Palladium-Catalyzed Synthesis of Triphenylenes via Sequential C-H Activation and Decarboxylation

Article abstract of DOI:10.1021/acs.orglett.8b02310

A novel tandem intermolecular decarboxylative coupling reaction of o-bromobenzoic acids and aryl iodides has been developed. The method affords a range of unsymmetrically triphenylenes and displays unique regioselectivity and broad substrate scope. Mechanistically, palladium/norbornene-catalyzed C-H activation and subsequent double decarboxylative coupling reactions were involved. Moreover, the triphenylenes can also be synthesized from 2-iodobiphenyls and o-bromobenzoic acids under norbornene-free conditions.

Full text of DOI:10.1021/acs.orglett.8b02310

Letter
pubs.acs.org/OrgLett
Cite This: Org. Lett. XXXX, XXX, XXX−XXX
Palladium-Catalyzed Synthesis of Triphenylenes via Sequential C−H
Activation and Decarboxylation
Yuzhong Yang,† Bang Zhou,† Xiaoming Zhu,† Guobo Deng,† Yun Liang,*,† and Yuan Yang*,†
†National & Local Joint Engineering Laboratory for New Petro-chemical Materials and Fine Utilization of Resources, Key
Laboratory of Chemical Biology and Traditional Chinese Medicine Research, Ministry of Education, Key Laboratory of the
Assembly and Application of Organic Functional Molecules of Hunan Province, Hunan Normal University, Changsha, Hunan
410081, China
S
* Supporting Information
ABSTRACT: A novel tandem intermolecular decarboxylative
coupling reaction of o-bromobenzoic acids and aryl iodides
has been developed. The method affords a range of
unsymmetrically triphenylenes and displays unique regiose-
lectivity and broad substrate scope. Mechanistically, palla-
dium/norbornene-catalyzed C−H activation and subsequent
double decarboxylative coupling reactions were involved.
Moreover, the triphenylenes can also be synthesized from 2-iodobiphenyls and o-bromobenzoic acids under norbornene-free
conditions.
ripenylenes are one of most important classes of
polycyclic aromatic hydrocarbons on account of their
which initially reacts with an electrophile to achieve ortho C−
H functionalization. Subsequently, the polysubstituted aro-
matic compounds are produced by sequential β-C elimination
of norbornene and the capture of a nucleophile. Very recently,
Kwong and co-workers found that the five-membered
palladacycle inserted a o-halobenzoic acid to give a cyclic
compound, which could translate into phenanthrene via retro-
Diels−Alder reaction when norbornene was replaced to the
norbornadiene (Scheme 1, eq 1).10a Subsequently, they further
discovered that phenanthrene could be synthesized by
introduction of an alkyne after the five-membered palladacycle
reacted with a o-haloaryl carboxylic acid (Scheme 1, eq 2).10b
In view of these previous research results and our research
T
planar rigidity and π-extended system,1 which could be widely
applied in supramolecular and materials chemistry.2 For these
reasons, many efficient strategies for the synthesis of
triphenylenes have been developed. From the structure analysis
of triphenylenes, three main synthetic strategies are as follows:
(1) via intramolecular C−C bond coupling reaction of
terphenyls;3 (2) via twice C−C bonds coupling reaction of
functionalized diphenyl units with functionalized benzene
units;4 and (3) via three times C−C bonds coupling reaction
of three functionalized benzene units.5−8 The first two
strategies require several steps to prepare the functionalized
starting materials of terphenyls and diphenyls, which limit their
practical application. Compared with the functionalized
terphenyls and biphenyls, the functionalized benzene units
are the ideal substrate for the synthesis of triphenylenes due to
their readily available materials. To date, three main method-
ologies were developed, including oxidative trimerization of
catechol derivatives,5 cyclotrimerization of arynes,6 and
transition-metal-catalyzed coupling reaction of 1,2-dibromo-
benzene.7 However, these methods were restricted to the
synthesis of symmetrical triphenylenes. In addition, only one
example for the synthesis of unsymmetrical triphenylenes from
arynes and iodobenzenes was reported, yet was limited to use
of symmetrical arynes.8 Therefore, new efficient strategies that
employ readily available functionalized benzene units to
achieve the regioselective construction of unsymmetrical
triphenylene molecules remains challenging.
Scheme 1. Palladium-Catalyzed Cross-Coupling Reaction of
o-Bromobenzoic Acids with Aryl Iodides
The Catellani reaction enables the selective functionalization
of the ortho and ipso positions of aryl halides.9 This procedure
starts with oxidative addition of C−X bond to palladium
catalyst, followed by a Heck-type reaction with norbornene,
and finally C−H bond activation to afford the palladacycle,
Received: July 23, 2018
© XXXX American Chemical Society
A
DOI: 10.1021/acs.orglett.8b02310
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
interest in the cross-coupling reactions involving pallada-
cycles,11 herein we developed a novel palladium/norbornene-
catalyzed coupling reaction of o-bromobenzoic acids with aryl
iodides. The approach allowed the regioselective assembly of
unsymmetrically functionalized triphenylenes via C−H activa-
tion and subsequent double decarboxylation (Scheme 1, eq 3).
We started our studies with reaction of o-iodotoluene and o-
bromobenzoic acid for obtaining the optimal reaction
conditions (Table 1). Gratifyingly, treatment of o-iodotoluene
mmol) in DMSO (1 mL) at 140 °C under N2 for 3 h. Finally,
we were pleased to find that 3aaa was isolated in 81% yield by
performing the reaction with a 1 mmol scale of 1a (entry 15).
When the amount of 1a was increased to 5 mmol, the product
3aaa was afforded in 66% yield.
With the optimal reaction conditions in hand, the scope of
the decarboxylative coupling reaction with respect to aryl
iodides 1 and o-bromobenzoic acids 2 was screened (Scheme
2). First, a wide range of aryl iodides were investigated.
a
Table 1. Optimization of the Reaction Conditions
Scheme 2. Variation of the Aryl Iodides 1 and o-
Bromobenzoic Acids 2
a
b
yield (%)
entry
[Pd]
base
solvent
3aaa
4aa
21
13
15
trace
14
trace
29
21
6
17
trace
trace
trace
trace
trace
trace
1
2
3
4
5
6
7
8
Pd(OAC)2
[Pd(π-allyl)Cl]2
PdCl2
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
Cs2CO3
Na2CO3
K3PO4
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
40
31
41
31
66
44
30
36
67
61
12
82
38
79
81
66
Pd(PPh3)4
PdCl2(PPh3)2
PdCl2(PPh3)2
PdCl2(PPh3)2
PdCl2(PPh3)2
PdCl2(PPh3)2
PdCl2(PPh3)2
PdCl2(PPh3)2
PdCl2(PPh3)2
PdCl2(PPh3)2
PdCl2(PPh3)2
PdCl2(PPh3)2
PdCl2(PPh3)2
9
DMSO
NMP
10
11
12
13
14
15
16
CH3CN
DMSO
DMSO
DMSO
DMSO
DMSO
c
c d
,
ce
,
f
a
g
Reaction conditions: 1 (0.2 mmol), 2 (0.44 mmol), norbornene (0.4
a
mmol), PdCl2(PPh3)2 (5 mol %), BQ (0.2 mmol), K2CO3 (0.6
mmol), and DMSO (0.2 M, 1 mL) at 140 °C under N2. o-
Chlorobenzoic acid instead of o-bromobenzoic acid.
Reaction conditions: 1a (0.2 mmol), 2a (0.44 mmol), norbornene
b
(0.4 mmol), Pd catalyst (5 mol %), base (0.6 mmol), and solvent (0.2
M, 1 mL) at 140 °C for 3 h under N2. BQ = 1,4-benzoquinone.
b
c
d
e
f
Isolated yield. BQ (0.2 mmol). 130 °C. 150 °C. 1a (1.0 mmol).
g
1a (5.0 mmol).
Iodobenzenes 1b−g containing the ortho-substituted groups
(Et, i-Pr, Ph, F, Cl, and CF3) reacted with o-bromobenzoic
acid, and the corresponding triphenylenes 3baa−gaa were
isolated in 55−99% yields. To our delight, both the electron-
donating group (Me, OMe, and OH) and electron-with-
drawing group (F and Cl) substituted 1-iodo-2-methylben-
zenes 1h−m could smoothly be converted into the desired
products 3haa−maa in moderate to perfect yields. Impor-
tantly, the polycylic aromatic 1-iodonaphthalene and polycyclic
heteroaromatic 5-iodoquinoline could successfully afford the π-
extend triphenylenes in 78% and 63% yields (3naa and 3oaa),
respectively. Subsequently, the optimal reaction conditions
were applicable to o-bromobenzoic acids 2b−g, and the
reaction was satisfactory to exhibit unique regioselectivity. The
o-bromobenzoic acids bearing a 4-Me, 5-Me, or 6-Me group
could give the triphenylenes 3abb, 3add, and 3agg in moderate
yields by reaction with o-iodotoluene. Nevertheless, the 2-
bromo-3-methylbenzoic acid was not a compatible substrate,
and no target product was detected (not shown in Scheme 2).
The results reveal that the steric congestion of ortho
substituents corresponding to the bromine atom of o-
bromobenzoic acids dramatically impaired the reactivity.
Furthermore, other substituents, namely 4-Cl, 5-OMe, and 5-
F, on the aryl ring were well tolerated (3acc, 3aee, and 3aff). It
1a with o-bromobenzoic acid 2a, Pd(OAc)2, norbornene, and
K2CO3 in DMF at 140 °C could afford 40% of the desired
product 3aaa and 21% of byproduct 4aa (entry 1).
Subsequently, a series of the palladium catalysts, including
[Pd(π-allyl)Cl]2, PdCl2, Pd(PPh3)4, and PdCl2(PPh3)2, were
tested, and PdCl2(PPh3)2 proved to be the most suitable
catalyst in terms of yield (entries 2−5). Further screening of
bases, such as Cs2CO3, Na2CO3, and K3PO4, revealed that
none were more efficient than K2CO3 (entries 6−8).
Compared with DMF, the reaction using DMSO as solvent
afforded an identical yield of the desired product and inhibited
production of byproduct (entry 9), but other solvents,
including NMP and CH3CN, displayed lower reactivity for
decarboxylative coupling reaction (entries 10 and 11).
Surprised, the 1,4-benzoquinone can improve efficiency of
the reaction, and 78% of 3aaa was obtained when 1 equiv of
1,4-benzoquinone was added (entry 12). The reason is still
under investigation. Examination of the reaction temperature
showed that lower yields were provided at 130 or 150 °C
(entries 13 and 14), Thus, the optimal reaction conditions are
as follows: 1a (0.2 mmol), 2a (0.44 mmol), Pd(OAc)2 (5 mol
%), norbornene (0.4 mmol), K2CO3 (0.6 mmol), and BQ (0.2
B
DOI: 10.1021/acs.orglett.8b02310
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
is noted that reaction of o-iodotoluene and 2-iodo-1,1′-
biphenyl, respectively, with o-chlorobenzoic acid was also
viable, delivering the desired products in diminished yields
(3aaa and 3gaa).
Scheme 4. Control Experiment and Possible Reaction
Mechanism
Further investigation revealed the 2-iodobiphenyls could
react with o-bromobenzoic acids to afford triphenylenes in
good to perfect yields in the absence of norbornene and BQ
(Scheme 3). The palladium-catalyzed coupling reaction of o-
Scheme 3. Variation of the 2-Iodobiphenyls 1 and o-
a
Bromobenzoic Acids 2
Under the catalytic system of Pd/norbornene, 1-iodo-2-
methylbenzene converts into the intermediate aryl norbornyl
palladacycle (ANP) via a tandem process, which starts with
oxidative addition of Pd(0) to C−I bond, followed by
carbopalladation of norbornene, and finally the ortho-C−H
bond activation. Seminal works by Kwong10 have shown the
ANP with o-bromobenzoic acid undergo a decarboxylative
cross-coupling cyclization, thus producing the intermediate A
which forms the palladacycle B via oxidative addition to C−Br
bond of o-bromobenzoic acid. On the other hand, selective
reductive elimination of A can afford the side product 4aa.
Subsequently, intermediate B provides tribenzopalladacyclo-
heptatrienes C through a process involving reductive
elimination of Pd(IV) species, extrusion of norbornene, and
decarboxylation. Finally, the triphenylene 3aaa is formed by
reductive elimination of intermediate C.
In conclusion, we have developed a regioselective approach
for the synthesis of unsymmetrical triphenylenes via
palladium/norbornene-catalyzed coupling reaction of o-bro-
mobenzoic acids and aryl iodides. As such, a wide range of
triphenylenes was synthesized in moderate to excellent yields.
A possible mechanism involving a palladium/norbornene
complex was proposed. At the same time, we also found the
synthesis of triphenylenes via a palladium-catalyzed coupling
reaction of o-bromobenzoic acids and 2-iodobiphenyls in the
absence of norbornene and BQ. Further investigation of the
detailed reaction mechanism and the application of this
method is still in progress in our laboratory.
a
Reaction conditions: 1 (0.2 mmol), 2 (0.22 mmol), PdCl2(PPh3)2 (5
mol %), K2CO3 (0.6 mmol), and DMSO (0.2 M, 1 mL) at 140 °C
under N2. o-Chlorobenzoic acid instead of o-bromobenzoic acid. 2-
b
c
d
Bromo-1,1′-biphenyl instead of 2-iodo-1,1′-biphenyl. The ratio of
e
the two isomers is 1:1.2. 3-Bromothiophene-2-carboxylic acid was
f
used. 2-(2-Iodophenyl)-1-methyl-1H-indole was used.
bromobenzoic acid and o-chorobenzoic acid, respectively, with
2-iodo-1,1′-biphenyl proceeded smoothly, and both of them
led to triphenylene 3ga in 99% yields. Using 2-bromo-1,1′-
biphenyl as substrate also delivered the corresponding product
3ga, albeit with a decreased yield. Then, substrates (1p, 1q, 2e,
2f, and 2h) bearing either electron-donating groups (Me and
OMe) or electron-withdrawing groups (F and Cl) underwent
reaction to afford the target products in excellent yields.
Notably, 2-bromo-5-methylbenzoic acid 2e reacted with
unsymmetrical 2-iodo-5-methyl-1,1′-biphenyl 1r to give a
mixture of regioisomers 3re with a ratio of 1:1.1 in 75%
1
overall yield (ratio determined by H NMR). Finally, the
heterocontaining polycyclic compound phenanthro[9,10-b]-
thiophene 3gi and dibenzo[a,c]carbazole 3sa were all
synthesized in 99% yields.
ASSOCIATED CONTENT
* Supporting Information
The control experiment of palladacycle D-Int with 2e was
carried out, and a mixture of regioisomers 3re was afforded in a
ratio of 1:1.2 (eq 1 in Scheme 4). The results proved that the
reaction of 2-iodobiphenyls and o-bromobenzoic acids led to
the intermediate of dibenzopalladacyclopentadienes12 in the
absence of norbornene and BQ. Simultaneously, the results
indicated that the reaction of aryl iodides and o-bromobenzoic
acids did not involve the formation of D in the presence of
norbornene
■
S
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.or-
glett.8b02310.
Experimental procedures, full characterization of prod-
ucts, and NMR spectra (PDF)
AUTHOR INFORMATION
Corresponding Authors
On the basis of the previous reports9,10 and our experimental
results, a hypothetical reaction mechanism for the synthesis of
unsymmetrical triphenylenes was illustrated (Scheme 4).
■
*E-mail: yliang@hunnu.edu.cn.
C
DOI: 10.1021/acs.orglett.8b02310
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
́ ́
̃
a, D.; Cobas, A.; Perez, D.; Guitian, E.; Castedo, L.
46, 8671. (c) Pen
Org. Lett. 2000, 2, 1629. (d) Pen
L. Org. Lett. 1999, 1, 1555. (e) Pen
*E-mail: yangyuan071@126.com.
ORCID
́ ́
a, D.; Perez, D.; Guitian, E.; Castedo,
̃
́
a, D.; Escudero, S.; Perez, D.;
̃
Guobo Deng: 0000-0002-5470-5706
Yun Liang: 0000-0002-2550-9220
Yuan Yang: 0000-0002-9061-1758
́
Guitian, E.; Castedo, L. Angew. Chem., Int. Ed. 1998, 37, 2659.
(7) (a) Hilton, C. L.; Jamison, C. R.; King, B. T. J. Am. Chem. Soc.
2006, 128, 14824. (b) Zhou, Z.-Z.; Yamamoto, T. J. Organomet.
Chem. 1991, 414, 119.
Notes
(8) Jayanth, T. T.; Cheng, C.-H. Chem. Commun. 2006, 894.
(9) Recent reviews on the Catellani reaction: (a) Kim, D.-S.; Park,
W.-J.; Jun, C.-H. Chem. Rev. 2017, 117, 8977. (b) Della Ca, N.;
Fontana, M.; Motti, E.; Catellani, M. Acc. Chem. Res. 2016, 49, 1389.
(c) Ye, J.; Lautens, M. Nat. Chem. 2015, 7, 863. (d) Ferraccioli, R.
Synthesis 2013, 45, 581. (e) Martins, A.; Mariampillai, B.; Lautens, M.
Top. Curr. Chem. 2009, 292, 1. Selected examples on the Catellani
reaction: (f) Cheng, H.-G.; Wu, C.; Chen, H.; Chen, R.; Qian, G.;
Geng, Z.; Wei, Q.; Xia, Y.; Zhang, J.; Zhang, Y.; Zhou, Q. Angew.
Chem., Int. Ed. 2018, 57, 3444. (g) Sui, X.; Ding, L.; Gu, Z. Chem.
Commun. 2016, 52, 13999. (h) Huang, Y.; Zhu, R.; Zhao, K.; Gu, Z.
Angew. Chem., Int. Ed. 2015, 54, 12669. (i) Zhou, P.-X.; Ye, Y.-Y.; Liu,
C.; Zhao, L.-B.; Hou, J.-Y.; Chen, D.-Q.; Tang, Q.; Wang, A.-Q.;
Zhang, J.-Y.; Huang, Q.-X.; Xu, P.-F.; Liang, Y.-M. ACS Catal. 2015,
5, 4927. (j) Zhang, H.; Chen, P.; Liu, G. Angew. Chem., Int. Ed. 2014,
53, 10174. (k) Catellani, M.; Frignani, F.; Rangoni, A. Angew. Chem.,
Int. Ed. Engl. 1997, 36, 119. (l) Chen, S.; Liu, Z.-S.; Yang, T.; Hua, Y.;
Zhou, Z.; Cheng, H.-G.; Zhou, Q. Angew. Chem., Int. Ed. 2018, 57,
7161. (m) Shi, G.; Shao, C.; Ma, X.; Gu, Y.; Zhang, Y. ACS Catal.
2018, 8, 3775.
(10) (a) Fu, W. C.; Wang, Z.; Chan, W. T. K.; Lin, Z.; Kwong, F. Y.
Angew. Chem., Int. Ed. 2017, 56, 7166. (b) Zhao, Q.; Fu, W. C.;
Kwong, F. Y. Angew. Chem., Int. Ed. 2018, 57, 3381.
(11) (a) Luo, X.; Xu, Y.; Xiao, G.; Liu, W.; Qian, C.; Deng, G.; Song,
J.; Liang, Y.; Yang, C. Org. Lett. 2018, 20, 2997. (b) Li, W.; Xiao, G.;
Deng, G.; Liang, Y. Org. Chem. Front. 2018, 5, 1488. (c) Xiao, G.;
Chen, L.; Deng, G.; Liu, J.; Liang, Y. Tetrahedron Lett. 2018, 59, 1836.
(d) Xiao, G.; Chen, L.; Zhou, B.; Deng, G.; Gong, J.; Liang, Y. Adv.
Synth. Catal. 2018, DOI: 10.1002/adsc.201800687. (e) Wu, L.; Deng,
G.; Liang, Y. Org. Biomol. Chem. 2017, 15, 6808.
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was supported by the National Natural Science
Foundation of China (21572051 and 21602057) and the
Opening Fund of Key Laboratory of Chemical Biology and
Traditional Chinese Medicine Research (Ministry of Educa-
t i o n o f C h i n a ) , H u n a n N o r m a l U n i v e r s i t y
(KLCBTCMR201707 and KLCBTCMR201708).
REFERENCES
■
(1) For selected reviews, see: (a) Zhang, H.; Wu, D.; Liu, S. H.; Yin,
J. Curr. Org. Chem. 2012, 16, 2124. (b) Feng, X.; Pisula, W.; Mullen,
K. Pure Appl. Chem. 2009, 81, 2203. (c) Wu, J.; Pisula, W.; Mullen, K.
Chem. Rev. 2007, 107, 718. (d) Laschat, S.; Baro, A.; Steinke, N.;
Giesselmann, F.; Hagele, C.; Scalia, G.; Judele, R.; Kapatsina, E.;
Sauer, S.; Schreivogel, A.; Tosoni, M. Angew. Chem., Int. Ed. 2007, 46,
4832. (e) Wu, J. Curr. Org. Chem. 2007, 11, 1220. (f) Harvey, R. G.
Curr. Org. Chem. 2004, 8, 303. (g) Scott, L. T. Angew. Chem., Int. Ed.
2004, 43, 4994. (h) Boorum, M. M.; Scott, L. T. In Modern Arene
Chemistry; Astruc, D., Ed.; Wiley-VCH: Weinheim, 2002; pp 20−31.
(i) Watson, M. D.; Fechtenkotter, A.; Mullen, K. Chem. Rev. 2001,
101, 1267. (j) Harvey, R. G. In Polycyclic Aromatic Hydrocarbons;
Wiley-VCH: New York, 1997; pp 43−128.
(2) (a) Tschierske, C. Annu. Rep. Prog. Chem., Sect. C: Phys. Chem.
2001, 97, 191. (b) Watson, M.; Fechtenkotter, A.; Mullen, K. Chem.
Rev. 2001, 101, 1267. (c) Collings, P. J.; Hird, M. Introduction to
Liquid Crystals; Taylor and Francis: London, 1997. (d) Buess, C. M.;
Lawson, D. D. Chem. Rev. 1960, 60, 313.
(3) (a) Daigle, M.; Picard-Lafond, A.; Soligo, E.; Morin, J.-F. Angew.
Chem., Int. Ed. 2016, 55, 2042. (b) Fujimoto, S.; Matsumoto, K.;
Shindo, M. Adv. Synth. Catal. 2016, 358, 3057. (c) Feng, C.; Tian, X.-
L.; Zhou, J.; Xiang, S.-K.; Yu, W.-H.; Wang, B. Q.; Hu, P.; Redshaw,
C.; Zhao, K.-Q. Org. Biomol. Chem. 2014, 12, 6977. (d) Xu, L.; Yu, R.;
Wang, Y.; Chen, J.; Yang, Z. J. Org. Chem. 2013, 78, 5744.
(e) Amsharov, K. Y.; Merz, P. J. Org. Chem. 2012, 77, 5445.
(f) Allemann, O.; Duttwyler, S.; Romanato, P.; Baldridge, K. K.;
Siegel, J. S. Science 2011, 332, 574. (g) King, B. T.; Kroulík, J.;
Robertson, C. R.; Rempala, P.; Hilton, C. L.; Korinek, J. D.; Gortari,
L. M. J. Org. Chem. 2007, 72, 2279.
(12) (a) Jiang, H.; Zhang, Y.; Chen, D.; Zhou, B.; Zhang, Y. Org.
Lett. 2016, 18, 2032. (b) Masselot, D.; Charmant, J. P. H.; Gallagher,
T. J. Am. Chem. Soc. 2006, 128, 694.
(4) (a) Yang, S.; Wang, F.; Wu, Y.; Hua, W.; Zhang, F. Org. Lett.
2018, 20, 1491. (b) Wu, Y.; Zhang, W.; Peng, Q.; Ran, C.-K.; Wang,
B.-Q.; Hu, P.; Zhao, K.-Q.; Feng, C.; Xiang, S.-K. Org. Lett. 2018, 20,
2278. (c) Yang, S.; Hua, W.; Wu, Y.; Hu, T.; Wang, F.; Zhang, X.;
Zhang, F. Chem. Commun. 2018, 54, 3239. (d) Wu, X.; Han, J.; Wang,
L. J. Org. Chem. 2018, 83, 49. (e) Kurata, Y.; Otsuka, S.; Fukui, N.;
Nogi, K.; Yorimitsu, H.; Osuka, A. Org. Lett. 2017, 19, 1274. (f) Pan,
S.; Jiang, H.; Zhang, Y.; Chen, D.; Zhang, Y. Org. Lett. 2016, 18, 5192.
(g) Iwasaki, M.; Iino, S.; Araki, Y.; Nishihara, Y. J. Org. Chem. 2015,
80, 9247. (h) Iwasaki, M.; Iino, S.; Nishihara, Y. Org. Lett. 2013, 15,
5326. (i) Shimizu, M.; Nagao, I.; Tomioka, Y.; Kadowaki, T.; Hiyama,
T. Tetrahedron 2011, 67, 8014. (j) Nagao, I.; Shimizu, M.; Hiyama, T.
Angew. Chem., Int. Ed. 2009, 48, 7573. (k) McIver, A.; Young, D. D.;
Deiters, D. Chem. Commun. 2008, 4750. (l) Liu, Z.; Larock, R. C. J.
Org. Chem. 2007, 72, 223. (m) Liu, Z.; Zhang, X.; Larock, R. C. J. Am.
Chem. Soc. 2005, 127, 15716.
(5) (a) Kumar, S.; Varshney, S. K. Synthesis 2001, 2001, 305.
(b) Kumar, S.; Manickam, M. Chem. Commun. 1997, 1615.
́
(6) (a) García-Lopez, J.-A.; Greaney, M. F. Org. Lett. 2014, 16, 2338.
(b) Cant, A. A.; Roberts, L.; Greaney, M. F. Chem. Commun. 2010,
D
DOI: 10.1021/acs.orglett.8b02310
Org. Lett. XXXX, XXX, XXX−XXX