Rh(III)-Catalyzed Enaminone-Directed Alkenyl C-H Activation for the Synthesis of Salicylaldehydes

Article abstract of DOI:10.1021/acs.orglett.8b01563

A Rh(III)-catalyzed enaminone-directed alkenyl C-H coupling with alkynes for the synthesis of salicylaldehyde derivatives is reported. This represents a unique example of benzene ring framework formation through a transition-metal-catalyzed, directed C-H activation strategy. The two incorporated reactive functionalities, aldehyde and hydroxy groups, provide convenient synthetic handles for further structural elaboration.

Full text of DOI:10.1021/acs.orglett.8b01563

Letter
pubs.acs.org/OrgLett
Cite This: Org. Lett. XXXX, XXX, XXX−XXX
Rh(III)-Catalyzed Enaminone-Directed Alkenyl C−H Activation for
the Synthesis of Salicylaldehydes
Bing Qi, Shan Guo, Wenjing Zhang, Xiaolong Yu, Chao Song, and Jin Zhu*
Department of Polymer Science and Engineering, School of Chemistry and Chemical Engineering, State Key Laboratory of
Coordination Chemistry, Nanjing University, Nanjing 210023, China
S
* Supporting Information
ABSTRACT: A Rh(III)-catalyzed enaminone-directed alkenyl C−H cou-
pling with alkynes for the synthesis of salicylaldehyde derivatives is reported.
This represents a unique example of benzene ring framework formation
through a transition-metal-catalyzed, directed C−H activation strategy. The
two incorporated reactive functionalities, aldehyde and hydroxy groups,
provide convenient synthetic handles for further structural elaboration.
ransition-metal-catalyzed, directed intermolecular C−H
involving several steps under severe conditions,12 (3) direct
oxidation of orthocresol, furnishing many byproducts,13 (4)
oxidation of saligenol, involving strong oxidants,14 and (5)
reduction of salicylic acid, requiring complicated and harsh
conditions.15 Ackermann’s group has synthesized salicylalde-
hydes via C−H hydroxylation of benzaldehydes (Scheme 1), but
T
functionalization has been developed as a powerful tool for
organic synthesis.1 This method has been particularly useful for
the construction of diverse cyclic compounds, such as
isoquinolines,2 isoquinolones,3 indoles,4 chromenes,5 cinno-
lines,6 etc.7 Typically, heteroatom-containing directing groups
are integrated, in part or as a whole, into the newly formed
heterocyclic frameworks. Synthetic access to pure carbocyclic
compounds therefore constitutes a persistent challenge in the
C−H activation field. We have recently demonstrated the use of
enaminones as highly reactive, aromatic C−H activation
directing synthons for coupling with alkynes and α-diazo-β-
ketoesters and facile access to 1-hydroxy-2-naphthaldehyde
derivatives, compounds containing both aldehyde and hydroxy
groups.8 Further extension of the enaminone reactivity profile to
the coupling with 1,4,2-dioxazol-5-ones allows ready synthesis of
quinolin-4(1H)-one derivatives.9 We envisioned that switching
from aromatic C−H activation to alkenyl C−H activation would
provide a synthetic pathway to the construction of a benzene
ring framework. Such a framework, to the best of our knowledge,
has not been synthetically accessed via a transition-metal-
catalyzed directed C−H activation method. Alkenyl C−H
activation and functionalization are synthetically more demand-
ing, and the aromatic C−H activation capability for a directing
group does not automatically translate to its ability to activate
the alkenyl C−H bond. Herein, we report the development of a
Rh(III)-catalyzed enaminone-directed alkenyl C−H activation
protocol for coupling with alkynes and synthesis of salicylalde-
hyde derivatives. Importantly, the two reactive functionalities,
aldehyde and hydroxy groups, provide convenient synthetic
handles for further structural manipulation.
Scheme 1. Synthetic Access to Salicylaldehydes by Rh(III)-
Catalyzed Enaminone-Directed C−H Activation
the protocol demands the use of a complex-structured oxidant.16
In contrast to the above strategies, the method reported herein
enables the simultaneous construction of a benzene ring and
installation of both aldehyde and hydroxy groups via a
straightforward C−H activation pathway.
We commenced our investigations by examining a model
reaction between (1E,4E)-1-(dimethylamino)-5-phenylpenta-
1,4-dien-3-one (1a) and prop-1-yn-1-yl benzene (2a) (Table 1).
The initial screening of the reaction conditions in dichloro-
ethane (DCE), with [RhCp*Cl2]2 (5 mol %) and AgSbF6 (20
mol %) as the catalyst precursor, indicates the required
participation of an oxidant. Thus, the reaction does not proceed
with the addition of 2 equiv of either NaOAc or HOAc (entries 1
and 2, Table 1). The participation of AgOAc as the oxidant
enables the achievement of 26% yield for the synthesis of target
salicylaldehyde derivative 3aa after 12 h reaction at 80 °C (entry
3, Table 1). The switching to Cu(OAc)2·H2O provides an ideal
Salicylaldehyde derivatives are an important class of organic
compounds used extensively in academia and industry.10 All
previously reported salicylaldehyde synthesis methods start
from the benzene ring framework and rely on functional group
installation or transformation. Conventional methods for
salicylaldehyde synthesis include: (1) Reimer−Tiemann re-
action, requiring a substantial amount of NaOH and chloroform
and with low yield (20−35%),11 (2) formylation of phenol,
Received: May 17, 2018
© XXXX American Chemical Society
A
DOI: 10.1021/acs.orglett.8b01563
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
a b
,
a b
,
Table 1. Optimization of Reaction Conditions
Scheme 2. Substrate Scope for Enaminones
entry
additive (equiv)
Ag salt (mol %)
solvent
DCE
DCE
DCE
DCE
DCE
DCE
DCE
DCE
DCE
DCE
TFE
MeCN
MeOH
1,4-dioxane
THF
HFIP
DCE
yield (%)
1
2
3
4
NaOAc (2)
HOAc (2)
AgOAc (2)
Cu(OAc)2·H2O (2)
Cu(OAc)2·H2O (2)
Cu(OAc)2·H2O (2)
-
AgSbF6 (20)
AgSbF6 (20)
AgSbF6 (20)
AgSbF6 (20)
AgSbF6 (20)
-
AgSbF6 (20)
AgSbF6 (20)
AgSbF6 (20)
AgSbF6 (20)
AgSbF6 (20)
AgSbF6 (20)
AgSbF6 (20)
AgSbF6 (20)
AgSbF6 (20)
AgSbF6 (20)
AgOTf (20)
AgBF4 (20)
AgO2CCF3 (20)
trace
0
26
73
0
49
0
0
62
c
5
6
7
8
9
Zn(OTf)2 (2)
Cu(OAc)2·H2O (1)
Cu(OAc)2·H2O (4)
Cu(OAc)2·H2O (2)
Cu(OAc)2·H2O (2)
Cu(OAc)2·H2O (2)
Cu(OAc)2·H2O (2)
Cu(OAc)2·H2O (2)
Cu(OAc)2·H2O (2)
Cu(OAc)2·H2O (2)
Cu(OAc)2·H2O (2)
Cu(OAc)2·H2O (2)
10
11
12
13
14
15
16
17
18
19
69
trace
trace
trace
trace
47
trace
55
61
a
Reaction conditions: 1a−1q (0.2 mmol, 1.0 equiv), 2a (0.3 mmol,
b
1.5 equiv), and DCE (2 mL). Isolated yields.
higher than that for electron-poor ones. Further, the ortho
substitution (F, 1n) is also compatible with the reaction.
Importantly, the thienyl (1o), furanyl (1p), and pyrrolyl (1q)
groups can also be accommodated, allowing the generation of as-
expected target products. Preliminary experiments with
(1E,4E)-1-cyclohexyl-5-(dimethylamino)penta-1,4-dien-3-one
and (E)-1-(cyclohex-1-en-1-yl)-3-(dimethylamino)prop-2-en-
1-one showed no reactivity.
DCE
DCE
45
a
Reaction conditions: 1a (0.2 mmol, 1.0 equiv), 2a (0.3 mmol, 1.5
b
c
equiv), solvent (2 mL). Isolated yields. Without [RhCp*Cl2]2.
reaction condition, furnishing 3aa in 73% yield (entry 4, Table
1). Cu(OAc)2 is believed to serve as an additive for providing
both the oxidant species, Cu(II), and the coordination ligand,
OAc−, for the catalysis. Rh(III) is indispensable, as no product is
generated in the absence of [RhCp*Cl2]2 (entry 5, Table 1).
AgSbF6 is beneficial for the reaction, as without it, a lower yield
(49%) is observed for 3aa (entry 6, Table 1). No conversion to
3aa is identified without Cu(OAc)2·H2O (entry 7, Table 1) or
with the change of Cu(OAc)2·H2O to Zn(OTf)2 (entry 8, Table
1), further supporting the necessity of using an oxidant. The
quantity of Cu(OAc)2·H2O was then explored. Deviation from 2
equiv negatively impacts the product yield (entries 9 and 10,
Table 1), suggesting 2 equiv as the optimum quantity. Further
screening of solvents (trifluoroethanol, or TFE; MeCN; MeOH;
1,4-dioxane; tetrahydrofuran, or THF; 1,1,1,3,3,3-hexafluoro-2-
propanol, or HFIP) proves that no other solvent gives a better
outcome than DCE (entries 11−16, Table 1). Similarly, the
screening of Ag salts (AgOTf, AgBF4, AgO2CCF3) confirms that
AgSbF6 is the best chloride abstracting reagent (entries 17−19,
Table 1).
With the optimized conditions established, we then
proceeded to the extensive evaluation of the synthetic scope.
The substrate scope of enaminones (1a−1q) was first examined
by reacting with 2a (Scheme 2). Satisfactorily, a wide range of
(1E,4E)-1-(dimethylamino)-5-phenylpenta-1,4-dien-3-one de-
rivatives are compatible with the protocol. The reaction
proceeds well for (1E,4E)-1-(dimethylamino)-5-phenylpenta-
1,4-dien-3-ones bearing both electron-donating (Me, 1b; OMe,
1c) and electron-withdrawing (F, 1d; Cl, 1e; Br, 1f; CF3, 1g)
groups at the para position. In general, the electron-rich
substrates give a better yield than the electron-poor substrates.
Various meta-substituted substrates (Me, 1h; OMe, 1i; F, 1j; Cl,
1k; Br, 1l; CF3, 1m) are also tolerated. However, in this case, the
product yield for electron-rich substrates is not necessarily
We then proceeded to establish the substrate scope of alkynes
by a reaction with 1a (Scheme 3). The reaction occurs in a
a b
,
Scheme 3. Substrate Scope for Alkynes
a
Reaction conditions: 1a (0.2 mmol, 1.0 equiv), 2b−2m (0.3 mmol,
b
1.5 equiv), and DCE (2 mL). Isolated yields.
regiospecific manner for a variety of unsymmetrically substituted
phenyl/alkyl (Et, 2b; nPr, 2c) alkynes. Also, diphenylacetylene
(2d) and its derivatives can also be successfully employed in the
reaction to afford respective target products. Both para- (Me, 2e;
OMe, 2f; F, 2g; Cl, 2h; Br, 2i) and meta-substituted (Me, 2j;
OMe, 2k; F, 2l; Cl, 2m), electron-rich and electron-poor
diphenylacetylenes can react smoothly. No reactivity is observed
for alkyl/alkyl and ester/ester alkynes under the experimental
conditions employed herein.
With the synthetic scope investigated, we next probed the
mechanism of the reaction by H−D scrambling, competition,
B
DOI: 10.1021/acs.orglett.8b01563
Org. Lett. XXXX, XXX, XXX−XXX

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Letter
and kinetic isotope effect (KIE) experiments (Scheme 4).
Treatment of 1a under the standard reaction conditions with
to generate rhodacycle complex II; further coordination of
alkyne 2a to yield III; migratory insertion of alkyne, migratory
insertion of the alkene portion of the enaminone moiety, and β-
hydride elimination provide intermediate species IV, V, and VI
([Cp*RhH]+) along with the formation of 3aa-N; oxidation of
[Cp*RhH]+ by Cu(OAc)2 regenerates I; and nucleophilic
attack of 3aa-N by H2O furnishes the final product 3aa. The
selectivity for 6-exo (insertion of alkene) rather than 5-exo
(insertion of ketone) cyclization likely reflects the dominance of
steric effect in this process.
Scheme 4. Mechanistic Studies
The aldehyde and hydroxy groups contained in these
salicylaldehyde derivatives suggest the ability to perform further
synthetic manipulation. Several conversions utilizing 3aa as the
model reactant are illustrated here to demonstrate the powerful
transformation capability enabled by our synthetic method
(Scheme 6). In particular, one can use both aldehyde and
Scheme 6. Transformations of 3aa
CD3CO2D results in an approximately 20% D incorporation at
the two alkene carbon atoms β to the ketone group (Scheme 4a),
supporting ketone as the C−H activation directing group and
formation of a five-membered rhodacycle after C−H activation.8
The high H−D scrambling efficiency indicates that the C−H
activation step is reversible for 1a. The competition between an
electron-rich and an electron-poor enaminone for reaction with
2a (Scheme 4b) shows a higher reactivity for the electron-rich
substrate, which is consistent with an electrophilic aromatic
substitution C−H activation pathway. The reaction of 1a/1a-d6
and 2a identified a high KIE value (kH/kD = 3.1) (Scheme 4c),
suggesting that C−H activation is the rate-determining step.
Based on the literature8 and the above mechanistic results, a
plausible reaction pathway is proposed (Scheme 5), using 1a
and 2a as the illustrative reactants: reaction of [RhCp*Cl2]2/
4AgSbF6 with Cu(OAc)2 to create rhodium acetate species I;
coordination of the ketone group from 1a and C−H activation
hydroxy groups to react with dimethyl malonate for the
generation of cyclized product 4a;17 the aldehyde group can
be used alone to react with the amino group for the formation of
imine product 5a; and the hydroxy group can serve as a
nucleophile to react with bromo-containing molecules for the
formation of ether linkages (6a and 7a).18
In summary, we have developed herein a Rh(III)-catalyzed
enaminone-directed alkenyl C−H activation method for
coupling with alkynes and synthesis of salicylaldehydes. This
represents a synthetically unique example of benzene ring
framewok formation through a transition-metal-catalyzed,
directed C−H activation strategy. The two reactive function-
alities (aldehyde and hydroxy groups) generated along the way
provide a powerful synthetic handle for further structural
manipulation.
Scheme 5. Proposed Reaction Pathway
ASSOCIATED CONTENT
* Supporting Information
■
S
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.orglett.8b01563.
Experimental procedures and product characterization
(PDF)
1
Copies of the H and 13C NMR spectra of selected
products (PDF)
Accession Codes
CCDC 1843803 contains the supplementary crystallographic
data for this paper. These data can be obtained free of charge via
www.ccdc.cam.ac.uk/data_request/cif, or by emailing data_
C
DOI: 10.1021/acs.orglett.8b01563
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
(6) (a) Rajkumar, S.; Savarimuthu, S. A.; Kumaran, R. S.; Nagaraja, C.
M.; Gandhi, T. Chem. Commun. 2016, 52, 2509. (b) Reddy, B. V. S.;
Reddy, C. R.; Reddy, M. R.; Yarlagadda, S.; Sridhar, B. Org. Lett. 2015,
17, 3730. (c) Zhao, D.; Wu, Q.; Huang, X.; Song, F.; Lv, T.; You, J.
Chem. - Eur. J. 2013, 19, 6239. (d) Muralirajan, K.; Cheng, C.-H. Chem.
- Eur. J. 2013, 19, 6198. (e) Sun, P.; Wu, Y.; Huang, Y.; Wu, X.; Xu, J.;
Yao, H.; Lin, A. Org. Chem. Front. 2016, 3, 91. (f) Song, C.; Yang, C.;
Zhang, F.; Wang, J.; Zhu, J. Org. Lett. 2016, 18, 4510.
(7) (a) Hummel, J. R.; Ellman, J. A. J. Am. Chem. Soc. 2015, 137, 490.
(b) Chen, J.; Chen, P.; Song, C.; Zhu, J. Chem. - Eur. J. 2014, 20, 14245.
(c) Lian, Y.; Bergman, R. G.; Lavis, L. D.; Ellman, J. A. J. Am. Chem. Soc.
2013, 135, 7122. (d) Yu, D.-G.; Suri, M.; Glorius, F. J. Am. Chem. Soc.
2013, 135, 8802. (e) Lian, Y.; Huber, T.; Hesp, K. D.; Bergman, R. G.;
Ellman, J. A. Angew. Chem., Int. Ed. 2013, 52, 629.
request@ccdc.cam.ac.uk, or by contacting The Cambridge
Crystallographic Data Centre, 12 Union Road, Cambridge
CB2 1EZ, UK; fax: +44 1223 336033.
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: jinz@nju.edu.cn.
ORCID
Jin Zhu: 0000-0003-4681-7895
Notes
The authors declare no competing financial interest.
(8) Zhou, S.; Wang, J.; Wang, L.; Song, C.; Chen, K.; Zhu, J. Angew.
Chem., Int. Ed. 2016, 55, 9384.
(9) Shi, P.; Wang, L.; Chen, K.; Wang, J.; Zhu, J. Org. Lett. 2017, 19,
2418.
ACKNOWLEDGMENTS
■
We gratefully acknowledge support from the National Natural
Science Foundation of China (21425415, 21774056) and the
National Basic Research Program of China (2015CB856303).
(10) (a) Minutolo, F.; Bellini, R.; Bertini, S.; Carboni, I.; Lapucci, A.;
Pistolesi, L.; Prota, G.; Rapposelli, S.; Solati, F.; Tuccinardi, T.;
Martinelli, A.; Stossi, F.; Carlson, K. E.; Katzenellenbogen, B. S.;
Katzenellenbogen, J. A.; Macchia, M. J. Med. Chem. 2008, 51, 1344.
(b) Mou, J.; Park, A.; Cai, Y.; Yuan, J.; Yuan, C. Bioorg. Med. Chem. Lett.
2015, 25, 3057. (c) Iftikhar, B.; Javed, K.; Khan, M. S. U.; Akhter, Z.;
Mirza, B.; Mckee, V. J. Mol. Struct. 2018, 1155, 337. (d) Yang, J.;
Yoshikai, N. Angew. Chem., Int. Ed. 2016, 55, 2870. (e) Kostikov, A. P.;
Popik, V. V. Org. Lett. 2008, 10, 5277. (f) Dittmer, D. C.; Li, Q.; Avilov,
D. V. J. Org. Chem. 2005, 70, 4682. (g) Raja, G. C. E.; Ryu, J. Y.; Lee, J.;
Lee, S. Org. Lett. 2017, 19, 6606. (h) Yada, A.; Liao, W.; Sato, Y.;
Murakami, M. Angew. Chem., Int. Ed. 2017, 56, 1073. (i) Gharpure, S. J.;
Nanda, S. K.; Padmaja; Shelke, Y. G. Chem. - Eur. J. 2017, 23, 10007.
(j) Cai, H.; Xia, L.; Lee, Y. R.; Shim, J.-J.; Kim, S. H. Eur. J. Org. Chem.
2015, 23, 5212.
(11) (a) Reimer, K.; Tiemann, F. Ber. Dtsch. Chem. Ges. 1876, 9, 824.
(b) Reimer, K. Ber. Dtsch. Chem. Ges. 1876, 9, 423. (c) Ferguson, L. N.
Chem. Rev. 1946, 38, 227. (d) Truce, W. E. Org. Reactions 1957, 9, 37.
(e) Wynberg, H. Chem. Rev. 1960, 60, 169. (f) Robinson, E. A. J. Chem.
Soc. 1961, 0, 1663. (g) Hine, J.; Van der Veen, J. M. J. Am. Chem. Soc.
1959, 81, 6446.
(12) (a) Balali, E.; Shameli, A.; Naeimi, H.; Ghanbari, M. Orient. J.
Chem. 2013, 29, 1611. (b) Deb, M. L.; Pegu, C. D.; Borpatra, P. J.;
Baruah, P. K. RSC Adv. 2016, 6, 40552.
(13) (a) Sahoo, S.; Badamali, S. K. Asian J. Chem. 2017, 29, 2197.
(b) Jiang, J.-A.; Du, J.-L.; Liao, D.-H.; Wang, Z.-G.; Ji, Y.-F. Tetrahedron
Lett. 2014, 55, 1406.
(14) (a) Buxaderas, E.; Graziano-Mayer, M.; Volpe, M. A.; Radivoy,
G. Synthesis 2017, 49, 1387. (b) Ji, S.; Chen, Y.; Fu, Q.; Chen, Y.; Dong,
J.; Chen, W.; Li, Z.; Wang, Y.; Gu, L.; He, W.; Chen, C.; Peng, Q.;
Huang, Y.; Duan, X.; Wang, D.; Draxl, C.; Li, Y. J. Am. Chem. Soc. 2017,
139, 9795. (c) Mannel, D. S.; Stahl, S. S.; Root, T. W. Org. Process Res.
Dev. 2014, 18, 1503. (d) Huang, D.-W.; Liu, Y.-H.; Peng, S.-M.; Liu, S.-
T. Organometallics 2016, 35, 151.
(15) Davies, R. R.; Hodgson, H. H. J. Chem. Soc. 1943, 0, 84.
(16) Yang, F.; Rauch, K.; Kettelhoit, K.; Ackermann, L. Angew. Chem.,
Int. Ed. 2014, 53, 11285.
REFERENCES
■
(1) (a) Shi, P.; Wang, L.; Guo, S.; Chen, K.; Wang, J.; Zhu, J. Org. Lett.
2017, 19, 4359. (b) Yang, F.; Yu, J.; Liu, Y.; Zhu, J. Org. Lett. 2017, 19,
2885. (c) Wang, J.; Wang, L.; Guo, S.; Zha, S.; Zhu, J. Org. Lett. 2017,
19, 3640. (d) Li, J.; Ackermann, L. Angew. Chem., Int. Ed. 2015, 54, 1.
(e) Zhao, D.; Kim, J. H.; Stegemann, L.; Strassert, C. A.; Glorius, F.
Angew. Chem., Int. Ed. 2015, 54, 4508. (f) Zhao, Y.; Li, S.; Zheng, X.;
Tang, J.; She, Z.; Gao, G.; You, J. Angew. Chem., Int. Ed. 2017, 56, 4286.
(g) Yang, Y.; Gao, P.; Zhao, Y.; Shi, Z. Angew. Chem., Int. Ed. 2017, 56,
3966. (h) Ackermann, L. Chem. Rev. 2011, 111, 1315. (i) Cheng, C.;
Hartwig, J. F. Chem. Rev. 2015, 115, 8946. (j) Zheng, Q.-Z.; Jiao, N.
Chem. Soc. Rev. 2016, 45, 4590. (k) Labinger, J. A. Chem. Rev. 2017,
117, 8483. (l) Kim, D.-S.; Park, W.-J.; Jun, C.-H. Chem. Rev. 2017, 117,
8977. (m) Liu, B.; Fan, Y.; Guo, Y.; Sun, C.; Xu, C.; Zhu, J. J. Am. Chem.
Soc. 2013, 135, 468.
(2) (a) Shi, Z.; Koester, D. C.; Boultadakis-Arapinis, M.; Glorius, F. J.
Am. Chem. Soc. 2013, 135, 12204. (b) Zhao, D.; Lied, F.; Glorius, F.
Chem. Sci. 2014, 5, 2869. (c) Zhu, Z.; Tang, X.; Li, X.; Wu, W.; Deng,
G.; Jiang, H. J. Org. Chem. 2016, 81, 1401. (d) Wang, Y.-F.; Toh, K. K.;
Lee, J.-Y.; Chiba, S. Angew. Chem., Int. Ed. 2011, 50, 5927. (e) Zhang,
X.; Chen, D.; Zhao, M.; Zhao, J.; Jia, A.; Li, X. Adv. Synth. Catal. 2011,
353, 719. (f) Muralirajan, K.; Kuppusamy, R.; Prakash, S.; Cheng, C.-H.
Adv. Synth. Catal. 2016, 358, 774. (g) Huang, X.-C.; Yang, X.-H.; Song,
R.-J.; Li, J.-H. J. Org. Chem. 2014, 79, 1025. (h) Kornhaaß, C.; Li, J.;
Ackermann, L. J. Org. Chem. 2012, 77, 9190. (i) Parthasarathy, K.;
Cheng, C.-H. J. Org. Chem. 2009, 74, 9359. (j) Wang, H.; Koeller, J.;
Liu, W.; Ackermann, L. Chem. - Eur. J. 2015, 21, 15525. (k) Sen, M.;
Kalsi, D.; Sundararaju, B. Chem. - Eur. J. 2015, 21, 15529.
(3) (a) Shi, L.; Yu, K.; Wang, B. Chem. Commun. 2015, 51, 17277.
(b) Wang, H.; Grohmann, C.; Nimphius, C.; Glorius, F. J. Am. Chem.
Soc. 2012, 134, 19592. (c) Guimond, N.; Gorelsky, S. I.; Fagnou, K. J.
Am. Chem. Soc. 2011, 133, 6449. (d) Ackermann, L.; Fenner, S. Org.
Lett. 2011, 13, 6548.
(4) (a) Zhang, G.; Yu, H.; Qin, G.; Huang, H. Chem. Commun. 2014,
50, 4331. (b) Wang, C.; Wang, D.; Yan, H.; Wang, H.; Pan, B.; Xin, X.;
Li, X.; Wu, F.; Wan, B. Angew. Chem., Int. Ed. 2014, 53, 11940. (c) Zhao,
D.; Shi, Z.; Glorius, F. Angew. Chem., Int. Ed. 2013, 52, 12426. (d) Kong,
L.; Xie, F.; Yu, S.; Qi, Z.; Li, X. Chin. J. Catal. 2015, 36, 925. (e) Wang,
(17) (a) Lim, C. J.; Choi, J. Y.; Lee, B. H.; Oh, K.-S.; Yi, K.-Y. Chem.
Pharm. Bull. 2013, 61, 1239. (b) Potowski, M.; Golz, C.; Strohmann,
C.; Antonchick, A. P.; Waldmann, H. Bioorg. Med. Chem. 2015, 23,
2895.
(18) Keskin, S.; Balci, M. Org. Lett. 2015, 17, 964.
́
H.; Moselage, M.; Gonzalez, M. J.; Ackermann, L. ACS Catal. 2016, 6,
2705. (f) Wang, J.; Wang, M.; Chen, K.; Zha, S.; Song, C.; Zhu, J. Org.
Lett. 2016, 18, 1178. (g) Zhou, S.; Wang, J.; Wang, L.; Chen, K.; Song,
C.; Zhu, J. Org. Lett. 2016, 18, 3806. (h) Liu, B.; Song, C.; Sun, C.;
Zhou, S.; Zhu, J. J. Am. Chem. Soc. 2013, 135, 16625.
(5) (a) Deponti, M.; Kozhushkov, S. I.; Yufit, D. S.; Ackermann, L.
Org. Biomol. Chem. 2013, 11, 142. (b) Thirunavukkarasu, V. S.; Donati,
M.; Ackermann, L. Org. Lett. 2012, 14, 3416. (c) Ackermann, L.;
Pospech, J.; Graczyk, K.; Rauch, K. Org. Lett. 2012, 14, 930. (d) Ueura,
K.; Satoh, T.; Miura, M. J. Org. Chem. 2007, 72, 5362.
D
DOI: 10.1021/acs.orglett.8b01563
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