedents exist for such a potentially valuable methodology with
alkenes;11f,13c the easy elimination of β-hydride elimination when
alkenes are added or a process of rapid self-oligomerisation may
be the reason. Herein, we disclose a Ni(0), generated in situ,
catalyzed cycloadditon of isatoic anhydrides with norbornenes by
carboamination to synthesize quinolone derivatives (Scheme 1,
C).
Scheme 1. Different Pathways of Nickel-Catalyzed Carboamination
Our initial experiment began with N-methylisatoic anhydride
(1a), which was treated with norbornene (1b),14 5 mol %
Ni(cod)2, and 10 mol % PCy3 in toluene at 100 ºC for 24 h.
Although only a trace of the desired product of 2a was obtained,
this result hinted to us that the reaction was practical. Therefore,
we screened different trialkylphosphine ligands such as PMe3, Pt-
Bu3, PPh3 or N-heterocarbnen ligands, but no good result was
found (Table 1, entry 2-5). Generally, some pioneering reports
have shown that the addition of appropriate Lewis acid (LA) will
effectively improve the conversion and yield of reactions.15
Results of investigating diverse Lewis acids served to correct our
tactics: the addition of Zn(OTf)2 or Zn promoted the reaction,
Table 1. Reaction Condition Screening a,b,c
———
 Corresponding author. Tel.: +86 931 891 2859; fax: +86 931 891 2859; e-mail: yangshd@lzu.edu.cn (S.-D. Yang)

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Tetrahedron letters
selected NiCl2(PMe3)2 and activated Zn powder as an additive in
the reaction, the quinolone 2a was obtained in 90% isolated yield
(Table 1, entry 16). In addition, the product was also obtained in
moderate yield under the condition of Ni(cod)2 with PMe3 and Zn.
Lastly, the solvent screening showed that toluene is the best
choice.
With the optimized conditions in hand, we next investigated
the scope of various isatoic anhydrides in the reactions. Initially,
a variety of N-protected isatoic anhydrides 1b-1d were surveyed,
which were readily prepared from isatoic anhydride 1e.16
Reaction of the isatoic anhydrides 1b-1d with norbornene
resulted in the corresponding N-substituted derivatives 2b-2d
with good-to-excellent yields (Table 2). The results demonstrated
that steric hindrance is not crucial to the cycloaddition reaction,
although the corresponding yields were depressed with the
increasing size of the N-substituted groups. It was encouraging
that isatoic anhydrides 1e also took part in this reaction, although
the quinolones product was only isolated in a 29% yield. In order
to study the impact of varying isatoic anhydride aromatic
substituents in the reaction of decarboxylative annulation, a wide
variety of N-methyl benzo-substituted isatoic anhydrides 1f-1o
were subjected to optimized conditions. The isatoic anhydrides,
Table 3. Nickel-Catalyzed Cycloaddition Reaction of Isatoic
Anhydride with Various Norbornenes a,b
[a] All the reactions were carried out in the presence of 0.5 mmol of 1a and
0.75 mmol of 1b in 5.0 mL toluene at 100 ºC; [b] Isolated yields; [c] 80 ºC.
Table 2. Nickel-Catalyzed Annulations of Norbornene with
Different Isatoic Anhydrides a,b,c
[a] All the reactions were carried out in the presence of 0.5 mmol of 1a and
0.75 mmol of norbornenes in 5.0 mL toluene at 120 ºC; [b] Isolated yields.
which possess electron-donating groups at the aromatic ring,
proceeded to completion. High yields of quinolones compounds
were therefore obtained. In particular, 1g and 1i, which had
methyl substituents at the para-position or ortho- position of
amides, provided quinolones 2g and 2i in 81% and 82% yields,
respectively. However, lower amounts of 2j and 2l were obtained
because of the high steric hindrance of 1j and the decomposition
of 1l in reaction conditions. On the other hand, the quinolones
were also isolated in good yields. The quinolones were originally
[a] All the reactions were carried out in the presence of 0.5 mmol of 1a and
0.75 mmol of 1b in 5.0 mL toluene at 100 ºC; [b] Isolated yields. [c]
NiCl2(PMe3)2 was replaced with Ni(cod)2 and PCy3.
thus improving the yield 20% or 51% (Table 1, entry 6-14). This
unsatisfying result prompted us to consider other accounts. We
all know that the nickel(0) species is very active and prone to
oxidation if stored improperly or imposed on an ill-defined
operation. With this in mind, we subsequently concentrated our
screening on the nickel (0) catalyst generated in situ and
guaranteed its genuine and high activity. To our delight, when we

3
with a high reactivity; 2) the Lewis acid of ZnCl2, which is
isatoic anhydrides, which we substituted with electron-
withdrawing groups as fluoro, trifluoromethyl, and
methoxycarbonyl groups. The addition of norbornene across 1m
and 1n afforded organofluorine quinolones in 74% and 70%
yields. Moreover, we attributed the moderate yield obtained for
2o to the separation of cycloadditon product, which was sensitive
to the flash column.
formed in situ by the reaction of NiCl2(PMe3)2 and activated Zn
powder, might coordinate a carbonyl moiety to facilitate
oxidative addition steps; 3) the Lewis acid of ZnCl2 promotes the
reductive elimination steps in this transformation. To the best of
our knowledge, Zn has been applied as an reductant or addition
in a variety of contexts,18 but it has not been employed in the
cycloaddition reactions of isatoic anhydrides.
Encouraged by these promising results, we further examined
the scope and limitations of the reaction using various substituted
norbornenes. The decarboxylative cycloaddition was also
compatible with electron-donating norbornenes, although the
corresponding yields were moderate (Table 3, entry 1-2). The
treatment of benzonorbornadiene and 5-ethylidene-2-norbornene
at a higher temperature gave annulation products 2p and 2q in
40% and 43% yields under the same conditions. To our delight,
the insertion of electron-deficient norbornenes afforded the
products in good yields. We were pleased to observe that the
reaction of 1a with the methyl-5-norbornene-2-carboxylate gave
the quinolones 2r in 88% yield. (Table 3, entry 3). In addition,
dimethyl-5-norbornene-2, 3-dicarboxylate, and 5-acetyl-2-
norbornene were both tolerated and provided the novel
quinolones 2s and 2t in moderate yields, respectively (Table 3,
entry 4-5). However, other alkenes, such as styrene and methyl
acrylate, failed to participate in the reaction due presumably to
rapid oligomerization or β-hydride elimination.
In conclusion, we have developed a novel nickel-catalyzed
decarboxylative cycloaddition of alkenes with isatoic anhydrides,
which provide a new method to synthesize quinolone derivatives.
Nickel(0) catalyst generated in situ from NiCl2(PMe3)2 and
activated Zn powder is found to be very important to ensure the
success of the reaction. Further efforts to expand the scope of the
chemistry and studies of the detailed mechanism are currently
underway in our laboratories.
Acknowledgments
We are grateful to the NSFC (Nos. 21072079), International
Cooperation and Exchanges NSFC (Nos. 20921120404) and
Research Fund for the Doctoral Program of Higher Education of
China (Nos. 20100211120014) financial support. S.F. Reichard,
MA contributed editing. Experiment details see Supporting
information.
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Graphical Abstract
Nickel-Catalyzed Decarboxylative
Cycloaddition of Isatoic Anhydrides with
Alkenes
Meng Sun, Yan-Na Ma, Ya-Min Li, Qiu-Ping Tian, Shang-Dong Yanga, 