Photoinduced Radical Borylation of Alkyl Bromides Catalyzed by 4-Phenylpyridine

Article abstract of DOI:10.1002/anie.201912564

Utilizing pyridine catalysis, we developed a visible-light-induced transition-metal-free radical borylation reaction of unactivated alkyl bromides that features a broad substrate scope and mild reaction conditions. Mechanistic studies revealed a novel nucleophilic substitution/photoinduced radical formation pathway, which could be utilized to trigger a variety of radical processes.

Full text of DOI:10.1002/anie.201912564

A Journal of the Gesellschaft Deutscher Chemiker
Angewandte
Chemie
International Edition
www.angewandte.org
Accepted Article
Title: Photoinduced Radical Borylation of Alkyl Bromides Catalyzed by
4-Phenylpyridine
Authors: Li Zhang, Zhong-Qian Wu, and Lei Jiao
This manuscript has been accepted after peer review and appears as an
Accepted Article online prior to editing, proofing, and formal publication
of the final Version of Record (VoR). This work is currently citable by
using the Digital Object Identifier (DOI) given below. The VoR will be
published online in Early View as soon as possible and may be different
to this Accepted Article as a result of editing. Readers should obtain
the VoR from the journal website shown below when it is published
to ensure accuracy of information. The authors are responsible for the
content of this Accepted Article.
To be cited as: Angew. Chem. Int. Ed. 10.1002/anie.201912564
Angew. Chem. 10.1002/ange.201912564
Link to VoR: http://dx.doi.org/10.1002/anie.201912564
http://dx.doi.org/10.1002/ange.201912564

10.1002/anie.201912564
Angewandte Chemie International Edition
COMMUNICATION
Photoinduced Radical Borylation of Alkyl Bromides Catalyzed by
4-Phenylpyridine
Li Zhang, Zhong-Qian Wu, and Lei Jiao*
Dedication ((optional))
Abstract: Utilizing pyridine catalysis, we developed a visible-light-
induced transition-metal-free radical borylation reaction of unactivated
alkyl bromides featuring a broad substrate scope and mild reaction
conditions. Mechanistic study disclosed
a novel nucleophilic
substitution/photoinduced radical formation pathway, which could be
utilized to trigger a variety of radical processes.
Alkylboronates are highly versatile intermediates in organic
synthesis, because the C-B bond could undergo diverse
transformations to forge a range of C-C, C-N, C-O, and C-X
bonds.[ 1 , 2 ] Due to this appealing feature, efficient synthetic
approaches to alkylboronates are consistantly pursued in the
organic community. Although alkylboronate syntheses from alkyl
halides utilizing transition-metal catalysis (Pd, Cu, Ni, Zn, Fe, and
Mn) have been well established (Scheme 1a),[3] practical methods
that enable the preparation of alkylboronates in a transition-metal-
free manner remain highly desirable. In this context, the groups of
Aggarwal,[4a,5a] Li,[4b] Shi,[5b] Glorius,[5c] and Studer[6] developed a
series of radical-type borylation reactions employing redox-active
esters, Katritzky’s pyridinium salts, and xanthates/oxalates as the
alkyl sources to produce alkylboronates without using a transition-
metal catalyst.
Scheme 1. Approaches to alkyl halide borylation.
Interestingly, as a most prevalent and readily available alkyl
source, alkyl halides have not been utilized in these reactions until
very recently. The Studer group reported a metal-free radical
borylation of alkyl iodides under visible-light irradiation,[7a,b] the Mo
group realized a t-BuOLi-promoted radical borylation of alkyl
iodides,[7c] and the Melchiorre group achieved a photoinduced
borylation of benzyl and allyl halides[7d]. However, in these reports,
more reactive alkyl halides should be employed (Scheme 1b), and
the transition-metal-free borylation of unactivated alkyl bromides
has not been achieved to date. Given that the transformation of
an alkyl bromide to the corresponding alkyl radical is much more
difficult than that of an alkyl iodide,[8] a new activation mode might
be required to tackle this challenge. Herein, we report an efficient
visible-light-induced radical borylation of alkyl bromides catalyzed
by 4-phenylpyridine (1), which features a broad substrate scope
and a novel reaction mechanism (Scheme 1c).
Studer group,[7a] only trace amount of the borylation product 3a
was observed (entry 1). Attempts to circumvent the reactivity
problem of alkyl bromide by the addition of NaI was
unsuccessful,[9] which prompted us to search for a new path to
alkyl bromide activation. Inspired by our previous finding that the
combination of 4-phenylpyridine (1) and diboron(4) exhibited
unique activities in the activation of aryl halides,[10] we sought to
test whether pyridine 1 could also enable the activation of this
alkyl bromide. It was found that, upon addition of a catalytic
amount of 1, the yield of 3a increased slightly (entry 2).
Gratifyingly, with the addition of both 1 and excess MeONa as the
base, a dramatic increase in the yield of 3a was observed (entry
3). Further study identified MeCN as the optimal solvent (entries
4-8). Control experiments demonstrated the essential role of
visible light, the base, and the pyridine catalyst in the reaction
(entries 9-11). Other bases, such as MeOK, Et3N, and DBU, were
found to be inferior (entries 12-14).
Our initial study started with the attempts on the borylation of
secondary alkyl bromide 2a with bis(catecholato)diboron (B2cat2)
(Table 1). Under the photochemical conditions developed by the
[*]
L. Zhang, Z.-Q. Wu, Prof. Dr. L. Jiao
Center of Basic Molecular Science (CBMS)
Department of Chemistry, Tsinghua University
Beijing 100084 (China)
E-mail: Leijiao@mail.tsinghua.edu.cn
Supporting information for this article is given via a link at the end of
the document.
This article is protected by copyright. All rights reserved.

10.1002/anie.201912564
Angewandte Chemie International Edition
COMMUNICATION
Table 1. Optimization of reaction conditions.[a]
Table 2. Borylation of alkyl bromides.[a]
[a] Reaction conditions: 2a (0.5 mmol, 1 equiv.), 1 (20 mol%), B2cat2 (3.0 equiv.),
base (3.0 equiv.) in 1 mL of solvent, Ar atmosphere, 10 W 400 nm LED, rt, 12
h; then pinacol (4 equiv.), Et3N (1 mL), rt, 1 h. [b] Determined by gas
chromatography (GC). [c] 4.0 equiv. of B2cat2 was used. [d] Yield of isolated
product. DMF = N,N’-dimethylformamide; DMAc = N,N’-dimethylacetamide;
MTBE
= methyl tert-butyl ether; DMSO = dimethylsulfoxide; THF =
tetrahydrofuran.
With the optimized reaction conditions in hand, the substrate
scope of this borylation reaction was tested. In general, the
reaction exhibited a broad substrate scope and good functional
group tolerance (Table 2). A series of secondary alkyl bromides,
both acyclic and cyclic, produced corresponding alkylboronates in
good yields (3a-h). Oxygen- and nitrogen-containing heterocycles
were tolerated under the reaction conditions (3f-g). Interestingly,
tertiary alkyl bromide 2i also underwent the borylation reaction
smoothly to produce tertiary alkylboronate 3i in a good yield, albeit
other tertiary alkyl bromides were not compatible, probably due to
the base-promoted elimination.
The present protocol was also suitable for efficient borylation of
primary alkyl bromides (3j-3aa). In particular, the borylation
occurred selectively on the alkyl C-Br bond in the presence of a
haloaryl group (3m-n), despite that the pyridine/diboron/base
system was able to activate haloarenes.[10a,c] A range of functional
groups, such as heterocycle (3p), acetal (3t), ether (3u-v), silyl
ether (3w), perfluoroalkyl (3x), amide (3z), and ester (3aa), were
tolerated in the borylation reaction. Bromochloroalkane 2y
underwent selective monoborylation to produce 3y, leaving the
chloroalkyl moiety intact. The practical syntheses of
alkylboronates 3a, 3d, and 3y were performed on gram scales
using the B2cat2 directly prepared from B2(OH)4 and catechol,[11]
and similarly good yields were obtained.
[a] Reaction conditions: 2 (0.5 mmol, 1 equiv.), 1 (20 mol%), B2cat2 (3.0 equiv.),
MeONa (3.0 equiv.), 1 mL CH3CN, Ar atmosphere, 10 W 400 nm LED, rt, 12 h;
then pinacol (4 equiv.), Et3N (1 mL), rt, 1 h. Yields of isolated products are
reported. [b] Reaction time: 24 h. [c] With 5% arylboronate.
found that, under the standard conditions, both (1R)- and (1S)-
menthyl bromide (2ab and 2ac) were transformed to the same
alkylboronate 3ab (Scheme 2a), indicating the intermediacy of a
planar intermediate with loss of stereochemical information at the
reaction center. When cyclopropylmethylbromide (2ad) was
employed as the substrate, the ring-opened borylation product
3ad was observed, which implied a radical ring-opening reaction
converting the cyclopropylmethyl radical to homoallylic radical
(Scheme 2b).[12] To figure out whether the C-B bond formation
event involves an alkyl radical, competition experiments were
performed by addition of varied amounts of a hydrogen atom
donor, dihydroanthracene (DHA), to the borylation reaction of 2a
(Scheme 2c). In the presence of DHA, dehalogenation product 4a
was produced together with the borylation product 3a, and the
ratio of 4a:3a exhibited a linear correlation with [DHA]. This
In the following study, we focused on elucidating the detailed
reaction mechanism of the borylation process that enables
efficient activation of alkyl bromides. First, we set out to probe
whether or not the reaction proceeds via a radical pathway. It was
This article is protected by copyright. All rights reserved.

10.1002/anie.201912564
Angewandte Chemie International Edition
COMMUNICATION
observation indicated that the alkyl bromide forms the
corresponding alkyl radical, which is either terminated by DHA via
hydrogen atom transfer (HAT) to produce 4a, or trapped by the
diboron reagent to produce 3a. Therefore, the above
experimental results confirmed the radical nature of the borylation
reaction.
Scheme 3. Investigation into the 1/B2cat2/MeONa system.
Next we sought to disclose the role of these complexes in alkyl
radical formation. Because the preparation of pure Int-A or Int-B
using the 1/B2cat2/MeONa system was difficult, we employed ate
complex 6, which only differed in the boryl moiety and could be
easily prepared in its pure form,[10b] to investigate the interaction
between alkyl bromide 2a and the electron-donating complex. To
our surprise, the expected direct photoinduced SET did not occur,
and a nucleophilic substitution reaction between complex 6 and
bromide 2a to afford 4-alkyl 1,4-DHP derivative 7 was observed
both with and without photoirradiation (Scheme 4). The structure
of 7 was confirmed by converting to its N-benzoyl derivative 8 and
corresponding spectroscopic analysis. These results revealed
that complexes Int-A and Int-B are not only electron donors, but
also strong nucleophiles, which was not realized in the previous
studies.[15]
Scheme 2. Probing the radical nature of the borylation reaction.
The following task was to figure out the mechanism of alkyl
radical formation from alkyl bromides. Our previous study on the
reaction between pyridine 1, bis(pinacolato)diboron (B2pin2), and
MeONa disclosed the formation of ate complex Int-B (Scheme 3),
which resembled a masked form of N-boryl pyridyl anion Int-A
and served as a super electron donor (SED) at both ground state
and excited state.[10] We speculated that, in the 1/B2cat2/MeONa
system, similar complexes might also form and act as SED to
activate the alkyl bromide by photoinduced single electron
transfer (SET).
Scheme 4. The reaction between SED complex and the alkyl bromide.
To confirm this hypothesis, NMR spectroscopic analysis was
performed on the 1/B2cat2/MeONa system. However, in contrast
to the previous reaction system employing B2pin2, a messy H
1
This interesting observation prompted us a new reaction
pathway alternative to the photoinduced SET. Previous studies
have established that, 4-alkyl Hantzsch ester could produce alkyl
radical under photoirradiation conditions.[16] We envisioned that,
NMR spectrum with a number of dearomatized pyridyl signals was
obtained, making the identification of intermediates difficult.
Nevertheless, trapping experiments provided a clue to solve this
problem. By performing the reaction between 1, diboron, and
MeONa in the presence of excess MeOD, we observed the
formation of deuterated 1,4-dihydropyridine (DHP) derivative 5,
the protonated product of Int-A, with both B2pin2 and B2cat2
(Scheme 3). This served as an evidence to support the generation
of Int-A- or Int-B-type intermediates in the 1/B2cat2/MeONa
system. The observation of multiple species in the NMR spectrum
might be attributed to the labile nature of the B-O bond in the
catecholatoboryl moiety.[13,14]
intermediate
7
might also produce alkyl radical upon
photoexcitation, due to its structural similarity to 4-alkyl Hantzsch
esters. It was found that, when intermediate 7 was irradiated by a
400 nm LED for 12 h, a minor amount of the expected C-C
cleavage/HAT product 4a was detected (Scheme 5, eq. 1). In the
presence of MeONa as a base, the yield of 4a increased slightly
(Scheme 5, eq. 2). This indicated that, photoinduced alkyl radical
generation from 4-alkyl DHP derivative 7 was possible, albeit in a
low efficiency. Interestingly, upon addition of 1 equiv. of alkyl
bromide 2a, the yield of 4a increased to 73% relative to 1 equiv.
This article is protected by copyright. All rights reserved.

10.1002/anie.201912564
Angewandte Chemie International Edition
COMMUNICATION
of 7 (Scheme 5, eq. 3), suggesting that intermediate 7 was able
to promote the formation of radical from alkyl bromide. A
crossover experiment employing 7 and 2-adamantyl bromide (2h),
together with DHA-d4 as a radical trapping reagent, afforded a low
yield of 4a together with a reasonable yield of adamatane 4h, both
with significant deuterium incorporation (Scheme 5, eq. 4). This
indicated that, in the presence of base, intermediate 7 could
undergo both direct radical formation (led to 4a) and photoinduced
SET to an external alkyl bromide (led to 4h), with the latter being
a major pathway in the radical borylation process. Successful
trapping of the generated alkyl radical by B2cat2 to afford
alkylboronate 3a supported the above mechanistic interpretation
(Scheme 5, eq. 5).
Scheme 6. Proposed reaction mechanism.
We reasoned that, borylation of primary and secondary alkyl
bromides mainly proceeds via this SN2/photoinduced radical
formation pathway. However, the direct photoinduced SET
between Int-A/Int-B and the alkyl bromide was not completely
excluded.[ 18 ] The fact that tertiary alkyl bromide 2i, which
disfavored nucleophilic substitution, exhibited a similarly good
reactivity implied the existence of direct photoinduced SET
pathway for specific alkyl bromide substrates.
This mechanism is able to trigger a variety of other radical
processes. Using B2pin2 instead of B2cat2 to minimize radical
borylation, and adding 1,4-cyclohexadiene (1,4-CHD) to
terminate the radical intermediate by HAT, dehalogenation,
intermolecular radical addition, and intramolecular radical
cyclization reactions of alkyl bromides have been realized (Table
3). Alkyl bromides 2j and 2h produced 4j and 4h smoothly. Alkyl
radicals generated from 2a and 2j were trapped by styrenes to
afford coupling products 9a and 9j, respectively. Alkyl bromides
2ae-ah bearing an alkene moiety were transformed to cyclization
products 10ae-ah in good yields. These results highlighted the
generality and synthetic potential of the present radical generation
protocol.
Scheme 5. Control experiments employing intermediate 7.
At this stage, a reaction mechanism could be proposed based
on the nucheophilic substitution/radical formation process
disclosed above (Scheme 6).[7d,17] First, pyridine 1, diboron, and
methoxide forms complexes Int-A and Int-B, which are
nucleophilic and undergo a SN2 reaction with the alkyl bromide to
generate 4-alkyl 1,4-DHP Int-C. Since the experimental results
showed that complex 7 reacted with the alkyl bromide in the
presence of MeONa to produce alkyl radical under
photoirradiation, we proposed that methoxide and Int-C first react
to afford Int-D, which is more electron-rich and thus undergoes
photoinduced SET to the alkyl bromide. This process leads to the
formation of the corresponding alkyl radical and radical
intermediate Int-E, which produces alkyl radical via a facile C-C
bond homolytic cleavage, together with the re-aromatization of
the pyridine core. The produced alkyl radical was trapped by
diboron to produce the alkylboronate product.[4-7]
In conclusion, a visible-light-induced organocatalytic borylation
reaction of alkyl halides was developed. This reaction features
broad substrate scope and intriguing mechanism. A key discovery
is that the SED complexes in the pyridine/diboron/base system is
not only electron-donating, but also nucleophilic. Activation of
unreactive alkyl bromides was made possible by
a
SN2/photoinduced radical formation pathway. Further studies on
the nucleophilic reaction patterns of these SED complexes are
undergoing in our lab.
This article is protected by copyright. All rights reserved.

10.1002/anie.201912564
Angewandte Chemie International Edition
COMMUNICATION
Table 3. Radical reactions triggered by the present reaction system.[a]
[a] Reaction conditions: 2 (0.5 mmol, 1 equiv.), 1 (20 mol%), B2pin2 (3.0 equiv.),
MeONa (3.0 equiv.), 1,4-CHD (3.0 equiv.), 1 mL THF, Ar atmosphere, 10 W 400
nm LED, rt. Yields of isolated products are reported. [b] GC yields are reported.
[c] 2.0 equiv. of 1,1-diphenylethylene was used. [d] 2.0 equiv. of styrene was
used.
Acknowledgements
The National Natural Science Foundation of China (Grant Nos.
21772110 and 21822304) is acknowledged for financial support.
Keywords: organocatalysis • photochemistry • borylation •
radical reaction • alkylboronates
This article is protected by copyright. All rights reserved.

10.1002/anie.201912564
Angewandte Chemie International Edition
COMMUNICATION
[1] Boronic Acids: Preparation and Applications in Organic Synthesis,
Medicine and Materials (Ed: D. G. Hall), 2nd ed., Wiley-VCH: Weinheim,
2011.
[11] The dehydration reaction between B2(OH)4 and catechol was only
reported in the following patent: Q. Liu, F. Sun, X. Wang, Z. Gao, Faming
Zhuanli Shengqing, CN 102718787 A 20121010, 2012.
[2] A. Suzuki, Acc. Chem. Res. 1982, 15, 178. (b) N. Miyaura, A. Suzuki,
Chem. Rev. 1995, 95, 2457. (c) Metal-Catalyzed Cross-Coupling
Reactions (Ed: A. D. Meijere), 2nd ed., Wiley-VCH: Weinheim, 2004.
[3] For selected examples of Cu-catalyzed borylation, see: a) C.-T. Yang, Z.-
Q. Zhang, H. Tajuddin, C.-C. Wu, J. Liang, J.-H. Liu, Y.Fu, M. Czyzewska,
P. G. Steel, T. B. Marder, L. Liu, Angew. Chem. Int. Ed. 2012, 51, 528;
Angew. Chem. 2012, 124, 543; b) H. Ito, K. Kubota, Org. Lett. 2012, 14,
890; For selected examples of Ni-catalyzed borylation, see: c) A. S.
Dudnik, G. C. Fu, J. Am. Chem. Soc. 2012, 134, 10693; d) J. Yi, J.-H. Liu,
J. Liang, J.-J. Dai, C.-T. Yang, Y. Fu, L. Liu, Adv. Synth. Catal. 2012, 354,
1685; For selected example of Zn-catalyzed borylation, see: e) S. K. Bose,
K. Fucke, L. Liu, P. G. Steel, T. B. Marder, Angew. Chem. Int. Ed. 2014,
53, 1799; Angew. Chem. 2014, 126, 1829; For selected example of Fe-
catalyzed borylation, see: f) T. C. Atack, S. P. Cook, J. Am. Chem. Soc.
2014, 136, 9521; For selected example of Mn-catalyzed borylation, see:
g) T. C. Atack, S. P. Cook, J. Am. Chem. Soc. 2016, 138, 6139.
[4] a) A. Fawcett, J. Pradeilles, Y. Wang, T. Mutsuga, E. L. Myers, V. K.
Aggarwal, Science 2017, 357, 283; b) D. Hu, L. Wang, P. Li, Org. Lett.
2017, 19, 2770.
[12] M. Newcomb, A. G. Glenn, J. Am. Chem. Soc. 1989, 111, 275.
[13] H. Braunschweig, A. Damme, R. D. Dewhurst, T. Kramer, T. Kupfer, K.
Radacki, E. Siedler, A. Trumpp, K. Wagner, C. Werner, J. Am. Chem. Soc.
2013, 135, 8702.
[14] I. A. Cade, W. Y. Chau, I. Vitorica-Yrezabal, M. J. Ingleson, Dalton Trans.
2015, 44, 7506.
[15] For the nucleophilic substitution reaction of α-boryl anion, see: a) K. Hong,
X. Liu, J. P. Morken, J. Am. Chem. Soc. 2014, 136, 10581; For the
nucleophilic substitution reaction of β-boryl anion, see: b) A. Bonet, C.
Pubill-Ulldemolins, C. Bo, H. Gulyás and E. Fernández, Angew. Chem.,
Int. Ed. 2011, 50, 7158; c) C. Pubill-Ulldemolins, A. Bonet, C. Bo, H.
Gulyás and E. Fernández, Chem. -Eur. J. 2012, 18, 1121; d) T. P. Blaisdell,
T. C. Caya, L. Zhang, A. Sanz-Marco and J. P. Morken, J. Am. Chem. Soc.
2014, 136, 9264; e) L. Fang, L. Yan, F. Haeffner and J. P. Morken, J. Am.
Chem. Soc. 2016, 138, 2508.
[16] For a review, see: a) W. Huang, X. Cheng, Synlett 2017, 28, 148; for
examples of 4-alkyl-1,4-dihydropyridines serving as radical precursors
under the action of external photoredox catalysts, see: b) K. Nakajima, S.
Nojima, K. Sakata, Y. Nishibayashi, ChemCatChem 2016, 8, 1028; c) A
Gutiꢁrrez-Bonet, J. C. Tellis, J. K. Matsui, B. A. Vara, G. A. Molander, ACS
Catal. 2016, 6, 8004; d) W. Chen, Z. Liu, J. Tian, J. Ma, X. Cheng, G. Li,
J. Am. Chem. Soc. 2016, 138, 12312; e) K. Nakajima, S. Nojima, Y.
Nishibayashi, Angew. Chem. Int. Ed. 2016, 55, 14106; Angew. Chem.
2016, 128, 14312; for examples of 4-alkyl-1,4-dihydropyridines serving as
radical precursors under the action of a stoichiometric oxidant, see: f) A
Gutiꢁrrez-Bonet, C. Remeur, J. K. Matsui, G. A. Molander, J. Am. Chem.
Soc. 2017, 139, 12251; for examples of 4-alkyl-1,4-dihydropyridines
serving as radical precursors under direct photoirradiation, see: (g) L.
Buzzetti, A. Prieto, S. R. Roy, P. Melchiorre, Angew. Chem. Int. Ed. 2017,
56, 15039; Angew. Chem. 2017, 129, 15235.
[5] a) J. Wu, L. He, A. Noble, V. K. Aggarwal, J. Am. Chem. Soc. 2018, 140,
10700; b) J. Hu, G. Wang, S. Li, Z. Shi, Angew. Chem. Int. Ed. 2018, 57,
15227; Angew. Chem. 2018, 130, 15477; c) F. Sandfort, F. Strieth-Kalthoff,
F. Klauck, M. James, F. Glorius, Chem. Eur. J. 2018, 24, 17210.
[6] F. W. Friese, A. Studer, Angew. Chem. Int. Ed. 2019, 58, 9561; Angew.
Chem. 2019, 131, 9661.
[7] a) Y. Cheng, C. Mꢀck-Lichtenfeld, A. Studer, J. Am. Chem. Soc. 2018,
140, 6221; b) Y. Cheng, C. Mꢀck-Lichtenfeld, A. Studer, Angew. Chem.
Int. Ed. 2018, 57, 16832; Angew. Chem. 2018, 130, 17074; [c] Q. Liu, J.
Hong, B. Sun, G. Bai, F. Li, G. Liu, Y. Yang, F. Mo, Org. Lett. 2019, 21,
6597; [d] D. Mazzarella, G. Magagnano, B. Schweitzer-Chaput, P.
Melchiorre, ACS Catal. 2019, 9, 5876.
[17] For an example demonstrating generation of alkyl radical utilizing
nucleophilic substitution strategy, see: B. Schweitzer-Chaput, M. A.
Horwitz, E. de Pedro Beato, P. Melchiorre, Nat. Chem. 2019, 11, 129.
[18] The reduction potential the complex 6 is -1.11 V vs Fc+/0 and reduction
potential the excited state complex 6 is -3.87 V vs Fc+/0, which allows for
SET reduction of most alkyl halides, see: J. M. Savéant, J. Am. Chem.
Soc. 1992, 114, 10595.
[8] D. J. Carlsson, K. U. Ingold, J. Am. Chem. Soc. 1968, 90, 7047.
[9] With the addition of 20 mol% and 1 equiv. of NaI to the reaction described
in entry 1 of Table 1, the borylation product 3a was obtained in 11% and
25% GC yields, respectively.
[10] a) L. Zhang, L. Jiao, J. Am. Chem. Soc. 2017, 139, 607; b) L. Zhang, L.
Jiao, Chem. Sci. 2018, 9, 2711; c) L. Zhang, L. Jiao, J. Am. Chem. Soc.
2019, 141, 9124.
This article is protected by copyright. All rights reserved.