Decarboxylative Borylation of Aliphatic Esters under Visible-Light Photoredox Conditions

Article abstract of DOI:10.1021/acs.orglett.7b01181

The conventional methods for preparing alkyl boronates often necessitate anhydrous and demanding reaction conditions. Herein, a new, operationally simple decarboxylative borylation reaction of readily available aliphatic acid derivatives under additive-free visible-light photoredox conditions in nonanhydrous solvents has been described. Primary and secondary alkyl boronates or tetrafluoroborates with various functional groups were prepared accordingly. A catalytic cycle involving alkyl radical reaction with base-activated diboron species has been proposed.

Full text of DOI:10.1021/acs.orglett.7b01181

Letter
pubs.acs.org/OrgLett
Decarboxylative Borylation of Aliphatic Esters under Visible-Light
Photoredox Conditions
Dawei Hu, Linghua Wang, and Pengfei Li*
Frontier Institute of Science and Technology, Xi’an Jiaotong University, Xi’an, Shaanxi 710054, China
S
* Supporting Information
ABSTRACT: The conventional methods for preparing alkyl
boronates often necessitate anhydrous and demanding reaction
conditions. Herein, a new, operationally simple decarboxylative
borylation reaction of readily available aliphatic acid derivatives
under additive-free visible-light photoredox conditions in
nonanhydrous solvents has been described. Primary and secondary alkyl boronates or tetrafluoroborates with various functional
groups were prepared accordingly. A catalytic cycle involving alkyl radical reaction with base-activated diboron species has been
proposed.
lkylboron compounds represent an important class of
reagents in organic synthesis of bioactive molecules and
decarboxylative C−C bond formation reactions under both
visible-light photoredox conditions and non-photochemical
conditions.19 The decarboxylative reactions were initiated by a
single-electron reduction process of N-acyloxyphthalimides,
which is different from most oxidizing decarboxylative reactions.
Therefore, we hypothesized that N-hydroxyphthalimides might
be amenable to generation of organoboron compounds.
A
functional materials.1 The most common methods to access
alkylboranes or boronates include transmetalation from highly
reactive organolithium or organomagnesium2 and the hydro-
boration of olefins.3 β-Borylation is another effective method but
largely limited to α,β-unsaturated carbonyls.4 Transition-metal-
catalyzed direct C−H borylation of alkanes has also been
reported for terminal methyl groups of simple alkanes or with
certain directing groups.5 A more general approach has been the
Miyaura borylation-type reaction of alkyl (pseudo)halides,6 and
to date, several effective catalyst systems based on Pd,7 Ni,8 Cu,9
Zn,10 and Fe11 have been reported. Although these methods have
been successful, they usually require strictly anhydrous
conditions, and many of them are incompatible with highly
polar or protic groups.
To test our hypothesis, we used N-acyloxyphthalimide 1a as a
model substrate and tetrahydroxydiboron B2(OH)417a,18a as the
borylating reagent to screen various reaction parameters under
visible-light photoredox conditions (Table 1). After extensive
experimentation, we found that a simple parameter combination
could already provide satisfactory results. Thus, a solution of 1a
and B2(OH)4 (4.0 equiv) in DMF (c[1a] = 0.3 M) together with
the catalyst [Ir(ppy)2dtbpy]PF6 (1 mol %) was placed in a glass
test tube and irradiated with a 45 W compact fluorescent lamp
(CFL, maximum at 465 nm) at room temperature for 12 h. NMR
analysis of the crude product indicated formation of the expected
boronic acid in 85% yield. After treatment with aqueous KHF2 to
facilitate the isolation, the expected alkyltrifluoroborates 2a was
isolated in 83% yield by filtration (entry 1). Remarkably, different
from many other visible light photoredox decarboxylative
reactions, no sacrificial additives were needed to regenerate the
active catalyst.19f−i This reaction did not require anhydrous
solvent, but addition of more water led to lower yields of 2a
(entries 2 and 3). Other solvents were inferior (entries 4 and 5).
Using a higher concentration (entry 6) or less B2(OH)2 (entry 7)
all led to lower yields. In all cases, the main side product was the
decarboxylation/hydrogenation product. Lastly, no reaction
occurred in the absence of light or the catalyst.
Aliphatic carboxylic acids are abundant and inexpensive basic
chemicals. Reactions involving a decarboxylative process and an
ensuing C−X bond formation process would produce various
functionalized aliphatic compounds.12 Indeed, since the
discovery of Hunsdiecker halogenation, many other decarbox-
ylative reactions have been disclosed, including fluorination,13
(hetero)arylation,14 and addition reactions.15 In sharp contrast,
however, the synthetically versatile C−B bond has not been
introduced in the same vein.16 The key challenge might be the
incompatibility between the reducing property of organo-
boranes17 and most oxidizing reaction conditions that are
necessary for inducing decarboxylation.
Recently, our group and the Larionov group have
independently discovered that aryl halides can react with
diboron reagents to form aryl boronate compounds under UV
light irradiation.18 The mechanistic studies revealed that highly
reactive aryl radicals were involved. Based on these observations,
we were interested in the possibility of making alkyl boronates via
alkyl radicals that may be generated from readily available
aliphatic acid derivatives.
We then moved on to examine the scope of this new
decarboxylative borylation reaction, and the results are
summarized in Scheme 1. Overall, both secondary and primary
carboxylic acid derived N-acyloxyphthalimides could smoothly
N-Acyloxyphthalimides can be prepared from the acids and N-
hydroxyphthalimide in one step and have been used for
Received: April 19, 2017
© XXXX American Chemical Society
A
DOI: 10.1021/acs.orglett.7b01181
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
decarboxylative borylation of the dehydrocholic acid derivative
successfully provided the corresponding product 2o in 67% yield.
To explore further the usefulness of the decarboxylative
borylation, we also examined bis(pinacolato)diboron (B2pin2) as
the borylating reagent. However, we did not succeed with
secondary carboxylic acid derivatives such as 1a. Only a small
amount (less than 10%) of the expected boronate could be
observed, and the mass balance was mostly the corresponding
hydrogenated product. In contrast, primary carboxylic acid
derived N-acyloxyphthalimide 1m14,16 was a viable substrate and
converted to the desired boronate 3m. Thus, a solution of 1m,
B2pin2, and the catalyst in DMF (c[1m] = 0.1 M) was irradiated
for 16 h, and 3a was formed in 41% yield on the basis of the 1H
NMR analysis of the crude product (Table 2, entry 1).
Table 1. Reaction Optimization of the Decarboxylative
Borylation with Tetrahydroxydiboron
a
c
entry
conditions
DMF (0.3 M)
yield (%)
d
1
2
3
4
5
6
85 (83 )
DMF/H2O = 10:1 (0.3 M)
DMF/H2O = 4:1 (0.3 M)
MeCN (0.3 M)
76
69
47
MeOH (0.3 M)
11
DMF (0.4 M)
60
Table 2. Reaction Optimization of the Decarboxylative
b
a
7
DMF (0.3 M)
60
Borylation with Bis(pinacolato)diboron B2pin2
8
9
DMF (0.3 M), dark
DMF (0.3 M), no catalyst
NR
NR
a
Reaction conditions: N-acyloxyphthalimide 1 (0.6 mmol), B2(OH)4
(2.4 mmol), [Ir(ppy)2(dtbpy)]PF6 (0.006 mmol) in solvent (2 mL)
b
d
was irradiated with a 45 W CFL for 12 h. 3.0 equiv of B2(OH)4 was
entry
solvent
concn (M)
NMR yield (%)
c
used. Yields of the intermediate boronic acids determined by crude
1
2
3
4
5
6
7
DMF
0.1
0.1
0.1
0.1
0.1
0.2
0.3
0.3
0.3
41
37
54
58
62
69
86
61
34
1H NMR with 1,3,5-trimethoxybenzene as an internal standard.
MeCN
d
Isolated yield of the tetrafluoroborate. NR: no reaction.
DMF/H2O = 1:1
MeCN/H2O = 1:1
Scheme 1. Substrate Scope of the Decarboxylative Borylation
a
DMF/MeCN/H2O = 1:1:1
DMF/MeCN/H2O = 1:1:1
DMF/MeCN/H2O = 1:1:1
DMF/MeCN/H2O = 1:1:1
DMF/MeCN/H2O = 1:1:1
with Tetrahydroxydiboron
b
8
c
9
a
Reaction conditions: N-acyloxyphthalimide 1 (0.3 mmol), B2pin2 (1.2
b
mmol), [Ir(ppy)2(dtbpy)]PF6 (0.003 mmol), 45 W CFL, 16 h. 3.0
c
d
equiv of B2pin2 used. 2.0 equiv of DMAP added. Determined by 1H
NMR with 1,3,5-trimethoxybenzene as an internal standard.
Acetonitrile as the solvent led to slightly lower yield (entry 2).
Screening various solvent combinations revealed that a ternary
solvent mixture could improve the yield to 62% (entries 3−5).
Increasing the concentration of 1m from 0.1 to 0.3 M further
improved the yield to 86% by decreasing the hydrogenated side
product (entries 6 and 7). By comparison, decreasing the
equivalents of B2pin2 led to an inferior result (entry 8). Finally,
various amines or pyridine-based additives were not helpful. For
example, addition of 2 equiv of DMAP led to significantly lower
yield (entry 9).
With the above optimized conditions in hand, we examined
the substrate scope of this reaction with B2pin2, as summarized in
Scheme 2. Primary N-acyloxyphthalimides with various electron-
donating, electron-neutral, and electron-withdrawing groups
were all efficiently converted to the corresponding alkyl pinacol
boronates in good to excellent yields. A (Z)-double bond in oleic
acid (3f) or a terminal alkyne (3j) could be tolerated, which is
interesting considering that the reaction might involve a reactive
carbon-centered radical. An aryl bromide (3e) and an alkyl
chloride (3g) also survived, demonstrating the orthogonal
reactivity of this reaction with previous alkyl metallic reagents-
based or metal-catalyzed borylation of halides. Again, dehy-
drocholic acid was successfully used in the reaction, providing a
highly functionalized alkyl boronate 3o.
a
Reaction conditions: N-acyloxyphthalimide 1 (0.6 mmol), B2(OH)4
(2.4 mmol), [Ir(ppy)2dtbpy]PF6 (0.006 mmol) in 2 mL of DMF, 45
W CFL for 12 h.
undergo decarboxylative borylation to afford the corresponding
alkyl tetrafluoroborates in moderate to good yields without
changing the standard conditions. Tertiary carboxylic acid
derived N-acyloxyphthalimides, however, led to only decarbox-
ylation/hydrogenation product. A variety of functional groups,
including ester (2b, 2m), ketone (2e, 2o), carbamate (2a, 2c),
and ether (2h) were well tolerated. The mild reaction conditions
and excellent functional group compatibility allowed the late-
stage borylation of complex molecules. For example, the
Stimulated by the success of aliphatic decarboxylative
borylation, we also tested an aryl acid-derived N-acyloxyph-
thalimide 1k. Under similar conditions, however, the expected
B
DOI: 10.1021/acs.orglett.7b01181
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
Scheme 2. Substrate Scope of the Decarboxylative Borylation
with Bis(pinacolato)diboron B2pin2
Scheme 4. Proposed Mechanism of Decarboxylative
Borylation
a
presence of water, the weakly basic 7 may generate hydroxide
that can react with a diboron reagent B2X4 to generate a sp3−sp2
diboron species (9).18a,21−23 Alkyl radical 8 then reacts with 9 to
form the desired product alkyl boronate 10 and concomitantly
boryl radical anion 11.18a Finally, the Ir(IV) species was reduced
by 11 to regenerate catalyst Ir(III) to complete the catalytic cycle.
In summary, we have developed a new method to prepare alkyl
boronates from readily available carboxylic acids via a novel
visible-light photoredox decarboxylative borylation reaction.
This reaction is operationally simple, works under mild reaction
conditions, and tolerates nonanhydrous solvents and polar
functional groups. This reaction represents a complementary
approach to the existing C(sp3)−B bond formation methods.
Further studies on the detailed mechanism and scope and
synthetic applications are ongoing.
a
Reaction conditions: N-acyloxyphthalimide 1 (0.3 mmol), B2pin2 (1.2
mmol), [Ir(ppy)2(dtbpy)]PF6 (0.003 mmol) in 1 mL of DMF/
b
MeCN/H2O (1/1/1), 45 W CFL for 16 h. Reaction time for 20 h.
c
d
Reaction time for 48 h. Yield of 1 mmol scale.
reaction with B2pin2 only provided arylboronic ester 3k in 10%
yield, and the most mass balance was m-methyl benzoic acid,
probably due to slow decarboxylation and competitive hydrogen
trapping.
To shed light on the mechanism of the present decarboxylative
borylation, we conducted two radical cascade experiments
(Scheme 3). The reaction of 1p,20 containing a cyclopropyl
Scheme 3. Reactions Probing the Mechanism
ASSOCIATED CONTENT
* Supporting Information
■
S
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.orglett.7b01181.
Detailed experimental procedures; spectral data of
products (PDF)
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: lipengfei@mail.xjtu.edu.cn.
ORCID
group, with B2pin2 afforded the ring-opening product 3p in 61%
yield. In the case of 1q, the decarboxylation was followed by 5-exo
cyclization prior to borylation, and 2q was thus obtained in 67%
yield. These results all support the involvement of an alkyl radical
and its reaction with the boron species.
A plausible mechanism for the visible-light photoredox
decarboxylative borylation reported herein is outlined in Scheme
4. Single-electron transfer from visible light-excited photocatalyst
Ir(III)* to the N-acyloxyphthalimide 4 generates a radical anion 5
that undergoes homolytic cleavage of the N−O bond, leading to
carboxyl radical 6 and phthalimide anion 7. Subsequent
decarboxylation of 6 generates alkyl radical R• (8). In the
Pengfei Li: 0000-0002-4736-2477
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We are grateful for financial support by the National Science
Foundation of China (Nos. 21672168 and 21472146), the
Ministry of Science and Technology of PRC (No.
2014CB548200), and the Department of Science and Technol-
ogy of Shaanxi Province (No. 2015KJXX-02). P.L. is a “Chung
Ying Scholar” of Xi’an Jiaotong University.
C
DOI: 10.1021/acs.orglett.7b01181
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
(c) Ochiai, H.; Uetake, Y.; Niwa, T.; Hosoya, T. Angew. Chem., Int. Ed.
2017, 56, 2482. (d) During preparation of this manuscript, a nickel-
catalyzed decarboxylative borylation appeared; see: Li, C.; Wang, J.;
Barton, L. M.; Yu, S.; Tian, M.; Peters, D. S.; Kumar, M.; Yu, A. W.;
Johnson, K. A.; Chatterjee, A. K.; Yan, M.; Baran, P. S. Science 2017,
No. eaam7355.
(17) (a) Ding, S.; Xu, L.; Li, P. ACS Catal. 2016, 6, 1329. (b) Sorin, G.;
Mallorquin, R. M.; Contie, Y.; Baralle, A.; Malacria, M.; Goddard, J. P.;
Fensterbank, L. Angew. Chem., Int. Ed. 2010, 49, 8721. (c) Huang, H.;
Zhang, G.; Gong, L.; Zhang, S.; Chen, Y. J. Am. Chem. Soc. 2014, 136,
2280.
REFERENCES
■
(1) For reviews on alkylboronic acid derivatives, see: (a) Miyaura, N.;
Suzuki, A. Chem. Rev. 1995, 95, 2457. (b) Hall, D. G. Boronic Acids:
Preparation and Applications in Organic Synthesis. Medicine and
Materials; Wiley-VCH: Weinheim, 2011. (c) Yamaguchi, J.; Yamaguchi,
A. D.; Itami, K. Angew. Chem., Int. Ed. 2012, 51, 8960. (d) Xu, L.; Zhang,
S.; Li, P. Chem. Soc. Rev. 2015, 44, 8848.
(2) Brown, H. C.; Cole, T. E. Organometallics 1983, 2, 1316.
(3) (a) Brown, H. C. Hydroboration; W. A. Benjamin, Inc.: New York,
1962. (b) Zhang, L.; Zuo, Z.; Leng, X.; Huang, Z. Angew. Chem., Int. Ed.
2014, 53, 2696 and references therein.
(18) (a) Chen, K.; Zhang, S.; He, P.; Li, P. Chem. Sci. 2016, 7, 3676.
(b) Chen, K.; Cheung, M. S.; Lin, Z.; Li, P. Org. Chem. Front. 2016, 3,
875. (c) Mfuh, A. M.; Doyle, J. D.; Chhetri, B.; Arman, H. D.; Larionov,
O. V. J. Am. Chem. Soc. 2016, 138, 2985. (d) Mfuh, A. M.; Nguyen, V. T.;
Chhetri, B.; Burch, J. E.; Doyle, J. D.; Nesterov, V. N.; Arman, H. D.;
Larionov, O. V. J. Am. Chem. Soc. 2016, 138, 8408. For other recent
borylation of aryl halides, see: (e) Zhang, L.; Jiao, L. J. Am. Chem. Soc.
2017, 139, 607. (f) Lee, Y.; Baek, S.-y.; Park, J.; Kim, S.-T.; Tussupbayev,
S.; Kim, J.; Baik, M.-H.; Cho, S. H. J. Am. Chem. Soc. 2017, 139, 976.
(g) Jiang, M.; Yang, H.; Fu, H. Org. Lett. 2016, 18, 5248.
(19) (a) Cornella, J.; Edwards, J. T.; Qin, T.; Kawamura, S.; Wang, J.;
Pan, C.; Gianatassio, R.; Schmidt, M.; Eastgate, M. D.; Baran, P. S. J. Am.
Chem. Soc. 2016, 138, 2174. (b) Toriyama, F.; Cornella, J.; Wimmer, L.;
Chen, T.; Dixon, D. D.; Creech, G.; Baran, P. S. J. Am. Chem. Soc. 2016,
138, 11132. (c) Qin, T.; Cornella, J.; Li, C.; Malins, L. R.; Edwards, J. T.;
Kawamura, S.; Maxwell, B. D.; Eastgate, M. D.; Baran, P. S. Science 2016,
352, 801. (d) Wang, J.; Qin, T.; Chen, T.; Wimmer, L.; Edwards, J. T.;
Cornella, J.; Vokits, B.; Shaw, S. A.; Baran, P. S. Angew. Chem. 2016, 128,
9828. (e) Huihui, K. M.; Caputo, J. A.; Melchor, Z.; Olivares, A. M.;
Spiewak, A. M.; Johnson, K. A.; DiBenedetto, T. A.; Kim, S.; Ackerman,
L. K.; Weix, D. J. J. Am. Chem. Soc. 2016, 138, 5016. (f) Schnermann, M.
J.; Overman, L. E. Angew. Chem., Int. Ed. 2012, 51, 9576. (g) Lackner, G.
L.; Quasdorf, K. W.; Overman, L. E. J. Am. Chem. Soc. 2013, 135, 15342.
(h) Yang, J.; Zhang, J.; Qi, L.; Hu, C.; Chen, Y. Chem. Commun. 2015,
51, 5275. (i) Kachkovskyi, G.; Faderl, C.; Reiser, O. Adv. Synth. Catal.
2013, 355, 2240. (j) Edwards, J. T.; Merchant, R. R.; McClymont, K. S.;
Knouse, K. W.; Qin, T.; Malins, L. R.; Vokits, B.; Shaw, S. A.; Bao, D.;
Wei, F.; Zhou, T.; Eastgate, M. D.; Baran, P. S. Nature 2017,
DOI: 10.1038/nature22307.
(4) For a recent review on conjugate additions with B-based
nucleophiles, see: Hartmann, E.; Vyas, D. J.; Oestreich, M. Chem.
Commun. 2011, 47, 7917.
(5) (a) Mkhalid, I. A. I.; Barnard, J. H.; Marder, T. B.; Murphy, J. M.;
Hartwig, J. F. Chem. Rev. 2010, 110, 890. For selected recent examples,
see: (b) Wang, G.; Liu, L.; Wang, H.; Ding, Y.-S.; Zhou, J.; Mao, S.; Li, P.
J. Am. Chem. Soc. 2017, 139, 91. (c) Palmer, W. N.; Zarate, C.; Chirik, P.
J. J. Am. Chem. Soc. 2017, 139, 2589. (d) Kawamorita, S.; Miyazaki, T.;
Iwai, T.; Ohmiya, H.; Sawamura, M. J. Am. Chem. Soc. 2012, 134, 12924.
(6) (a) Ishiyama, T.; Murata, M.; Miyaura, N. J. Org. Chem. 1995, 60,
7508. (b) Takagi, J.; Takahashi, K.; Ishiyama, T.; Miyaura, N. J. Am.
Chem. Soc. 2002, 124, 8001.
(7) (a) Bej, A.; Srimani, D.; Sarkar, A. Green Chem. 2012, 14, 661.
(b) Yi, J.; Liu, J.-H.; Liang, J.; Dai, J.-J.; Yang, C.-T.; Fu, Y.; Liu, L. Adv.
Synth. Catal. 2012, 354, 1685. (c) Joshi-Pangu, A.; Ma, X.; Diane, M.;
Iqbal, S.; Kribs, R. J.; Huang, R.; Wang, C.-Y.; Biscoe, M. R. J. Org. Chem.
2012, 77, 6629.
(8) Dudnik, A. S.; Fu, G. C. J. Am. Chem. Soc. 2012, 134, 10693.
(9) (a) Kleeberg, C.; Dang, L.; Lin, Z.; Marder, T. B. Angew. Chem., Int.
Ed. 2009, 48, 5350. (b) Yang, C.-T.; Zhang, Z.-Q.; Tajuddin, H.; Wu, C.-
C.; Liang, J.; Liu, J.-H.; Fu, Y.; Czyzewska, M.; Steel, P. G.; Marder, T. B.;
Liu, L. Angew. Chem., Int. Ed. 2012, 51, 528. (c) Ito, H.; Kubota, K. Org.
Lett. 2012, 14, 890.
(10) Bose, S. K.; Fucke, K.; Liu, L.; Steel, P. G.; Marder, T. B. Angew.
Chem., Int. Ed. 2014, 53, 1799−1803.
(11) Atack, T. C.; Lecker, R. M.; Cook, S. P. J. Am. Chem. Soc. 2014,
136, 9521.
(12) For selected references of photoredox decarboxylation, see:
(a) Liu, J.; Liu, Q.; Yi, H.; Qin, C.; Bai, R.; Qi, X.; Lan, Y.; Lei, A. Angew.
Chem., Int. Ed. 2014, 53, 502. (b) Zuo, Z.; MacMillan, D. W. C. J. Am.
Chem. Soc. 2014, 136, 5257. (c) Zuo, Z.; Ahneman, D. T.; Chu, L.;
Terrett, J. A.; Doyle, A. G.; MacMillan, D. W. C. Science 2014, 345, 437.
(d) Noble, A.; McCarver, S. J.; MacMillan, D. W. C. J. Am. Chem. Soc.
2015, 137, 624. (e) Noble, A.; MacMillan, D. W. C. J. Am. Chem. Soc.
2014, 136, 11602. (f) Miyake, Y.; Nakajima, K.; Nishibayashi, Y. Chem.
Commun. 2013, 49, 7854. (g) Zhou, Q.; Guo, W.; Ding, W.; Wu, X.;
Chen, X.; Lu, L.; Xiao, W. Angew. Chem., Int. Ed. 2015, 54, 11196.
(h) Lang, S. B.; O’Nele, K. M.; Tunge, J. A. J. Am. Chem. Soc. 2014, 136,
13606. (i) Ventre, S.; Petronijevic, F. R.; MacMillan, D. W. C. J. Am.
(20) (a) Barczak, N. T.; Jarvo, E. R. Chem. - Eur. J. 2011, 17, 12912−
12916. (b) Hu, F.; Shao, X.; Zhu, D.; Lu, L.; Shen, Q. Angew. Chem., Int.
Ed. 2014, 53, 6105−6109.
(21) Miralles, N.; Romero, R. M.; Fernan
Commun. 2015, 51, 14068.
́
dez, E.; Muniz, K. Chem.
(22) (a) Power, P. P. Chem. Rev. 2003, 103, 789. (b) Braunschweig, H.;
Dyakonov, V.; Jimenez-Halla, J. O. C.; Kraft, K.; Krummenacher, I.;
Radacki, K.; Sperlich, A.; Wahler, J. Angew. Chem., Int. Ed. 2012, 51,
2977.
(23) (a) Ueng, S.-H.; Brahmi, M. M.; Derat, E.; Fensterbank, L.;
̂
Lacote, E.; Malacria, M.; Curran, D. P. J. Am. Chem. Soc. 2008, 130,
10082. (b) Lu, D.; Wu, C.; Li, P. Chem. - Eur. J. 2014, 20, 1630.
(c) Rablen, P. R.; Hartwig, J. F. J. Am. Chem. Soc. 1996, 118, 4648.
(d) Wang, J.; Qin, T.; Chen, T.; Wimmer, L.; Edwards, J. T.; Cornella, J.;
Vokits, B.; Shaw, S. A.; Baran, P. S. Angew. Chem. 2016, 128, 9828.
(e) Lu, D.; Wu, C.; Li, P. Org. Lett. 2014, 16, 1486. (f) Lalevee, J.;
Blanchard, N.; Tehfe, M.-A.; Chany, A.-C.; Fouassier, J.-P. Chem. - Eur. J.
2010, 16, 12920.
́
Chem. Soc. 2015, 137, 5654. (j) Rueda-Becerril, M.; Mahe, O.; Drouin,
M.; Majewski, M. B.; West, J. G.; Wolf, M. O.; Sammis, G. M.; Paquin, J.
J. Am. Chem. Soc. 2014, 136, 2637. (k) Cassani, C.; Bergonzini, G.;
Wallentin, C. Org. Lett. 2014, 16, 4228. (l) Okada, K.; Okamoto, K.;
Oda, M. J. Am. Chem. Soc. 1988, 110, 8736. (m) Pratsch, G.; Lackner, G.
L.; Overman, L. E. J. Org. Chem. 2015, 80, 6025. (n) Okada, K.;
Okamoto, K.; Morita, N.; Okubo, K.; Oda, M. J. Am. Chem. Soc. 1991,
113, 9401. (o) Okada, K.; Okubo, K.; Morita, N.; Oda, M. Tetrahedron
Lett. 1992, 33, 7377. (p) Okada, K.; Okamoto, K.; Oda, M. J. Chem. Soc.,
Chem. Commun. 1989, 1636. (q) Jiang, M.; Yang, H.; Fu, H. Org. Lett.
2016, 18, 1968. (r) Okada, K.; Okubo, K.; Morita, N.; Oda, M. Chem.
Lett. 1993, 22, 2021.
(13) Yin, F.; Wang, Z.; Li, Z.; Li, C. J. Am. Chem. Soc. 2012, 134, 10401.
(14) Wang, C.; Hwang, F.; Horng, J.; Chen, C. Heterocycles 1979, 12,
1191.
(15) Li, C.; Grugel, C.; Breit, B. Chem. Commun. 2016, 52, 5840.
(16) For decarbonylative borylation of aromatic acid derivatives, see:
(a) Hu, J.; Zhao, Y.; Liu, J.; Zhang, Y.; Shi, Z. Angew. Chem., Int. Ed. 2016,
55, 8718. (b) Guo, L.; Rueping, M. Chem. - Eur. J. 2016, 22, 16787.
D
DOI: 10.1021/acs.orglett.7b01181
Org. Lett. XXXX, XXX, XXX−XXX