Enantioselective Access to Spirocyclic Sultams by Chiral Cpx-Rhodium(III)-Catalyzed Annulations

Article abstract of DOI:10.1002/chem.201504998

Chiral spirocyclic sultams are a valuable compound class in organic and medicinal chemistry. A rapid entry to this structural motif involves a [3+2] annulation of an N-sulfonyl ketimine and an alkyne. Although the directing-group properties of the imino group for C-H activation have been exploited, the developments of related asymmetric variants have remained very challenging. The use of rhodium(III) complexes equipped with a suitable atropchiral cyclopentadienyl ligand, in conjunction with a carboxylic acid additive, enables an enantioselective and high yielding access to such spirocyclic sultams.

Full text of DOI:10.1002/chem.201504998

DOI: 10.1002/chem.201504998
Communication
&
Synthetic Methods
Enantioselective Access to Spirocyclic Sultams by Chiral
Cpx–Rhodium(III)-Catalyzed Annulations
Manh V. Pham and Nicolai Cramer*[a]
CÀH functionalizations have emerged as a powerful strategy
Abstract: Chiral spirocyclic sultams are a valuable com-
pound class in organic and medicinal chemistry. A rapid
entry to this structural motif involves a [3+2] annulation
of an N-sulfonyl ketimine and an alkyne. Although the di-
recting-group properties of the imino group for CÀH acti-
vation have been exploited, the developments of related
asymmetric variants have remained very challenging. The
use of rhodium(III) complexes equipped with a suitable
atropchiral cyclopentadienyl ligand, in conjunction with
a carboxylic acid additive, enables an enantioselective and
high yielding access to such spirocyclic sultams.
to access versatile building blocks from simple starting materi-
als.[12,13] In this context, myriad transformations catalyzed by
[Cp*RhIII] complexes have been reported over the past few
years.[14,15] Recently, the development of chiral cyclopentadienyl
ligands[16] provided the requisite tools to embark on the devel-
opment of asymmetric variants. In this regard, applications of
chiral cyclopentadienyl ligands (Cpx) in asymmetric catalysis
have been devised.[17] By and large, the enantiodetermining
step of the RhIII-catalyzed transformation consisted of selective
addition across an olefin.[16,17j] Despite their great utility, corre-
sponding enantioselective additions across carbonyls[17f] or
imines remain underexplored.[18] The RhIII-catalyzed annulation
reported by Deng and co-workers[9d] represents an opportunity
to investigate the required catalyst properties and the feasibili-
ty of such additions. Herein, we report an enantioselective
access to spirocyclic sultams 3 from N-sulfonyl ketimines 1 and
alkynes using a chiral [CpxRhIII]-catalyzed [3+2] annulation reac-
tion (Scheme 1).
Chiral sultams are an important class of compounds in organic
and medicinal chemistry. They are used as reagents[1] and as
chiral auxiliaries[2] in various asymmetric reactions. A number
of chiral sultams have potent biological activities with medici-
nal value[3] and several synthetic approaches,[4] including enan-
tioselective syntheses, have been devised.[5] Chiral spirocyclic
sultams have been less investigated, despite biological activi-
ties such as g-secretase inhibition[6] and aldose reductase inhib-
ition (Figure 1).[7] Racemic syntheses of this valuable structural
motif have been reported using intramolecular cyclizations of
elaborated precursors[8] or transition-metal-catalyzed [3+2] an-
nulations.[9,10] Enantioselective syntheses of spirocyclic sultams
are scarce and have so far been limited to one reported orga-
nocatalyzed reaction.[11]
We initially explored this transformation with two chiral
[CpxRhI] complex families, using N-sulfonyl ketimine 1a and di-
phenyl acetylene 2a as substrates (Table 1). The well soluble
Cu(OPiv)2 was used as oxidant to generate the chiral [CpxRhIII]
catalyst in situ. Both Cp families afforded the desired product
in excellent yield at ambient temperature (Table 1, entries 1
and 2). Complex Rh2, with an atropchiral biaryl ligand scaffold,
afforded a better enantioselectivity (Table 1, entry 2). Bulkier
ortho substituents on the biaryl portion of the ligand (R=OiPr
Figure 1. Spirocyclic sultams with relevant biological properties.
[a] M. V. Pham, Prof. Dr. N. Cramer
Laboratory of Asymmetric Catalysis and Synthesis
EPFL SB ISIC LCSA, BCH 4305
1015 Lausanne (Switzerland)
E-mail: nicolai.cramer@epfl.ch
Homepage: http://isic.epfl.ch/lcsa
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201504998.
Scheme 1. Enantioselective additions of [ArRhIII] species across C=C, C=O,
and C=N acceptors.
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proved to be compatible with different substituents at the
para position of the ketimine-aryl ring. For instance, both elec-
tron-rich and electron-poor substituents were well tolerated
and the respective spirocyclic sultams were obtained in good
to excellent yields and high enantioselectivities (Table 2, en-
tries 1–7). Notably, several synthetically valuable functional
Table 1. Optimization of Enantioselective Spirocyclic Sultam Synthesis.[a]
Table 2. Enantioselective spirosultam synthesis.[a]
Entry
Rh
Additive
Solvent
T [8C] Yield [%][b] e.r.[c]
1
2
3
4
5
6
7
8
9[d]
10[d]
11[e]
12[f]
13[e]
14[g]
15[h]
Rh1 Cu(OPiv)2
Rh2 Cu(OPiv)2
Rh3 Cu(OPiv)2
Rh4 Cu(OPiv)2
Rh5 Cu(OPiv)2
Rh6 Cu(OPiv)2
Rh2 Cu(OPiv)2
Rh2 Cu(OPiv)2
DCE
DCE
DCE
DCE
DCE
DCE
DCE
PhCl
Cl-p-Xyl 80
Cl-p-Xyl 80
Cl-p-Xyl 80
Cl-p-Xyl 80
Cl-p-Xyl 80
Cl-p-Xyl 80
Cl-p-Xyl 80
30
30
30
30
30
30
80
80
99
99
99
90
19
52
99
99
81
81
99
99
99
0
61:39
84.5:15.5
77.5:22.5
47:53
60.5:39.5
66:34
86:14
90:10
92.5:7.5
91:9
Entry
3
Yield
[%][b]
e.r.[c]
1[d]
2
3ba (R1 =OCF3)
3ca (R1 =OTf)
3da (R1 =OMe)
3ea (R1 =CF3)
3 fa (R1 =F)
3ga (R1 =Ac)
3ha (R1 =CHO)
99
70
71
99
88
91
99
95.5:4.5
94.5:5.5
94.5:5.5
96:4
94:6
95.5:4.5
95:5
3
4[d]
5
Rh2
Rh2
Rh2
Rh2
Rh2
Rh2
Rh2
PivOH
AcOH
4
4
ent-4
4
6
7
93:7
92.5:7.5
93:7
–
8
3ia
3ja
65
90:10
95:5
–
19
89:11
[a] Conditions (unless otherwise stated): 1a (0.05 mmol), 2a (0.06 mmol),
Rh (1.00 mmol), AgSbF6 (10.0 mmol), 0.10m solution in solvent, 18 h;
[b] isolated product; [c] determined by HPLC with a chiral stationary
phase; [d] 10 mol% AgSbF6, 5 mol% additive, 2 h; [e] 10 mol% AgNTf2 in-
stead of AgSbF6, 5 mol% additive, 2 h; [f] 1 mmol scale and 10 mol%
AgNTf2; [g] 5 mol% 4, no AgSbF6, 2 h; [h] 10 mol% AgSbF6, 2 h.
9[d]
99
or OTIPS; Table 1, entries 3 and 4), as well as smaller groups
(R=H or Me; entries 5 and 6), decreased the enantioselectivity.
In addition, the smaller ligands displayed significantly reduced
reactivity. A higher reaction temperature resulted in better
enantioselectivity (Table 1, entry 7). This behavior may be at-
tributed to enhanced equilibration rate between conforma-
tions. Solvent screening revealed that chlorinated aromatic sol-
vents were beneficial. For instance, chlorobenzene gave 3aa in
virtually quantitative yields with 90:10 e.r. (Table 1, entry 8).
Combining AgSbF6 and a simple carboxylic acid (PivOH or
AcOH) in 2-chloro-p-xylene solvent resulted in enhanced reac-
tivity, giving 3aa in good yield and improved enantioselectivity
in a shorter reaction time of 2 h (Table 1, entries 9 and 10).
Using protected l-phenylalanine (4) and AgNTf2 further en-
hanced the reactivity while maintaining a very good level of
enantioselectivity (Table 1, entry 11), which was retained when
the reaction was carried out on a larger scale (entry 12). Nota-
bly, the chirality of the additive 4 proved to be irrelevant as
ent-4 provided identical selectivity (Table 1, entry 13). Omitting
the silver oxidant shut down the reactivity completely, and in
the absence of a carboxylic acid, poor yields of 3aa were ob-
served (Table 1, entries 14 and 15).
10
11
3ka
3la
99
50
94:6
88:12
12
13
14
15
3eb (R3 =R4 =p-ClPh)
3ec (R3 =R4 =p-F3CPh)
3ed (R3 =R4 =3,5-Xyl)
3ee (R3 =R4 =2-Np)
3ef (R3 =Ph, R4 =2-Np)
3ef’ (R3 =2-Np, R4 =Ph)
3eg (R3 =PMP, R4 =p-
F3CPh)
3eg’ (R3 =p-F3CPh,
R4 =PMP)
3eh (R3 =CO2Me, R4 =Ph)
3eh’ (R3 =Ph, R4 =CO2Me)
3ei (R3 =Me, R4 =Ph)
3ei’ (R3 =Ph, R4 =Me)
3ej (R3 =R4 =Bu)
86
70
99
99
60
40
66
97:3
97:3
96:4
97:3
96:4
97:3
94:6
16
17
18
33
96.5:3.5
71
28
70
29
49
87.5:12.5
88.5:11.5
70:30
90.5:9.5
68:32
19
20
[a] Conditions (unless otherwise stated): 1 (0.05 mmol), 2 (0.06 mmol),
Rh2 (1.00 mmol), AgNTf2 (5.00 mmol), 4 (2.50 mmol), 0.10m in 2-chloro-p-
xylene, 808C, 14 h; [b] isolated product; [c] determined by HPLC with
a chiral stationary phase; [d] 1 mmol scale.
Under the aforementioned optimized conditions, the scope
of the cyclization was investigated (Table 2). The reaction
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Communication
groups, such as a triflate, aldehyde, or ketone are well tolerat-
ed in this process (Table 2, entries 2, 6, and 7). A m-CF3 group
led to slightly reduced yield and selectivity (Table 2, entry 8),
whereas a 2-naphthyl moiety had no detrimental effect on the
selectivity (entry 9). Substitution (p-Cl) on the arenesulfonyl
core is also possible (Table 2, entry 10). Besides the cyclic N-sul-
fonyl ketimines, a cyclic sulfamidate substrate could be used,
affording spirocyclic product 3la (Table 2, entry 11). We next
evaluated the influence of different alkynes in this transforma-
tion. Aryl alkynes with different electronic and steric properties
were excellent coupling partners, delivering the chiral spirocy-
clic sultams in high enantioselectivities (Table 2, entries 12–15).
Although unsymmetrical aryl alkynes reacted with weak regio-
selectivities, excellent enantioselectivities were maintained
(Table 2, entries 16 and 17). Alkynes with a single aryl substitu-
ent reacted well, albeit with moderate regioselectivities and
enantioselectivities depending on the substituent and the re-
gioisomer (Table 2, entries 18 and 19). A dialkyl alkyne dis-
played reduced reactivity and selectivity (entry 20).
The absolute configuration of the sultams were unambigu-
ously established by X-ray crystallographic analysis of 3ja to
be R (Figure 2).
Scheme 2. Proposed mechanism for enantioselective spirocycle formation
and controls.
In conclusion, we have reported a chiral Cpx–rhodium(III)-
catalyzed synthesis of spirocyclic indenyl sultams by enantiose-
lective annulation of N-sulfonyl ketimines and alkynes. The
enantiodetermining addition across the imine is shown to be
influenced by the chiral Cpx ligand, as well as a judicious
choice of carboxylic acid additives. The spirocyclic sultams
were obtained in high yields and enantiomeric ratios and their
relevance renders this method attractive for synthetic and me-
dicinal chemistry. Moreover, this study further adds to the gen-
erality of the chiral cyclopentadienyls based on an atropchiral
biaryl backbone as a versatile chiral ligand class.
Figure 2. X-ray crystal structure and absolute configuration of sultam 3ja.
The following mechanistic scenario is plausible for this trans-
formation (Scheme 2). Oxidation of the [CpxRhI] complex by
the silver salt generates a cationic [CpxRhIII] species.[19] The car- Acknowledgements
boxylic acid additive should give a monocationic species. CÀH
activation directed by the N-sulfonyl imino group gives cyclo-
metalated compound 5.[20] Association of alkyne 2 and migra-
tory insertion would lead to intermediate 6. The subsequent
enantiodetermining addition across the C=N bond would set
the spirocyclic stereocenter of 7. Finally, protonation would de-
liver product 3 and closes the catalytic cycle. An alternative re-
action pathway could be envisioned involving first a hydroary-
lation of 1a giving alkene 8. A subsequent asymmetric Friedel-
Crafts cyclization[21] with [CpxRhIII] bound to the imine could
yield 9 and then product 3aa.[9b] Exposure of independently
prepared intermediate 8 to the reaction conditions gave
sultam 3aa in completely racemic fashion, indicating that this
pathway is less likely. AgSbF6 alone was able to induce cycliza-
tion, whereas AgNTf2 proved to be inert.
This work was supported by the European Research Council
under the European Community’s Seventh Framework Pro-
gram (FP7 2007-2013)/ERC Grant agreement no. 257891 and
the Swiss National Science Foundation (155967). We thank Dr.
R. Scopelliti for X-ray crystallographic analysis of compound
3ja.
Keywords: asymmetric catalysis · CÀH activation · chiral Cp
ligands · rhodium · sultams
[1] a) F. A. Davis, B. C. Chen, Chem. Rev. 1992, 92, 919; b) E. Differding, G. M.
Rüegg, R. W. Lang, Tetrahedron Lett. 1991, 32, 1779.
[2] a) A. W. M. Lee, W. H. Chan, S.-J. Zhang, H.-K. Zhang, Curr. Org. Chem.
2007, 11, 213; b) B. Hyean Kim, D. P. Curran, Tetrahedron 1993, 49, 293;
Chem. Eur. J. 2016, 22, 2270 – 2273
www.chemeurj.org
2272
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Communication
c) W. Oppolzer, Pure Appl. Chem. 1990, 62, 1241; d) W. Oppolzer, Tetrahe-
dron 1987, 43, 1969.
2011, 111, 1780; j) S. H. Cho, J. Y. Kim, J. Kwak, S. Chang, Chem. Soc. Rev.
2011, 40, 5068; k) J. Wencel-Delord, T. Droge, F. Liu, F. Glorius, Chem.
Soc. Rev. 2011, 40, 4740; l) W. R. Gutekunst, P. S. Baran, Chem. Soc. Rev.
2011, 40, 1976; m) L. McMurray, F. O’Hara, M. J. Gaunt, Chem. Soc. Rev.
2011, 40, 1885; n) J. Le Bras, J. Muzart, Chem. Rev. 2011, 111, 1170;
o) T. W. Lyons, M. S. Sanford, Chem. Rev. 2010, 110, 1147; p) D. A. Colby,
R. G. Bergman, J. A. Ellman, Chem. Rev. 2010, 110, 624; q) X. Chen, K. M.
Engle, D.-H. Wang, J.-Q. Yu, Angew. Chem. Int. Ed. 2009, 48, 5094;
Angew. Chem. 2009, 121, 5196.
[3] a) R. Bihovsky, M. Tao, J. P. Mallamo, G. J. Wells, Bioorg. Med. Chem. Lett.
2004, 14, 1035; b) G. J. Wells, M. Tao, K. A. Josef, R. Bihovsky, J. Med.
Chem. 2001, 44, 3488; c) D. C. Baker, B. Jiang (The University Of Tennes-
see Research Corporation), US6353112 B1, 2002; d) J. Mao, D. C. Baker
(The University Of Tennessee Research Corporation), US6458962 B1,
2002; e) A. Jirgensons, G. Leitis, I. Kalvinsh, D. Robinson, P. Finn, N. Khan
(InhibOx Ltd., Oxford), WO2008142376 A1, 2008.
[4] a) V. A. Rassadin, D. S. Grosheva, A. A. Tomashevskii, V. V. Sokolov, Chem.
Heterocycl. Compd. 2013, 49, 39; b) K. C. Majumdar, S. Mondal, Chem.
Rev. 2011, 111, 7749; c) Z. Liu, Y. Takeuchi, Heterocycles 2009, 78, 1387.
[5] a) S. Zhang, L. Li, Y. Hu, Z. Zha, Z. Wang, T.-P. Loh, Org. Lett. 2015, 17,
1050; b) S. Nakamura, M. Sano, A. Toda, D. Nakane, H. Masuda, Chem.
Eur. J. 2015, 21, 3929; c) T. Nishimura, A. Noishiki, G. Chit Tsui, T. Hayashi,
J. Am. Chem. Soc. 2012, 134, 5056; d) M. Rommel, T. Fukuzumi, J. W.
Bode, J. Am. Chem. Soc. 2008, 130, 17266; e) M. Ichinose, H. Suematsu,
Y. Yasutomi, Y. Nishioka, T. Uchida, T. Katsuki, Angew. Chem. Int. Ed. 2011,
50, 9884; Angew. Chem. 2011, 123, 10058; f) W. Oppolzer, M. Wills, C.
Starkemann, G. Bernardinelli, Tetrahedron Lett. 1990, 31, 4117.
[6] a) E. R. Andersson, U. Lendahl, Nat. Rev. Drug. Discovery 2014, 13, 357;
b) C. Timme, M. Gruidl, T. Yeatman, Apoptosis 2013, 18, 1163; c) V. Ram-
akrishnan, S. Ansell, J. Haug, D. Grote, T. Kimlinger, M. Stenson, M.
Timm, L. Wellik, T. Halling, S. V. Rajkumar, S. Kumar, Leukemia 2012, 26,
340; d) J. L. Castro Pineiro, I. J. Collins, T. Harrison, US20050143369 A1,
2005.
[7] J. Wrobel, A. Dietrich, S. A. Woolson, J. Millen, M. McCaleb, M. C. Harri-
son, T. C. Hohman, J. Sredy, D. Sullivan, J. Med. Chem. 1992, 35, 4613.
[8] a) L. Sun, Y. Zhu, J. Wang, P. Lu, Y. Wang, Org. Lett. 2015, 17, 242; b) Z.
Liu, N. Shibata, Y. Takeuchi, J. Chem. Soc. Perkin Trans. 1 2002, 3, 302.
[9] a) Y. Ebe, M. Hatano, T. Nishimura, Adv. Synth. Catal. 2015, 357, 1425;
b) M. Nagamoto, T. Nishimura, Chem. Commun. 2014, 50, 6274; c) T.
Nishimura, Y. Ebe, T. Hayashi, J. Am. Chem. Soc. 2013, 135, 2092; d) L.
Dong, C.-H. Qu, J.-R. Huang, W. Zhang, Q.-R. Zhang, J.-G. Deng, Chem.
Eur. J. 2013, 19, 16537.
[10] For examples of related indenamines and indanamines via [3+2] annu-
lation, see: a) J. Zhang, A. Ugrinov, P. Zhao, Angew. Chem. Int. Ed. 2013,
52, 6681; Angew. Chem. 2013, 125, 6813; b) P. Zhao, F. Wang, K. Han, X.
Li, Org. Lett. 2012, 14, 5506; c) D. N. Tran, N. Cramer, Angew. Chem. Int.
Ed. 2011, 50, 11098; Angew. Chem. 2011, 123, 11294; d) Z.-M. Sun, S.-P.
Chen, P. Zhao, Chem. Eur. J. 2010, 16, 2619; e) D. N. Tran, N. Cramer,
Angew. Chem. Int. Ed. 2013, 52, 10630; Angew. Chem. 2013, 125, 10824;
f) D. N. Tran, N. Cramer, Angew. Chem. Int. Ed. 2010, 49, 8181; Angew.
Chem. 2010, 122, 8357; g) Y. Kuninobu, P. Yu, K. Takai, Org. Lett. 2010,
12, 4274.
[13] For reviews on asymmetric CÀH functionalizations, see: a) C. Zheng, S.-
L. You, RSC Adv. 2014, 4, 6173; b) J. Wencel-Delord, F. Colobert, Chem.
Eur. J. 2013, 19, 14010; c) R. Giri, B.-F. Shi, K. M. Engle, N. Maugel, J.-Q.
Yu, Chem. Soc. Rev. 2009, 38, 3242; d) H. M. L. Davies, J. R. Manning,
Nature 2008, 451, 417–424.
[14] For reviews on [Cp*RhIII]-catalyzed CÀH functionalizations, see: a) G.
Song, X. Li, Acc. Chem. Res. 2015, 48, 1007; b) X.-S. Zhang, K. Chen, Z.-J.
Shi, Chem. Sci. 2014, 5, 2146; c) N. Kuhl, N. Schrçder, F. Glorius, Adv.
Synth. Catal. 2014, 356, 1443; d) G. Song, F. Wang, X. Li, Chem. Soc. Rev.
2012, 41, 3651; e) F. W. Patureau, J. Wencel-Delord, F. Glorius, Aldrichimi-
ca Acta 2012, 45, 31; f) T. Satoh, M. Miura, Chem. Eur. J. 2010, 16, 11212.
[15] For some contributions from us, see: a) M. V. Pham, N. Cramer, Angew.
Chem. Int. Ed. 2014, 53, 14575; Angew. Chem. 2014, 126, 14803; b) M. V.
Pham, N. Cramer, Angew. Chem. Int. Ed. 2014, 53, 3484; Angew. Chem.
2014, 126, 3552; c) M. V. Pham, B. Ye, N. Cramer, Angew. Chem. Int. Ed.
2012, 51, 10610; Angew. Chem. 2012, 124, 10762.
[16] a) T. K. Hyster, L. Knçrr, T. R. Ward, T. Rovis, Science 2012, 338, 500; b) B.
Ye, N. Cramer, Science 2012, 338, 504.
[17] a) B. Ye, N. Cramer, Acc. Chem. Res. 2015, 48, 1308; b) S. Reddy Chidipu-
di, D. J. Burns, I. Khan, H. W. Lam, Angew. Chem. Int. Ed. 2015, 54, 13975;
Angew. Chem. 2015, 127, 14181; c) D. Kossler, N. Cramer, J. Am. Chem.
Soc. 2015, 137, 12478; d) M. Dieckmann, Y.-S. Jang, N. Cramer, Angew.
Chem. Int. Ed. 2015, 54, 12149; Angew. Chem. 2015, 127, 12317; e) J.
Zheng, S.-B. Wang, C. Zheng, S.-L. You, J. Am. Chem. Soc. 2015, 137,
4880; f) B. Ye, N. Cramer, Synlett 2015, 26, 1490; g) J. Zheng, S.-L. You,
Angew. Chem. Int. Ed. 2014, 53, 13244; Angew. Chem. 2014, 126, 13460;
h) G. Song, W. W. N. O, Z. Hou, J. Am. Chem. Soc. 2014, 136, 12209; i) B.
Ye, N. Cramer, Angew. Chem. Int. Ed. 2014, 53, 7896; Angew. Chem.
2014, 126, 8030; j) B. Ye, P. A. Donets, N. Cramer, Angew. Chem. Int. Ed.
2014, 53, 507; Angew. Chem. 2014, 126, 517; k) B. Ye, N. Cramer, J. Am.
Chem. Soc. 2013, 135, 636.
[18] For a diastereoselective addition, see: A. Wangweerawong, R. G. Berg-
man, J. A. Ellman, J. Am. Chem. Soc. 2014, 136, 8520.
[19] Silver mirror formation indicated reduction to Ag0.
[20] a) S.-T. Mei, N.-J. Wang, Q. Ouyang, Y. Wei, Chem. Commun. 2015, 51,
2980; b) M. E. Tauchert, C. D. Incarvito, A. L. Rheingold, R. G. Bergman,
J. A. Ellman, J. Am. Chem. Soc. 2012, 134, 1482; c) Y. Li, X.-S. Zhang, H.
Li, W.-H. Wang, K. Chen, B.-J. Li, Z.-J. Shi, Chem. Sci. 2012, 3, 1634.
[21] For reviews on asymmetric Friedel-Crafts reaction, see: a) M. Bandini, A.
Eichholzer, Angew. Chem. Int. Ed. 2009, 48, 9608; Angew. Chem. 2009,
121, 9786; b) T. B. Poulsen, K. A. Jørgensen, Chem. Rev. 2008, 108, 2903;
c) M. Bandini, A. Melloni, A. Umani-Ronchi, Angew. Chem. Int. Ed. 2004,
43, 550; Angew. Chem. 2004, 116, 560.
[11] X.-L. He, Y.-C. Xiao, W. Du, Y.-C. Chen, Chem. Eur. J. 2015, 21, 3443.
[12] For selected reviews, see: a) C. Cheng, J. F. Hartwig, Chem. Rev. 2015,
115, 8946; b) L. Yang, H. Huang, Chem. Rev. 2015, 115, 3468; c) O. Dau-
gulis, J. Roane, L. D. Tran, Acc. Chem. Res. 2015, 48, 1053; d) Y. Segawa,
T. Maekawa, K. Itami, Angew. Chem. Int. Ed. 2015, 54, 66; Angew. Chem.
2015, 127, 68; e) S. De Sarkar, W. Liu, S. I. Kozhushkov, L. Ackermann,
Adv. Synth. Catal. 2014, 356, 1461; f) G. Rouquet, N. Chatani, Angew.
Chem. Int. Ed. 2013, 52, 11726; Angew. Chem. 2013, 125, 11942; g) J.
Wencel-Delord, F. Glorius, Nat. Chem. 2013, 5, 369; h) J. Yamaguchi,
A. D. Yamaguchi, K. Itami, Angew. Chem. Int. Ed. 2012, 51, 8960; Angew.
Chem. 2012, 124, 9092; i) C. Liu, H. Zhang, W. Shi, A. Lei, Chem. Rev.
Received: December 11, 2015
Published online on January 11, 2016
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