Direct Borylation of Tertiary Anilines via C-N Bond Activation

Article abstract of DOI:10.1021/acs.orglett.8b00545

The first successful catalytic borylation of unactivated aromatic C-N bonds of tertiary anilines without the preactivation or any directing groups is demonstrated. The reactivity of both N,N-dialkylarylamines and N-arylpyrroles were investigated systematically, and the targeted products were furnished in moderate to good yields. The DFT calculation results indicated that the catalytic cycle is furnished via a five-membered cyclic transition-state due to the steric hindrance of the Ni/NHC catalytic system.

Full text of DOI:10.1021/acs.orglett.8b00545

Letter
pubs.acs.org/OrgLett
Cite This: Org. Lett. XXXX, XXX, XXX−XXX
Direct Borylation of Tertiary Anilines via C−N Bond Activation
Zhi-Chao Cao,†,‡,∥ Xiao-Lei Li,‡,∥ Qin-Yu Luo,‡ Huayi Fang,*,† and Zhang-Jie Shi*,†,‡,§
†Department of Chemistry, Fudan University, Shanghai 200433, China
‡College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, China
§State Key Laboratory of Organometallic Chemistry, Chinese Academy of Science, Shanghai 200032, China
S
* Supporting Information
ABSTRACT: The first successful catalytic borylation of unactivated
aromatic C−N bonds of tertiary anilines without the preactivation or
any directing groups is demonstrated. The reactivity of both N,N-
dialkylarylamines and N-arylpyrroles were investigated systematically,
and the targeted products were furnished in moderate to good yields.
The DFT calculation results indicated that the catalytic cycle is
furnished via a five-membered cyclic transition-state due to the steric hindrance of the Ni/NHC catalytic system.
ertiary aniline is a mainstay in organic chemistry and can
be found in bioactive natural products and pharmaceut-
process to cleave aromatic C−N bonds was facilitated by the
electron-withdrawing effect of the acyl group, and the π-
extended aromatic ring containing substrates showed better
reactivity (Scheme 1b). Kakiuchi and co-workers successfully
applied a directing strategy into C−N bond activation to cleave
aromatic C−N bonds of tertiary anilines via ruthenium-
catalyzed Suzuki−Miyaura cross-coupling with the clear
understanding of the catalytic mechanism.7 The introduction
of the acyl group at ortho-position not only played a role as a
directing group but also possibly activated the C−N bonds as
an electron-withdrawing group (Scheme 1c). Another beautiful
example on the activation of C−N bonds by directing strategy
was demonstrated by Zeng and co-workers via chromium
catalysis.8 However, to the best of our knowledge, there were
indeed no successful examples to carry out the catalytic direct
cleavage of C−N bonds of tertiary anilines in the absence of
directing group or without preactivation, although the
stoichiometric C−N cleavage of unprotected aniline by a
tantalum complex was previously reported.9 Thus, simple and
direct methods to apply for tertiary anilines as electronically
neutral aromatic C−N electrophiles in cross-coupling reactions
are highly appealing. Such studies are also beneficial for
understanding the intrinsic inertness of aromatic C−N bonds.
Herein, we reported the first successful example on nickel-
catalyzed borylation of unactivated aromatic C−N bonds of N-
aryl pyrroles and tertiary anilines (Scheme 1d).
T
icals. However, transition-metal-catalyzed direct transformation
of tertiary anilines remained a challenge due to the kinetic and
thermodynamic stability of their aromatic C−N bonds and the
strong coordination ability of both anilines themselves and in
1
−
situ generated anion amino species (NR2 ). To solve the
problem in activation and application of C−N bonds of tertiary
anilines, great achievements have been made by modifying the
substrates, and different strategies have been developed
(Scheme 1).2 At the early stage, tertiary anilines could be
Scheme 1. Strategies To Carry out the Catalytic C−N Bond
Activation of Tertiary Anilines
With the recent successes in Ni-catalyzed C−O bond
activation of ethers and phenols,10 we envisaged that the C−
N bonds of unactivated aniline derivatives might be cleaved if a
proper combination of transition metal and ligand set was
submitted as catalyst. The key factor for the proposed
transformation might be a suitable coupling partner. To
approach our design, the right coupling partner might have
the potential to act as a good scavenger to quench the formed
transformed into highly reactive cationic intermediates,3 such as
ammonium salts,4 which were employed as coupling partners in
transition-metal-catalyzed cross-coupling reactions. This strat-
egy benefited from the release of neutral small molecules, thus
promoting the conversion efficiently (Scheme 1a).
Recently, Chatani and co-workers reported the aromatic C−
N cleavage via nickel-catalyzed reduction and borylation of N-
aryl amides.5 In this case, the oxidative transformation of
tertiary anilines into N-arylamides was necessary,6 and the
Received: February 13, 2018
© XXXX American Chemical Society
A
DOI: 10.1021/acs.orglett.8b00545
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−
NR2 , which might poison the transition-metal catalyst as a
exhibited low efficiency in previous report on catalytic cleavage
of aromatic C−N bond.5 To our satisfaction, the desired
product 2d was isolated in an acceptable yield (49%). The
reactivity of heterocyclic substrate (1e) was also examined, and
2e was obtained in 52% yield. Notably, non-π-extended
aromatic substrates usually demonstrated low reactivity in C−
O and C−N bond activation in the previous work.5,10d
However, in our case, the simple N-phenylpyrrole bearing a
phenyl group at the para-position (1f) were found to transform
into the borylation product in a satisfying yield (55%).
Substrate 1g was also submitted to the catalytic system and
the corresponding borylation products 2g were obtained.
We further investigated the borylation of unactivated tertiary
anilines with different substituents on the N atom (Scheme 3).
strong σ-donor ligand. Thus, the direct borylation of aniline
derivatives as desirable transformation, in which the in situ
generated amino species might be quenched by the rest part of
diboron reagent to form the stable B−N bonds at the latter
stage. In another aspect, the targeted borylation products are
versatile building blocks in organic synthesis.11
With the idea in mind, we first selected the less basic N-
(naphthalen-2-yl)-pyrrole (1a) as the model substrate to react
with B2nep2 via Ni catalysis.12 By systematically optimizing the
conditions, to our delight, a cocktail containing Ni(cod)2 (10
mol %) as the catalyst, IMes (11 mol %) as the ligand, and
PhCO2Na (4.0 equiv) as the base in PhMe promoted the
desired borylation, and the product 2a was observed in 54%
NMR yield with the use of CH2Br2 as an internal standard
(entry 12, Table S1). Interestingly, different phosphine ligands,
which played key roles in transition-metal-catalyzed C−O
activation, completely failed the transformation with the full
recovery of the substrate 1a. We then turned to screen the
NHC (nitrogen hetero cyclic carbene) ligands, which also
proved to be efficient in transition-metal-catalyzed cross-
couplings.13 Different NHC ligands, including IPr, SIPr, and
SIMes, were used to take place of IMes, only ItBu showed a
partial efficiency, and the targeted product 2a was obtained in
lower yield (entries 1−9, Table S2). Furthermore, we modified
the IMes ligand with assembling two methyl groups at the 4-
and 5-positions (IMesMe),14 and fortunately, 2a was obtained in
62% isolated yield (entry 10, Table S2). In this case, the
substrate 1a was fully consumed, and naphthalene was observed
as a byproduct. B2pin2 was also used to instead of B2nep2 as the
borylation reagent, and the desired product was obtained in
52% NMR yield.
a
Scheme 3. Catalytic Borylation of Tertiary Anilines
With the optimal conditions in hand, we tested the reactivity
of various N-arylpyrroles (Scheme 2). The N-arylpyrrole
a
The reactions were performed on a 0.2 mmol scale, Ni(cod)2 (10 mol
%, 5.6 mg), IMesMe (35 mol %, 23.2 mg), THF (1.0 mL), 135 °C, 48
Scheme 2. Catalytic Borylation of Unactivated C−N Bonds
b
a
h. The reactions were performed on a 0.2 mmol scale, Ni(cod)2 (30
of N-Arylpyrroles
mol %, 16.8 mg), IMesMe (75 mol %, 49.8 mg), PhMe (1.0 mL), 125
°C, 24 h.
Compared to the borylation of N-arylpyrroles, the borylation of
dialkyl-protected anilines occurred in the absence of any
additional bases. On the contrary, the borylation was
dramatically terminated if the additional base was present.
The additional base might coordinate to the borylation reagent
and decrease the capability of B2nep2 to quench the generated
amino species. We found that N,N-dimethyl(2-naphthyl)amine
(1h) showed a moderate conversion under modified
conditions.16 Although tertiary aniline 1i had a better leaving
group (−NMePh) than of 1h, a lower yield was obtained,
probably arising from the steric hindrance.17 The reactivity of
different cyclic tertiary anilines was also tested, and the targeted
borylation product 2a was furnished in 65% yield when N-
(naphthalen-2-yl)morpholine (1k) was used as the substrate.
Substrate 1l was also submitted, while a low yield was obtained.
It is worth noting that, under the modified conditions, the
targeted borylation product 2a was furnished in low yield
(<10%) when 1-(naphthalen-2-yl)pyrrolidine (1j) was used,
and a similar result was also observed in the reported amide C−
N bond activation of pyrrolidine-type substrate.18 The better
result of 1k might be owed to the traceless directing effect of
morpholine substituent.19 At the current stage, the substrates
a
The reactions were performed on a 0.2 mmol scale, Ni(cod)2 (10 mol
%, 5.6 mg), IMesMe (11 mol %, 7.6 mg), PhCO2Na (0.8 mmol), PhMe
b
c
(1.0 mL), 110 °C, 7 h. PhCO2Na (5.0 equiv). The reaction was
d
performed in 0.4 mmol scale. Ni(cod)2 (15 mol %, 8.4 mg), IMesMe
(16.5 mol %, 11.0 mg), PhCO2Na (0.8 mmol), PhMe (1.0 mL), 110
e
°C, 12 h. Ni(cod)2 (20 mol %, 11.2 mg), IMesMe (22 mol %, 14.6
mg), 120 °C, 12 h.
bearing a methyl group exhibited credible reactivity and
furnished the targeted borylation product smoothly (1b).
Although sodium benzoate was used as the base, substrate
bearing an ester group at the naphthyl ring also exhibited
credible reactivity (1c).15 We also investigated the reactivity of
N-(1-naphthyl)pyrrole 1d. In general, 1-naphthyl derivatives
B
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with free N−H bond (1m and 1n) were unable to furnish the
borylation products.
Scheme 5. Proposed Mechanism for the Nickel-Catalyzed
Borylation of Tertiary aniline
In order to extend the substrate scope of the borylation of
tertiary anilines, we further examined the reactivity of various
N-arylmorpholines (Scheme 3). Borylation of N-naphthylmor-
pholines was conducted, and the targeted products were
obtained in moderate to good yields (1o, 1p, and 1q). It is
noteworthy that the THP-protected alcohol could be tolerated
under the borylation conditions (1p). The other π-extended
aromatic substrate was also examined, and the desired product
was obtained in moderate yield (1r). To our delight, non-π-
extended aromatic substrates also proved suitable substrates in
the modified catalytic borylation system, and the targeted
products were obtained in moderate to high yield (1s−w). For
example, substrates with phenyl- or electron-withdrawing
groups (CF3) at different positions exhibited high reactivity
(1s, 1t and 1v). For the simple N-arylmorpholines 1u and 1w,
the desired products were also isolated in acceptable yields.
To demonstrate the potential application of this borylation
system, we conducted experiments to discriminate between
different aromatic C−N bonds in one molecule (Scheme 4a).
preorganization of this intermediate, both the borylation
product and (nep)BNMe2 were formed simultaneously via a
five-membered intramolecular transition state. The succeeding
product release and the coordination of 1,5-cyclooctadiene led
to the regeneration of the initial catalyst.20
Scheme 4. Cascade Activation of Different Aromatic C−X
a
Bonds via Transition-Metal Catalysis
In summary, we demonstrated the first borylation protocol of
unactivated aromatic C−N bonds of tertiary anilines and N-
arylpyrroles via nickel catalysis. Both π-extended aromatic and
non-π-extended aromatic N-arylpyrroles were transformed into
the desired products. Moreover, the direct borylation of N,N-
dialkylarylamines was conducted, and the targeted products
were obtained in acceptable yields in the absence of any
additives. The method showed alternatives to extend the N-
based electrophiles in transition-metal-catalyzed cross-coupling
reactions. Density functional theory calculations were con-
ducted and provided insight into the catalytic cycle of tertiary
aniline to aryl boronate transformation. Efforts to extend the
substrate scope and improve the efficiency of the C−N
borylation are underway.
a
Reaction conditions: HBpin (2.0 equiv), Ni(cod)2 (20 mol %), PCy3
b
(40 mol %), toluene, 80 °C, 36 h. Conditions as in Scheme 3.
c
Reaction conditions: Pd(OAc)2 (10.0 mol %), p-OMePhB(OH)2 (1.5
equiv), Na2CO3 (2.0 equiv), acetone/H2O (3:3.5), 50 °C, 3 h.
d
Reaction conditions: Ni(cod)2 (10 mol %), PCy3 (40 mol %),
MeMgI (2.0 equiv), PhMe, 110 °C, 3 h. [N] = 4-morpholinyl.
Product 1n was furnished in 82% yield via nickel-catalyzed
reductive cleavage of the first C−N bond of compound 3,
which could be further borylated to give 2a through the
cleavage of the second C−N bond. Furthermore, we conducted
the cascade activation of C−Br, C−O, and C−N bond at
different stages to produce the functionalized molecules. For
example, we prepared the compound 5 via palladium-catalyzed
Suzuki−Miyaura cross-coupling of 4 and then conducted the
Kumada coupling of 5 with Grignard reagent to furnish 6.
Compound 6 was submitted to the catalytic borylation of C−N
bond to offer 2m in 67% yield (Scheme 4b).
On the basis of our observations and DFT calculations (see
details in the Supporting Information), the catalytic borylation
of C−N bonds, taking N,N-dimethyl-2-naphthylamine 1h as
the example, was envisioned to proceed via the steps illustrated
in Scheme 5. The whole process was triggered by the
coordination of N,N-dimethyl-2-naphthylamine 1h to the
Ni(0) metal center via ligand exchange. After the oxidative
addition of a C−N bond to the Ni center, B2nep2 could
coordinate to the −NMe2 group. The B−B bond in B2nep2 was
activated during the coordination, and the uncoordinated B
atom was oriented to the naphthyl group as a result of the steric
hindrance of the carbene ligand. As a benefit of the
ASSOCIATED CONTENT
* Supporting Information
■
S
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.or-
glett.8b00545.
General methods, analytical data for the products,
spectral data (PDF)
AUTHOR INFORMATION
Corresponding Authors
■
*E-mail: zjshi@fudan.edu.cn, zshi@pku.edu.cn.
*E-mail: hfang@fudan.edu.cn.
ORCID
Huayi Fang: 0000-0002-8008-0383
Zhang-Jie Shi: 0000-0002-0919-752X
Author Contributions
∥Z.-C.C. and X.-L.L. contributed equally.
Notes
The authors declare no competing financial interest.
C
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(13) (a) Glorius, F. N-Heterocyclic Carbenes in Transition Metal
Catalysis; Springer, 2007; Vol. 21. (b) Nolan, S. P. N-Heterocyclic
ACKNOWLEDGMENTS
■
Support of this work by the “973” Project from the MOST
(2015CB856600) and NSFC (Nos. 21332001 and 21431008)
is gratefully acknowledged.
Carbenes in Synthesis; John Wiley & Sons, 2006. (c) Díez-Gonzal
́
ez, S.;
Marion, N.; Nolan, S. P. Chem. Rev. 2009, 109, 3612.
(14) (a) Hirano, K.; Urban, S.; Wang, C.; Glorius, F. Org. Lett. 2009,
11, 1019. (b) Michalska, M.; Grela, K. Synlett 2016, 27, 599.
(c) Morioka, T.; Nishizawa, A.; Furukawa, T.; Tobisu, M.; Chatani, N.
J. Am. Chem. Soc. 2017, 139, 1416.
(15) Pu, X. H.; Hu, J. F.; Zhao, Y.; Shi, Z. Z. ACS Catal. 2016, 6,
6692.
(16) The modified conditions used in the borylation of tertiary
anilines, 35 mol % IMesMe was used as the ligand. The extra amount of
NHC ligand is beneficial to the regeneration of catalyst and may play a
role in activating the diboron reagent nucleophilically; see: Wu, H.;
Garcia, J. M.; Haeffner, F.; Radomkit, S.; Zhugralin, A. R.; Hoveyda, A.
H. J. Am. Chem. Soc. 2015, 137, 10585.
(17) Kakiuchi, F.; Usui, M.; Ueno, S.; Chatani, N.; Murai, S. J. Am.
Chem. Soc. 2004, 126, 2706.
(18) Hie, L.; Fine Nathel, N. F.; Shah, T. K.; Baker, E. L.; Hong, X.;
Yang, Y.-F.; Liu, P.; Houk, K. N.; Garg, N. K. Nature 2015, 524, 79.
(19) Chen, Y. H.; Ellwart, M.; Toupalas, G.; Ebe, Y.; Knochel, P.
Angew. Chem., Int. Ed. 2017, 56, 4612.
(20) The typical mechanism of transition-metal-catalyzed Miyaura
borylation consisting of oxidative addition, transmetalation, and
reductive elimination was also considered during the DFT calculation,
while the four-membered cyclic transition state in transmetalation is
unable to form due to the steric hindrance of diboron reagent and
IMesMe ligand. Although DFT calculation of transmetalation with
diboron reagent was reported, the experimentally used diboron
reagent and ligand were replaced by the diboron reagent and ligand
with smaller steric repulsion in these works; see: (a) Sumimoto, M.;
Iwane, N.; Takahama, T.; Sakaki, S. J. Am. Chem. Soc. 2004, 126,
10457. (b) Kleeberg, C.; Cheung, M. S.; Lin, Z.; Marder, T. B. J. Am.
Chem. Soc. 2011, 133, 19060. (c) Zhao, H.; Dang, L.; Marder, T. B.;
Lin, Z. J. Am. Chem. Soc. 2008, 130, 5586. (d) Dang, L.; Zhao, H.; Lin,
Z.; Marder, T. B. Organometallics 2008, 27, 1178. (e) Dang, L.; Lin, Z.;
Marder, T. B. Organometallics 2008, 27, 4443. (f) Dang, L.; Zhao, H.;
Lin, Z.; Marder, T. B. Organometallics 2007, 26, 2824.
REFERENCES
■
(1) (a) Luo, Y.-R. Handbook of Bond Dissociation Energies in Organic
Compounds. CRC Press, 2002. (b) Smith, M. B.; March, J. March’s
Advanced Organic Chemistry: Reactions, Mechanisms, and Structure; John
Wiley & Sons, 2007. (c) Carey, F. A.; Sundberg, R. J. Advanced Organic
Chemistry: Part A: Structure and Mechanisms; Springer Science &
Business Media, 2007. (d) Hartwig, J. F. Organotransition Metal
Chemistry: From Bonding to Catalysis; Univ Science Books, 2010.
(e) Crabtree, R. H. The Organometallic Chemistry of the Transition
Metals; John Wiley & Sons, 2009.
(2) (a) Ouyang, K.; Hao, W.; Zhang, W.-X.; Xi, Z. Chem. Rev. 2015,
115, 12045. (b) Wang, Q.; Su, Y.; Li, L.; Huang, H. Chem. Soc. Rev.
2016, 45, 1257.
(3) (a) Saeki, T.; Son, E.-C.; Tamao, K. Org. Lett. 2004, 6, 617.
(b) Zhu, M.-K.; Zhao, J.-F.; Loh, T.-P. Org. Lett. 2011, 13, 6308.
(c) Bai, Y.; Kim, L. M. H.; Liao, H.; Liu, X.-W. J. Org. Chem. 2013, 78,
8821. (d) Chen, Y.; Guo, S.; Li, K.; Qu, J.; Yuan, H.; Hua, Q.; Chen, B.
Adv. Synth. Catal. 2013, 355, 711. (e) Liu, J.-B.; Yan, H.; Chen, H.-X.;
Luo, Y.; Weng, J.; Lu, G. Chem. Commun. 2013, 49, 5268. (f) Peng, Z.;
Hu, G.; Qiao, H.; Xu, P.; Gao, Y.; Zhao, Y. J. Org. Chem. 2014, 79,
2733. (g) Xu, W.; Hu, G.; Xu, P.; Gao, Y.; Yin, Y.; Zhao, Y. Adv. Synth.
Catal. 2014, 356, 2948. (h) Yao, P. Appl. Organomet. Chem. 2014, 28,
194. (i) Zhou, H.-P.; Liu, J.-B.; Yuan, J.-J.; Peng, Y.-Y. RSC Adv. 2014,
4, 25576. (j) Liu, J.; Robins, M. J. Org. Lett. 2004, 6, 3421.
(4) (a) Akiyama, F.; Miyazaki, H.; Kaneda, K.; Teranishi, S.; Fujiwara,
Y.; Abe, M.; Taniguchi, H. J. Org. Chem. 1980, 45, 2359. (b) Akiyama,
F.; Teranishi, S.; Fujiwara, Y.; Taniguchi, H. J. Organomet. Chem. 1977,
140, C7. (c) Wenkert, E.; Han, A.-L.; Jenny, C.-J. J. Chem. Soc., Chem.
Commun. 1988, 975. (d) Blakey, S. B.; MacMillan, D. W. J. Am. Chem.
Soc. 2003, 125, 6046. (e) Reeves, J. T.; Fandrick, D. R.; Tan, Z.; Song,
J. J.; Lee, H.; Yee, N. K.; Senanayake, C. H. Org. Lett. 2010, 12, 4388.
(f) Xie, L.-G.; Wang, Z.-X. Angew. Chem., Int. Ed. 2011, 50, 4901.
(g) Guo, W.-J.; Wang, Z.-X. Tetrahedron 2013, 69, 9580. (h) Zhang,
X.-Q.; Wang, Z.-X. J. Org. Chem. 2012, 77, 3658. (i) Maity, P.;
Shacklady-McAtee, D. M.; Yap, G. P.; Sirianni, E. R.; Watson, M. P. J.
Am. Chem. Soc. 2013, 135, 280. (j) Moragas, T.; Gaydou, M.; Martin,
R. Angew. Chem., Int. Ed. 2016, 55, 5053.
(5) Tobisu, M.; Nakamura, K.; Chatani, N. J. Am. Chem. Soc. 2014,
136, 5587.
(6) (a) Markgraf, J. H.; Stickney, C. A. J. Heterocycl. Chem. 2000, 37,
109. (b) Rao, H.; Muthanna, N. Synlett 2016, 27, 2014.
(7) (a) Ueno, S.; Chatani, N.; Kakiuchi, F. J. Am. Chem. Soc. 2007,
129, 6098. (b) Koreeda, T.; Kochi, T.; Kakiuchi, F. J. Am. Chem. Soc.
2009, 131, 7238. (c) Koreeda, T.; Kochi, T.; Kakiuchi, F. J. Organomet.
Chem. 2013, 741−742, 148. (d) Koreeda, T.; Kochi, T.; Kakiuchi, F.
Organometallics 2013, 32, 682.
(8) Cong, X.; Fan, F.; Ma, P.; Luo, M.; Chen, H.; Zeng, X. J. Am.
Chem. Soc. 2017, 139, 15182.
(9) Bonanno, J. B.; Henry, T. P.; Neithamer, D. R.; Wolczanski, P. T.;
Lobkovsky, E. B. J. Am. Chem. Soc. 1996, 118, 5132.
(10) (a) Tollefson, E. J.; Hanna, L. E.; Jarvo, E. R. Acc. Chem. Res.
2015, 48, 2344. (b) Tobisu, M.; Chatani, N. Acc. Chem. Res. 2015, 48,
1717. (c) Rosen, B. M.; Quasdorf, K. W.; Wilson, D. A.; Zhang, N.;
Resmerita, A.-M.; Garg, N. K.; Percec, V. Chem. Rev. 2011, 111, 1346.
(d) Cornella, J.; Zarate, C.; Martin, R. Chem. Soc. Rev. 2014, 43, 8081.
(e) Yu, D.-G.; Li, B.-J.; Shi, Z.-J. Acc. Chem. Res. 2010, 43, 1486. (f) Li,
B.-J.; Yu, D.-G.; Sun, C.-L.; Shi, Z.-J. Chem. - Eur. J. 2011, 17, 1728.
(g) Su, B.; Cao, Z.-C.; Shi, Z.-J. Acc. Chem. Res. 2015, 48, 886.
(11) (a) Miyaura, N.; Suzuki, A. Chem. Rev. 1995, 95, 2457. (b) Hall,
D. G. Boronic Acids: Preparation, Applications in Organic Synthesis and
Medicine; John Wiley & Sons, 2006.
(12) During the borylation of N-arylpyrroles, the aromaticity of
leaving group may be benfinecial for the C−N bond cleavage.
D
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