Rh/Cu-catalyzed multiple C-H, C-C, and C-N bond cleavage: Facile synthesis of pyrido[2,1-a]indoles from 1-(pyridin-2-yl)-1H-indoles and γ-substituted propargyl alcohols

Article abstract of DOI:10.1039/c5cc01412c

An unusual Rh/Cu-catalyzed synthesis of pyrido[2,1-a]indoles starting from 1-(pyridin-2-yl)-1H-indoles and γ-substituted propargyl alcohols was presented. The multi-step cascade transformations formally involve the cleavage of two C-H, three C-C, and one C-N bonds with concomitant construction of two C-H, four C-C, and one C-N bonds with excellent chemoselectivity in one-pot reaction.

Full text of DOI:10.1039/c5cc01412c

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Rh/Cu-catalyzed multiple C–H, C–C, and C–N
bond cleavage: facile synthesis of pyrido[2,1-a]-
indoles from 1-(pyridin-2-yl)-1H-indoles and
c-substituted propargyl alcohols†
Cite this:DOI: 10.1039/c5cc01412c
Received 14th February 2015,
Accepted 9th March 2015
Ting Li, Zhen Wang, Mingliang Zhang, Hui-Jun Zhang and Ting-Bin Wen*
DOI: 10.1039/c5cc01412c
www.rsc.org/chemcomm
An unusual Rh/Cu-catalyzed synthesis of pyrido[2,1-a]indoles starting alkynylation methods for broadly defined arenes via a C–H activation
from 1-(pyridin-2-yl)-1H-indoles and c-substituted propargyl alcohols pathway. In this context, it is worth noting that tert-propargyl alcohols
was presented. The multi-step cascade transformations formally involve have been involved in Sonogashira-type reactions as masked terminal
12
the cleavage of two C–H, three C–C, and one C–N bonds with alkynes. Moreover, Miura discovered that [Rh(OH)(COD)]
2
could
concomitant construction of two C–H, four C–C, and one C–N catalyze regio- and stereo-selective homo-coupling of g-arylated tert-
bonds with excellent chemoselectivity in one-pot reaction.
propargyl alcohols via b-carbon elimination with liberation of ketone, in
which an alkynyl rhodium generated in situ was proposed as the key
13
The selective cleavage and construction of chemical bonds has always intermediate. Furthermore, given the great success and advantages of
1
been a central topic in modern synthetic organic chemistry. In recent rhodium catalysis in the construction of C–X bonds (X = C, N, O, etc.)
14,15
decades, transition metal-catalyzed direct cleavage of inert chemical based on C–H activation in recent years,
we were prompted
bonds such as C–H, C–C and C–N bonds, and thus associated to design the Rh-catalyzed direct C–H alkynylation of arenes utilizing
transformations have garnered increasing attention by the synthetic g-substituted tert-propargyl alcohols as the alkynyl coupling partner.
community. In particular, significant developments have been Following this idea, we have thus examined the reactions of 1-(pyridin-
2
acquired in the area of C–H activation. However, reports of C–C 2-yl)-1H-indoles with tert-propargyl alcohols under the Rh/Cu catalyst
activation are less prominent in the literature probably owing to the system, which serendipitously led to the formation of pyrido[2,1-a]-
thermodynamic stability of these bonds and the kinetic factors arising indoles instead of the expected alkynylation products (Scheme 1).
from the greater steric hindrance as well as the competing C–H Herein, we communicate this unusual cascade reaction, whereby at
3,4
activation. Therefore, examples for C–C bond activation are still least six bonds, including two C–H, three C–C and one C–N bonds,
mostly limited to strained C–C bonds, decarboxylation reactions, or were cleaved and seven bonds (two C–H, four C–C and one C–N bonds)
3,4
performed with the help of strong chelation assistants. Similarly, were constructed in one pot. The reaction reported here is unprece-
16
due to the high C–N bond dissociation energy, catalytic transforma- dented especially when the efficiency is considered.
tions involving selective cleavage of C–N bonds have been scarce We initiated our study by choosing 1-(pyridin-2-yl)-1H-indole
so far. Not surprisingly, the simultaneous cleavage of both C–C 1a and 2-methyl-4-phenyl-3-butyn-2-ol 2a as model substrates.
and C–N bonds under one set of conditions would be even more Surprisingly, when [Cp*RhCl and Cu(OAc) O were employed as
ÁH
the catalytic system, the unexpected product 3aa, which contains
5
,6
2
]
2
2
2
7
challenging, which is limited to a few reports.
On the other hand, transition-metal mediated direct C–H alkynyl- a pyrido[2,1-a]indole skeleton, was isolated in 24% yield (Table 1,
ation for the introduction of the alkynyl functionality has received entry 1). The definite structures of 3 came from the X-ray
8
9
10
much attention recently. Although terminal alkynes, alkynylhalides
11
as well as benziodoxolone-based hypervalent iodine reagents have
been used as alkynyl coupling partners to achieve direct C–H alkynyla-
tion of intrinsically different arenes, the substrate scope remains
limited. It is still necessary to develop highly efficient and general
Department of Chemistry, College of Chemistry and Chemical Engineering,
Xiamen University, Xiamen, 361005, Fujian, P. R. China.
E-mail: chwtb@xmu.edu.cn; Tel: +86 592-218-6085
†
Electronic supplementary information (ESI) available: Experimental and crys-
tallographic details. CCDC 1032402–1032406. For ESI and crystallographic data in
CIF or other electronic format see DOI: 10.1039/c5cc01412c
Scheme 1 Rh/Cu-catalyzed facile synthesis of pyrido[2,1-a]indoles via
multiple C–H, C–C, and C–N bond cleavage.
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a
a
Table 1 Optimization of reaction conditions
Table 2 Reaction scope of g-substituted tert-propargyl alcohols
Yield (%)
Temp.
Solvent (1C)
b
Entry [M]
Oxidant
3aa
c
1
2
[Cp*RhCI
[Cp*Rh(CH
SbF
Cp*Rh(OAc)
2
]
2
Cu(OAc)
2
ÁH
ÁH
2
2
O PhMe
O PhMe
125
125
24/(4a 64 )
32
3
CN)
3
]- Cu(OAc)
2
[
6 2
]
3
4
5
6
7
8
9
1
1
1
1
1
1
1
2
Cu(OAc)
Cu(OAc)
Cu(OAc)
Cu(OAc)
Cu(OAc)
Cu(OAc)
NO
2
2
2
2
2
2
ÁH
ÁH
ÁH
ÁH
ÁH
ÁH
2
2
2
2
2
2
O PhMe
O PhMe
O PhMe
O Xylene 125
O DCE 125
O Dioxane 125
PhMe
O PhMe
O PhMe
PhMe
125
125
125
40
[RhOH(COD)]
2
57/(4a 54)
78/(4a 41)
[RhCI(COD)]
[RhCI(COD)]
[RhCI(COD)]
[RhCI(COD)]
[RhCI(COD)]
NO
[RhCI(COD)]
[RhCI(COD)]
[RhCI(COD)]
[RhCI(COD)]
[RhCI(COD)]
[RhCI(COD)]
2
2
2
2
2
67
56
20
0
125
125
125
125
125
110
140
125
a
0
1
2
3
4
5
6
Cu(OAc)
Cu(OAc)
AgOAc
2
ÁH
ÁH
2
2
0/(4a 98)
General reaction conditions: 1a (0.2 mmol), 2 (0.8 mmol),
d
2
2
2
2
2
2
2
Trace
[RhCl(COD)]2 (1.5 mol%), Cu(OAc) ÁH O (2.2 equiv.), PhMe (2 mL),
2
2
0
0
125 1C, air, 6 h. Yield of isolated products based on 1a.
Ag
2
CO
3
PhMe
Cu(OAc)
Cu(OAc)
Cu(OAc)
2
2
2
ÁH
ÁH
ÁH
2
2
2
O PhMe
O PhMe
O PhMe
0/(4a 84)
Trace
Substrates bearing methoxy groups at the meta and para posi-
tions on the phenyl ring proceeded well (3ag, 3ah), while that
e
21/(4a 71)
a
Reaction conditions: 1a (0.20 mmol), 2a (0.80 mmol, 4 equiv.), [M] with a methoxy group at the ortho position on the phenyl ring
(
1.5 mol%), oxidant (2.2 equiv.) and solvent (2 mL) under air for about 6 h.
failed to yield the desired product 3ai, possibly due to the steric
hindrance. It is worth noting that the methodology could be
further extended to thiophene containing substrate 2j to afford
b
c
Yield of isolated products based on 1a. Yield of isolated products based on
d
e
2
a. 2.0 equiv. of K
2
CO
3
was added. Phenylacetylene instead of 2a.
3aj in 76% yield, while g-furan tert-propargyl alcohol 2k did not
crystallographic studies of a series of pyrido[2,1-a]indole pro- work at all. Moreover, aliphatic 2-methyloct-3-yn-2-ol 2l was
ducts 3af, 3ag (vide infra, see ESI†), 3la (Table 3), and 3jga also investigated to produce 3al in 41% yield, which represents
1
9
(Scheme 3). To the best of our knowledge, efficient strategies for the the first example of C(alkyl)–C(alkynyl) single bond cleavage.
construction of pyrido[2,1-a]indoles, a recurring structural motif
Subsequently, the scope of 1-(pyridin-2-yl)-1H-indoles was
found in many pharmaceuticals and functional materials, have further investigated (Table 3). Gratifyingly, reactions of 1b with
1
7,18
rarely been reported.
precatalysts, [RhCl(COD)]
After screening of a variety of rhodium g-arylated tert-propargyl achohols worked well to yield 3ba and 3bg
was found to be the best choice and 3aa in good yields. Other indoles with a substituent group such as OMe
2
was obtained in 78% isolated yield (entries 2–5). Investigation of or Cl at the C-5 position on the indole ring were also compatible
solvent effects indicated that toluene was the most suitable solvent with this transformation, thus affording the corresponding pro-
(
entries 5–8). Control experiments revealed that no desired product 3aa ducts 3ca, 3cg, and 3fa, while substrates with Me or F at the C-5
was detected in the absence of either [RhCl(COD)] or Cu(OAc) position on the indole ring did not work (3da, 3ga). In contrast,
ÁH
entries 9 and 10). Notably, the reaction was suddenly shut down in when the Me group was at the C-6 position, the reaction proceeded
the presence of an extra basic additive, K CO (entry 11). The use of smoothly to give 3ea in 74% yield. More importantly, when
other common oxidants such as AgOAc or Ag CO did not provide 2-(2-methyl-1H-pyrrol-1-yl)pyridine, 1h, was used as the substrate,
aa at all (entries 12 and 13). 125 1C was found to be the optimal indolizine derivatives 3ha and 3hg could be obtained in 61% and
temperature (entries 14 and 15). We have also examined the 66% yields respectively, which represent the rare examples of
2
2
2
O
(
2
3
2
3
3
18b,c
possibility of employing a simple terminal alkyne instead of 2a for this indolizine synthesis starting from pyrrole.
transformation, which gave 3aa in only 21% yield accompanied by a We next examined the influence of the substituent at the
large amount of Glaser coupling product 4a in 71% yield (entry 16). pyridyl directing groups for the reaction (Table 3). Firstly, when
This result clearly showed that Glaser coupling was inhibited effectively the C-3 position of the pyridyl group, which is subject to the
in this reaction by using tert-propargyl alcohol as the alkynylating consequent C–C bond formation, was blocked with a Me group,
reagent instead of phenylacetylene.
the reaction was completely suppressed to yield only 4a. In addition,
With these optimized reaction conditions in hand, the scope of this installation of the Me substituent on the pyridyl C-4 position furn-
reaction was extensively studied. First, a series of g-substituted tert- ished product 3ia in only 31% yield. Further studies revealed that the
propargyl alcohols were investigated (Table 2). To our satisfaction, 5-methylpyridin-2-yl directing group gave the best result, providing the
g-arylated tert-propargyl alcohols with electron-donating or electron- target products in particularly high yields (3ja–3na, 74–91%), and even
withdrawing substituents, such as Me, Et, Cl, CF , and Ph, at the para substrates with Me or F at the C-5 position on the indole ring were
3
position on the phenyl ring were well tolerated to provide the corres- converted into the corresponding target products 3ka, 3kg, and 3na
ponding products in moderate to good yields (3aa–3af, 41–78% yield). effectively. It should be noted that changing the directing group from
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a
Table 3 Reaction scope of the 1-(pyridin-2-yl)-1H-indoles
Scheme 2 Mechanistic studies.
2
Cu(OAc)
2
ÁH
2
O (eqn (3)), which clearly indicated that the Csp –H bond
III
cleavage of substrate 1a was enforced by the Rh species. The
structure of 5 was confirmed by single-crystal X-ray diffraction.
Furthermore, the reactivity of complex 5 was tested. Again, no reaction
took place when complex 5 was mixed with 2a at 125 1C (eqn (4)).
In sharp contrast, the reaction of 5 and 2a in the ratio of 1 : 1.1 in the
presence of Cu(OAc)
(eqn (4)). However, further efforts to isolate intermediates from the
O (2.2 equiv.), PhMe (2 mL), 125 1C, air, 6 h. reaction mixtures by adjusting the ratio of 5 and 2a failed. Reaction of
Yield of isolated products based on 1.
2
ÁH
2
O did proceed to yield the target product 3aa
a
General reaction conditions: 1 (0.2 mmol), 2 (0.8 mmol), [RhCl(COD)]
ÁH
2
(1.5 mol%), Cu(OAc)
2
2
5
with copper phenylacetylide 6 was also investigated to give product
3
aa, albeit in 34% yield. Of note, the addition of extra Cu(OAc) O
2
ÁH
2
pyridin-2-yl to 6-methylpyridin-2-yl significantly affected the reactivity as an oxidant and HOAc was essential to promote the reaction. No
and only the alkynylation product 3oa was isolated. The steric desired product could be observed in the absence of Cu(OAc) ÁH O
2
2
hindrance of the Me group at the C-6 position may account for this or HOAc (eqn (5)). These observations implied that the acetylide
difference. Isolation of the alkynylation product 3oa indicated that the copper species generated from the reaction of 2a with Cu(OAc)
alkynylation step was possibly involved in the catalytic cycle for the could undergo transmetalation of the alkynyl group to rhodium to
formation of pyrido[2,1-a]indoles 3. afford acetylide rhodium, which then participated in the subsequent
2 2
ÁH O
To get some mechanistic insights into this transformation, transformations. The catalytic activity of complex 5 under standard
several experiments were carried out (Scheme 2). First, addition conditions was also tested to provide 3aa in 68% yield, which
of TEMPO to the reaction mixture had a negligible effect on the indicated that complex 5 could be a possible intermediate in the
reaction, which suggested that a free-radical pathway might be catalytic cycle (eqn (6)).
ruled out. Next, stoichiometric reaction of 2a with [RhCl(COD)]
2
The possibility of cross reactions between two different indoles or
was performed and no reaction could be observed indeed, even propargyl alcohols was also investigated (Scheme 3). The reaction of
if an excess of NaOAc was added (eqn (1)). Notably, it was found indole substrates 1b and 1j with 2a afforded only the corresponding
that the Glaser coupling product 4a was generated quantita- 3ba and 3ja, while the crossover products 3bja and 3jba were not
tively when Cu(OAc)
These results indicated that it is Cu(OAc)
RhCl(COD)] that is responsible for the C–C bond cleavage of 2a via manner. In contrast, reaction of 1j with a mixture of 2a and 2g led to
2
ÁH
2
O was mixed with 2a at 125 1C (eqn (2)). detected at all, clearly indicating that the C–N bond cleavage and
2
ÁH O rather than the concomitant transformations proceeded in an intramolecular
2
[
2
13
b-carbon elimination. Reaction of [RhCl(COD)] with 1a was also the isolation of products 3ja and 3jg as well as the expected crossover
2
investigated and no appreciable reaction could be observed when products 3jga and 3jag with the latter two as a mixture.
the reaction was performed in the absence of Cu(OAc)
However, the biscyclometalated Rh(III) complex 5 was obtained able to believe that the reaction is presumably initiated by the
in 85% yield when the reaction was performed in the presence of cyclometallation of 1-(pyridin-2-yl)-1H-indoles with Rh species.
2
ÁH
2
O.
Given the results of the above control experiments, it is reason-
III
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N. Chatani, Chem. Soc. Rev., 2008, 37, 300; ( f ) C. Winter and
N. Krause, Angew. Chem., Int. Ed., 2009, 48, 2460; (g) F. Chen,
T. Wang and N. Jiao, Chem. Rev., 2014, 114, 8613.
4
For selected recent examples, see: (a) C.-H. Jun, H. Lee and S.-G.
Lim, J. Am. Chem. Soc., 2001, 123, 751; (b) A. Sattler and G. Parkin,
Nature, 2010, 463, 523; (c) C. Qin, P. Feng, Y. Ou, T. Shen, T. Wang
and N. Jiao, Angew. Chem., Int. Ed., 2013, 52, 7850; (d) M. Saydou and
A. M. Echavarren, Angew. Chem., Int. Ed., 2013, 52, 13468; (e) H. M.
Ko and G. Dong, Nat. Chem., 2014, 6, 739; ( f ) L. Souillart, E. Parker
and N. Cramer, Angew. Chem., Int. Ed., 2014, 53, 3001; (g) X. Huang,
X. Li, M. Zou, S. Song, C. Tang, Y. Yuan and N. Jiao, J. Am. Chem.
Soc., 2014, 136, 14858.
5
6
For reviews of C–N bond cleavage, see: (a) K. Khumtaveeporn and
H. Alper, Acc. Chem. Res., 1995, 28, 414; (b) A. Roglans, A. Pla-Quintana
and M. Moreno-Ma n˜ as, Chem. Rev., 2006, 106, 4622; (c) N. J. Turner,
Chem. Rev., 2011, 111, 4073.
For selected examples, see: (a) T. Koreeda, T. Kochi and F. Kakiuchi,
J. Am. Chem. Soc., 2009, 131, 7238; (b) W. Geng, W.-X. Zhang, W. Hao and
Z. Xi, J. Am. Chem. Soc., 2012, 134, 20230; (c) B.-J. Li, H.-Y. Wang, Q.-L.
Zhu and Z.-J. Shi, Angew. Chem., Int. Ed., 2012, 51, 3948; (d) M. Tobisu,
K. Nakamura and N. Chatani, J. Am. Chem. Soc., 2014, 136, 5587.
For some recent reports on both C–C and C–N bond cleavage, see:
7
8
9
(
a) C. Li, W.-T. Zhang and X.-S. Wang, J. Org. Chem., 2014, 79, 5847;
Scheme 3 Cross reactions.
(b) P. Feng, X. Sun, Y. Su, X. Li, L.-H. Zhang, X. Shi and N. Jiao,
Org. Lett., 2014, 16, 3388.
(a) K. Sonogashira, J. Organomet. Chem., 2002, 653, 46; (b) E. Negishi
and L. Anastasia, Chem. Rev., 2003, 103, 1979; (c) W. Shi, C. Liu and
A. Lei, Chem. Soc. Rev., 2011, 40, 2761; (d) J. P. Brand and J. Waser,
Chem. Soc. Rev., 2012, 41, 4165.
Selected examples, see: (a) Y. Wei, H. Zhao, J. Kan, W. Su and
M. Hong, J. Am. Chem. Soc., 2010, 132, 2522; (b) N. Matsuyama,
M. Kitahara, K. Hirano, T. Satoh and M. Miura, Org. Lett., 2010,
12, 2358; (c) S. H. Kim, J. Yoon and S. Chang, Org. Lett., 2011,
Transmetalation of the alkynyl group from the acetylide copper
species generated in situ to Rh followed by a reductive elimination
yields the alkynylation product (see ESI†), which then proceeds to
undergo a series of transformations to afford the target product
finally. The mechanistic details for the further transformation
of the alkynylation product to give the pyrido[2,1-a]indole skeleton
are unclear yet.
In conclusion, we have discovered a novel Rh/Cu catalyzed cascade
reaction involving multiple C–H, C–C, and C–N bond cleavage and
formation, giving rise to a practical approach for the construction
of pyrido[2,1-a]indoles. Remarkably, the highly selective cleavage of
several types of extremely inert chemical bonds such as C(aryl)–
C(alkynyl), C(alkyl)–C(alkynyl), and C(aryl)–N bonds was realized in
this transformation. Further studies aimed at revealing the detailed
mechanism of this complicated reaction and applications of this
protocol are currently being investigated in our laboratory.
1
3, 1474; (d) M. Shang, H.-L. Wang, S.-Z. Sun, H.-X. Dai and J.-Q. Yu,
J. Am. Chem. Soc., 2014, 136, 11590.
1
0 Selected examples, see: (a) K. Kobayashi, M. Arisawa and
M. Yamaguchi, J. Am. Chem. Soc., 2002, 124, 8528; (b) I. V. Seregin,
V. Ryabova and V. Gevorgyan, J. Am. Chem. Soc., 2007, 129, 7742;
(
1
c) Y. Ano, M. Tobisu and N. Chatani, J. Am. Chem. Soc., 2011,
33, 12984; (d) J. He, M. Wasa, K. S. L. Chan and J.-Q. Yu, J. Am.
Chem. Soc., 2013, 135, 3387.
1 (a) J. P. Brand, L. Charpentier and J. Waster, Angew. Chem., Int. Ed.,
1
1
2
2
2
009, 48, 9346; (b) C. Feng and T.-P. Loh, Angew. Chem., Int. Ed.,
014, 53, 2722; (c) F. Xie, Z. Qi, S. Yu and X. Li, J. Am. Chem. Soc.,
014, 136, 4780; (d) K. D. Collins, F. Lied and F. Glorius, Chem.
Commun., 2014, 50, 4459.
2 (a) T. Nishimura, H. Ariki, Y. Maeda and S. Uemura, Org. Lett., 2003,
5
Lett., 2003, 5, 2997.
, 2997; (b) T. Nishimura, H. Ariki, Y. Maeda and S. Uemura, Org.
We thank the National Basic Research Program of China (973
Program 2012CB821600), the National Natural Science Foundation 13 A. Funayama, T. Satoh and M. Miura, J. Am. Chem. Soc., 2005, 127, 15354.
1
4 See for selected reviews: (a) T. Satoh and M. Miura, Chem. – Eur. J.,
of China (21072161), and Program for Changjiang Scholars and
Innovative Research Team (PCSIRT) in the University.
2
010, 16, 11212; (b) D. A. Colby, R. G. Bergman and J. A. Ellman,
Chem. Rev., 2010, 110, 624; (c) G. Song, F. Wang and X. Li, Chem. Soc.
Rev., 2012, 41, 3651.
1
1
5 Rh-catalyzed C–H alkynylation, see ref. 11b–d.
6 (a) B. M. Trost, Science, 1991, 254, 1471; (b) C.-J. Li and B. M. Trost,
Proc. Natl. Acad. Sci. U. S. A., 2008, 105, 13197.
Notes and references
1
M. B. Smith and J. March, March’s Advanced Organic Chemisty:
Reactions Mechanisms and Structure, Wiley, Hoboken, NJ, 2007.
Selected reviews: (a) R. Giri, B.-F. Shi, K. M. Engle, N. Maugel and
J.-Q. Yu, Chem. Soc. Rev., 2009, 38, 3242; (b) C. I. Herrer ´ı as, X. Yao,
17 (a) F. De Simone, J. Gertsch and J. Waser, Angew. Chem., Int. Ed.,
2010, 49, 5767; (b) M. Mizutani, F. Inagaki, T. Nakanishi,
C. Yangagihara, I. Tamai and C. Mukai, Org. Lett., 2011, 13, 1796.
2
Z. Li and C.-J. Li, Chem. Rev., 2007, 107, 2456; (c) T. W. Lyons and 18 (a) A. Ohsawa, T. Kawaguchi and H. Igeta, J. Org. Chem., 1982, 47, 3497;
M. S. Sanford, Chem. Rev., 2010, 110, 1147; (d) C. S. Yeung and
V. M. Dong, Chem. Rev., 2011, 111, 1215; (e) J. L. Bras and J. Muzart,
Chem. Rev., 2011, 111, 1170; ( f ) C.-L. Sun, B.-J. Li and Z.-J. Shi,
Chem. Rev., 2011, 111, 1293; (g) J. Wencel-Delord, T. Drge, F. Liu and
F. Glorius, Chem. Soc. Rev., 2011, 40, 4740; (h) P. B. Arockiam,
(b) H. Zhu, J. St ¨o ckigt, Y. Yu and H. Zou, Org. Lett., 2011, 13, 2792;
(c) D. C. Rogness, N. A. Markina, J. P. Waldo and R. C. Larock, J. Org.
Chem., 2012, 77, 2743; (d) S. Samala, P. Pallavi, R. Kumar, R. K. Arigela,
G. Singh, R. S. Ampapathi, A. Priya, S. Datta, A. Patra and B. Kundu,
Chem. – Eur. J., 2014, 20, 14344.
C. Bruneau and P. H. Dixneuf, Chem. Rev., 2012, 112, 5879; 19 Rare examples for C(aryl)–C(alkynyl) bond cleavage, see: (a) M. Gaydou
(
i) L. Ackermann, Acc. Chem. Res., 2014, 47, 281.
For selected reviews, see: (a) R. H. Crabtree, Nature, 2000, 408, 415;
b) C.-H. Jun, Chem. Soc. Rev., 2004, 33, 610; (c) M. Rubin, M. Rubina
and A. M. Echavarren, Angew. Chem., Int. Ed., 2013, 52, 13468;
(b) X.-R. Song, Y.-P. Han, Y.-F. Qiu, Z.-H. Qiu, X.-Y. Liu, P.-F. Xu and
Y.-M. Liang, Chem. – Eur. J., 2014, 20, 12046; (c) ref. 4c; (d) C. M u¨ ller,
C. N. Iverson, R. J. Lachicotte and W. D. Jones, J. Am. Chem. Soc., 2001,
123, 9718.
3
(
and V. Gevorgyan, Chem. Rev., 2007, 107, 3117; (d) Y. Horino,
Angew. Chem., Int. Ed., 2007, 46, 2144; (e) M. Tobisu and
Chem. Commun.
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