Divergent Functionalization of Indoles with Acryloyl Silanes via Rhodium-Catalyzed C-H Activation

Article abstract of DOI:10.1021/acs.orglett.5b01258

(Chemical Equation Presented) A protocol enabled by rhodium-catalyzed C-H functionalization of indoles with acryloyl silanes was developed, providing a convenient and highly effective method for the synthesis of functionalized acylsilane derivatives. By tuning the reaction condition, this C-H-activation-initiated reaction proceeds divergently with acryloyl silianes to selectively afford alkylation or alkenylation products via hydroarylation or oxidative cross-coupling, respectively. The mild reaction conditions employed in both cases enable the tolerance of a wide scope of functionalities as well as high reaction efficiency. Furthermore, polycyclic indole derivatives were easily accessed from 2-alkenylation products through a visible-light-induced reaction cascade.

Full text of DOI:10.1021/acs.orglett.5b01258

Letter
pubs.acs.org/OrgLett
Divergent Functionalization of Indoles with Acryloyl Silanes via
Rhodium-Catalyzed C−H Activation
†
,†,‡
,†,‡
Ping Lu, Chao Feng,* and Teck-Peng Loh*
†
Department of Chemistry, University of Science and Technology of China, Hefei, Anhui 230026, P. R. China
‡
Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences, Nanyang Technological University,
Singapore, 637616, Singapore
*
S Supporting Information
ABSTRACT: A protocol enabled by rhodium-catalyzed C−H functionalization of indoles with acryloyl silanes was developed,
providing a convenient and highly effective method for the synthesis of functionalized acylsilane derivatives. By tuning the
reaction condition, this C−H-activation-initiated reaction proceeds divergently with acryloyl silianes to selectively afford
alkylation or alkenylation products via hydroarylation or oxidative cross-coupling, respectively. The mild reaction conditions
employed in both cases enable the tolerance of a wide scope of functionalities as well as high reaction efficiency. Furthermore,
polycyclic indole derivatives were easily accessed from 2-alkenylation products through a visible-light-induced reaction cascade.
cylsilanes represent a class of very important structural
product of aroylsilanes could in turn be employed in the
photoirradiation for the synthesis of indanone derivatives via
siloxycarbenes. While this strategy is effective, the prerequisite of
using aroylsilanes as substrates more or less detracts from its
synthetic potential, especially in cases where the acylsilane
derivatives were not readily accessible. Therefore, we envisage
tackling this problem by obviating the use of acylsilane as a
directing group but instead introducing the acryloyl silane moiety
onto arenes through oxidative alkenylation using traditional
functionality as the directing group. Considering the importance
of indole derivatives and their ubiquity as the key fragments in
various biologically active alkaloids, our privileged endeavor was
A
motifs, which find widespread use in the fields of synthetic
1
organic chemistry, materials science, and photochemistry. The
2
unique reactivity of acylsilane to act as oxycarboanion,
3
4
uncoventional acyl anion, or siloxycarbene equivalents under
certain reaction conditions stems from the thermodynamically5
favored 1,2-silyl migration process (Brook rearrangement).
Furthermore, the steric and electronic properties of the embeded
silyl group could also be capitalized to steer the reaction
6
selectivity on C−C bond formations. While reliable synthetic
sequences for the acylsilane synthesis exist, traditional linear
synthetic protocols suffer from either low step economy or harsh
reaction conditions, which potentially limited the scope of
acylsilane attainable, especially of those highly functionalized
13
made in the functionalization of indoles. As exemplified in
Scheme 1, oxidative cross-coupling between N-protected indole
and acryloyl silane is conceived to afford a 2-alkenylation
product, which may undergo a cascade sequence encompassing
7
ones. Therefore, the development of a novel synthetic protocol,
which streamlines the synthetic access of functionalized
acylsilanes, is still highly desirable and of academic importance.
In the past several years, the Rh(III)-catalyzed C−H
functionalization has witnessed an explosive evolvement and
6
-π electrocyclization and a 1,3-hydrogen shift to deliver a
polycyclic indole derivative via a photogenerated alkenyl
14
siloxycarbene intermediate.
8
9
To make our envisaged reaction sequence work effectively, the
identification of suitable reaction conditions for oxidative cross-
coupling between indole and acryloyl silane is the premise. To
this end, the model reaction between 2-pyrimidyl indole 1a and
TBS-derived acryloyl silane 2a was systematically examined.
Unexpectedly, when substrates 1a and 2a were treated with
diverse transformations such as C−C, C−heteroatom bond
10
formation, and annulation reactions in either a redox-neutral or
an oxidative manner were disclosed by many research groups as
1
1
well as our group. Notwithstanding the advancements
obtained, the development of an effective protocol in the realm
of Rh(III)-catalyzed C−H transformation, which allows easy
access of synthetically useful or bioactive relevant structural
motifs, is still highly sought after in the synthetic organic
community. Recently, by using the acylsilane as the directing
group, the Bolm group reported an elegant work of Rh(III)-
[
RhCp*Cl ] as catalyst and 1 equiv Cu(OAc) ·H O as oxidant
2 2 2 2
under air atmosphere, no alkenylation product but the alkylation
Received: April 29, 2015
12
catalyzed C−H alkenylation of aroylsilanes. The alkenylation
©
XXXX American Chemical Society
A
DOI: 10.1021/acs.orglett.5b01258
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Organic Letters
Letter
a
Scheme 1. Rhodium Catalyzed Synthesis of Functionalized
Acylsilanes and Visible-Light-Induced Electrocyclization
Scheme 2. Reaction Scope of Hydroarylation
a
Unless otherwise noted, the reactions were carried out at 60 °C using
(0.1 mmol), 2 (0.15 mmol), Cu(OAc) ·H O (0.01 mmol),
product 3aa was obtained in 74% yield (refer to Supporting
1
2
2
Information, Table S1, entry 1). Notably, compared to the well-
[RhCp*Cl ] (0.0025 mmol) in DCE (1 mL) under a N atmosphere
for 5 h. Yields of isolated products are given.
2
2
2
15
studied Rh(III)-catalyzed hydroarylation of alkynes, related
hydroarylation of alkenes, however, were much underdevel-
1
6
oped. The scarcity of this transformation may be in part due to
their substitution patterns on the indole core, were employed,
the reaction occurred smoothly to provide the desired products
in high yield (3ba, 3ea, 3ha, 3ka, 3la). Taking the steric
hindrance of 3-methyl substituent into account, the outcome of
the reaction between 1k and 2a was quite noteworthy. A
substrate bearing ester group also worked nicely to provide
product 3da in 80% yield. Pleasingly, halogen substituents were
also well compatible with the reaction conditions and afforded
the desired products in excellent yields (3ca, 3fa, 3ga, 3ia, 3ja),
which provide the synthetic handles for further elaboration. It
needs to be pointed out that the reaction was not restricted to
indole substrates and when pyrroles were subjected to the
reaction, the corresponding alkylation products could also be
obtained in high yield (3ma, 3na). Finally, acryloyl silanes
containing different silyl groups such as TMS, TIPS, and DMPS
were examined, which delivered the desired hydroarylation
products in moderate yields (3ab, 3ac, and 3ad).
Subsequently, the oxidative alkenylation reactions are ex-
plored, and the results were summarized in Scheme 3. Indole
derivatives containing an electron-donating group, such as 4-Me,
5-Me, and 5-OMe, provided the olefination product in good to
high yield (4ba, 4ea, 4ha). Substrates with electron-withdrawing
groups delivered the desired products in moderate yields (4da,
4pa). It appears that the oxidative alkenylation was somewhat
steric sensitive, and when 1k, 1l were employed, the reactions
afforded desired products in diminished yields (4ka, 4la). In
accordance with hydroarylation reaction, halogen atoms were
also well tolerated in the olefination reaction (4ca, 4fa, 4ga, 4ia,
4ja). Gratifyingly, pyrroles derivatives also provided the desired
products in excellent yield (4ma, 4na). Moreover, when a
thiophene derivative was employed, the olefination product was
obtained in 70% yield. In addition, acryloyl silanes with different
silyl groups were examined again. A substrate with TIPS
substitution gave the olefination product in 81% yield (4ab),
3
a) the relative slow protonation of C(sp )-Rh intermediate
2
compared with that of C(sp )-Rh counterpart; b) the presence of
β-hydrogen atoms, which are inclined to undergo elimination.
Subsequent attempts revealed that the hydroarylation reaction
could be advanced to afford product 2a in 88% yield by using 10
mol % amount of Cu(OAc) ·H O and under N atmosphere
2
2
2
(
Table S1, entry 3). To our surprise, copper salt and N2
protection (in case of using catalytic amount of copper acetate)
were identified to be two crucial factors for the success of
17
hydroarylation (Table S1, entries 2, 4). These outcomes
implicated that in the hydroarylation reaction the copper salt
should have an intimate effect on the rhodium catalyst turnover
and the active copper species mediating this process is most likely
the Cu(I). Further exploration of reaction parameters led to the
optimal reaction condition for the hydroarylation to be using
DCE as solvent and 10 mol % Cu(OAc) ·H O as additive under
2
2
N atmosphere (refer to Supporting Information). It also needs
2
to be noted that during the optimization of hydroarylation
reaction condition trace amount of oxidative alkenylation
product was often observed, which prompted us toward further
investigations, aiming at the realization of controllable divergent
functionalization of indole derivatives through C−H activation.
Fortunately, we found that alkenylation product 4aa could be
increased to 24% yield simply using MeCN as reaction solvent
1
8
(
(
(
Table S1, entry 7). Changing the catalyst to RhCp*-
MeCN) (SbF ) further increase the yield of 4aa to 62%
Table S1, entry 8). Further improvement was obtained when
3
6 2
adding additional TEMPO as an additive, which delivered the
19
product 4aa in 71% yield. A control experiment revealed that
rhodium catalyst was essential for both hydroarylation reactions
and olefination reactions, without which no reaction occurred.
With the optimal reaction conditions for the divergent
functionalization of indole established, the substrate scopes
with respect to indole and acryloyl silane for hydroarylation
reaction were investigated first and the results are summarized in
Scheme 2. It turns out that the reaction showed both high
efficiency and good functional group tolerance. When indole
derivatives 1 containing electron-donating groups, irrespective of
while substrates bearing TMS and SiMe Ph groups afforded the
2
products in moderate yield (4ac, 4ad).
With the olefination products in hand, the subsequent visible-
light-induced reaction cascade was examined (Scheme 1). When
2-alkenylation product 4aa was irradiated with a 23 W compact
B
DOI: 10.1021/acs.orglett.5b01258
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Organic Letters
Letter
a
Scheme 3. Reaction Scope of Olefination Reaction
Scheme 5. Proposed Reaction Mechanism
process. On the other hand, deuterium was not incorporated into
the alkenylation product when the oxidative coupling reaction
was carried out in CD CN. It was also found that there is no
3
deuterium incorporation on the recovered indole substrate in
both hydroarylation and oxidative alkenylation reactions
performed in either CH OD or CD CN. In addition, when the
a
Unless otherwise noted, the reactions were carried out at 60 °C using
(0.1 mmol), 2 (0.15 mmol), Cu(OAc) ·H O (0.2 mmol), TEMPO
1
2
2
3
3
(
0.1 mmol), RhCp*(MeCN) (SbF ) (0.005 mmol) in MeCN (1 mL)
3 6 2
hydroarylation product 3aa was subjected to the optimized
reaction conditions of oxidative alkenylation, no transformation
into product 4aa was observed, indicating the independent
nature of these two reaction pathways. Based on these results, the
reaction mechanism for the hydroarylation and olefination
reactions was proposed and presented in Scheme 5. Both the
hydroarylation and olefination reactions start with directing
group assisted irreversible C−H activation of indole 1a with the
under air for 12 h. Yields of isolated products are given.
fluorescent lamp in CHCl CHCl as solvent, the expected
2
2
cyclization indeed happened; however, not the silyl enol eher 5a′
but product 5a was obtained in 54% yield, indicating the
involvement of a 1,3-silicon shift process (Scheme 4). By using
these preliminary reaction conditions, several other indole
functionalized acryloyl silanes were tested.
Substrates containing functional groups such as ester, fluorine,
and methoxyl were compatible with the reaction conditions,
albeit producing the cyclization products in low to moderate
yields (5b−5e).
20
Rh(III) catalyst to generate rhodacycle I, which underwent
21
further alkene insertion to afford intermediate II. In view of the
indispensability of Cu salt in the hydroarylation reaction, a Rh−
Cu transmetalation process was envisioned to produce
intermediate III and regenerate the active Rh(III) catalyst
22
(
Scheme 2, path a). Protodecupration in III would produce the
Scheme 4. Visible-Light-Induced Electrocyclization of
Products 4
alkylation product 3aa and regenerate the copper catalyst. For
the olefination reaction, intermediate II goes through path b via
β-H elimination to deliver product 4aa accompanied by the
23
generation of Rh(I), which in turn is oxidized by copper acetate
to complete the catalytic cycle.
In conclusion, we have reported a novel strategy for the
synthesis of indole functionalized acylsilane derivatives by taking
advantage of the Rh(III)-catalyzed C−H activation manifold.
Besides the advantage of using readily available reaction
substrates, the controllable nature of chemoselectively generat-
ing either hydroarylation or oxidative alkenylation products
greatly boosts the synthetic utility of this protocol. Furthermore,
the amenability of a wide variety of functional groups and
practicality of this reaction provide a straightforward pathway for
the synthesis of functionalized acylsilane derivatives. For the 2-
alkenylation product obtained, facile access to polycyclic indole
derivatives could be gained by taking advantage of visible-light-
induced 6-π electrocyclization.
In order to gain more insight into the reaction mechanism of
this divergent C−H functionalization, some control experiments
were carried out. A hydroarylation reaction carried out with an
additional 0.1 mL of CH OD for 2 h delivered 3aa-d1 with 33%
ASSOCIATED CONTENT
3
■
deuteration content on the α-position of the acylsilane functional
group, while no deuterium incorporation was observed when 3aa
was submitted to the same conditions. These results indicate that
in the hydroarylation reaction (a) the β-H elimination/
reinsertion process was not involved and (b) a protonation of
the carbon−metal bond step is present during the catalytic
*
S
Supporting Information
Detailed experiment procedures and compound characterization
data. The Supporting Information is available free of charge on
the ACS Publications website at DOI: 10.1021/acs.or-
glett.5b01258.
C
DOI: 10.1021/acs.orglett.5b01258
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
(
10) For selected examples of Rh(III)-catalyzed annulation reaction,
AUTHOR INFORMATION
Corresponding Authors
■
see: (a) Ueura, K.; Satoh, T.; Miura, M. J. Org. Chem. 2007, 72, 5362.
b) Stuart, D. R.; Bertrand-Laperle, M.; Burgess, K. M.; Fagnou, K. J. Am.
(
*
E-mail: fengchao@ntu.edu.sg.
E-mail: teckpeng@ntu.edu.sg.
Chem. Soc. 2008, 130, 16474. (c) Du, Y.; Hyster, T. K.; Rovis, T. Chem.
Commun. 2011, 47, 12074. (d) Muralirajan, K.; Parthasarathy, K.;
Cheng, C.-H. Angew. Chem., Int. Ed. 2011, 50, 4169. (e) Wang, Y.-F.;
Toh, K. K.; Lee, J.-Y.; Chiba, S. Angew. Chem., Int. Ed. 2011, 50, 5927.
(f) Li, B.-J.; Wang, H.-Y.; Zhu, Q.-L.; Shi, Z.-J. Angew. Chem., Int. Ed.
*
Notes
The authors declare no competing financial interest.
2
012, 51, 3948. (g) Tan, X.; Liu, B.; Li, X.; Li, B.; Xu, S.; Song, H.; Wang,
ACKNOWLEDGMENTS
B. J. Am. Chem. Soc. 2012, 134, 16163. (h) Cui, S.; Zhang, Y.; Wang, D.;
Wu, Q. Chem. Sci. 2013, 4, 3912. (i) Dong, W.; Wang, L.; Parthasarathy,
K.; Pan, F.; Bolm, C. Angew. Chem., Int. Ed. 2013, 52, 11573. (j) Lian, Y.;
Hummel, J. R.; Bergman, R. G.; Ellman, J. A. J. Am. Chem. Soc. 2013, 135,
■
We gratefully acknowledge the National Natural Science
Foundation of China (Nos. 21372210, 21432009), the Nanyang
Technological University for the funding of this research. The
authors are grateful to Mr. Koh Peng Fei Jackson (from Nanyang
Technological University, Singapore) for his careful proof-
reading of the final manuscript.
1
2548. (k) Qi, Z.; Li, X. Angew. Chem., Int. Ed. 2013, 52, 8995. (l) Shi, X.-
Y.; Li, C.-J. Org. Lett. 2013, 15, 1476. (m) Shi, Z.; Koester, D. C.;
Boultadakis-Arapinis, M.; Glorius, F. J. Am. Chem. Soc. 2013, 135, 12204.
(11) (a) Feng, C.; Loh, T.-P. Chem. Commun. 2011, 47, 10458.
(b) Zhang, J.; Loh, T.-P. Chem. Commun. 2012, 48, 11232. (c) Feng, C.;
Feng, D.; Loh, T. P. Org. Lett. 2013, 15, 3670. (d) Feng, C.; Loh, T. P.
Angew. Chem., Int. Ed. 2014, 53, 2722. (e) Feng, C.; Loh, T. P. Org. Lett.
REFERENCES
■
(
1
1) (a) Page, P. C. B.; Klair, S. S.; Rosenthal, S. Chem. Soc. Rev. 1990,
9, 147. (b) Zhang, H.-J.; Priebbenow, D. L.; Bolm, C. Chem. Soc. Rev.
013, 42, 8540.
2
014, 16, 3444. (f) Lu, M. Z.; Lu, P.; Xu, Y. H.; Loh, T. P. Org. Lett. 2014,
1
6, 2614.
2
(
4
4
(
12) Becker, P.; Priebbenow, D. L.; Pirwerdjan, R.; Bolm, C. Angew.
Chem., Int. Ed. 2014, 53, 269.
13) For selected examples of functionalization of indoles, see:
a) Grimster, N. P.; Gauntlett, C.; Godfrey, C. R.; Gaunt, M. J. Angew.
2) (a) Saleur, D.; Bouillon, J. P.; Portella, C. Tetrahedron Lett. 2001,
2, 6535. (b) Linghu, X.; Nicewicz, D. A.; Johnson, J. S. Org. Lett. 2002,
, 2957. (c) Lettan, R. B., II; Reynolds, T. E.; Galliford, C. V.; Scheidt, K.
A. J. Am. Chem. Soc. 2006, 128, 15566.
3) (a) Obora, Y.; Ogawa, Y.; Imai, Y.; Kawamura, T.; Tsuji, Y. J. Am.
Chem. Soc. 2001, 123, 10489. (b) Mattson, A. E.; Bharadwaj, A. R.;
Scheidt, K. A. J. Am. Chem. Soc. 2004, 126, 2314. (c) Schmink, J. R.;
Krska, S. W. J. Am. Chem. Soc. 2011, 133, 19574.
4) (a) Shen, Z.; Dong, V. M. Angew. Chem., Int. Ed. 2009, 48, 784.
b) Ito, K.; Tamashima, H.; Iwasawa, N.; Kusama, H. J. Am. Chem. Soc.
011, 133, 3716.
5) (a) Brook, A. G. Acc. Chem. Res. 1974, 7, 77. (b) Moser, W. H.
Tetrahedron 2001, 57, 2065.
6) (a) Nakada, M.; Urano, Y.; Kobayashi, S.; Ohno, M. J. Am. Chem.
Soc. 1988, 110, 4826. (b) Chen, J.-P.; Ding, C.-H.; Liu, W.; Hou, X.-L.;
Dai, L.-X. J. Am. Chem. Soc. 2010, 132, 15493. (c) Reddy, G. P.; Murthy,
A. S.; Reddy, J. S.; Das, S.; Roisnel, T.; Yadav, J. S.; Chandrasekhar, S.;
Gree, R. Tetrahedron Lett. 2014, 55, 365.
7) (a) Reich, H. J.; Kelly, M. J.; Olson, R. E.; Holtan, R. C. Tetrahedron
983, 39, 949. (b) Danheiser, R. L.; Fink, D. M.; Okano, K.; Tsai, Y. M.;
Szczepanski, S. W. J. Org. Chem. 1985, 50, 5393. (c) Patrocinio, A. F.;
Moran, P. J. S. J. Organomet. Chem. 2000, 603, 220.
8) For selected examples of Rh(III)-catalyzed C−C bond formation,
see: (a) Umeda, N.; Hirano, K.; Satoh, T.; Miura, M. J. Org. Chem. 2009,
4, 7094. (b) Patureau, F. W.; Glorius, F. J. Am. Chem. Soc. 2010, 132,
982. (c) Hesp, K. D.; Bergman, R. G.; Ellman, J. A. J. Am. Chem. Soc.
011, 133, 11430. (d) Li, H.; Li, Y.; Zhang, X.-S.; Chen, K.; Wang, X.;
Shi, Z.-J. J. Am. Chem. Soc. 2011, 133, 15244. (e) Chan, W.-W.; Lo, S.-F.;
Zhou, Z.; Yu, W.-Y. J. Am. Chem. Soc. 2012, 134, 13565. (f) Gong, T. J.;
Xiao, B.; Cheng, W. M.; Su, W.; Xu, J.; Liu, Z. J.; Liu, L.; Fu, Y. J. Am.
Chem. Soc. 2013, 135, 10630. (g) Huang, X.; Huang, J.; Du, C.; Zhang,
X.; Song, F.; You, J. Angew. Chem., Int. Ed. 2013, 52, 12970. (h) Li, X.;
Yu, S.; Wang, F.; Wan, B.; Yu, X. Angew. Chem., Int. Ed. 2013, 52, 2577.
(
(
Chem., Int. Ed. 2005, 44, 3125. (b) Phipps, R. J.; Grimster, N. P.; Gaunt,
M. J. J. Am. Chem. Soc. 2008, 130, 8172. (c) Garcia-Rubia, A.; Gomez
Arrayas, R.; Carretero, J. C. Angew. Chem., Int. Ed. 2009, 48, 6511.
(
(
d) Lanke, V.; Prabhu, K. R. Org. Lett. 2013, 15, 2818. (e) Gong, B.; Shi,
J.; Wang, X.; Yan, Y.; Li, Q.; Meng, Y.; Xu, H. E.; Yi, W. Adv. Synth. Catal.
014, 356, 137.
(
(
2
2
(
14) The direct carbene insertion into C−H bond could also be an
alternative pathway for access of the cyclization product. See: (a) Wang,
P.; Adams, J. J. Am. Chem. Soc. 1994, 116, 3296. (b) Bhanu Prasad, B. A.;
Yoshimoto, F. K.; Sarpong, R. J. Am. Chem. Soc. 2005, 127, 12468.
(
(
(15) (a) Schipper, D. J.; Hutchinson, M.; Fagnou, K. J. Am. Chem. Soc.
2
010, 132, 6910. (b) Liu, B.; Zhou, T.; Li, B.; Xu, S.; Song, H.; Wang, B.
Angew. Chem., Int. Ed. 2014, 53, 4191. (c) Nobushige, K.; Hirano, K.;
Satoh, T.; Miura, M. Org. Lett. 2014, 16, 1188.
(16) (a) Yang, L.; Correia, C. A.; Li, C.-J. Org. Biomol. Chem. 2011, 9,
(
1
7
176. (b) Davis, T. A.; Hyster, T. K.; Rovis, T. Angew. Chem., Int. Ed.
2
013, 52, 14181.
(17) When the reaction was performed under air using a stoichiometric
amount of [RhCp*Cl ] or [RhCp*Cl ] /AgSbF (1:4) but without
2
2
2
2
6
(
Cu(OAc) ·H O, no reaction occurred.
2
2
(18) Performing the reaction under air and using MeCN as reaction
7
9
2
solvent, which could either inhibit the formation of reactive Cu(I)
species or sequester the in situ formed acid, were believed to be two key
factors guaranteeing the selective formation of alkenylation product.
(19) The beneficial effect of TEMPO on the oxidative alkenylation
reaction was assumed to be due to the inhibition of polymerization of
acryloyl silane and assistance of the oxidative turnover of Rh(III)
catalyst. For the Rh(III) catalyzed C−H activation reaction in which
TEMPO employed as oxidant, see: Park, S.; Seo, B.; Shin, S.; Son, J. Y.;
Lee, P. H. Chem. Commun. 2013, 49, 8671.
(
i) Wang, Y.; Li, C.; Li, Y.; Yin, F.; Wang, X.-S. Adv. Synth. Catal. 2013,
(
20) (a) Yang, L.; Zhang, G.; Huang, H. Adv. Synth. Catal. 2014, 356,
509. (b) Brasse, M.; Campora, J.; Ellman, J. A.; Bergman, R. G. J. Am.
Chem. Soc. 2013, 135, 6427.
3
1
4
55, 1724. (j) Zeng, R.; Wu, S.; Fu, C.; Ma, S. J. Am. Chem. Soc. 2013,
35, 18284. (k) Xie, F.; Qi, Z.; Yu, S.; Li, X. J. Am. Chem. Soc. 2014, 136,
780. (l) Wangweerawong, A.; Bergman, R. G.; Ellman, J. A. J. Am.
Chem. Soc. 2014, 136, 8520. (m) Tsai, A. S.; Tauchert, M. E.; Bergman,
R. G.; Ellman, J. A. J. Am. Chem. Soc. 2011, 133, 1248.
1
(21) Otley, K. D.; Ellman, J. A. Org. Lett. 2015, 17, 1332.
(22) For the Rh/Cu transmetallation, see: Pham, M. V.; Cramer, N.
Angew. Chem., Int. Ed. 2014, 53, 14575.
23) Zhang, G.; Yang, L.; Wang, Y.; Xie, Y.; Huang, H. J. Am. Chem. Soc.
013, 135, 8850.
(
9) For selected examples of Rh(III)-catalyzed C−heteroatom bond
(
2
formation, see: (a) Kim, J. Y.; Park, S. H.; Ryu, J.; Cho, S. H.; Kim, S. H.;
Chang, S. J. Am. Chem. Soc. 2012, 134, 9110. (b) Schroder, N.; Wencel-
Delord, J.; Glorius, F. J. Am. Chem. Soc. 2012, 134, 8298. (c) Wu, K.; Fan,
Z.; Xue, Y.; Yao, Q.; Zhang, A. Org. Lett. 2014, 16, 42. (d) Xie, F.; Qi, Z.;
Li, X. Angew. Chem., Int. Ed. 2013, 52, 11862. (e) Yang, Y.; Hou, W.; Qin,
L.; Du, J.; Feng, H.; Zhou, B.; Li, Y. Chem.Eur. J. 2014, 20, 416. (f) Yu,
S.; Wan, B.; Li, X. Org. Lett. 2015, 17, 58.
D
DOI: 10.1021/acs.orglett.5b01258
Org. Lett. XXXX, XXX, XXX−XXX