Nickel-Catalyzed Insertion of Alkynes and Electron-Deficient Olefins into Unactivated sp3 C-H Bonds

Article abstract of DOI:10.1002/chem.201501962

Insertion of unsaturated systems such as alkynes and olefins into unactivated sp³ C-H bonds remains an unexplored problem. We herein address this issue by successfully incorporating a wide variety of functionalized alkynes and electron-deficient olefins into the unactivated sp³ C-H bond of pivalic acid derivatives with excellent syn- and linear- selectivity. A strongly chelating 8-aminoquinoline directing group proved beneficial for these insertion reactions, while an air-stable and inexpensive Ni^II salt has been employed as the active catalyst. Unactive duty: A wide variety of functionalized alkynes and electron-deficient olefins has been incorporated into the unactivated sp³ C-H bond of pivalic acid derivatives with excellent syn and linear selectivity. A strongly chelating 8-aminoquinoline directing group proved beneficial for these insertion reactions, while an air-stable and inexpensive Ni^II salt was used as the active catalyst. EWG=electron-withdrawing group.

Full text of DOI:10.1002/chem.201501962

DOI: 10.1002/chem.201501962
Communication
&
CÀH Activation
Nickel-Catalyzed Insertion of Alkynes and Electron-Deficient
Olefins into Unactivated sp3 CÀH Bonds
Soham Maity, Soumitra Agasti, Arif Mahammad Earsad, Avijit Hazra, and Debabrata Maiti*[a]
Abstract: Insertion of unsaturated systems such as alkynes
and olefins into unactivated sp3 CÀH bonds remains an
unexplored problem. We herein address this issue by suc-
cessfully incorporating a wide variety of functionalized al-
kynes and electron-deficient olefins into the unactivated
sp3 CÀH bond of pivalic acid derivatives with excellent
syn- and linear- selectivity. A strongly chelating 8-amino-
quinoline directing group proved beneficial for these in-
sertion reactions, while an air-stable and inexpensive NiII
salt has been employed as the active catalyst.
Scheme 1. Alkyne and olefin insertions into CÀH bonds: conventional ap-
proaches and present work. EWG=electron-withdrawing group.
Alkyne and olefin insertion into CÀH bonds are among the
most profoundly studied transformations in transition-metal
chemistry. To date, a wide variety of Rh,[1] Ir,[2] Pd,[3] Ru,[4] Ni,[5]
and Co[6] based catalysts have been developed for these char-
acteristic CÀC bond-forming processes. Even relatively less
used first-row congeners such as Mn[7] and Fe,[8] and rare-earth
metals[9] have been found to deliver promising results. It
should be noted that the majority of these insertion reactions
were accomplished through the activation of a sp2 CÀH bond
irrespective of the transition metal involved (Scheme 1).[4d,6h,10]
The related insertion chemistry at sp3 CÀH, however, remains
underdeveloped so far.
ciency[16] and/or [2+2+2] cyclotrimerization reactions.[17] We
found that these potential problems can be circumvented in
pivalic acid derivatives with the help of Daugulis’ chelating 8-
aminoquinoline[18] and an appropriate Ni catalyst.[19] Several
other directing group/metal catalyst combinations were also
tested but promising results could not be obtained in any of
the cases. Even stoichiometric reactions with a preformed pal-
ladacycle intermediate failed to provide the desired products
(Scheme 2). Notably, chelation-assisted insertion into aromatic
Previous attempts to incorporate an alkyne/olefin
into aliphatic compounds largely focused on those
sp3 CÀH bonds that are activated by virtue of their
position in the molecule. The scope of the reaction
was therefore explored with benzyl,[11] allyl,[12] activat-
ed methylene systems[13] and substrates with CÀH
Scheme 2. Observations with directing groups and catalyst systems.
bonds next to a heteroatom.[14] Accordingly, insertion
of alkynes/olefins into unactivated aliphatic sp3 CÀH
bonds remains a formidable task.[15]
CÀH bonds has been disclosed previously by the independent
To address this problem, a suitable substrate–catalyst combi-
nation had to be identified. Owing to the absence of a p-elec-
tron cloud and a low-lying s* orbital, metal-mediated cleavage
of aliphatic CÀH bonds becomes troublesome. Binding with
alkyne and olefin might result in undermining the catalyst effi-
research groups of Chatani and Daugulis.[20]
The scope of alkyne insertion with various aliphatic sub-
strates is described in Scheme 3. The first alkenylated product
was obtained from N-(quinolin-8-yl)pivalamide and diphenyla-
cetylene in 81% isolated yield (3a, Z/E, 7:1). The stereoisomeric
configuration of the products was determined by 1D NOE and/
or 2D NMR (NOESY) experiments. Although an excess of amide
was used for alkyne insertion, no side reaction was observed
and unreacted starting materials were recovered in considera-
ble amount. It was found that the steric environment of the
substrates had a major influence on the reaction outcome. An
ethyl group at the a-carbon posed a slight hindrance for the
reaction owing to the enhanced steric congestion around the
[a] S. Maity,+ S. Agasti,+ A. M. Earsad, A. Hazra, Prof. D. Maiti
Department of Chemistry
Indian Institute of Technology Bombay
Powai, Mumbai-400076 (India)
E-mail: dmaiti@chem.iitb.ac.in
[+] S.M. and S.A. contributed equally to this work.
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201501962.
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5a). Phenyl propiolic acid underwent decarboxylation
prior to insertion into the aliphatic CÀH bond, thus
providing the styrenyl derivative in useful yield (5b,
61%). This observation inspired us to examine termi-
nal alkynes as probable substrates, substrates that
are usually incompatible under nickel catalysis. It was
found that alkenylation could be performed with ter-
minal alkynes with excellent regio- and stereoselec-
tivity albeit in low yields. Unfortunately, dialkyl al-
kynes (such as 4-octyne) were found to generate
a mixture of regioisomers in less than 30% isolated
yield.
After successful demonstration of the insertion of
alkynes into the unactivated sp3 CÀH bond, we tried
to incorporate other unsaturated systems with the
present method. In fact, a related development with
olefins should provide a unique opportunity for
(sp3)CÀC(sp3) bond formation. Surprisingly, despite
Murai’s seminal discovery back in 2001,[14b] and San-
ford[21] and Yu’s impressive work on sp3 CÀH olefina-
tion,[22] a general olefin insertion into an unactivated
aliphatic set-up is yet to be reported. We found that
with minor modifications of the reaction conditions,
a variety of activated olefins such as functionalized
Scheme 3. Scope of aliphatic substrates with symmetrical alkynes. Z/E ratios were deter-
mined by H NMR analysis of the isolated compound and given in parenthesis. [a] 68%
yield by GC with 1 equiv of amide. [b] Reaction at 1508C with 20 mol% PPh3 ligand.
[c] Reaction in NMP solvent. [d] Reaction in DMA solvent with 20 mol% PPh3 ligand.
1
quaternary center (3b, 69%). Similar results were ob-
tained with successive homologation of alkyl groups
in one direction (3c, 67% and 3d, 66%). Other sym-
metrical diphenylacetylenes with methoxy (3e, 3 f,
and 3h) methyl (3g), and fluoro (3i and 3j) groups
also proved amenable to the current system. Interest-
ingly, diphenylacetylene coupled with an allylic sp3
CÀH bond in preference to an evenly placed vinylic
sp2 CÀH bond (3k, 35% and 3l, 40%).[10c]
Usually, unsymmetrical alkynes are considered as
problematic substrates for insertion reactions as they
often generate mixtures of regioisomers, which are
difficult to isolate and characterize. Nevertheless,
a systematic variation of substituents at para-, meta-
and ortho- positions of an alkyne would give the op-
portunity to look into the underlying mechanism. It
was observed that the reaction could distinguish be-
tween slight electronic differences imparted by an
Scheme 4. Scope with unsymmetrical internal alkyne. Z/E ratios were determined by
1H NMR analysis of the isolated compound (see the Supporting Information).
[a] 20 mol% PPh3. [b] Reaction in NMP solvent. [c] Another isomer present in 7:1 ratio.
electron donating 4-methyl group (4a/4a’, 67%; r.r.=
1.14) or an electron-withdrawing 4-carbomethoxy
group (4c/4c’, 70%; r.r.=1.33) while retaining the
synthetic efficiency (Scheme 4; combined yields: 67–
72%). Intriguingly, alkylnickelation preferentially oc-
curred in a way so as to put the metal at the a-styr-
enyl position of the more electron deficient ring. Sim-
ilar observations with 4-OMe (4b/4b’, 72%), 3-NO2
(4d/4d’, 71%), 3,5-di-CF3 (4e/4e’, 72%) and most
prominently with 2-CF3 (4g, 70%) substituted diphe-
nylacetylenes supported electronic dependence of
the insertion step.
Alkyl aromatic alkyne, 1-phenyl-1-propyne, gave
a single regioisomer in 63% isolated yield (Scheme 5, Scheme 5. Regioselective alkyne insertion.
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Communication
cy of a seven-membered nickellacycle, the formation
and stability of which can be influenced by the steric
environment of the adjacent quaternary center (see
below, migratory insertion from IV to V in Scheme 8).
The absence of a bis-alkenylated product with al-
kynes in Schemes 3 and 4 further supports the steric
dependence of the present reaction. In sharp con-
trast, minor amounts bis-alkylation were observed in
case of the sterically less demanding acrylates/acrylo-
nitriles on several occasions. We thought to take ad-
vantage of this observation and planned for succes-
sive insertion of activated olefins into the aliphatic
amides (Scheme 7).
Similar to the hetero-bis-alkylation, iterative olefin
and alkyne insertion was also envisaged. It should be
noted that tethered functional groups with ligating
atoms might inhibit the progress of the reaction by
competitive coordination of the vacant site on the
nickellacycle intermediate IV (Scheme 8). In reality,
substrates with
a nitrile group at d-positions
Scheme 6. Insertion of electron-deficient olefins at unactivated sp3 CÀH. Isolated yields
(Scheme 6, 6h and 6i) were found to be completely
unreactive in the sequential alkyne insertion step.
Nonetheless, ester functional groups containing alky-
lated products were further alkenylated with a slight
excess of nickel catalyst.
of bis-alkylated products are given in parenthesis.
The modest stereoselectivity observed in several
cases might be attributed to a long-lived NiÀH spe-
cies, although any experimental evidence for such
species could not be obtained at this point. In terms
of the crucial CÀH activation step, a direct oxidative
addition of NiII to the sp3 CÀH bond seems less likely.
A concerted metalation–deprotonation (CMD) path-
way can be proposed, despite the fact that addition
of bases did not help in the progress of the reac-
tion.[19b,h,23] In our best assumption, an acetate coun-
ter anion is aiding the CÀH activation step and acting
as a proton shuttle to close the catalytic cycle
(Scheme 8). A detail investigation is planned for
mechanistic understanding of these insertion reac-
tions.
In summary, we have developed the first insertion
of alkynes and electron-deficient olefins into unacti-
vated sp3 CÀH bonds. A broad range of symmetrical
and unsymmetrical alkynes and activated olefins with
different functional groups such as -OMe, -F, -Cl, -Br,
-CO2Me, -NO2, -CF3 have been included in this study.
Rational design of the substrates shed light on the
electronic dependence of the insertion step. In addi-
Scheme 7. Sequential insertion of electron-deficient olefins and alkynes. Isolated yields of
second insertion step given. Z/E ratios are given in parenthesis. [a] Reaction at 1608C
with PPh3 as ligand.
acrylates (with -OMe, -F, -Cl groups), and acrylonitriles could be
successfully reacted with useful synthetic yields and exclusive
linear selectivity (Scheme 6).
tion, inexpensive and a shelf-stable NiII salt has been success-
fully employed for the synthesis of more than 50 new chemical
entities. This work is expected to inspire related developments
in the near future.
Various alkyl (6d and 6 f), benzyl (6o) and phenyl (6p)
groups at the a-carbon can be tolerated as well. Even heavily
substituted 2,2-diphenyl-N-(quinolin-8-yl)propanamide, which
remained completely unreacted with diphenylacetylene, was
found to undergo the desired reaction with acrylates albeit in
low yield (6q). These results indicate the potential intermedia-
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K. S. Kanyiva, T. Hiyama, J. Am. Chem. Soc. 2008, 130, 16170;
e) Y. Nakao, H. Idei, K. S. Kanyiva, T. Hiyama, J. Am. Chem.
Soc. 2009, 131, 15996; f) Y. Nakao, N. Kashihara, K. S. Kanyi-
va, T. Hiyama, Angew. Chem. Int. Ed. 2010, 49, 4451; Angew.
Chem. 2010, 122, 4553; g) R. Tamura, Y. Yamada, Y. Nakao, T.
Hiyama, Angew. Chem. Int. Ed. 2012, 51, 5679; Angew. Chem.
2012, 124, 5777; h) J. S. Bair, Y. Schramm, A. G. Sergeev, E.
Clot, O. Eisenstein, J. F. Hartwig, J. Am. Chem. Soc. 2014, 136,
13098; i) P. A. Donets, N. Cramer, Angew. Chem. Int. Ed. 2015,
54, 633; Angew. Chem. 2015, 127, 643.
[6] a) K. Gao, P.-S. Lee, T. Fujita, N. Yoshikai, J. Am. Chem. Soc.
2010, 132, 12249; b) K. Gao, N. Yoshikai, J. Am. Chem. Soc.
2011, 133, 400; c) K. Gao, N. Yoshikai, Angew. Chem. Int. Ed.
2011, 50, 6888; Angew. Chem. 2011, 123, 7020; d) P.-S. Lee,
T. Fujita, N. Yoshikai, J. Am. Chem. Soc. 2011, 133, 17283;
e) L. Ilies, Q. Chen, X. Zeng, E. Nakamura, J. Am. Chem. Soc.
2011, 133, 5221; f) Z. Ding, N. Yoshikai, Angew. Chem. Int. Ed.
2013, 52, 8574; Angew. Chem. 2013, 125, 8736; g) P.-S. Lee,
N. Yoshikai, Angew. Chem. Int. Ed. 2013, 52, 1240; Angew.
Chem. 2013, 125, 1278; h) T. Andou, Y. Saga, H. Komai, S.
Matsunaga, M. Kanai, Angew. Chem. Int. Ed. 2013, 52, 3213;
Angew. Chem. 2013, 125, 3295.
[7] a) B. Zhou, H. Chen, C. Wang, J. Am. Chem. Soc. 2013, 135,
1264; b) R. He, Z.-T. Huang, Q.-Y. Zheng, C. Wang, Angew.
Chem. Int. Ed. 2014, 53, 4950; Angew. Chem. 2014, 126,
5050; c) B. Zhou, P. Ma, H. Chen, C. Wang, Chem. Commun.
2014, 50, 14558.
Scheme 8. Plausible mechanism for alkyne and olefin insertion.
[8] a) J. Kischel, I. Jovel, K. Mertins, A. Zapf, M. Beller, Org. Lett.
2006, 8, 19; b) M. Y. Wong, T. Yamakawa, N. Yoshikai, Org.
Lett. 2015, 17, 442.
Acknowledgements
[9] a) B.-T. Guan, Z. Hou, J. Am. Chem. Soc. 2011, 133, 18086; b) G. Luo, Y.
Luo, J. Qu, Z. Hou, Organometallics 2012, 31, 3930; c) J. Oyamada, Z.
Hou, Angew. Chem. Int. Ed. 2012, 51, 12828; Angew. Chem. 2012, 124,
13000; d) G. Song, W. N. O. Wylie, Z. Hou, J. Am. Chem. Soc. 2014, 136,
12209.
This research activity was supported by SERB, India. Financial
assistance from CSIR-New Delhi (fellowships to S.M., S.A., and
A.M.E.) is gratefully acknowledged.
[10] a) K. Gao, N. Yoshikai, Acc. Chem. Res. 2014, 47, 1208; b) D.-G. Yu, F.
de Azambuja, T. Gensch, C. G. Daniliuc, F. Glorius, Angew. Chem. Int. Ed.
2014, 53, 9650; Angew. Chem. 2014, 126, 9804; c) D. Zhao, F. Lied, F.
Glorius, Chem. Sci. 2014, 5, 2869; d) W. Xu, N. Yoshikai, Angew. Chem.
Int. Ed. 2014, 53, 14166; Angew. Chem. 2014, 126, 14390; e) X. Hu, D.
Martin, M. Melaimi, G. Bertrand, J. Am. Chem. Soc. 2014, 136, 13594;
f) M. C. Reddy, M. Jeganmohan, Chem. Commun. 2013, 49, 481; g) Q.
Tang, D. Xia, X. Jin, Q. Zhang, X.-Q. Sun, C. Wang, J. Am. Chem. Soc.
2013, 135, 4628; h) T. A. Davis, T. K. Hyster, T. Rovis, Angew. Chem. Int.
Ed. 2013, 52, 14181; Angew. Chem. 2013, 125, 14431; i) P. A. Donets, N.
Cramer, J. Am. Chem. Soc. 2013, 135, 11772; j) S. Pan, N. Ryu, T. Shibata,
J. Am. Chem. Soc. 2012, 134, 17474; k) J. Ryu, S. H. Cho, S. Chang,
Angew. Chem. Int. Ed. 2012, 51, 3677; Angew. Chem. 2012, 124, 3737.
[11] a) Y. Minami, K. Yamada, T. Hiyama, Angew. Chem. Int. Ed. 2013, 52,
10611; Angew. Chem. 2013, 125, 10805; b) B. Liu, T. Zhou, B. Li, S. Xu, H.
Song, B. Wang, Angew. Chem. Int. Ed. 2014, 53, 4191; Angew. Chem.
2014, 126, 4275.
Keywords: alkynes · insertion · nickel · olefins · unactivated
sp3
[1] a) D. J. Schipper, M. Hutchinson, K. Fagnou, J. Am. Chem. Soc. 2010, 132,
6910; b) N. Guimond, S. I. Gorelsky, K. Fagnou, J. Am. Chem. Soc. 2011,
133, 6449; c) J. Kwak, Y. Ohk, Y. Jung, S. Chang, J. Am. Chem. Soc. 2012,
134, 17778–17788; d) B. Ye, N. Cramer, Science 2012, 338, 504; e) D.
Zhao, Z. Shi, F. Glorius, Angew. Chem. Int. Ed. 2013, 52, 12426; Angew.
Chem. 2013, 125, 12652; f) C. M. Filloux, T. Rovis, J. Am. Chem. Soc.
2014, 136, 508; g) B. Ye, P. A. Donets, N. Cramer, Angew. Chem. Int. Ed.
2014, 53, 507; Angew. Chem. 2014, 126, 517.
[2] a) C. S. Sevov, J. F. Hartwig, J. Am. Chem. Soc. 2013, 135, 2116; b) T. Shi-
bata, T. Shizuno, Angew. Chem. Int. Ed. 2014, 53, 5410; Angew. Chem.
2014, 126, 5514; c) G. E. M. Crisenza, N. G. McCreanor, J. F. Bower, J. Am.
Chem. Soc. 2014, 136, 10258.
[12] S. Rakshit, F. W. Patureau, F. Glorius, J. Am. Chem. Soc. 2010, 132, 9585.
[13] N. Chernyak, S. I. Gorelsky, V. Gevorgyan, Angew. Chem. Int. Ed. 2011, 50,
2342; Angew. Chem. 2011, 123, 2390.
[3] a) C. G. Jia, W. J. Lu, J. Oyamada, T. Kitamura, K. Matsuda, M. Irie, Y. Fuji-
wara, J. Am. Chem. Soc. 2000, 122, 7252; b) C. G. Jia, D. G. Piao, J. Z. Oya-
mada, W. J. Lu, T. Kitamura, Y. Fujiwara, Science 2000, 287, 1992; c) N.
Tsukada, T. Mitsuboshi, H. Setoguchi, Y. Inoue, J. Am. Chem. Soc. 2003,
125, 12102; d) M. Ahlquist, G. Fabrizi, S. Cacchi, P.-O. Norrby, J. Am.
Chem. Soc. 2006, 128, 12785; e) N. Chernyak, V. Gevorgyan, J. Am.
Chem. Soc. 2008, 130, 5636; f) Y. Minami, Y. Shiraishi, K. Yamada, T.
Hiyama, J. Am. Chem. Soc. 2012, 134, 6124; g) M. R. Kuram, M. Bhanu-
chandra, A. K. Sahoo, Angew. Chem. Int. Ed. 2013, 52, 4607; Angew.
Chem. 2013, 125, 4705.
[4] a) S. Murai, F. Kakiuchi, S. Sekine, Y. Tanaka, A. Kamatani, M. Sonoda, N.
Chatani, Nature 1993, 366, 529–531; b) F. Kakiuchi, S. Murai, Acc. Chem.
Res. 2002, 35, 826–834; c) M. Schinkel, I. Marek, L. Ackermann, Angew.
Chem. Int. Ed. 2013, 52, 3977; Angew. Chem. 2013, 125, 4069; d) L. Ac-
kermann, Acc. Chem. Res. 2014, 47, 281.
[14] a) C.-H. Jun, Chem. Commun. 1998, 1405; b) N. Chatani, T. Asaumi, S.
Yorimitsu, T. Ikeda, F. Kakiuchi, S. Murai, J. Am. Chem. Soc. 2001, 123,
10935; c) S. Pan, K. Endo, T. Shibata, Org. Lett. 2011, 13, 4692; d) G.
Lahm, T. Opatz, Org. Lett. 2014, 16, 4201; e) M. Schinkel, L. Wang, K. Bie-
lefeld, L. Ackermann, Org. Lett. 2014, 16, 1876; f) E. Chong, J. W. Brandt,
L. L. Schafer, J. Am. Chem. Soc. 2014, 136, 10898; g) B. DeBoef, S. J. Pas-
tine, D. Sames, J. Am. Chem. Soc. 2004, 126, 6556; h) L. Shi, Y.-Q. Tu, M.
Wang, F.-M. Zhang, C.-A. Fan, Y.-M. Zhao, W.-J. Xia, J. Am. Chem. Soc.
2005, 127, 10836; i) Y.-J. Jiang, Y.-Q. Tu, E. Zhang, S.-Y. Zhang, K. Cao, L.
Shi, Adv. Synth. Catal. 2008, 350, 552; j) A. A. Kulago, B. F. Van Steijvoort,
E. A. Mitchell, L. Meerpoel, B. U. W. Maes, Adv. Synth. Catal. 2014, 356,
1610; k) S. D. Bergman, T. E. Storr, H. Prokopcova, K. Aelvoet, G. Diels, L.
Meerpoel, B. U. W. Maes, Chem. Eur. J. 2012, 18, 10393; l) S. Pan, Y.
Matsuo, K. Endo, T. Shibata, Tetrahedron 2012, 68, 9009; m) L. Huang, K.
Cheng, B. Yao, J. Zhao, Y. Zhang, Synthesis 2009, 3504.
[5] a) Y. Nakao, K. S. Kanyiva, S. Oda, T. Hiyama, J. Am. Chem. Soc. 2006, 128,
8146; b) K. S. Kanyiva, Y. Nakao, T. Hiyama, Angew. Chem. Int. Ed. 2007,
46, 8872; Angew. Chem. 2007, 119, 9028; c) Y. Nakao, K. S. Kanyiva, T.
Hiyama, J. Am. Chem. Soc. 2008, 130, 2448; d) Y. Nakao, N. Kashihara,
[15] Y. Nakao, E. Morita, H. Idei, T. Hiyama, J. Am. Chem. Soc. 2011, 133, 3264.
Chem. Eur. J. 2015, 21, 11320 – 11324
www.chemeurj.org
11323
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Communication
[16] R. Jazzar, J. Hitce, A. Renaudat, J. Sofack-Kreutzer, O. Baudoin, Chem.
Eur. J. 2010, 16, 2654.
[17] N. Mori, S. Ikeda, K. Odashima, Chem. Commun. 2001, 181.
[18] a) V. G. Zaitsev, D. Shabashov, O. Daugulis, J. Am. Chem. Soc. 2005, 127,
13154; b) G. Qiu, J. Wu, Org. Chem. Front. 2015, 2, 169; c) Z. Huang, G.
Dong, Tetrahedron Lett. 2014, 55, 5869.
[19] a) G. Rouquet, N. Chatani, Angew. Chem. Int. Ed. 2013, 52, 11726; Angew.
Chem. 2013, 125, 11942; b) Y. Aihara, N. Chatani, J. Am. Chem. Soc.
2014, 136, 898; c) Y. Aihara, N. Chatani, J. Am. Chem. Soc. 2013, 135,
5308; d) Y. Aihara, M. Tobisu, Y. Fukumoto, N. Chatani, J. Am. Chem. Soc.
2014, 136, 15509; e) R. Shang, L. Ilies, A. Matsumoto, E. Nakamura, J.
Am. Chem. Soc. 2013, 135, 6030; f) M. Iyanaga, Y. Aihara, N. Chatani, J.
Org. Chem. 2014, 79, 11933; g) A. Yokota, Y. Aihara, N. Chatani, J. Org.
Chem. 2014, 79, 11922; h) X. Wu, Y. Zhao, H. Ge, J. Am. Chem. Soc. 2014,
136, 1789; i) X. Wu, Y. Zhao, H. Ge, Chem. Eur. J. 2014, 20, 9530.
[20] a) H. Shiota, Y. Ano, Y. Aihara, Y. Fukumoto, N. Chatani, J. Am. Chem. Soc.
2011, 133, 14952; b) G. Rouquet, N. Chatani, Chem. Sci. 2013, 4, 2201;
c) K. Shibata, N. Chatani, Org. Lett. 2014, 16, 5148; d) L. Grigorjeva, O.
Daugulis, Angew. Chem. Int. Ed. 2014, 53, 10209; Angew. Chem. 2014,
126, 10373; e) L. Grigorjeva, O. Daugulis, Org. Lett. 2014, 16, 4684.
[21] K. J. Stowers, K. C. Fortner, M. S. Sanford, J. Am. Chem. Soc. 2011, 133,
6541.
[22] a) M. Wasa, K. M. Engle, J.-Q. Yu, J. Am. Chem. Soc. 2010, 132, 3680; b) S.
Li, G. Chen, C.-G. Feng, W. Gong, J.-Q. Yu, J. Am. Chem. Soc. 2014, 136,
5267; c) R.-Y. Zhu, J. He, X.-C. Wang, J.-Q. Yu, J. Am. Chem. Soc. 2014,
136, 13194.
[23] Y. Dang, S. Qu, J. W. Nelson, H. D. Pham, Z.-X. Wang, X. Wang, J. Am.
Chem. Soc. 2015, 137, 2006.
Received: May 19, 2015
Published online on June 29, 2015
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