Synthesis of ferrocene[c]pyridin-2(1H)-one derivatives via Pd(II)-catalyzed C–H activation reaction under air

Article abstract of DOI:10.1016/j.tetlet.2016.09.006

A Pd(II)-catalyzed C–H activation annulation under air has been successfully developed for efficient synthesis of ferrocene[c]pyridin-2(1H)-one derivatives with high yields and good regiochemistry. This method shows highly atom- and step-economical access to prepare ferrocene-fused heterocycles under mild conditions.

Full text of DOI:10.1016/j.tetlet.2016.09.006

Accepted Manuscript
Synthesis of ferrocene[c]pyridin-2(1H)-one derivatives via Pd(II)-catalyzed
C–H activation reaction under air
Hua-Yu Liu, Rui-Qi Mou, Chuan-Zhi Sun, Sheng-Yan Zhang, Dian-Shun Guo
PII:
S0040-4039(16)31154-6
DOI:
http://dx.doi.org/10.1016/j.tetlet.2016.09.006
TETL 48076
Reference:
Tetrahedron Letters
To appear in:
Received Date:
Revised Date:
Accepted Date:
12 July 2016
31 August 2016
2 September 2016
Please cite this article as: Liu, H-Y., Mou, R-Q., Sun, C-Z., Zhang, S-Y., Guo, D-S., Synthesis of
ferrocene[c]pyridin-2(1H)-one derivatives via Pd(II)-catalyzed C–H activation reaction under air, Tetrahedron
Letters (2016), doi: http://dx.doi.org/10.1016/j.tetlet.2016.09.006
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers
we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and
review of the resulting proof before it is published in its final form. Please note that during the production process
errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Graphical Abstract
Synthesis of ferrocene[c]pyridin-2(1H)-one
derivatives via Pd(II)-catalyzed C–H
activation reaction under air
Leave this area blank for abstract info.
Hua-Yu Liu, Rui-Qi Mou, Chuan-Zhi Sun, Sheng-Yan Zhang and Dian-Shun Guo

Tetrahedron
1
Tetrahedron Letters
Synthesis of ferrocene[c]pyridin-2(1H)-one derivatives via Pd(II)-catalyzed C–H
activation reaction under air
Hua-Yu Liu, Rui-Qi Mou, Chuan-Zhi Sun, Sheng-Yan Zhang and Dian-Shun Guo
College of Chemistry, Chemical Engineering and Materials Science, Collaborative Innovation Center of Functionalized Probes for Chemical Imaging in
Universities of Shandong, Shandong Normal University, Jinan 250014, P. R. China
ARTICLE INFO
ABSTRACT
Article history:
Received
Received in revised form
Accepted
A Pd(II)-catalyzed C–H activation annulation under air has been successfully developed for
efficient synthesis of ferrocene[c]pyridin-2(1H)-one derivatives with high yields and good
regiochemistry. This method shows highly atom- and step-economical access to prepare
ferrocene-fused heterocycles under mild conditions.
Available online
2009 Elsevier Ltd. All rights reserved.
Keywords:
Palladium-catalysis
C–H activation
N-Methoxy amide
Ferrocene-fused heterocycle
Annulation
———
 Corresponding author. E-mail: chdsguo@sdnu.edu.cn

2
Tetrahedron
Ferrocene possesses unique structural and electronic
our reaction. Additionally, there was no detection of olefin
1
features, and its derivatives now serve as a very popular
organometallic scaffold and have been extensively applied in
asymmetric catalysis,1 organic synthesis,2 materials science,3 and
biomedicinal chemistry.4 With the progress of the green
chemistry,5 chemists are strongly desired to minimize synthetic
steps and the amounts of toxic waste formed, and moreover, to
find milder and more selective transformation. Recent years,
transition metal-catalyzed CH bond functionalization has
emerged as a powerful tool in synthesis of novel ferrocene
derivatives because such a strategy circumvents the need for prior
steps to activate the substrate and offers a more robust
transformation than the conventional synthesis.6
product in the recovered alkyne identified by H NMR analysis
when excess alkyne (2 equiv) used in the reaction, exhibiting that
excess alkyne is not an external oxidant. Furthermore, there was
no H2 formed in the reaction monitored by gas chromatography.
Therefore, we believe that oxygen in air is the sole oxidant for
this reaction. While, we found that adding a low loading (2 mol
%) of Cu(OAc)2 can accelerate the reaction and improve the
yield (78% vs 93%, Table 1, entries 1 and 2).
Table 1
Optimization of reaction conditions a
However, this strategy usually needs an external oxidant to
account for the change in oxidation state of the CH bond and to
enable the catalyst turnover along with high temperature, which
would dispose a stoichiometric amount of waste and reduce the
overall greenness of the process. As a consequence, building on
the seminal strategy of using an internally oxidizing NO
directing group pioneered by Fagnou,7 Glorius,8 and Wu,9 were
developed in organic synthesis by taking advantages of oxidizing
potential of NO and NN bonds in oximes,10 N-
pivaloxybenzamide,11 hydrazines,12 phenoxyamides,13 N-oxides,14
and others.15 Very recently, such a kind of internally oxidizing
groups have been introduced to the Rh(III)-catalyzed C−H bond
functionalization of ferrocene derivatives (Scheme 1).16
Entry
1
Solvent
toluene
toluene
MeOH
CH3CN
THF
Base
PTC
Time (h)
10
Yield (%)b
NaOAc
NaOAc
NaOAc
NaOAc
NaOAc
NaOAc
none
CTAB
CTAB
CTAB
CTAB
CTAB
CTAB
CTAB
CTAB
CTAB
CTAB
CTAB
CTAB
TBAB
TBAI
none
78c
93
68
85
75
39
77
79
66
83
6
2
8
3
13
4
13
5
11
6
MEKd
13
Moreover, fused oligocyclic lactams and their derivatives are
widespread in drugs and natural products with pharmacological
7
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
11
relevance.17 Frequently, when
a
ferrocene fragment is
8
NaHCO3
NaH2PO4
KH2PO4
K2CO3
10
incorporated into a bioactive molecule, its biological activities
may be enhanced markedly.18 Encouraged by these results, we
envisioned using N-methoxy amide moiety of N-
methoxylferrocenecarboxamide as a directing group to pursue
our interest in constructing ferrocene fused nitrogen-containing
heterocycles. Herein, we report an efficient method for synthesis
of ferrocene[c]pyridin-2(1H)-one derivatives via Pd(II)-catalyzed
C–H activation reaction under air, and some mechanistic insights
as well as electrochemical and photochemical properties.
We initiated our studies by the use of N-methoxylferrocene-
carboxamide 1 and diphenylacetylene 2a as model substrates. As
shown in Table 1, when 1 (0.4 mmol) was treated with 2a (0.8
mmol) in the presence of Pd(OAc)2 (0.04 mmol), NaOAc (0.4
mmol), CTAB (cetyl trimethylammonium bromide, 0.08 mmol),
and toluene (2 mL) at 70 C for 10 h under air, we were pleased
to find that the reaction can conduct successfully to give product
3a in 78% yield (Table 1, entry 1).
9
17
10
11
12
13
14
11
13
Na2CO3
NaOAc
NaOAc
NaOAc
13
50
48
30
trace
24
24
15
24
a
Reaction conditions: 1 (0.4 mmol), 2a (0.8 mmol), Pd(OAc)2 (0.04 mmol),
PTC (0.08 mmol), Cu(OAc)2 (0.008 mmol), base (0.4 mmol), solvent (2 mL),
65oC, under air.
b Isolated yields.
c Cu(OAc)2 free, 70 C.
d MEK: 2-butanone.
Through extensive screening, we found that toluene is the best
solvent for the reaction (93% yield, Table 1, entry 2) among the
solvents tested (Table 1, entries 2-6). Furthermore, changing the
amount of 2a has a big effect on the yield (ESI). Among the
selected additives (Table 1, entries 7-12), NaOAc is the best one,
whereas no base or other bases such as NaHCO3, NaH2PO4,
KH2PO4, K2CO3 and Na2CO3 were used, the yield decreased.
Remarkably, CTAB, as a phase transfer catalyst, is indispensable
and the best one to the reaction, which may be ascribed to its
excellent lipophilicity (Table 1, entries 2, 13-15).
With the optimized reaction conditions in hand, the scope of
ferrocene[c]pyridin-2(1H)-one formation was demonstrated by a
variety of unsymmetrical internal alkynes. As shown in Table 2,
in most cases, unsymmetrical diary alkynes and alkyl-aryl
alkynes furnished the desired products 3a-3n in moderate to
excellent yields with good regioselectivity. The unsymmetrical
alkynes with an electron-withdrawing moiety (3b-3d, 3g, 3h, 3k
and 3m) showed somewhat more reactivity and afforded higher
yields than those attaching an electron-donating group (3e, 3i, 3j,
3l and 3n). When 5-phenylethynylpyrimidine was used, the
reaction took place at higher temperature (75oC) and gave the
Scheme 1. Dehyrogenation annulation via metal-catalyzed C-H
activation.
To our surprise, the methoxy moiety still remains in the
1
structure of 3a, which was confirmed by H, 13C NMR, HR-MS
and X-ray diffraction techniques (ESI). This result indicates that
the N-methoxy amide group does not act as an internal oxidant in

Tetrahedron
3
corresponding product 3n in 42% yield. Unfortunately, attempts
on the reaction employing terminal alkynes are not successful. In
addition, ferrocenecarboxamide instead of
investigated, giving no product.
1
was also
Table 2
Substrate scope of alkynes a
Scheme 2. Deprotection of 3a.
Electrochemical and photochemical studies of the ferrocene
fused pyridinone derivatives 3 were carried out and the results
are summarized in Table S5 and Figures. S5-S7 (ESI). The cyclic
voltammetry (CV) curves exhibit the typical reversible wave
corresponding to the ferrocene/ferrocenium (Fc/Fc+) redox
couple. In comparison with the ferrocene, E1/2 values of 3 are
positively shifted for ca. 150 to 360 mV, varied markedly with
the different substituents. This indicated that the ferrocene-fused
heterocycles 3 are more difficult to be oxidized than the
ferrocene owing to the electron-withdrawing character of the
pyridinone moiety. In the UV-vis absorption spectra, some
compounds show two peaks at 311-325 nm and 471-478 nm,
respectively. Compared with the ferrocene (325 nm, 440 nm), the
former made a slightly hypsochromic shift, whereas the latter
produced a bathochromic shift. Additionally, the fluorescent
spectrum of 3a exhibits an emission maximum at 370 nm.
To understand the plausible mechanism of this new reaction,
some additional experiments were performed. First, although
excess alkyne (2 equiv) needed in the reaction, there was no
detection of olefin product in the recovered alkyne, indicating
that alkyne does not play an external oxidant. Second, there was
no H2 yielded in the reaction. Moreover, the reaction could be
promoted by the catalytic amounts of Cu(OAc)2. All these results
reveal that this reaction is a dehydrogenation annulation with the
loss of one molecule of H2O under air. It should be pointed out
that Cu(OAc)2 is not an external oxidant in our reaction,20 but
its mechanism of actual function is not clear at present.
Based on these observations, the following catalytic cycle is
proposed (Figure 1). In the presence of base, molecule 1 would
coordinate to active Pd(II) A to create a five-membered
palladacycle B with the loss of one molecule of acetic acid.21
Insertion of 2 into the Pd–Csp2, Cp bond of B via the Pd alkyne
complex C yields the seven-membered palladacycle D. The
regioselectivity results from the steric effect of the two
substituents of the alkyne whereby the more hindered RL is
favored to sit next to the less hindered amide side than the Cp
ring. After reduction elimination, the desired product was
obtained and then the Pd(0) pieces can be reoxidized by air to
regenerate Pd(II) species for the next catalytic cycle.
a
Reaction conditions: 1 (0.4 mmol), 2 (0.8 mmol), Pd(OAc)2 (0.04 mmol),
CTAB (0.08 mmol), Cu(OAc)2 (0.008 mmol), NaOAc (0.4 mmol), toluene (2
mL), 65 C, under air. Isolated yields.
b 75 C.
c Isolated yield with a ratio of 3e:3e' = 3:2.
The regiochemistry of this reaction was mainly controlled by
the steric effect. As displayed in Table 2, when unsymmetrical
alkyl-aryl, ferrocenyl-aryl alkynes and diphenyltutadiyne are
used, the major regioisomer is the ferrocene[c]pyridin-2(1H)-one
with the larger group attached close to the nitrogen atom (3f-3l).
While, in the case of unsymmetrical aryl-aryl alkynes are utilized,
the aryl with an electron-withdrawing group at the para-position
were linked adjacently to the ferrocene unit, which is likely
ascribed to the electron-effect (3b-3d, 3m). However, when 4-
methoxydiphenylacetylene was used, two regioisomers (3e, 3e’)
were isolated in 3:2 ratio.
Simple derivation of the ferrocene[c]pyridin-2(1H)-ones was
also tried to access other privileged ferrocene derivatives by
removal of the methoxy group (Scheme 2).19 We found that the
methoxy group could be easily removed in the presence of
LiAlH4 (ESI).

4
Tetrahedron
Beer, P. D.; Faulkner, S. J. Am. Chem. Soc. 2011, 133, 11847-
11849. (c) Fabre, B. Acc. Chem. Res. 2010, 43, 1509-1518.
(a) Braga, S. S.; Silva, A. M. S. Organometallics 2013, 32, 5626-
5639. (b) Moriuchi, T.; Hirao, T. Acc. Chem. Res. 2010, 43, 1040-
1051. (c) Hartinger, C. G.; Dyson, P. J. Chem. Soc. Rev. 2009, 38,
391-401. (d) van Staveren, D. R.; Metzler-Nolte, N. Chem. Rev.
2004, 104, 5931-5985.
Anastas, P.; Eghbali, N. Chem. Soc. Rev. 2010, 39, 301-312.
(a) Zhu, D.-Y.; Chen, P.; Xia, J.-B. ChemCatChem 2016, 8, 68-73.
(b) López, L. A.; López, E. Dalton Trans. 2015, 44, 10128-10135.
(c) Wang, Y.-F.; Zhang, A.-A.; Liu, L.-T.; Kang, J.-X.; Zhang, F.-
Q.; Ma, W.-J. Chin. J. Org. Chem. 2015, 35, 1399-1406. (d) Xie,
W.-C.; Li, B.; Xu, S.-S.; Song, H.-B.; Wang, B.-Q.
Organometallics 2014, 33, 2138-2141.
Figure 1. Proposed catalytic cycle.
To gain deeper mechanistic insight, preliminarily theoretical
4.
study on the formation of the five-membered palladacycle B was
conducted (Figure 2). Molecule 1 and Pd(OAc)2 first form IM1,
which needs nearly no energy barrier to transition state TS1. In
the pathway of the Ccp−H bond activation, transition state TS3 is
the highest stationary point and overall kinetic barrier, with an
attainable activation free energy (17.5 kcal/mol) (ESI).
5.
6.
7.
8.
9.
(a) Guimond, N.; Gorelsky, S. I.; Fagnou, K. J. Am. Chem. Soc.
2011, 133, 6449-6457; (b) Guimond, N.; Gouliaras, C.; Fagnou,
K. J. Am. Chem. Soc. 2010, 132, 6908-6909.
(a) Rakshit, S.; Grohmann, C.; Besset, T.; Glorius, F. J. Am.
Chem. Soc. 2011, 133, 2350-2353. (b) Patureau, F. W.; Glorius, F.
Angew. Chem., Int. Ed. 2011, 50, 1977-1979.
Wu, J.-L.; Cui, X.-L.; Chen, L.-M.; Jiang, G.-J.; Wu, Y.-J. J. Am.
Chem. Soc. 2009, 131, 13888-13889.
10. (a) Kornhaaß, C.; Kuper, C.; Ackermanna, L. Adv. Synth. Catal.
2014, 356, 1619-1624. (b) Huckins, J. R.; Bercot, E. A.; Thiel, O.
R.; Hwang, T.-L.; Bio, M. M. J. Am. Chem. Soc. 2013, 135,
14492-14495. (c) Neely, J. M.; Rovis, T. J. Am. Chem. Soc. 2013,
135, 66-69. (d) Hyster, T. K.; Rovis, T. Chem. Commun. 2011, 47,
11846-11848. (e) Too, P. C.; Wang, Y.-F.; Chiba, S. Org. Lett.,
2010, 12, 5688-5691.
11. (a) Huang, H.; Ji, X.; Wu, W.; Jiang, H. Chem. Soc. Rev. 2015, 44,
1155-1171. (b) Mo, J.-Y.; Wang, L.-H.; Cui, X.-L. Org. Lett.
2015, 17, 4960-4963. (c) Webb, N. J.; Marsden, S. P.; Raw, S. A.
Org. Lett. 2014, 16, 4718-4721. (d) Hyster, T. K.; Ruhl, K. E.;
Rovis, T. J. Am. Chem. Soc. 2013, 135, 5364-5367. (e) Cui, S.-L.;
Zhang, Y.; Wu, Q.-F. Chem. Sci. 2013, 4, 3421-3426.
12. (a) Liang, Y.; Yu, K.; Li, B.; Xu, S.; Song, H.; Wang, B. Chem.
Commun. 2014, 50, 6130-6133. (b) Muralirajan, K.; Cheng, C.-H.
Adv. Synth. Catal. 2014, 356, 1571-1576. (c) Zhao, D.; Shi, Z.;
Glorius, F. Angew. Chem., Int. Ed. 2013, 52, 12426-12429. (d)
Chuang, S.-C.; Gandeepan, P.; Cheng, C.-H. Org. Lett. 2013, 15,
5750-5753.
Figure 2. Free energy profile of cyclopalladation intermediate B.
In conclusion, we have developed a highly efficient method
for synthesis of ferrocene fused pyridinone derivatives by N-
methoxy amide-directed C−H activation under air. We found that
Pd(II)-catalyzed dehydrogenative annulation between N-methoxy
ferrocenecarboxamide and diverse internal alkynes can give
novel ferrocene[c]pyridin-2(1H)-one derivatives in high yields
with generally good regioselectivity. This method may contribute
to the preparation of new bioactive ferrocene fued hetecycles as
well as optical- and redox-active receptors.
Acknowledgments
13. (a) Hu, F.; Xia, Y.; Ye, F.; Liu, Z.; Ma, C.; Zhang, Y.; Wang, J.
Angew. Chem., Int. Ed. 2014, 53, 1364-1391. (b) Liu, G.; Shen,
Y.; Zhou, Z.; Lu, X. Angew. Chem., Int. Ed. 2013, 52, 6033-6153.
14. (a) Zhang, S.-S.; Wu, J.-Q.; Liu, X.-G.; Wang, H.-G. ACS Catal.
2015, 5, 210-214. (b) Shi, Z.-Z.; Boultadakis-Arapinis, M.;
Koester, D. C.; Glorius, F. Chem. Commun. 2014, 50, 2650-2652.
(c) Zhang, X.; Qi, Z.; Li, X. Angew. Chem., Int. Ed. 2014, 53,
10794-10974. (d) Ackermann, L.; Lygin, A. V.; Hofmann, N.
Angew. Chem., Int. Ed. 2011, 123, 6503-6506.
Financial support of this work from the National Natural
Science Foundation of China (grant No. 21372147) and the
Undergraduate Innovative Research Training Program of China
(grant No. 201510445168) is gratefully acknowledged.
Supplementary data
15. (a) Yu, S.-J.; Liu, S.; Lan, Y.; Wan, B.-S.; Li, X.-W. J. Am. Chem.
Soc. 2015, 137, 1623-1631. (b) Zhang, Q.-R.; Huang, J.-R.; Zhang,
W.; Dong, L. Org. Lett. 2014, 16, 1684-1687. (c) Liu, B.; Song, C.;
Sun, C.; Zhou, S.; Zhu, J. J. Am. Chem. Soc. 2013, 135, 16625-
16631. (d) Shen, Y.-Y.; Liu, G.-X.; Zhou, Z.; Lu, X.-Y. Org. Lett.
2013, 15, 3366-3369.
Supplementary data (ESI) available: Experimental procedures,
NMR spectra, HR-MS, CV, UV-vis, fluoresence data, and X-ray
crystallography can be found in ESI. Crystallographic data for
the structures 3a, 3b, 3h and 3n have been deposited with the
Cambridge Crystallography Data Centre (CCDC No. 1471312,
1471313, 1471314 and 1471315, respectively).
16. Wang, S.-B.; Zheng, J.; You, S.-L. Organometallics, 2016, 35,
1420-1425.
17. (a) Butler, J. R.; Wang, C.; Bian, J.; Ready, J. M. J. Am. Chem.
Soc. 2011, 133, 9956-9959. (b) Sloman, D. L.; Bacon, J. W.;
Porco, J. A. J. Am. Chem. Soc. 2011, 133, 9952-9955. (c) Michael,
J. P. Nat. Prod. Rep. 2008, 25, 139-165. (d) Ratnayake, R.; Lacey,
E.; Tennant, S.; Gill, J. H.; Capon, R. J. Chem. -Eur. J. 2007, 13,
1610-1619.
18. (a) Salmon, A. J.; Williams, M. L.; Wu, Q. K.; Morizzi, J.; Gregg,
D.; Charman, S. A.; Vullo, D.; Supuran, C. T.; Poulsen, S.-A. J.
Med. Chem. 2012, 55, 5506-5517. (b) Wu, C.; Ye, H.; Bai, W.; Li,
Q.; Guo, D.; Lv, G.; Yan, H.; Wang, X. Bioconjugate Chem. 2011,
22, 16-25. (c) Monserrat, J.-P.; Chabot, G. G.; Hamon, L.;
Quentin, L. Scherman, D.; Jaouen, G.; Hillard, E. A. Chem.
Commun. 2010, 46, 5145-5147. (d) Hamels, D.; Dansette, P. M.;
Hillard, E. A.; Top, S.; Vessieres, A.; Herson, P.; Jaouen, G.;
Mansuy, D. Angew. Chem., Int. Ed. 2009, 48, 9124-9126. (e) Top,
S.; Tang, J.; Vessieres, A.; Carrez, D.; Provot, C.; Jaouen, G.
Chem. Commun. 1996, 955-956.
References and notes
1.
(a) Xu, Q.-L.; Dai, L.-X.; You, S.-L. Chem. Sci. 2013, 4, 97-102.
(b) Arae, S.; Ogasawara, M. J. Synth. Org. Chem. Jpn. 2012, 70,
593-598. (c) Mellah, M.; Voituriez, A.; Schulz, E. Chem. Rev.
2007, 107, 5133-5209. (d) Dai, L.-X.; Hou, X.-L. Chiral
Ferrocenes in Asymmetric Catalysis, Wiley-VCH: Weinheim,
2009. (e) Arrayás, R. G.; Adrio, J.; Carretero, J. C. Angew. Chem.,
Int. Ed. 2006, 45, 7674-7715.
2.
3.
(a) Zhang, C.; Hu, X. H.; Wang, Y. H.; Zheng, Z.; Xu, J.; Hu, X.
P. J. Am. Chem. Soc. 2012, 134, 9585-9588. (b) Dai, L.-X.; Tu, T.;
You, S.-L.; Deng, W.-P.; Hou, X.-L. Acc. Chem. Res. 2003, 36,
659-667. (c) Colacot, T. J. Chem. Rev. 2003, 103, 3101-3118. (d)
Halterman, R. L. Chem. Rev. 1992, 92, 965-994. (e) Hayashi, T.;
Kumada, M. Acc. Chem. Res. 1982, 15, 395-401.
(a) Tarafder, K.; Surendranath, Y.; Olshansky, J. H.; Alivisatos, A.
P.; Wang, L. J. Am. Chem. Soc. 2014, 136, 5121-5131. (b)
Tropiano, M.; Kilah, N. L.; Morten, M.; Rahman, H.; Davis, J. J.;
19. (a) Cutulic, S. P. Y.; Murphy, J. A.; Farwaha, H.; Zhou, S.-Z.;
Chrystal, E. Synlett 2008, 2132-2136. (b) Taillier, C.; Bellosta, V.;
Meyer, C.; Cossy, J. Org. Lett. 2004, 6, 2145-2147. (c) Cui, S.-L.;
Zhang, Y.; Wu, Q.-F. Chem. Sci. 2013, 4, 3421-3426.

Tetrahedron
5
20. Hyster, T. K.; Rovis, T. J. Am. Chem. Soc. 2010, 132, 10565-
10569.
21. Dang, Y.-Y.; Qu, S.-L.; Nelson, J. W.; Pham, H. D.; Wang, Z.-X.;
Wang, X.-T. J. Am. Chem. Soc. 2015, 137, 2006-2014.

6
Tetrahedron
Hihlights
Pd-catalyzed C–H activation annulation of N-
methoxylferrocenecarboxamide in air.
Novel N-methoxylferrocene[c]pyridin-2(1H)-one
derivatives could be synthesized.
Formation of the five-membered palladacycle with
ferrocene core is rationalized.