Cobalt(III)-Catalyzed Dehydrative [4+2] Annulation of Oxime with Alkyne by C-H and N-OH Activation

Article abstract of DOI:10.1002/chem.201503643

Efficient, scalable cobalt-catalyzed redox-neutral [4+2] annulation of readily available oximes and alkyne is reported. The developed synthetic methodology is widely applicable and tolerates various functional groups including heterocycles. A stable CpCo^III neutral complex is employed as the catalyst for this redox-neutral [4+2] annulation reaction, which progresses smoothly by way of a reversible cyclometallation without any external oxidizing agent, and produces only water as the side product.

Full text of DOI:10.1002/chem.201503643

DOI: 10.1002/chem.201503643
Communication
&
CÀH Activation
Cobalt(III)-Catalyzed Dehydrative [4+2] Annulation of Oxime with
Alkyne by CÀH and NÀOH Activation
Malay Sen, Deepti Kalsi, and Basker Sundararaju*[a]
bond functionalization using base metal catalysts,[10] we herein
Abstract: Efficient, scalable cobalt-catalyzed redox-neutral
report the CoIII-catalyzed redox-neutral dehydrative [4+2] an-
[4+2] annulation of readily available oximes and alkyne is
nulation of oxime with various alkynes using [Cp*Co(CO)I2] to
reported. The developed synthetic methodology is widely
pragmatically furnish multi-substituted isoquinoline derivatives
applicable and tolerates various functional groups includ-
via CÀH and NÀOH activation (Scheme 1). The reaction does
not require any external oxidant and produces only water as
a side product, ensuring the efficient synthesis of isoquinoline
with complete atom- and step-economy.
ing heterocycles. A stable Cp*CoIII neutral complex is em-
ployed as the catalyst for this redox-neutral [4+2] annula-
tion reaction, which progresses smoothly by way of a re-
versible cyclometallation without any external oxidizing
agent, and produces only water as the side product.
Transition-metal-catalyzed CÀH bond functionalization has
become prolific in the last decade and is widely applied in
many targeted syntheses.[1] Numerous transformations apply
noble metal catalysts such as Pd, Rh, Ir, and Ru.[2] Due to cost
efficiency and sustainability, these catalysts cannot be widely
applied in industry. Hence there is a growing interest in devel-
oping catalysts based on cheap, abundant metals for CÀH
bond functionalization.[3] Among them, cobalt seems to be
a promising contender due to efficient transformations by its
congeners rhodium and iridium in both low- and high-valent
oxidation states. In the past, low-valent cobalt complexes were
generated in situ for CÀH bond functionalization by using
a Grignard reagent as a reductant.[3g,i,4] However, more recently
the importance of high-valent CoIII-catalyzed chelate-assisted
CÀH bond functionalizations without any base or reductant
have been demonstrated by Glorius, Ackermann, Ellman, and
Chang following pioneering work by Matsunaga and Kanai.[5]
Isoquinolines are found in many pharmaceuticals and bio-
logically active alkaloids.[6] Elegant methods have been devel-
oped recently for the synthesis of isoquinoline via CÀH bond
activation using [Ru] and [Rh] noble metal catalysts and with
or without external oxidant.[7,8] Nitrogen-containing chelating
groups have been commonly used to activate ortho CÀH
bonds but often these directing groups are not involved in
new CÀC and CÀN bond formation. Incorporation of directing
Scheme 1. Dehydrative annulation of oxime with alkyne.
Optimization studies on the isoquinoline synthesis are sum-
marized in Table 1 (for a detailed study see Table S1 in the Sup-
porting Information). Use of 10 mol% of the Cp*CoIII catalyst
using MeOH or EtOH as solvent did not promote the reaction
of oxime 1a with tolane (2a) (entries 1 and 2). Change of sol-
vent and increasing the temperature moderately improves the
yield (entries 3–5). While employing 2,2,2-trifluoroethanol (TFE)
as solvent at 1208C significantly improves the yield of 3aa
(65%; entry 5). Use of KOAc instead of NaOAc as additive
lowers the yield of product formation, whereas use of AgOPiv
provided the deoxygenated product of oxime 1a (entries 6, 7).
By lowering the temperature and using TFE and NaOAc we ob-
tained the product in higher yield (entry 8). No annulation was
observed when the reaction was performed without catalyst
(entry 9). On the other hand, the yield of the reaction decreas-
es when the reaction is carried out in the absence of NaOAc,
which is indicative of the participation of the acetate in the
groups such as nitrogen in the synthesis of heterocycles via CÀ catalytic cycle (entry 10). Although the cost effectiveness of the
H/NÀX bond activation should improve the atom- and step-
base metal catalyst is emphasized, often an expensive silver
salt is required in addition to form the cationic CoIII in situ.
Thus overall often the cost of a catalyst equivalent can be
more than that from using a noble metal catalyst. Hence we
performed the reaction without using a silver salt and ob-
tained similar or better results to those with our standard con-
ditions (808C, TFE, NaOAc). We were delighted to obtain a high
yield of 3aa using a neutral CoIII complex as a precursor with-
out the need for ionization using a silver salt (entry 11).[5b] Fur-
economy.[9] In continuation of our ongoing exploration of CÀH
[a] M. Sen, D. Kalsi, Prof. Dr. B. Sundararaju
Fine Chemical Laboratory
Department of Chemistry
Indian Institute of Technology Kanpur, Kanpur (India)
E-mail: basker@iitk.ac.in
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201503643.
Chem. Eur. J. 2015, 21, 15529 – 15533
15529
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Communication
Table 1. Optimization conditions for CoIII-catalyzed [4+2] annulation of
oxime with alkyne.[a]
Entry
[Co]
[Ag]
Solvent
Temp [8C]
Yield [%][b]
1
2
3
4
5
6
7
8
[Cp*Co(CO)I2]
[Cp*Co(CO)I2]
[Cp*Co(CO)I2]
[Cp*Co(CO)I2]
[Cp*Co(CO)I2]
[Cp*Co(CO)I2]
[Cp*Co(CO)I2]
[Cp*Co(CO)I2]
–
[Cp*Co(CO)I2]
[Cp*Co(CO)I2]
[Cp*Co(CO)I2]
[Cp*Co(CO)I2]
AgSbF6
AgSbF6
AgSbF6
AgSbF6
AgSbF6
AgSbF6
AgSbF6
AgSbF
–
MeOH
EtOH
tAmOH
DCE
TFE
TFE
TFE
TFE
TFE
TFE
TFE
TFE
TFE
80
80
–
–
120
120
120
120
120
80
120
80
80
29
56
65
40[c,d]
–
86
[e,f]
9
–
10
11
12
13
AgSbF6
–
–
76[g]
92
80
120
67[h]
55[i]
AgSbF6
[a] All reactions were carried out under an argon atmosphere using 1a/
2a/[Co]/[Ag]/additive in 0.2/0.24/0.02/0.04/0.04 mmol in 1.5 mL solvent at
the above-mentioned temperature for 24 h unless otherwise stated.
[b] Isolated yield of 3aa. [c] Conversion instead of yield using dodecane
as internal standard. [d] KOAc was used instead of NaOAc. [e] Deoxygen-
ated imine was obtained instead of 3aa. [f] Ag(OPiv) was used instead of
NaOAc. [g] No NaOAc was added. [h] 5 mol% of [Co] used instead of
10 mol%. [i] Reaction performed under air for 48 h.
Scheme 2. Scope of oxime 1.
oxime, which led to a drastic reduction in the yield of the
product (3a’a–3a’’a), confirming that the OH group partici-
pates as well in the catalytic cycle.
thermore, decreasing the catalyst load or carrying out the reac-
tion under air did not improve the yield of 3aa (entries 12 and
13). Evaluation of the annulation reaction under optimized
conditions with other Group 9 metals gave only 78% yield
with Cp*IrIII, but Cp*RhIII provided a comparable yield of 94%
(see Table S1 in the Supporting Information).
The scope of the reaction was extended to oximes derived
from heterocycles. Fused heterocycles were obtained in mod-
erate to good yield with excellent regioselectivity by dehydra-
tive CÀH annulation 3sa–3va (Scheme 3). When methyl-3-pyr-
idyl ketone oxime (1w) was employed as a substrate with
tolane, two regioisomers of C2 and C4 selective products were
formed in a 1.4:1 ratio in good yield.
With the optimized reaction conditions in hand, the scope
of the oxime was then examined (Scheme 2). The annulation
proceeded efficiently for a broad range of substrates with
varied substitution patterns at the para-position to provide
chemoselective isoquinoline in good yield (3ba–3ha). Substitu-
ents on the ortho- and meta-position allowed CÀH activation
to take place exclusively on the less hindered position (3ja–
3la). A gram-scale reaction was performed to assess the scala-
bility of this high-valent cobalt-catalyzed annulation of oxime
1a with tolane (Scheme 2, 5 mmol scale). The yield of the reac-
tion product was not compromised; using 4 mol% of the [Co]
catalyst and 10 mol% of NaOAc provided 3aa in 68% yield (cf.
entry 12, Table 1). Furthermore an oxime-containing bicyclic
substrate and sterically more demanding substituents fur-
nished desired products in good yield (3ma). Increasing the
steric bulk by incorporating an ethyl or phenyl group a- to ni-
trogen atom did not diminish the yield (3na–3oa). Using an
oxime derived from a bicyclic system provides the benzo[h]iso-
quinoline in good yield (3pa). Valuable functional groups such
as alkynes and alkenes situated para to the oxime group were
tolerable for dehydrative annulation in good yield (3qa–3ra).
To understand the influence of the OH group of the oxime, we
performed the reaction with methyl- or acetyl-substituted
Subsequently, the scope of the alkynes was explored by em-
ploying CoIII with symmetrical and unsymmetrical alkynes
using 1a as coupling partner (Scheme 4). Efficient conversion
was obtained with various symmetrical aryl- and alkyl-substi-
tuted alkynes to provide multisubstituted isoquinolines (3ab–
3ae). Unsymmetrical alkynes subjected to our optimized condi-
tions generated compounds with phenyl substituents next to
nitrogen (3af–3aj). Furthermore, cyclic alkyne 2k underwent
a [4+2] annulation with 1a to give the tricyclic compound 3ak
in low yield in 24 h. Terminal alkynes were amenable for
Scheme 3. Scope of oxime-containing heterocycles 1.
Chem. Eur. J. 2015, 21, 15529 – 15533
www.chemeurj.org
15530
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Communication
Scheme 6. Control experiments.
Scheme 4. Scope of alkynes with 1a.
of the cobalt catalyst. The above experiments indicate that the
reversible cyclometallation via carboxylate-assisted deprotona-
tion is followed by an alkyne insertion to cobalt(III).
cobalt-catalyzed cyclization albeit giving moderate yields of
the products with good regioselectivity (3al–3am).
We successfully carried out the challenging one-pot, three-
component reactions directly from commercially available ace-
tophenone upon in situ condensation with hydroxylamine fol-
lowed by dehydrative annulation of the oxime by cobalt(III)-
catalyzed CÀH bond activation to give 3aa in 72% yield
(Scheme 5). Given the high catalytic activity for dehydrative
[4+2] annulation exhibited by the cobalt catalyst, we decided
to conduct preliminary studies to get a better understanding
of the reaction mechanism (Scheme 6). Intermolecular compe-
tition experiments with p-substituted oximes 1b and 1g with
2a revealed that the annulation occurred favorably with the
electron-poor oxime 1g. Similarly, intermolecular competition
experiments with 4-octyne (2e) and tolane (2a) with 1a result-
ed in a favorable formation of the product from the electron-
deficient alkyne (2a).A substantial amount of deuterium incor-
poration (44%) was observed at the ortho position of oxime
1a when it was exposed to the cobalt catalytic system with
CD3OD in the absence of 2a. Importantly, the deuterium incor-
poration was detected at the ortho-position when CD3OD was
added under our standard reaction conditions in the presence
of alkyne 2a. No deuterium was incorporated in the absence
Based on our preliminary studies, and relevant reports on
CoIII and RhIII annulation reactions,[5p,11] a plausible mechanism
was formulated (Scheme 7). [Cp*Co(CO)I2] readily undergoes
decarbonylation in the presence of NaOAc to possibly give the
neutral diacetate–cobalt(III) complex, which may in turn be in
equilibrium with the monocationic complex I.[11] Coordination
of oxime 1 followed by reversible concerted cyclometallation–
deprotonation leads to the intermediate complex III. Coordina-
tion of alkyne 2 followed by insertion gives the key alkenyl in-
termediate V. Reductive elimination followed by proto-deme-
Scheme 5. Cascade, one-pot synthesis of isoquinoline.
Scheme 7. Proposed mechanism.
Chem. Eur. J. 2015, 21, 15529 – 15533
www.chemeurj.org
15531
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Communication
Liang, Y.-F. Liang, N. Jiao, Org. Chem. Front. 2015, 2, 403–415; c) T.
Hyster, Catal. Lett. 2015, 145, 458–467; d) X. H. Cai, B. Xie, ARKIVOC
(Gainesville, FL, U.S.) 2015, 184; e) I. Bauer, H. J. Knçlker, Chem. Rev.
2015, 115, 3170; f) S. Z. Tasker, E. A. Standley, T. F. Jamison, Nature 2014,
509, 299; g) K. Gao, N. Yoshikai, Acc. Chem. Res. 2014, 47, 1208–
1219;h) L. Ackermann, J. Org. Chem. 2014, 79, 8948–8954; i) J. Yamagu-
chi, K. Muto, K. Itami, Eur. J. Org. Chem. 2013, 2013, 19–30; j) J. J. Mous-
seau, A. B. Charette, Acc. Chem. Res. 2013, 46, 412–424; k) R. T. Gephart,
T. H. Warren, Organometallics 2012, 31, 7728; l) N. Yoshikai, Synlett 2011,
2011, 1047–1051; m) Y. Nakao, Chem. Rec. 2011, 11, 242–251; n) M.
Zhang, Appl. Organomet. Chem. 2010, 24, 269; o) E. Nakamura, N. Yoshi-
kai, J. Org. Chem. 2010, 75, 6061–6067; p) A. A. Kulkarni, O. Daugulis,
Synthesis 2009, 2009, 4087–4109.
tallation gives compound 3 and regenerates the catalytically
active species.
In conclusion, we have demonstrated the CoIII-catalyzed de-
hydrative annulation of oximes with alkynes via CÀH and NÀ
OH bond activation. The reaction did not require any external
oxidant and produces water as a sole side product. Several
functional groups were amenable for [Co]-catalyzed annulation
reactions under mild conditions. Both symmetrical and unsym-
metrical alkynes (including terminal ones) were employed in
the reaction to give access to multi-substituted isoquinoline
derivatives. We have shown that a neutral CoIII complex can be
used in combination with NaOAc for annulation of oximes
with alkynes. We have demonstrated that a functionalized iso-
quinoline can be obtained from commercially available aceto-
phenone via a one-pot, three-component cascade reaction cat-
alyzed by Cp*CoIII.[12]
[4] a) T. Yamakawa, N. Yoshikai, Org. Lett. 2013, 15, 196; b) B. Wu, N. Yoshi-
kai, Angew. Chem. Int. Ed. 2013, 52, 10496; Angew. Chem. 2013, 125,
10690; c) B. Punji, W. Song, G. A. Shevchenko, L. Ackermann, Chem. Eur.
J. 2013, 19, 10605; d) P. S. Lee, N. Yoshikai, Angew. Chem. Int. Ed. 2013,
52, 1240; Angew. Chem. 2013, 125, 1278; e) K. Gao, N. Yoshikai, J. Am.
Chem. Soc. 2013, 135, 9279; f) B. H. Tan, J. Dong, N. Yoshikai, Angew.
Chem. Int. Ed. 2012, 51, 9610; Angew. Chem. 2012, 124, 9748; g) K. Gao,
N. Yoshikai, Chem. Commun. 2012, 48, 4305; h) K. Gao, P. S. Lee, C. Long,
N. Yoshikai, Org. Lett. 2012, 14, 4234; i) K. Gao, N. Yoshikai, Angew.
Chem. Int. Ed. 2011, 50, 6888; Angew. Chem. 2011, 123, 7020; j) K. Gao,
N. Yoshikai, J. Am. Chem. Soc. 2011, 133, 400.
Acknowledgements
[5] For Cp*CoIII-catalyzed CÀH bond functionalization: a) D. Zhao, J. H. Kim,
L. Stegemann, C. A. Strassert, F. Glorius, Angew. Chem. Int. Ed. 2015, 54,
4508–4511; Angew. Chem. 2015, 127, 4591–4594; b) J. R. Hummel, J. A.
Ellman, J. Am. Chem. Soc. 2015, 137, 490–498; c) Y. Suzuki, B. Sun, T.
Yoshino, M. Kanai, S. Matsunaga, Tetrahedron 2015, 71, 4552–4556; d) Y.
Suzuki, B. Sun, K. Sakata, T. Yoshino, S. Matsunaga, M. Kanai, Angew.
Chem. Int. Ed. 2015, 54, 9944–9947; Angew. Chem. 2015, 127, 10082–
10085; e) B. Sun, T. Yoshino, S. Matsunaga, M. Kanai, Chem. Commun.
2015, 51, 4659–4661; f) A. B. Pawar, S. Chang, Org. Lett. 2015, 17, 660–
663; g) P. Patel, S. Chang, ACS Catal. 2015, 5, 853–858; h) M. Moselage,
N. Sauermann, J. Koeller, W. Liu, D. Gelman, L. Ackermann, Synlett 2015,
26, 1596–1600; i) X.-G. Liu, S.-S. Zhang, J.-Q. Wu, Q. Li, H. Wang, Tetrahe-
dron Lett. 2015, 56, 4093–4095; j) J. Li, L. Ackermann, Angew. Chem. Int.
Ed. 2015, 54, 8551–8554; Angew. Chem. 2015, 127, 8671–8674; k) J. Li,
L. Ackermann, Angew. Chem. Int. Ed. 2015, 54, 3635–3638; Angew.
Chem. 2015, 127, 3706–3709; l) J. R. Hummel, J. A. Ellman, Org. Lett.
2015, 17, 2400–2403; m) T. Gensch, S. Vµsquez-CØspedes, D.-G. Yu, F.
Glorius, Org. Lett. 2015, 17, 3714–3717; n) D.-G. Yu, T. Gensch, F. de A-
zambuja, S. Vµsquez-CØspedes, F. Glorius, J. Am. Chem. Soc. 2014, 136,
17722–17725; o) B. Sun, T. Yoshino, S. Matsunaga, M. Kanai, Adv. Synth.
Catal. 2014, 356, 1491–1495; p) H. Ikemoto, T. Yoshino, K. Sakata, S.
Matsunaga, M. Kanai, J. Am. Chem. Soc. 2014, 136, 5424–5431; q) T. M.
Figg, S. Park, J. Park, S. Chang, D. G. Musaev, Organometallics 2014, 33,
4076–4085; r) T. Yoshino, H. Ikemoto, S. Matsunaga, M. Kanai, Angew.
Chem. Int. Ed. 2013, 52, 2207–2211; Angew. Chem. 2013, 125, 2263–
2267; s) T. Yoshino, H. Ikemoto, S. Matsunaga, M. Kanai, Chem. Eur. J.
2013, 19, 9142–9146.
[6] a) K. W. Bentley, Nat. Prod. Rep. 2006, 23, 444–463; b) K. W. Bentley, Nat.
Prod. Rep. 2004, 21, 395–424; c) J. D. Scott, R. M. Williams, Chem. Rev.
2002, 102, 1669–1730.
[7] For a comprehensive review on the synthesis of isoquinoline via CÀH
bond functionalization see: R. He, Z.-T. Huang, Q.-Y. Zheng, C. Wang,
Tetrahedron Lett. 2014, 55, 5705–5713, and references therein.
[8] Selected examples on redox-neutral dehydrative annulation using ke-
toxime via CÀH bond functionalization: a) D. Zhao, F. Lied, F. Glorius,
Chem. Sci. 2014, 5, 2869–2873; b) L. Zheng, J. Ju, Y. Bin, R. Hua, J. Org.
Chem. 2012, 77, 5794–5800; c) H. Wang, C. Grohmann, C. Nimphius, F.
Glorius, J. Am. Chem. Soc. 2012, 134, 19592–19595; d) C. Kornhaaß, J.
Li, L. Ackermann, J. Org. Chem. 2012, 77, 9190–9198; e) R. K. Chinnagol-
la, S. Pimparkar, M. Jeganmohan, Org. Lett. 2012, 14, 3032–3035; f) X.
Zhang, D. Chen, M. Zhao, J. Zhao, A. Jia, X. Li, Adv. Synth. Catal. 2011,
353, 719–723; g) Y. Yoshida, T. Kurahashi, S. Matsubara, Chem. Lett.
2011, 40, 1140–1142; h) P. C. Too, S. H. Chua, S. H. Wong, S. Chiba, J.
Org. Chem. 2011, 76, 6159–6168; i) T. K. Hyster, T. Rovis, Chem. Commun.
2011, 47, 11846–11848; j) N. Guimond, S. I. Gorelsky, K. Fagnou, J. Am.
Chem. Soc. 2011, 133, 6449–6457; k) K. Parthasarathy, C.-H. Cheng, J.
Org. Chem. 2009, 74, 9359–9364; l) T. Gerfaud, L. Neuville, J. Zhu,
Financial support provided by the Indian Institute of Technolo-
gy Kanpur through an initiation grant (IITK/CHM/20130187)
and the DAE-BRNS (BRNS/CHM/2014110) young scientist re-
search fund award to B.S. is gratefully acknowledged. M.S. and
D.K. acknowledge the CSIR and IITK for their fellowships. B.S.
thanks Johnson Matthey for their generous support through
providing metal precursors.
Keywords: annulation · CÀH activation · cobalt · heterocycles ·
isoquinoline
[1] a) J. Yamaguchi, A. D. Yamaguchi, K. Itami, Angew. Chem. Int. Ed. 2012,
51, 8960–9009; Angew. Chem. 2012, 124, 9092–9142; b) D. Y. K. Chen,
S. W. Youn, Chem. Eur. J. 2012, 18, 9452–9474; c) H. M. L. Davies, J.
Du Bois, J.-Q. Yu, Chem. Soc. Rev. 2011, 40, 1855–1856; d) H. M. L.
Davies, J. R. Manning, Nature 2008, 451, 417–424; e) K. Godula, D.
Sames, Science 2006, 312, 67–72; f) J. Wencel-Delord, F. Glorius, Nat.
Chem. 2013, 5, 369–375.
[2] For selected recent reviews on CÀH bond functionalization: a) G. Song,
X. Li, Acc. Chem. Res. 2015, 48, 1007; b) L. Ackermann, Org. Process Res.
Dev. 2015, 19, 260–269; c) B. Ye, N. Cramer, Acc. Chem. Res. 2015, 48,
1308; d) T. Mesganaw, J. A. Ellman, Org. Process Res. Dev. 2014, 18,
1097–1104; e) L. Ackermann, Acc. Chem. Res. 2014, 47, 281; f) S. A.
Girard, T. Knauber, C. J. Li, Angew. Chem. Int. Ed. 2014, 53, 74; Angew.
Chem. 2014, 126, 76; g) K. D. Collins, F. Glorius, Nat. Chem. 2013, 5,
597–601; h) T. Brückl, R. D. Baxter, Y. Ishihara, P. S. Baran, Acc. Chem. Res.
2012, 45, 826; i) K. M. Engle, T. S. Mei, M. Wasa, J. Q. Yu, Acc. Chem. Res.
2012, 45, 788; j) S. R. Neufeldt, M. S. Sanford, Acc. Chem. Res. 2012, 45,
936; k) F. W. Patureau, J. Wencel-Delord, F. Glorius, Aldrichimica Acta
2012, 45, 31; l) P. B. Arockiam, C. Bruneau, P. H. Dixneuf, Chem. Rev.
2012, 112, 5879–5918; m) N. Kuhl, M. N. Hopkinson, J. Wencel-Delord,
F. Glorius, Angew. Chem. Int. Ed. 2012, 51, 10236; Angew. Chem. 2012,
124, 10382; n) D. Zhao, J. You, C. Hu, Chem. Eur. J. 2011, 17, 5466;
o) D. J. Schipper, K. Fagnou, Chem. Mater. 2011, 23, 1594; p) C. Liu, H.
Zhang, W. Shi, A. Lei, Chem. Rev. 2011, 111, 1780; q) L. Ackermann,
Chem. Rev. 2011, 111, 1315–1345; r) J. Wencel-Delord, T. Droge, F. Liu, F.
Glorius, Chem. Soc. Rev. 2011, 40, 4740–4761; s) T. Satoh, M. Miura,
Chem. Eur. J. 2010, 16, 11212; t) D. A. Colby, R. G. Bergman, J. A. Ellman,
Chem. Rev. 2010, 110, 624; u) T. W. Lyons, M. S. Sanford, Chem. Rev.
2010, 110, 1147–1169; v) F. Kakiuchi, T. Kochi, Synthesis 2008, 2008,
3013–3039.
[3] Reviews on CÀH bond functionalization using first-row transition-metal
catalysts see: a) N. Yoshikai, ChemCatChem 2015, 7, 732–734; b) Y.
Chem. Eur. J. 2015, 21, 15529 – 15533
www.chemeurj.org
15532
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Communication
Angew. Chem. Int. Ed. 2009, 48, 572–577; Angew. Chem. 2009, 121,
580–585.
[9] B. Trost, Science 1991, 254, 1471–1477.
[10] N. Barsu, D. Kalsi, B. Sundararaju, Chem. Eur. J. 2015, 21, 9364–9368.
[11] a) K. J. T. Carr, D. L. Davies, S. A. Macgregor, K. Singh, B. Villa-Marcos,
Chem. Sci. 2014, 5, 2340–2346; b) A. P. Walsh, W. D. Jones, Organometal-
lics 2015, 34, 3400–3407.
Kanai, S. Matsunaga, Angew. Chem. Int. Ed. 2015, 54, DOI: 10.1002/
anie.201507744; Angew. Chem. 2015, 127, DOI: 10.1002/
ange.201507744 and H. Wang, J. Koeller, W. Liu, L. Ackermann, Chem.
Eur. J. 2015, 21, DOI: 10.1002/chem.201503624.
Received: August 10, 2015
Revised: September 11, 2015
Published online on September 25, 2015
[12] Editorial Note (15.9.2015): Two very closely related papers were sub-
mitted almost simultaneously to this one, see: B. Sun, T. Yoshino, M.
Chem. Eur. J. 2015, 21, 15529 – 15533
www.chemeurj.org
15533
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim