Cu-Catalyzed Stereoselective Borylation of gem-Difluoroalkenes with B2pin2

Article abstract of DOI:10.1021/acs.orglett.7b01430

A novel and efficient method for the synthesis of (Z)-fluorinated alkenylboronic acid pinacol esters via Cu-catalyzed stereoselective borylation of gem-difluoroalkenes using bis(pinacolato)diboron (B₂pin₂) as the boron source with the assistance of NaOtBu and Xantphos at room temperature was developed.

Full text of DOI:10.1021/acs.orglett.7b01430

Letter
pubs.acs.org/OrgLett
Cu-Catalyzed Stereoselective Borylation of gem-Difluoroalkenes with
B2pin2
Juan Zhang, Wenpeng Dai, Qingyun Liu, and Song Cao*
Shanghai Key Laboratory of Chemical Biology, School of Pharmacy, East China University of Science and Technology (ECUST),
Shanghai 200237, China
S
* Supporting Information
ABSTRACT: A novel and efficient method for the synthesis of
(Z)-fluorinated alkenylboronic acid pinacol esters via Cu-catalyzed
stereoselective borylation of gem-difluoroalkenes using bis-
(pinacolato)diboron (B2pin2) as the boron source with the
assistance of NaOtBu and Xantphos at room temperature was developed.
rganoboronic acid and their derivatives, especially
alkenylboronic esters, are important and versatile reagents
obtained (Scheme 1a).11 In 2015, the group of Martin described
the Ni-catalyzed borylation of monofluoroarenes with B2nep2 via
O
in organic synthesis because of their high stability, low toxicity,
and great synthetic utility in the Suzuki−Miyaura coupling
reaction.1 Consequently, considerable attention has been
devoted to the development of novel and efficient methods for
the synthesis of vinylboronate esters (VBEs).2 Traditional
methods for the synthesis of alkenylboronic esters involve the
transmetalation of 1-alkenyllithium or Grignard reagents with
trialkylborates.3 Transition-metal-catalyzed hydroboration of
alkynes is one of the most efficient and straightforward methods
to access a variety of alkenylboron compounds.4 Alternatively,
rhodium- or iridium-catalyzed direct C−H dehydrogenative
borylation of alkenes represents an attractive approach due to its
atom and step economy.5 In addition, a palladium-catalyzed
cross-coupling reaction of bis(pinacolato)diboron (B2pin2, pin =
Me4C2O2) with alkenyl halides or triflates provides a convenient
and alternative method for the preparation of alkenylboronic
esters.6 However, attempts by Miyaura and Ishiyama to borylate
dihaloalkenes such as 2,2-dibromo-1-phenylethene with B2pin2
in the presence of PdCl2(PPh3)2 and Ph3P were unsuccessful.6a
Interestingly, when 1,1-dibromoalkenes reacted with B2pin2 with
the assistance of n-butyllithium at −110 °C, 1,1-diborylalkenes
were obtained.7 It should be noted that when an alkenyl halide
containing both an alkene C−F and C−Br bond such as (Z)-(2-
bromo-2-fluorovinyl)benzene was used as a substrate, the
borylation reaction took place selectively at the C−Br bond
and the C−F bond remained intact.8
The cleavage, activation, and functionalization of the carbon−
fluorine bond have received considerable attention in recent
years because they offer unique methods for synthesis of
structurally diverse molecules from fluoroorganic compounds.9
The transition-metal-catalyzed borylation of the inert C−F bond
in polyfluorinated alkenes and arenes is of particular interest to
the synthetic community due to the ability of borylated products
to be readily converted into the fluorinated amine, alcohol, alkyl,
and aryl functionalities.10 In 2015, Zhang et al. disclosed the first
example of an ortho-selective C−F bond borylation of
polyfluoroarenes with commercially available [Rh(cod)2]BF4 as
a catalyst, and a wide range of borylated fluoroarenes were
Scheme 1. C−F Bond Borylation of Fluoroarenes and
Fluoroalkenes
C−F activation (Scheme 1b).12 Almost at the same time, the
group of Niwa and Hosoya independently developed an efficient
method for the synthesis of various borylarenes by the Ni/Cu-
catalyzed borylation of monofluoroarenes with B2pin2 (Scheme
1c).13 In 2016, Marder and Radius et al. reported an alternative
method for the C−F borylation of polyfluoroarenes using
Ni(IMes)2 as a catalyst and B2pin2 as the boron source (Scheme
1d).14 Unfortunately, to date, examples regarding the trans-
formation of alkenyl fluorides into alkenylboronic acid pinacol
esters are very scarce. The first and only example of C−F bond
borylation of fluorinated olefin was described by Braun and co-
workers in 2009. They found that hexafluoropropene can be
coupled with HBpin in the presence of 0.4 mol % RhH(PEt3)3
and a mixture of 2-fluoroalkyl-1,3,2-dioxaborolanes was obtained
in quantitative yields (Scheme 1e).15
Received: May 11, 2017
Published: June 5, 2017
© 2017 American Chemical Society
3283
DOI: 10.1021/acs.orglett.7b01430
Org. Lett. 2017, 19, 3283−3286

Organic Letters
Letter
It is well-known that gem-difluoroalkenes exhibit excellent
reactivity toward nucleophiles due to their highly electron-
deficient nature of carbon−carbon double bond and the high
leaving-group ability of the fluoride ion.16 Although gem-
difluoroalkenes could react readily with strong nucleophiles
such as nitrogen, oxygen, and sulfur nucleophiles through an
addition−elimination process (SNV reaction),17 the cross-
coupling reaction of gem-difluoroalkenes with organometallic
reagents such as Grignard reagents,18 organozinc reagents,19
organosilicon reagents,20 and arylboronic acids21 requires the use
of a catalytic amount of transition-metal catalyst to activate the
carbon−fluorine bond. Even though the intermolecular
activation of bis(pinacolato)diboron can generate a reactive
nucleophilic boryl B(sp2) synthon,22 the borylation of
fluoroalkenes with B2pin2 remains an extremely attractive but
challenging subject for organic chemists due to the attenuated
nucleophilicity of the boryl moiety. In continuation of our
research on the functionalization of the C−F bond of gem-
difluoroalkenes,23 in this letter, we reported a novel and efficient
method for the synthesis of (Z)-fluorinated alkenylboronic acid
pinacol esters via Cu-catalyzed stereoselective borylation of gem-
difluoroalkenes with B2pin2 in the presence of NaOtBu and
Xantphos at room temperature (Scheme 1f).
in the absence of a copper catalyst (entry 1). When cupric salts
such as Cu(OAc)2 were used as catalyst, the reaction did not
proceed at all. Xantphos is a preferred ligand compared to other
common ligands such as dppe, dppf, dppb, PPh3, PCy3, and
DPEphos (entries 6 and 8−13). Notably, the reaction has proven
to be ineffective without addition of ligand, as only 43% of the
borylated product was obtained (entry 7). Further screening of
different bases revealed that only NaOtBu could afford the
desired product 3a in optimal yield (entries 6 and 14−17).
Solvent played an important role in this transformation. DMF
was the most suitable solvent for the reaction (entry 6). Other
solvents such as THF, MeOH, CH3CN, toluene, and DMAc (N,
N-dimethylacetamide) all resulted in no reaction or low
efficiency (entries 18−22). To our delight, this borylation
reaction occurred with high (Z)-selectivity and no (E)-isomer
was detected.
With the optimal reaction conditions in hand (Table 1, entry
6), the scope of this Cu(OAc)-catalyzed borylation of various
gem-difluoroalkenes was investigated (Scheme 2). In most cases,
Scheme 2. Reactions of gem-Difluoroalkenes 1a−t with
a
B2pin2
We began our investigation using the borylation of 1-(2,2-
difluorovinyl)-4-methoxybenzene 1a with bis(pinacolato)-dibor-
on B2pin2 2 as the model reaction to optimize the reaction
conditions (Table 1). Initially, the borylation reaction was
performed in the presence of various cuprous compounds.
Among the copper(I) salts examined, CuCN and Cu(OAc)
turned out to be the most effective, providing 3a in 81% yields
(entries 2−6). Expectedly, no detectable product was observed
a
Table 1. Optimization of the Reaction Conditions
b
entry
Cu salt
none
ligand
base
solvent
yield (%)
1
Xantphos
Xantphos
Xantphos
Xantphos
Xantphos
Xantphos
none
NaOtBu
NaOtBu
NaOtBu
NaOtBu
NaOtBu
NaOtBu
NaOtBu
NaOtBu
NaOtBu
NaOtBu
NaOtBu
NaOtBu
NaOtBu
CsF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
THF
0
2
CuI
trace
trace
60
3
CuBr
4
CuCl
5
CuCN
81
6
Cu(OAc)
Cu(OAc)
Cu(OAc)
Cu(OAc)
Cu(OAc)
Cu(OAc)
Cu(OAc)
Cu(OAc)
Cu(OAc)
Cu(OAc)
Cu(OAc)
Cu(OAc)
Cu(OAc)
Cu(OAc)
Cu(OAc)
Cu(OAc)
Cu(OAc)
81
a
7
43
Reaction conditions: 1a−t (1.0 mmol), 2 (1.2 mmol), Cu(OAc) (0.1
mmol), Xantphos (0.1 mmol), NaOtBu (2.0 mmol), DMF (6 mL), 25
°C, 6−12 h, Ar. Isolated yields. The configuration of the (Z)-isomer
3a−t was determined by its JH−F coupling constant in the H NMR
spectra (ca. 46.0 Hz for (Z)-isomer and 16.0 Hz for (E)-isomer).
8
dppe
16
9
dppf
20
3
1
10
11
12
13
14
15
16
17
18
19
20
21
22
dppb
23
PPh3
18
PCy3
25
this novel borylation reaction proceeded efficiently to give the
corresponding (Z)-fluorinated alkenyl boronates in moderate to
good yields and no (E)-isomers were observed. gem-Difluor-
oalkenes having a strong electron-donating group on the
benzene ring proceeded smoothly, whereas a substrate bearing
a strong electron-withdrawing group such as cyano failed to give
the desired product. Substituents, such as methylthio (1f),
acetoxy (1l), chloro (1m−o), bromo (1p and 1t), and iodo (1q)
groups, were tolerated under the optimized reaction conditions.
The tolerance of chloride, bromide, and iodide substituents was
particularly useful, which offers the opportunity for further
modifications. When the aryl ring of the substrates was changed
to naphthalene or thiophene, the reactions could also provide the
DPEphos
Xantphos
Xantphos
Xantphos
Xantphos
Xantphos
Xantphos
Xantphos
Xantphos
Xantphos
40
trace
trace
53
NaOMe
KOtBu
LiOtBu
NaOtBu
NaOtBu
NaOtBu
NaOtBu
NaOtBu
65
trace
0
MeOH
toluene
CH3CN
DMAc
0
0
60
a
Reaction conditions: 1a (0.2 mmol), 2 (0.24 mmol), solvent (3 mL),
b
6 h. Yields determined by GC analysis and based on 1a.
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DOI: 10.1021/acs.orglett.7b01430
Org. Lett. 2017, 19, 3283−3286

Organic Letters
Letter
borylation products in modest yields (3r and 3t). In addition,
(E)-(4,4-difluorobuta-1,3-dien-1-yl)benzene was a suitable sub-
strate for this reaction, the corresponding product (3s) being
obtained in moderate yield. Unfortunately, when 1,1-diaryl-2,2-
difluoroethenes, gem-dibromoalkenes, and gem-dichloroalkenes
were used as substrates under the optimal reaction conditions,
only a trace amount of borylated products was detected.
Furthermore, when (4,4-difluorobut-3-en-1-yl)benzene was
subjected to this borylation reaction, a small amount of a
mixture of E/Z-borylated product was observed (GC-MS).
The activation and functionalization of the C−F bond of
monofluoroalkenes remain a largely unexplored area. Generally,
monofluorinated alkenes are much less reactive in the addition−
elimination reaction than gem-difluoroalkenes. Encouraged by
the above results obtained with the gem-difluoroalkenes, we next
applied the Cu-catalyzed borylation process to examine some
monofluoroalkenes (Scheme 3). Much to our surprise, the
Scheme 4. Derivatization of (Z)-3a
gem-difluoroalkenes (for detailed experimental procedures and
characterization of products, see the Supporting Information).
Based on the above observations and previous reports,24 the
mechanism for the Cu-Catalyzed stereoselective borylation of
gem-difluoroalkenes with B2pin2 is proposed (Scheme 5).
Scheme 3. Reactions of Vinyl Monofluorides 1u−x with
a
B2pin2
Scheme 5. Proposed Reaction Mechanism
a
Reaction conditions: 1u−x (1.0 mmol), 2 (1.2 mmol), Cu(OAc) (0.1
mmol), Xantphos (0.1 mmol), NaOtBu (2.0 mmol), DMF (6 mL), 25
°C, 3−6 h, Ar. Isolated yields. The configuration of the (E)-isomer
3u−x was determined by its JH−H coupling constant in the H NMR
spectra (ca. 16.0 Hz for (Z)-isomer and 18.0 Hz for (E)-isomer).
3
1
borylation of a mixture of E/Z-monofluoroalkenes (1u−x) under
the same conditions afforded the (E)-isomers (3u−x)
exclusively. No unreacted (Z)-monofluoroalkene starting
materials and (Z)-borylated products were observed. Notably,
the borylation of pure (Z)-1-(2-fluorovinyl)-4-methoxybenzene
1u alone also gave (E)-borylated product 3u, though a longer
reaction time was required to complete the reaction (12 h).
These results therefore suggested that carbon−carbon double
bond cleavage might be involved in the reaction.
The novel pure (Z)-fluorinated pinacol alkenylboronates we
reported here are expected to be highly useful and versatile
building blocks in organic synthesis due to the unique reactivity
of the boryl moiety. To demonstrate the synthetic utility of (Z)-
β-fluorinated vinylboronates, we converted pure (Z)-3a into
other valuable β-fluorostyrene derivatives using established
chemistry (Scheme 4). We were delighted to find that these
derivatization reactions proceeded smoothly and afforded the
corresponding (Z)- or (E)-fluorinated olefins in moderate to
good yields with complete retention of configuration of the
double bond. No obvious isomerization was observed. One of
the remarkable advantages of this method is that it provides
direct and facile access to expensive and not readily available
isomerically pure mixed-halogen alkenes ((E)-5−7). More
importantly, the C−F bond of (E)-7 and (Z)-11 could also be
transformed into a C−N bond ((E)-12) and C−C bond ((E)-
13) through an addition−elimination process and coupling
reaction, respectively, despite the lower reactivity of the C−F
bond of monofluoroalkenes compared with the C−F bond in
Initially, transmetalation of the phosphine-ligated copper catalyst
LCuOtBu, which is generated in situ from LCu(OAc) and
NaOtBu, with the diboron reagent B2pin2 provides nucleophilic
phosphine-coordinated Cu(I)-boryl complexes LCu−Bpin.
Subsequently, insertion of a difluoroalkene into the Cu−B
bond of borylcopper complex would lead to the generation of β-
borylalkyl copper species I. Rotation of the key intermediate I by
60° results in the formation of two conformations, II and III.
The intermediate III was relatively unstable due to steric
repulsion between the bulky boryl group and the aryl group. β-
Fluoride elimination of borylalkyl copper intermediate II affords
the desired pure (Z)-fluorinated pinacol alkenylboronate along
with LCuF. Finally, LCuF further reacts with B2pin2 and NaOtBu
to regenerate the active catalyst LCu−Bpin and finish the
catalytic cycle.
In summary, we have developed an efficient and practical
method for the synthesis of (Z)-fluorinated alkenylboronic acid
pinacol esters via Cu-catalyzed stereoselective borylation of gem-
difluoroalkenes with B2pin2 in the presence of NaOtBu and
Xantphos at room temperature. The borylation reaction exhibits
a wide substrate scope and good functional group compatibility
and affords a variety of (Z)-fluorinated borylation products in
moderate to good yields. Specifically, the borylation of
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DOI: 10.1021/acs.orglett.7b01430
Org. Lett. 2017, 19, 3283−3286

Organic Letters
Letter
(5) (a) Sasaki, I.; Taguchi, J.; Doi, H.; Ito, H.; Ishiyama, T. Chem. -
Asian J. 2016, 11, 1400. (b) Coapes, R. B.; Souza, F. E. S.; Thomas, R. L.;
Hall, J. J.; Marder, T. B. Chem. Commun. 2003, 614. (c) Mkhalid, I. A.;
Coapes, R. B.; Edes, S. N.; Coventry, D. N.; Souza, F. E.; Thomas, R. L.;
Hall, J. J.; Bi, S. W.; Lin, Z.; Marder, T. B. Dalton Trans. 2008, 1055.
(d) Hu, T. J.; Zhang, G.; Chen, Y.-H.; Feng, C.-G.; Lin, G.-Q. J. Am.
monofluoroalkenes also proceeds smoothly and furnishes the
geometrically pure (E)-borylated alkenes only, irrespective of the
configuration (E or Z) of the starting monofluoroalkenes. To
demonstrate the synthetic utility of the valuable fluorinated and
borylated building blocks obtained by the present method,
derivatizations of the product pure (Z)-3a using the boryl group,
such as protodeboronation, halogenation, and Suzuki−Miyaura
coupling, were conducted. Delightfully, (Z)-configuration of a
borylation product such as 3a can be retained completely in these
transformations and a range of versatile geometrically pure
multisubstituted alkenes were obtained. This method has
allowed convenient access to the novel (Z)-fluorinated
alkenylboronic acid pinacol esters, which are anticipated to be
a powerful synthetic module for the construction of isomerically
pure β-fluorostyrene derivatives.
́
Chem. Soc. 2016, 138, 2897. (e) Olsson, V. J.; Szabo, K. J. Org. Lett. 2008,
10, 3129. (f) Kondoh, A.; Jamison, T. F. Chem. Commun. 2010, 46, 907.
(6) (a) Takagi, J.; Takahashi, K.; Ishiyama, T.; Miyaura, N. J. Am. Chem.
Soc. 2002, 124, 8001. (b) Takahashi, K.; Takagi, J.; Ishiyama, T.;
́
Miyaura, N. Chem. Lett. 2000, 29, 126. (c) Euzenat, L.; Horhant, D.;
Brielles, C.; Alcaraz, G.; Vaultier, M. J. Organomet. Chem. 2005, 690,
2721. (d) Billingsley, K. L.; Buchwald, S. L. J. Org. Chem. 2008, 73, 5589.
(e) Murata, M.; Oyama, T.; Watanabe, S.; Masuda, Y. Synthesis 2000,
778.
(7) Hata, T.; Kitagawa, H.; Masai, H.; Kurahashi, T.; Shimizu, M.;
Hiyama, T. Angew. Chem., Int. Ed. 2001, 40, 790.
(8) Eddarir, S.; Rolando, C. J. Fluorine Chem. 2004, 125, 377.
(9) (a) Ahrens, T.; Kohlmann, J.; Ahrens, M.; Braun, T. Chem. Rev.
2015, 115, 931. (b) Amii, H.; Uneyama, K. Chem. Rev. 2009, 109, 2119.
(c) Shen, Q.; Huang, Y.-G.; Liu, C.; Xiao, J.-C.; Chen, Q.-Y.; Guo, Y. J.
Fluorine Chem. 2015, 179, 14.
ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.orglett.7b01430.
■
S
(10) (a) Crimmin, M. R.; Chen, W.; Bakewell, C. Synthesis 2017, 49,
810. (b) Kubota, K.; Iwamoto, H.; Ito, H. Org. Biomol. Chem. 2017, 15,
Experimental details and spectral data for all products
(PDF)
285. (c) Kallane, S. I.; Teltewskoi, M.; Braun, T.; Braun, B.
̈
Organometallics 2015, 34, 1156. (d) Teltewskoi, M.; Panetier, J. A.;
Macgregor, S. A.; Braun, T. Angew. Chem., Int. Ed. 2010, 49, 3947.
(e) Lindup, R. J.; Marder, T. B.; Perutz, R. N.; Whitwood, A. C. Chem.
Commun. 2007, 3664. (f) Chen, K.; Cheung, M.-S.; Lin, Z.; Li, P. Org.
Chem. Front. 2016, 3, 875.
(11) Guo, W.; Min, Q.; Gu, J.; Zhang, X. Angew. Chem., Int. Ed. 2015,
54, 9075.
(12) Liu, X.-W.; Echavarren, J.; Zarate, C.; Martin, R. J. Am. Chem. Soc.
2015, 137, 12470.
(13) Niwa, T.; Ochiai, H.; Watanabe, Y.; Hosoya, T. J. Am. Chem. Soc.
2015, 137, 14313.
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: scao@ecust.edu.cn.
ORCID
Song Cao: 0000-0002-3231-6136
Notes
The authors declare no competing financial interest.
(14) Zhou, J.; Kuntze-Fechner, M. W.; Bertermann, R.; Paul, U. S. D.;
Berthel, J. H. J.; Friedrich, A.; Du, Z.; Marder, T. B.; Radius, U. J. Am.
Chem. Soc. 2016, 138, 5250.
ACKNOWLEDGMENTS
■
We are grateful for financial support from the National Natural
Science Foundation of China (Grant Nos. 21472043 and
21272070).
(15) Braun, T.; Salomon, M. A.; Altenhoner, K.; Teltewskoi, M.;
̈
Hinze, S. Angew. Chem., Int. Ed. 2009, 48, 1818.
(16) (a) Ichikawa, J.; Wada, Y.; Fujiwara, M.; Sakoda, K. Synthesis 2002,
1917. (b) Zhang, X.; Cao, S. Tetrahedron Lett. 2017, 58, 375.
(17) (a) Fuchibe, K.; Takahashi, M.; Ichikawa, J. Angew. Chem., Int. Ed.
2012, 51, 12059. (b) Huang, X.-H.; He, P.-Y.; Shi, G.-Q. J. Org. Chem.
2000, 65, 627. (c) Kim, M. S.; Jeong, I. H. Tetrahedron Lett. 2005, 46,
3545. (d) Strobach, D. R. J. Org. Chem. 1971, 36, 1438.
(18) Dai, W.; Xiao, J.; Jin, G.; Wu, J.; Cao, S. J. Org. Chem. 2014, 79,
10537.
REFERENCES
■
(1) (a) Schmidt, J.; Choi, J.; Liu, A. T.; Slusarczyk, M.; Fu, G. C. Science
2016, 354, 1265. (b) Kischkewitz, M.; Okamoto, K.; Muck-Lichtenfeld,
C.; Studer, A. Science 2017, 355, 936. (c) Yun, J. Asian J. Org. Chem.
2013, 2, 1016. (d) Semba, K.; Fujihara, T.; Terao, J.; Tsuji, Y.
Tetrahedron 2015, 71, 2183. (e) Yamamoto, E.; Ukigai, S.; Ito, H. Chem.
Sci. 2015, 6, 2943. (f) Cuenca, A. B.; Shishido, R.; Ito, H.; Fernan
Chem. Soc. Rev. 2017, 46, 415.
(2) (a) Wang, C.; Wu, C.; Ge, S. ACS Catal. 2016, 6, 7585. (b) Takaya,
J.; Kirai, N.; Iwasawa, N. J. Am. Chem. Soc. 2011, 133, 12980. (c) Yeung,
K.; Ruscoe, R. E.; Rae, J.; Pulis, A. P.; Procter, D. J. Angew. Chem., Int. Ed.
̈
́
dez, E.
(19) Ohashi, M.; Kambara, T.; Hatanaka, T.; Saijo, H.; Doi, R.; Ogoshi,
S. J. Am. Chem. Soc. 2011, 133, 3256.
(20) Saijo, H.; Sakaguchi, H.; Ohashi, M.; Ogoshi, S. Organometallics
2014, 33, 3669.
(21) (a) Thornbury, R. T.; Toste, F. D. Angew. Chem., Int. Ed. 2016, 55,
11629. (b) Ohashi, M.; Saijo, H.; Shibata, M.; Ogoshi, S. Eur. J. Org.
Chem. 2013, 443.
2016, 55, 11912. (d) Qiu, Y.; Yang, B.; Zhu, C.; Backvall, J. E. Angew.
̈
Chem., Int. Ed. 2016, 55, 6520. (e) Yang, F.; Cheng, C. J. Am. Chem. Soc.
2001, 123, 761. (f) Kurahashi, T.; Hata, T.; Masai, H.; Kitagawa, H.;
Shimizu, M.; Hiyama, T. Tetrahedron 2002, 58, 6381. (g) Krautwald, S.;
Bezdek, M. J.; Chirik, P. J. J. Am. Chem. Soc. 2017, 139, 3868.
(3) Suzuki, A. In Boronic Acids: Preparation and Applications in Organic
Synthesis and Medicine; Hall, D. G., Ed.; Wiley-VCH: Weinheim,
Germany, 2005; p 123.
(4) (a) Krautwald, S.; Bezdek, M. J.; Chirik, P. J. J. Am. Chem. Soc. 2017,
139, 3868. (b) Bismuto, A.; Thomas, S. P.; Cowley, M. J. Angew. Chem.,
Int. Ed. 2016, 55, 15356. (c) Feng, Q.; Yang, K.; Song, Q. Chem.
(22) (a) Cid, J.; Carbo,
́
J. J.; Fernan
́
dez, E. Chem. - Eur. J. 2012, 18,
12794. (b) Cid, J.; Gulyas
́
, H.; Carbo, J. J.; Fernan
́
́
dez, E. Chem. Soc. Rev.
2012, 41, 3558. (c) Liu, S.; Zeng, X.; Xu, B. Tetrahedron Lett. 2016, 57,
3706.
(23) (a) Zhang, X.; Dai, W.; Wu, W.; Cao, S. Org. Lett. 2015, 17, 2708.
(b) Zhang, J.; Xu, C.; Wu, W.; Cao, S. Chem. - Eur. J. 2016, 22, 9902.
(c) Dai, W.; Shi, H.; Zhao, X.; Cao, S. Org. Lett. 2016, 18, 4284.
(24) (a) Smith, K. B.; Logan, K. M.; You, W.; Brown, M. K. Chem. - Eur.
J. 2014, 20, 12032. (b) Xu, Z.; Jiang, Y.; Su, W.; Yu, H.; Fu, Y. Chem. -
Eur. J. 2016, 22, 14611. (c) Lee, J.-E.; Kwon, J.; Yun, J. Chem. Commun.
2008, 733. (d) Ito, H.; Kawakami, C.; Sawamura, M. J. Am. Chem. Soc.
2005, 127, 16034.
́
Commun. 2015, 51, 15394. (d) Alfaro, R.; Parra, A.; Aleman, J.; García
Ruano, J. L.; Tortosa, M. J. Am. Chem. Soc. 2012, 134, 15165. (e) Itoh,
T.; Shimizu, Y.; Kanai, M. J. Am. Chem. Soc. 2016, 138, 7528. (f) Xu, S.;
Zhang, Y.; Li, B.; Liu, S.-Y. J. Am. Chem. Soc. 2016, 138, 14566. (g) Ojha,
D. P.; Prabhu, K. R. Org. Lett. 2016, 18, 432.
3286
DOI: 10.1021/acs.orglett.7b01430
Org. Lett. 2017, 19, 3283−3286