Bromide-Mediated C-H Bond Functionalization: Intermolecular Annulation of Phenylethanone Derivatives with Alkynes for the Synthesis of 1-Naphthols

Article abstract of DOI:10.1021/acs.orglett.7b03186

Bromide-mediated intermolecular annulation of phenylethanone derivatives with alkynes has been developed, which allows for the regioselective formation of polysubstituted 1-naphthols. The usage of readily available bromine catalyst, broad substrate scope, and mild conditions make this protocol very practical. Mechanistic investigations reveal that the bromination of phenylethanone derivatives occurs to yield bromo-substituted intermediates, which react in situ with alkynes to furnish the desired 1-naphthols.

Full text of DOI:10.1021/acs.orglett.7b03186

Letter
pubs.acs.org/OrgLett
Cite This: Org. Lett. XXXX, XXX, XXX-XXX
Bromide-Mediated C−H Bond Functionalization: Intermolecular
Annulation of Phenylethanone Derivatives with Alkynes for the
Synthesis of 1‑Naphthols
Tao Lu, Ya-Ting Jiang, Feng-Ping Ma, Zi-Jing Tang, Liu Kuang, Yu-Xuan Wang, and Bin Wang*
State Key Laboratory of Medicinal Chemical Biology, College of Pharmacy and Tianjin Key Laboratory of Molecular Drug Research,
Nankai University, Haihe Education Park, 38 Tongyan Road, Tianjin 300353, People’s Republic of China
S
* Supporting Information
ABSTRACT: Bromide-mediated intermolecular annulation of
phenylethanone derivatives with alkynes has been developed,
which allows for the regioselective formation of polysubstituted 1-
naphthols. The usage of readily available bromine catalyst, broad
substrate scope, and mild conditions make this protocol very
practical. Mechanistic investigations reveal that the bromination of
phenylethanone derivatives occurs to yield bromo-substituted
intermediates, which react in situ with alkynes to furnish the
desired 1-naphthols.
he synthesis of polycyclic compounds has always been of
continued strong interest to organic chemists for their
synthesize isoquinolones.10c A similar hypervalent iodine(III)-
promoted synthesis of isoquinolones was described byZheng and
co-workers.10d Although hypervalent iodines,11 molecular
iodine,12 and even simple iodide salts12,13 have been extensively
investigated as the useful alternatives to transition-metal catalysts
in the direct C−H functionalization, the catalytic utilization of
bromine reagents in such transformations has received far less
attention.14 Here, we report a metal-free bromide-mediated
oxidative annulation of phenylethanone derivatives with alkynes
to furnish polysubstituted 1-naphthols under mild conditions.
Highlysubstituted1-naphtholisprevalentinnaturalproductsand
biologically active molecules.15 More recently, polysubstituted 1-
naphthol synthesis via the direct oxidative annulation of alkynes
with various readily available acetophenone derivatives catalyzed
by transition metal catalysts, such as Rh(III),2c,16 Pd(II),17 and
Ag(I),18 have been reported (Scheme 1). Our reaction represents
the first example of bromide-mediated C−H bond functionaliza-
tion of arenes with alkynes and features readily available bromine
T
widespread application. In this context, the intermolecular
annulation reactions of alkynes with arenes or heteroarenes via
transition-metal-catalyzed C−H activation, which showed their
atom- and step-economy without prefunctionalizing starting
materials,1 have attracted considerable attention. A variety of
transition-metals, such as Rh,2 Ru,3 Pd,4 Ni,5 Cu,6 Au,7 Fe,8 and
Co,9 were revealed to catalyze the annulations by constructing a
C−N, C−O, or C−C bond to produce varying target molecules
such as naphthanol, isoquinolines, indole, pyrroles, and so on.
While these methods have recently emerged as reliable tools in
generating diverse polycyclic compounds, they require the
participation of metals, and certain reactions proceed at high
temperatures. Because the terminal alkynes are prone to
homocoupling under transition-metal-catalyzed conditions,
most annulations of alkyne with arene are mainly limited to the
use of internal alkynes.1c Moreover, one of the main problems
encountered is the regioselectivity during the annulation of
unsymmetrical alkynes, and this often results in the formation of
the mixture of isomers. Therefore, development of metal-free,
efficient, regioselective cyclization methods based on direct C−H
bond functionalization is highly desirable. To our knowledge, the
metal-free direct intermolecular annulationof arenes withalkynes
is rare.10 Early studies by Spyroudis and co-workers on the use of
phenyliodonium ylides of 1,3-dicarbonyl compounds and
terminal arynes for cyclizations revealed the limitations of this
transformation due to the very high reactivity of iodonium ylides
and low yields.10a Recently, Wei developed an oxidative
benzannulation of enamines with alkynes for the synthesis of 1-
amino-2-naphthalenecarboxylic acid derivatives by use of
stoichiometric amounts of iodosylbenzene.10b Antonchick
reported an elegant iodobenzene-catalyzed regioselective annu-
lation of N-alkoxybenzamide derivatives with alkynes to
Scheme 1. Annulation for Synthesis of 1-Naphthols
Received: October 12, 2017
© XXXX American Chemical Society
A
DOI: 10.1021/acs.orglett.7b03186
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
catalyst, metal-free intermolecular annulation, broad substrate
scope, and complete regioselectivity. The annulation and
aromatization readily proceeds with sp, sp3, and unactivated sp2
C−H bonds to form two C−C bonds simultaneously, providing a
versatile,mild,andenvironmentallyfriendlyalternativetoexisting
protocols (Scheme 1).
With the best reaction conditions established, we applied this
metal-free strategy to the cyclization of a wide range of alkynes. As
illustrated in Scheme 2, both electron-donating and electron-
a
Scheme 2. Scope of the Alkynes
At the outset of our investigation, the readily available ethyl
benzoylacetate 1a and phenylacetylene 2a were employed as the
modelsubstrates, and various halides wereexamined usingTBHP
as oxidant. I2 and iodide salts were inefficient as catalysts.19 We
next carried out the reaction using simple bromine reagents
(Table 1). The expected annulation reaction took place, but gave
a
Table 1. Optimization of Reaction Conditions
entry
catalyst
additive
solvent
dioxane
yield (%)
1
2
3
4
5
6
7
Bu4NBr
LiBr
6
dioxane
11
31
25
51
41
61
85
49
77
0
NBS
NBP
NBP
NBP
NBP
NBP
dioxane
dioxane
PPh3
pyridine
BEA
dioxane
dioxane
a
Reaction conditions: 1a (0.5 mmol), 2 (1.0 mmol), NBP (20 mol %),
dioxane
BEA (0.15 mmol), and TBHP (3.5 equiv, 70% aq) in dioxane/EtOH
(1:1, 4.0 mL) under air, isolated yield.
b
8
BEA
dioxane/EtOH
dioxane/EtOH
dioxane/EtOH
dioxane/EtOH
b
9
BEA
b
10
BEA
NBP
withdrawing substituents were well tolerated on the phenyl
fragment (3aa-ap). Para-, meta-, and ortho-substituted arylacety-
lenes participated smoothly in the annulation to generate 3aa−ap
as single regioisomers in 36−87% yields. We think that two
electron-donating groups (−OMe and −OEt) might decrease the
reactivity of alkynes, thus affording the product in slightly lower
yields (3ab and 3ac). It is noteworthy that aryl bromides, which
are often unsuitable substrates for transition-metal-catalyzed C−
HactivationduetothecompetitiveinsertionofC−BrbondvsC−
H bond, proved to be amenable to the current system (3ak). 2-
Ethynylthiophene, which contained a heterocycle moiety, was
compatible with the reaction conditions and provided product
3aq in 61% yield. In the case of unsymmetrical disubstituted
alkyne, they underwent exclusively regioselective annulation to
afford the naphthols with the phenyl group being located at the
C4-position (3ar and 3as); however, only low yields were
obtained, along with the recovered starting materials. The present
metal-free oxidative conditions also allowed for additional
functional groups on the alkyl moiety of alkyl terminal alkynes.
It displayed a tolerance of sensitive alkenyl and hydroxyl groups,
leading to the 3at and 3au in moderate yields. Unfortunately,
other terminal alkynes with long alkyl chains, cyclopropyl, and
ethyl carboxylate ester afforded the corresponding products in
low yields (3av−ay). Diphenylacetylene was also subjected to the
reaction conditions; however, none of the desired product was
observed (3az). After investigation of the scope of alkynes,
different aryl and heteroaryl ethanones were tested in annulation
with alkynes 2a, 2c, and 2k (Scheme 3). A range of ethyl
benzoylacetates with different functional groups on the aryl
moiety were compatible under the annulation conditions (3ba-
ka). Para-substituted ethyl benzoylacetates bearing electron-
donating and halide substituents afforded the corresponding 6-
substituted naphthols 3ba, 3ca, and 3fa−ha in good yields. 3,5-
b
11
a
Reaction conditions: 1a (0.5 mmol), 2a (0.75 mmol), catalyst (20
mol %), additive (0.15 mmol), and TBHP (3.5 equiv, 70% aq) in 1,4-
dioxane (2.0 mL) under air, isolated yield. Compound 2a (1.0
mmol), dioxane/EtOH (1:1, 4.0 mL).
b
very low yields of 3aa with bromide salts (entries 1 and 2). To our
delight, two N-bromoimides, N-bromosuccinimide (NBS) and
N-bromophthalimide (NBP), increased the yield to 31% and
25%, respectively (entries 3 and 4). Although NBP gave a slight
lower yield than NBS, we found that NBP-catalyzed annulation
was almost free of side reaction. Based on the preliminary results,
NBP was selected as the catalyst for further exploration.
Gratifyingly, the yield of 3aa could be significantly improved by
the addition of 30 mol % of additives, such as PPh3, pyridine, and
2-bromoethylamine hydrobromide (BEA) (entries 5−7).
Especially BEA was the reaction additive that could afford the
desired product 3aa in 61% isolated yield (entry 7). When the
amount of 2a was raised to 200 mol %, higher yield of 3aa was
observed using a solvent combination of 1,4-dioxane and ethanol
(entry 8). A control experiment showed that the yield was
dramatically decreased in the absence of NBP (entry 9).
Interestingly, when we used BEA as a catalyst and NBP as an
additive, a good yield of 3aa was also achieved (entry 10). It is
worth noting that the present annulation cannot occur without
bromine reagents (entry 11). Apart from the NMR spectroscopic
analysis, the structure of 3aa was further confirmed by single-
crystal X-ray diffraction. Moreover, the annulation is completely
regioselective since the phenyl group of phenylacetylene was
installed at C4, without observing any of the C3 phenyl-
substituted product.
B
DOI: 10.1021/acs.orglett.7b03186
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
a
Scheme 3. Scope of the Aryl Ethanone
Scheme 4. Control Experiments
intermediategeneratedbybrominationofalkynes. Noconversion
was observed when 4 was subjected to the reaction conditions (eq
2). The results exclude the possibility that 4 is involved as an
intermediate in the annulation. The free radical inhibition study
was then performed in the presence of TEMPO (3.5 equiv), and
neither 3aa nor intermediate A was detected (eq 3). Considering
that the bromination of 1a may involve a radical pathway, which
can be blocked by TEMPO, bromide A was subsequently
subjected to the reaction, and 3aa was not observed either (eq 4).
The experimental information indicates that the annulation of the
resulting intermediate A with alkyne 2a is in accordance with a
free radical mechanism. Interestingly, when we treated A (20 mol
%) with a mixture of 1b and 2a in the absence of Br mediators, the
reaction produced 3aaand3bain81% and64%yield, respectively
(eq 5). It indicates that the released bromine species from A
perform the bromination with 1b, which led to the subsequent
cyclization with 2a. Moreover, this result demonstrates that the
bromine species is recycled in the reaction.
a
Reaction conditions: 1 (0.5 mmol), 2 (1.0 mmol), NBP (20 mol %),
BEA (0.15 mmol), and TBHP (3.5 equiv, 70% aq) in dioxane/EtOH
(1:1, 4.0 mL) under air, isolated yield.
Dimethyl substituted ethyl benzoylacetate produced desired
product 3da in high yield. However, in the case of ortho-methyl
substituted ethyl benzoylacetate, a low yield of 39% was observed
(3ea). Consideringtherearetwopossibleannulationpositionson
the aryl moiety of the meta-substituted ethyl benzoylacetate, we
conducted thereactionwithmeta-Brsubstrate touncover thesite-
selectivity. Here, the annulation provided a 78% overall yield of
two easily separable isomeric 1-naphthols 3ia−1 and 3ia−2 in 1:2
ratio in favor of the less sterically hindered isomer (3ia−2). The
presence of electron-withdrawing substituents, such as NO2 and
CN, significantly decreases the yields of the products (3ja and
3ka). In addition to the ethyl benzoylacetates, we were pleased to
observe that the readily available benzoylacetone, dibenzoyl-
methane, and even 2-benzoylacetanilide are suitable substrates,
providing the naphthols in high yields (3la−na). When ethyl 2-
naphtholylacetate was employed, the annulation occurred
regioselectively at the C3 position of the naphthyl ring to
produce 3oa as a single regioisomer in good yield. The
unsaturated heterocycles, such as thiophene, furan, pyrrole, and
pyridine may also serve as the aryl moiety, which coupled with 2a
at their C3 positions to furnish the valuable polysubstituted
heterocycles (3pa−sa). We further applied the present
annulation to the benzoylacetonitrile with different terminal
alkynes, and the corresponding 2-nitrile substituted 1-naphthols
were formed regioselectively in 56−60% yields (3ta, 3tc, and
3tk).
Onthe basisoftheabove observations andpreviousreports,20 a
plausible mechanism is proposed in Scheme 5. Initially, the
Scheme 5. Proposed Mechanism
Having established the scope of the method, some inves-
tigations were carried out to study the reaction mechanism.
During the reaction, in all cases, the formation of an unknown
compound was observed, which gradually disappeared with the
formation of products. In the model reaction, this compound was
isolated from the crude reaction mixture and characterized by
NMR and HRMS, and it was found to be ethyl 2-benzoyl-2-
bromoacetate A (Scheme 4). Independently synthesized A was
then subjected to reaction conditions. Regardless of whether Br
mediators were used, the annulation proceeded smoothly to give
the desired 3aa in moderate yields (eq 1), thus suggesting that the
present annulation is most likely to proceed through the
intermediate A. Similar control experiments were carried out
with phenylethynyl bromide 4, which could be another possible
oxidation of NBP and BEA generates the electrophilic active
species “Br+”, which is believed to be a complex mixture of Br2,
21
+
BrOtBu, BrOH, and BrOH2 . The radicals tBuO• and tBuOO•
arealsogeneratedfrom tBuOOH viaaSETprocess. Theresulting
“Br+” undergoes bromination with 1 to form intermediate A.22
Subsequent homolytic cleavage of C−Br bond takes place to
generate carbonyl alkyl radical B,20a−c which initiates a catalytic
cycle.23 Radical B couples with alkyne 2 to form vinyl radical C.
We think that the stable arylvinyl radical C (R2 = Ar) is formed
preferentially in the cases of arylacetylenes, leading to naphthols
with the complete regioselectivity. An intramolecular homolytic
aromatic substitution (HAS) of C occurs to provide radical
intermediate D.20d,e SET-oxidation of D by A generates a cationic
C
DOI: 10.1021/acs.orglett.7b03186
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
(5) (a) Yamaguchi, J.; Muto, K.; Itami, K. Top. Curr. Chem. 2016, 374,
374. (b) Misal Castro, L. C.; Obata, A.; Aihara, Y.; Chatani, N. Chem. -
Eur. J. 2016, 22, 1362.
(6) (a) Guo, X. X.; Gu, D. W.; Wu, Z. X.; Zhang, W. B. Chem. Rev. 2015,
115, 1622. (b) Sagadevan, A.; Ragupathi, A.; Hwang, K. C. Angew. Chem.,
Int. Ed. 2015, 54, 13896. (c) Liu, J. D.; Chen, G. S.; Tan, Z. Adv. Synth.
Catal. 2016, 358, 1174.
(7) (a) Dorel, R.; Echavarren, A. M. Chem. Rev. 2015, 115, 9028.
(b) Xiao, Y.; Zhang, J. In Transition Metal-Catalyzed Heterocycle Synthesis
via C-H Activation; Wu, X.-F., Ed.; Wiley-VCH: Weinheim, 2016;
Chapter 12, pp 359−401.
(8) Shang, R.; Ilies, L.; Nakamura, E. Chem. Rev. 2017, 117, 9086.
(9) Chirila, P. G.; Whiteoak, C. J. Dalton Trans 2017, 46, 9721.
(10) (a) Kalogiannis, S.; Spyroudis, S. J. Org. Chem. 1990, 55, 5041.
(b) Gao, P.; Liu, J.; Wei, Y. Org. Lett. 2013, 15, 2872. (c) Manna, S.;
Antonchick, A. P. Angew. Chem., Int. Ed. 2014, 53, 7324. (d) Chen, Z. W.;
Zhu, Y. Z.; Ou, J. W.; Wang, Y. P.; Zheng, J. Y. J. Org. Chem. 2014, 79,
10988. (e) Zhang, X.; Xu, X.; Yu, L.; Zhao, Q. Asian J. Org. Chem. 2014, 3,
281. (f)Zhao, P.;Yan, X.;Yin, H.; Xi, C. Org. Lett. 2014, 16, 1120. (g)Liu,
L.; Ji, X. Y.; Dong, J. Y.; Zhou, Y. B.; Yin, S. F. Org. Lett. 2016, 18, 3138.
(h) Chang, L.; Guo, T.; Wang, Z. Y.; Wang, S. Z.; Yao, Z. J. J. Org. Chem.
2017, 82, 1567.
(11) For selected reviews, see: (a) Zhdankin, V. V.; Stang, P. J. Chem.
Rev. 2008, 108, 5299. (b) Yoshimura, A.; Zhdankin, V. V. Chem. Rev.
2016, 116, 3328.
(12) For selected reviews, see: (a) Finkbeiner, P.; Nachtsheim, B. J.
Synthesis 2013, 45, 979. (b) Liu, D.; Lei, A. W. Chem. - Asian J. 2015, 10,
806.
(13) (a) Uyanik, M.; Ishihara, K. ChemCatChem 2012, 4, 177. (b) Wu,
X. F.; Gong, J. L.; Qi, X. X. Org. Biomol. Chem. 2014, 12, 5807.
(14) (a) Nagano, T.; Jia, Z.; Li, X.; Yan, M.; Lu, G.; Chan, A. S. C.;
Hayashi, T. Chem. Lett. 2010, 39, 929. (b) Guo, F.; Wang, L.; Mao, S.;
Zhang, C.; Yu, J.; Han, J. Tetrahedron 2012, 68, 8367.
(15)(a)Ward, R. S. Nat. Prod. Rep. 1995,12, 183. (b)Eich, E.;Pertz, H.;
Kaloga, M.; Schulz, J.; Fesen, M. R.; Mazumder, A.; Pommier, Y. J. Med.
Chem. 1996, 39, 86. (c) Ukita, T.; Nakamura, Y.; Kubo, A.; Yamamoto,
Y.; Takahashi, M.; Kotera, J.; Ikeo, T. J. Med. Chem. 1999, 42, 1293.
(d) Yeo, H.;Li, Y.;Fu, L.;Zhu, J.-L.;Gullen, E. A.;Dutschman, G. E.;Lee,
Y.; Chung, R.; Huang, E.-S.; Austin, D. J.; Cheng, Y.-C. J. Med. Chem.
2005, 48, 534. (e) Vasilev, N.; Elfahmi; Bos, R.; Kayser, O.; Momekov,
G.; Konstantinov, S.; Ionkova, I. J. Nat. Prod. 2006, 69, 1014.
(16) (a) Hojo, D.; Tanaka, K. Org. Lett. 2012, 14, 1492. (b) Tan, X.; Liu,
B.; Li, X.; Li, B.; Xu, S.; Song, H.; Wang, B. J. Am. Chem. Soc. 2012, 134,
16163.
intermediate E, which eventually yields naphthol 3 via
deprotonation. Radical B and Br− were regenerated through the
oxidation (outside cycle).23a,b Alternatively, radical D can first be
deprotonated to the corresponding radical anion F, which upon
oxidation by A provides radical anion [A]•− and final product 3.
Fragmentation of [A]•− affords radical B and Br− (inside
cycle).23a,b In addition, the radical−radical coupling of D with
more stabilized tBuOO• followed by elimination of tBuOOH is
also possible.24
In conclusion, employing simple and readily available bromine
reagents, a mild and metal-free C−H bond functionalization for
the synthesis of polysubstituted 1-naphthols with complete
regioselectivity was developed. A comprehensive scope of this
annulation reaction and tolerance of a wide range of functional
groups were successfully demonstrated. Through the mechanistic
study, the key reaction intermediate has been identified.
ASSOCIATED CONTENT
* Supporting Information
■
S
TheSupportingInformationisavailablefreeofchargeontheACS
Publications website at DOI: 10.1021/acs.orglett.7b03186.
Detailed experimental procedures and spectral data (PDF)
Accession Codes
CCDC 912549 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_
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: wangbin@nankai.edu.cn.
ORCID
Bin Wang: 0000-0002-3674-8980
Notes
The authors declare no competing financial interest.
(17) Peng, S.; Wang, L.; Wang, J. Chem. - Eur. J. 2013, 19, 13322.
(18) Naresh, G.; Kant, R.; Narender, T. Org. Lett. 2015, 17, 3446.
(19) See Table 1S in Supporting Information.
ACKNOWLEDGMENTS
■
We gratefully acknowledge National Natural Science Foundation
of China (Nos. 21172120 and 21472093), Tianjin Municipal
Science and Technology Commission (No. 14JCYBJC20600),
and the National University Student Innovation Program (No.
201710055117) for the funding support.
(20) (a) Jiang, H.; Cheng, Y.; Zhang, Y.; Yu, S. Org. Lett. 2013, 15, 4884.
(b)Yuan,Z. G.;Wang, Q.;Zheng, A.;Zhang, K.;Lu,L.Q.;Tang, Z.;Xiao,
W. J. Chem. Commun. 2016, 52, 5128. (c) Wang, H.; Wang, Z.; Wang, Y.-
L.; Zhou, R.-R.; Wu, G.-C.; Yin, S.-Y.; Yan, X.; Wang, B. Org. Lett. 2017,
DOI: 10.1021/acs.orglett.7b03021. (d) Chen, Z.-Z.; Liu, S.; Hao, W.-J.;
Xu, G.; Wu, S.; Miao, J.-N.; Jiang, B.; Wang, S.-L.; Tu, S.-J.; Li, G. Chem.
Sci. 2015, 6, 6654. (e) Hartmann, M.; Daniliuc, C. G.; Studer, A. Chem.
Commun. 2015, 51, 3121.
REFERENCES
■
(1) For selected reviews, see: (a) Boyarskiy, V. P.; Ryabukhin, D. S.;
Bokach, N. A.; Vasilyev, A. V. Chem. Rev. 2016, 116, 5894. (b) Gulías, M.;
̌
(21) (a) Podgorsek, A.; Zupan, M.; Iskra, J. Angew. Chem., Int. Ed. 2009,
48, 8424. (b) Espenson, J. H.; Zhu, Z.; Zauche, T. H. J. Org. Chem. 1999,
64, 1191. (c) Bray, W. C. Chem. Rev. 1932, 10, 161. (d) Detty, M. R.;
Zhou, F.; Friedman, A. E. J. Am. Chem. Soc. 1996, 118, 313.
Mascarenas, J. L. Angew. Chem., Int. Ed. 2016, 55, 11000. (c) Le Bras, J.;
̃
Muzart, J. Synthesis 2014, 46, 1555.
(2) (a) Song, G. Y.;Li, X. W. Acc. Chem. Res. 2015, 48, 1007. (b)Li, S. S.;
Qin, L.; Dong, L. Org. Biomol. Chem. 2016, 14, 4554. (c) Zhou, S.; Wang,
J.; Wang, L.; Song, C.; Chen, K.; Zhu, J. Angew. Chem., Int. Ed. 2016, 55,
9384. (d) Zhou, Z.; Liu, G.; Chen, Y.; Lu, X. Adv. Synth. Catal. 2015, 357,
2944. (e) Zhou, S.; Wang, J.; Zhang, F.; Song, C.; Zhu, J. Org. Lett. 2016,
18, 2427. (f) Krieger, J.-P.; Lesuisse, D.; Ricci, G.; Perrin, M.-A.; Meyer,
C.; Cossy, J. Org. Lett. 2017, 19, 2706.
(22) Saikia, I.; Borah, A. J.; Phukan, P. Chem. Rev. 2016, 116, 6837.
(23) (a) Studer, A.; Curran, D. P. Angew. Chem., Int. Ed. 2016, 55, 58.
(b) Studer, A.; Curran, D. P. Nat. Chem. 2014, 6, 765. (c) Arceo, E.;
Montroni, E.; Melchiorre, P. Angew. Chem., Int. Ed. 2014, 53, 12064.
(24) Studer, A. Chem. - Eur. J. 2001, 7, 1159.
(3)(a)Ackermann, L. Acc. Chem. Res. 2014, 47,281. (b)Tulichala, R. N.
P.; Shankar, M.; Swamy, K. C. K. J. Org. Chem. 2017, 82, 5068.
(4) (a) Wencel-Delord, J.; Droge, T.; Liu, F.; Glorius, F. Chem. Soc. Rev.
́
2011, 40, 4740. (b)Chinchilla, R.;Najera, C. Chem. Rev. 2014, 114, 1783.
D
DOI: 10.1021/acs.orglett.7b03186
Org. Lett. XXXX, XXX, XXX−XXX