Synthesis of Benzoxaboroles by ortho-Oxalkylation of Arylboronic Acids with Aldehydes/Ketones in the Presence of Br?nsted Acids

Article abstract of DOI:10.1021/acs.orglett.1c00032

Herein we describe a simple and efficient synthesis of benzoxaboroles from arylboronic acids and aldehydes or ketones in the presence of a Br?nsted acid. This method greatly simplifies the starting materials and reduces the number of reaction steps. The reaction can also be accomplished with acetals and ketals. The reaction has a wide substrate scope and high practicability.

Full text of DOI:10.1021/acs.orglett.1c00032

pubs.acs.org/OrgLett
Letter
Synthesis of Benzoxaboroles by ortho-Oxalkylation of Arylboronic
Acids with Aldehydes/Ketones in the Presence of Brønsted Acids
Jing Zhao, Jiuxi Chen, Qing Xu, and Huan Li*
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ABSTRACT: Herein we describe a simple and efficient synthesis of
benzoxaboroles from arylboronic acids and aldehydes or ketones in the
presence of a Brønsted acid. This method greatly simplifies the starting
materials and reduces the number of reaction steps. The reaction can also be
accomplished with acetals and ketals. The reaction has a wide substrate scope
and high practicability.
enzoxaborole is a class of five-membered cyclic arylbor-
onic acid hemiesters. Compound A, the simplest example,
coworkers discovered that benzoxaboroles have exceptional
sugar-binding properties under physiological conditions.3
With the expanding role of benzoxaboroles in medicinal
chemistry, many methods have been developed for their
synthesis (Scheme 2).2c,d,f−i,4 One of the methods (method A)
B
was first obtained by Torssell in 1957 (Scheme 1);1 however,
Scheme 1. Medicinal Application of Benzoxaboroles
Scheme 2. Methods for Synthesis of Benzoxaboroles
involves an addition reaction of nucleophiles to ortho-formyl
arylboronic acid. This strategy is feasible for various types of
nucleophiles, including NaBH4, organozinc reagents, indoles,
nitroalkanes, amines, N-ethyl aniline, carbonyl compounds,
α,β-unsaturated carbonyl compounds, acrylonitrile, silyl
cyanide, and isocyanide. The second method (method B)
this type of compound was underestimated for a long time.
The increasing interest in benzoxaboroles was supported by
the discovery of the biologically activities of tavaborole (B)
and crisaborole (C) and their FDA approval for the treatment
of onychomycosis and atopic dermatitis, respectively.2 In the
past two decades, the vast majority of benzoxaboroles have
been synthesized and found to have various biological
activities, including antifungal, antibacterial, antiviral, anti-
inflammatory, and antiprotozoal properties.2 For example,
AN5568 (D) was in clinical trials for the treatment of human
African trypanosomiasis. Compounds E, F, and G were found
to be an efficient antimalarial agent, antibacterial agent, and β-
lactamases inhibitor, respectively. Additionally, Hall and
Received: January 5, 2021
Published: March 1, 2021
https://dx.doi.org/10.1021/acs.orglett.1c00032
© 2021 American Chemical Society
Org. Lett. 2021, 23, 1986−1990
1986

Organic Letters
pubs.acs.org/OrgLett
Letter
involves the introduction of a boron substituent to the
aromatic ring, either by metalation−borylation or by
transition-metal-catalyzed borylation. The third method
(method C) involves the intramolecular electrophilic or
nucleophilic O-addition of boronic acid to alkenes of ortho-
alkenyl-substituted arylboronic acids. Nevertheless, these
methods use relatively complex arylboron compounds as the
starting substrates or intermediates. Moreover, strict manipu-
lations are essential for some cases involving highly reactive
organometallic reagents and metal-catalyzed reactions. Un-
doubtedly, these requirements will increase the difficulty of the
synthesis and decrease the practical utility of the methods. It is
clear that benzoxaboroles can be regarded as the intra-
molecular dehydration product of ortho-hydroxyalkyl-substi-
tuted arylboronic acids (H). In consideration of the atom
economy, an ideal method to obtain H is the direct ortho-
hydroxyalkylation of arylboronic acids with aldehydes or
ketones; however, arylboronic acids are highly reactive, and
only a few types of functionalization of arylboron compounds
have been previously reported, and most of them deal with
halogenations and nitration.5
obtained a relatively low yield (entry 6). Increasing or reducing
the loading amount of TFA lead to a lower yield due to
overhydroxymethylation or the insufficient conversion of 1a
(entries 7 and 8). The optimization of solvents showed that
only the reaction carried out in chlorohydrocarbon solvents
worked (entries 9−14). When the reaction time was extended,
the yield decreased, presumably due to overalkylation (entry
15). A reasonable explanation for this is that product 3a is
somewhat more nucleophilic than substrate 1a as a result of
the electronic effect. In comparison, when 1,3-dimethoxyben-
zene was applied to the reaction with paraformaldehyde under
the optimized conditions, the desired hydroxymethylation
product was not observed, with the exception of some
polymer-like precipitate.7 This indicates that in the presence
of a strong Brønsted acid, benzoxaborole was more stable than
the corresponding benzylic alcohol.
The reaction of various arylboronic acids with paraformal-
dehyde was examined (Scheme 3). In general, arylboronic
a
Scheme 3. Substrates Scope of Arylboronic Acids
Previously, we reported an intramolecular arylative ring
opening of donor−acceptor cyclopropanes in the presence of
triflic acid.6 We found that the strong Brønsted acid showed
exceptional function in the Friedel−Crafts alkylation reaction.
In view of the nature of the same reaction type, we first
investigated the reaction of 3,5-dimethoxyl phenylboronic acid
with paraformaldehyde in the presence of different commonly
used Brønsted acids (Table 1). Trifluoroacetic acid (TFA) was
shown to be the most efficient catalyst (entry 1). The stronger
acids, p-toluenesulfonic acid (TsOH), triflic acid (TfOH), and
sulfuric acid, gave lower yields (entries 2−4), whereas the
weaker acid, acetic acid (AcOH), gave no product (entry 5).
We also tested Amberlyst 15, a heterogeneous acid catalyst, but
Table 1. Optimization of the Reaction of Boronic Acid 1a
a
with Paraformaldehyde 2a
entry
cat. (equiv)
solvent
yield (%)
1
2
3
4
5
6
7
8
TFA (0.2)
CHCl3
CHCl3
CHCl3
CHCl3
CHCl3
CHCl3
CHCl3
CHCl3
DCM
CCl4
DCE
CH3CN
THF
n-hexane
CHCl3
80
27
14
14
N.R.
34
54
28
29
44
29
trace
N.R.
N.R.
49
TsOH (0.05)
TfOH (0.01)
H2SO4 (0.2)
AcOH (5)
a
Reaction conditions: arylboronic acid (0.5 to 1 mmol), 2a (1.2
b
Amberlyst 15
TFA (0.1)
TFA (0.3)
TFA (0.2)
TFA (0.2)
TFA (0.2)
TFA (0.2)
TFA (0.2)
TFA (0.2)
TFA (0.2)
equiv), catalyst, CHCl3 (0.1 M). The reaction was monitored by TLC
analysis, and the product was isolated by silica gel chromatography.
9
10
11
12
13
14
acids with electron-donating groups at the meta position gave
the desired products in moderate to good yield. When the
nucleophilicity of the aryl ring was reduced, stronger acids,
TfOH or TsOH, were necessary for the reaction to succeed.
Compounds 3d and 3e were intermediates in the synthesis of
bioactive molecules, but three to five steps were needed in the
previously reported synthetic route.8 With this method,
starting from simple and commercially available substrates,
only one step is required. Thus this methodology greatly
simplifies and shortens the preparation of benzoxaboroles.
c
15
a
Reaction conditions: 1a (0.5 mmol), 2a (0.6 mmol), catalyst, solvent
(5 mL), rt, 48 h. The product was isolated by silica gel
b
c
chromatography. 150 mg of Amberlyst 15 was used. Reaction
time was prolonged to 72 h. N.R., no reaction.
1987
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Letter
Then, various aldehydes and ketones were applied in the
reaction with arylboronic acid 1a (Scheme 4). For both
Scheme 5. Reactions of 1a with Acetal and Ketal
a
Scheme 4. Substrates Scope of Aldehydes and Ketones
compound using the previously reported method.9 When
acetone was replaced by the corresponding dimethyl ketal, the
yield of 5a was greatly improved, even in gram-scale
manipulation.
For the formation of benzoxaboroles, we proposed an
intermolecular (path a) and an intramolecular (path b)
Friedel−Crafts alkylation mechanism (Scheme 6). The arenes
Scheme 6. Proposed Mechanism
with electron-donating groups could react with aldehydes in
the presence of Brønsted acids,7 so path a is possible for similar
aryl boronic acids. For the formation of 3j and 3k, it was
possible for both of the two ortho positions of the methoxyl
group of the aryl boronic acid substrates to be alkylated. The
yields of both 3j and 3k were >60%, and this result means that
the ortho position near the boronic acid group is more reactive
than the other one. A rational explanation is that the boronic
acid segment serves as a directing group. Literature reports10
confirm that some ortho-formyl arylboronic acids contain both
formyl and acetal forms, and so a similar intermediate I might
also form. I could be converted to a carbon cation J, which
subsequently undergoes an intramolecular Friedel−Crafts
reaction to form the benzoxaborole K (path b). A similar
effect was also proposed by Hall and coworkers to explain the
silver(I)-mediated ortho-halogenation of arylboronic acids.5g
In summary, we have developed a simple and efficient
method for the synthesis of benzoxaboroles. This methodology
enriches the range of the functionalization of arylboron
compounds. The method has a very broad substrate scope of
aldehydes and ketones. With this strategy, benzoxaboroles,
especially C3-substituted benzoxaboroles, can be conveniently
obtained. Furthermore, metals are not required for this
transformation. This method may be very practical and
beneficial in the synthesis of pharmaceuticals involving
benzoxaboroles. Other types of functionalization of organo-
boron compounds are currently under investigation in our
laboratory.
a
Reaction conditions: 1a (0.5 to 1 mmol), aldehyde or ketone (1.2
equiv), catalyst (see the SI for details), CHCl3 (0.1 M). The reaction
was monitored by TLC analysis, and the product was isolated by silica
gel chromatography. 75% aqueous solution of trifluoroacetaldehyde
b
c
monohydrate was used. Reaction was carried out on a 5 mmol scale.
aliphatic and aromatic aldehydes, the yields were moderate to
excellent. For 4f, an aqueous solution of trifluoroacetaldehyde
was used, and the yield was satisfactory. For ketones, the
stronger acid TfOH must be used due to the diminished
electrophilicity of the reactants. For linear or cyclic ketones,
the yield was good to excellent; however, it is necessary to
point out that the general aryl ketone failed to react (5g),
except for substrates bearing electron-withdrawing groups
(5h−j). In some cases, the reactions were carried out on a
gram scales and produced a satisfactory yield (4j and 5f).
We also noticed that some aldehydes are not stable, but the
corresponding acetals are stable. Therefore, it is essential and
valuable to test acetals and ketals in the reaction with
arylboronic acid (Scheme 5). To our delight, compound 6
could be obtained in moderately high yield from a one-step
reaction of 1a with a commercially available acetal, and 6 could
be converted to F by subsequent hydrolysis. In comparison, F
was synthesized in four steps from a commercially available
1988
https://dx.doi.org/10.1021/acs.orglett.1c00032
Org. Lett. 2021, 23, 1986−1990

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pubs.acs.org/OrgLett
Letter
́
́
A.; Cyranski, M. K.; Zubrowska, A.; Sporzynski, A. Benzoxaboroles −
Old Compounds with New Applications. J. Organomet. Chem. 2009,
694, 3533.
ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acs.orglett.1c00032.
■
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(3) (a) Dowlut, M.; Hall, D. G. An Improved Class of Sugar-Binding
Boronic Acids, Soluble and Capable of Complexing Glycosides in
Neutral Water. J. Am. Chem. Soc. 2006, 128, 4226. (b) Berube, M.;
Dowlut, M.; Hall, D. G. Benzoboroxoles as Efficient Glycopyranoside-
Binding Agents in Physiological Conditions: Structure and Selectivity
of Complex Formation. J. Org. Chem. 2008, 73, 6471.
Experimental procedures, characterization data, and
1
copies of H and 13C NMR spectra (PDF)
(4) For reviews, see: Yang, F.; Zhu, M.; Zhang, J.; Zhou, H.
Synthesis of Biologically Active Boron-Containing Compounds.
MedChemComm 2018, 9, 201.
AUTHOR INFORMATION
Corresponding Author
■
Huan Li − College of Chemistry and Materials Engineering,
Wenzhou University, Wenzhou, Zhejiang 325035, China;
orcid.org/0000-0002-8321-1692; Email: lihuan@
wzu.edu.cn
(5) For nitration, see: (a) Lennarz, W. J.; Snyder, H. R. Arylboronic
Acids. IV. Reactions of Boronophthalide. J. Am. Chem. Soc. 1960, 82,
2172. (b) Ni, W.; Fang, H.; Springsteen, G.; Wang, B. The Design of
Boronic Acid Spectroscopic Reporter Compounds by Taking
Advantage of the pKa-Lowering Effect of Diol Binding: Nitro-
phenol-Based Color Reporters for Diols. J. Org. Chem. 2004, 69, 1999.
(c) Tomita, D.; Yamatsugu, K.; Kanai, M.; Shibasaki, M.
Enantioselective Synthesis of SM-130686 Based on the Development
of Asymmetric Cu(I)F Catalysis To Access 2-Oxindoles Containing a
Tetrasubstituted Carbon. J. Am. Chem. Soc. 2009, 131, 6946.
(d) Faury, T.; Dumur, F.; Clair, S.; Abel, M.; Porte, L.; Gigmes, D.
Side Functionalization of Diboronic Acid Precursors for Covalent
Organic Frameworks. CrystEngComm 2013, 15, 2067. (e) Xue, F.; Li,
C.-G.; Zhu, Y.; Lou, T.-J. Synthesis of 2-Amino-4-(methoxycarbonyl)-
phenylboronic Acid Hydrochloride, a Key Intermediate for the
Synthesis of Quinolines Derivatives. J. Chem. Res. 2014, 38, 719. For
halogenations, see: (f) Kuivila, H. G.; Benjamin, L. E.; Murphy, C. J.;
Price, A. D.; Polevy, J. H. Electrophilic Displacement Reactions. XIV.
Two Novel Reactions Involving Areneboronic Acids and Halogens. J.
Org. Chem. 1962, 27, 825. (g) Al-Zoubi, R. M.; Hall, D. G. Mild
Silver(I)-Mediated Regioselective Iodination and Bromination of
Arylboronic Acids. Org. Lett. 2010, 12, 2480. (h) Qiu, D.; Mo, F.;
Zheng, Z.; Zhang, Y.; Wang, J. Gold(III)-Catalyzed Halogenation of
Aromatic Boronates with N-Halosuccinimides. Org. Lett. 2010, 12,
5474. (i) Fuse, S.; Sugiyama, S.; Takahashi, T. Rapid Assembly of
Resorcylic Acid Lactone Frameworks through Sequential Palladium-
Catalyzed Coupling Reactions. Chem. - Asian J. 2010, 5, 2459.
(j) Kamei, T.; Ishibashi, A.; Shimada, T. Metal-Free Halogenation of
Arylboronate with N-halosuccinimide. Tetrahedron Lett. 2014, 55,
4245. (k) Close, A. J.; Kemmitt, P.; Mark Roe, S.; Spencer, J.
Regioselective Routes to Orthogonally-Substituted Aromatic MIDA
Boronates. Org. Biomol. Chem. 2016, 14, 6751. (l) Lee, C.-Y.; Cheon,
C.-H. Preparation of Building Blocks for Iterative Suzuki-Miyaura
Reactions via Direct Bromination of Aryl Boronic Acids: One-Pot
Total Syntheses of Dictyoterphenyls A and B. Adv. Synth. Catal. 2017,
359, 3831. Recently, palladium catalyzed meta-C−H alkenylation,
acetoxylation, and arylation were reported: (m) Williams, A. F.;
White, A. J. P.; Spivey, A. C.; Cordier, C. J. meta-Selective C−H
Functionalisation of Aryl Boronic Acids Directed by a MIDA-Derived
Boronate Ester. Chem. Sci. 2020, 11, 3301.
Authors
Jing Zhao − College of Chemistry and Materials Engineering,
Wenzhou University, Wenzhou, Zhejiang 325035, China
Jiuxi Chen − College of Chemistry and Materials Engineering,
Wenzhou University, Wenzhou, Zhejiang 325035, China;
orcid.org/0000-0001-6666-9813
Qing Xu − College of Chemistry and Materials Engineering,
Wenzhou University, Wenzhou, Zhejiang 325035, China;
orcid.org/0000-0002-4283-1799
Complete contact information is available at:
https://pubs.acs.org/10.1021/acs.orglett.1c00032
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
This research was supported by the Natural Science
Foundation of China (grant no. 21502143).
■
REFERENCES
■
(1) Torssell, K. Arylboronic Acids. III. Bromination of Tolylboronic
Acids According to Wohl-Ziegler. Ark. Kemi 1957, 10, 507−511.
(2) See the following reviews and the related references therein:
(a) Fernandes, G. F. S.; Denny, W. A.; Dos Santos, J. L. Boron in
Drug Design: Recent Advances in the Development of New
Therapeutic Agents. Eur. J. Med. Chem. 2019, 179, 791. (b) Nocentini,
A.; Supuran, C. T.; Winum, J.-Y. Benzoxaborole Compounds for
Therapeutic Uses: A Patent Review (2010−2018). Expert Opin. Ther.
́
Pat. 2018, 28, 493. (c) Gozdalik, J. T.; Adamczyk-Wozniak, A.;
́
Sporzynski, A. Influence of Fluorine Substituents on the Properties of
Phenylboronic Compounds. Pure Appl. Chem. 2018, 90, 677.
(d) Mereddy, G. R.; Chakradhar, A.; Rutkoski, R. M.;
Jonnalagadda, S. C. Benzoboroxoles: Synthesis and Applications in
Medicinal Chemistry. J. Organomet. Chem. 2018, 865, 12.
(6) Wang, D.; Zhao, J.; Chen, J.; Xu, Q.; Li, H. Intramolecular
Arylative Ring Opening of Donor-Acceptor Cyclopropanes in the
Presence of Triflic Acid: Synthesis of 9H-Fluorenes and 9,10-
Dihydrophenanthrenes. Asian J. Org. Chem. 2019, 8, 2032.
(7) For the macrocyclization reaction of 1,3-dimethoxybenzene with
paraformaldehyde in the presence of TFA, see: (a) Boinski, T.;
Cieszkowski, A.; Rosa, B.; Szumna, A. Hybrid [n]Arenes through
Thermodynamically Driven Macrocyclization Reactions. J. Org. Chem.
2015, 80, 3488. (b) Boinski, T.; Cieszkowski, A.; Rosa, B.;
́
́
(e) Adamczyk-Wozniak, A.; Borys, K. M.; Sporzynski, A. Recent
Developments in the Chemistry and Biological Applications of
Benzoxaboroles. Chem. Rev. 2015, 115, 5224. (f) Liu, C. T.; Tomsho,
J. W.; Benkovic, S. J. The Unique Chemistry of Benzoxaboroles:
Current and Emerging Applications in Biotechnology and Ther-
apeutic Treatments. Bioorg. Med. Chem. 2014, 22, 4462. (g) Wring, S.;
Gaukel, E.; Nare, B.; Jacobs, R.; Beaudet, B.; Bowling, T.; Mercer, L.;
Bacchi, C.; Yarlett, N.; Randolph, R.; Parham, R.; Rewerts, C.;
Platner, J.; Don, R. Pharmacokinetics and Pharmacodynamics
Utilizing Unbound Target Tissue Exposure as Part of a Disposition-
Based Rationale for Lead Optimization of Benzoxaboroles in the
Treatment of Stage 2 Human African Trypanosomiasis. Parasitology
2014, 141, 104. (h) Zhang, J.; Zhu, M.; Lin, Y.; Zhou, H. The
Synthesis of Benzoxaboroles and Their Applications in Medicinal
́
Lesniewska, B.; Szumna, A. Calixarenes with Naphthalene Units:
Calix[4]naphthalenes and Hybrid[4]arenes. New J. Chem. 2016, 40,
8892. For similar reactions in the presence of BF3·Et2O, see:
(c) Ogoshi, T.; Kitajima, K.; Umeda, K.; Hiramitsu, S.; Kanai, S.;
Fujinami, S.; Yamagishi, T.; Nakamoto, Y. Lewis Acid-Catalyzed
Synthesis of Dodecamethoxycalix[4]arene from 1,3,5-Trimethoxy-
benzene and Its Conformational Behavior and Host−Guest Property.
Tetrahedron 2009, 65, 10644. (d) Della Sala, P.; Gaeta, C.; Navarra,
́
Chemistry. Sci. China: Chem. 2013, 56, 1372. (i) Adamczyk-Wozniak,
1989
https://dx.doi.org/10.1021/acs.orglett.1c00032
Org. Lett. 2021, 23, 1986−1990

Organic Letters
pubs.acs.org/OrgLett
Letter
W.; Talotta, C.; De Rosa, M.; Brancatelli, G.; Geremia, S.; Capitelli,
F.; Neri, P. Improved Synthesis of Larger Resorcinarenes. J. Org.
Chem. 2016, 81, 5726. For a similar reaction in the presence of HCl,
see: (e) Li, D.; Kusunoki, T.; Yamagishi, T.-A.; Nakamoto, Y.
Synthesis of C-Unalkylated Calix[4]resorcinarene from 1,3-Dime-
thoxybenzene-Formaldehyde Condensation. Polym. Bull. 2002, 47,
493.
(8) For the synthesis of 3d, see: (a) Ding, D.; Zhao, Y.; Meng, Q.;
Xie, D.; Nare, B.; Chen, D.; Bacchi, C. J.; Yarlett, N.; Zhang, Y.-K.;
Hernandez, V.; Xia, Y.; Freund, Y.; Abdulla, M.; Ang, K.-H.; Ratnam,
J.; McKerrow, J. H.; Jacobs, R. T.; Zhou, H.; Plattner, J. J. Discovery
of Novel Benzoxaborole-Based Potent Antitrypanosomal Agents. ACS
Med. Chem. Lett. 2010, 1, 165. (b) Ding, D.; Meng, Q.; Gao, G.;
Zhao, Y.; Wang, Q.; Nare, B.; Jacobs, R.; Rock, F.; Alley, M. R. K.;
Plattner, J. J.; Chen, G.; Li, D.; Zhou, H. Design, Synthesis, and
Structure-Activity Relationship of Trypanosoma brucei Leucyl-tRNA
Synthetase Inhibitors as Antitrypanosomal Agents. J. Med. Chem.
2011, 54, 1276. For the synthesis of 3e, see: (c) Xia, Y.; Cao, K.;
Zhou, Y.; Alley, M. R. K.; Rock, F.; Mohan, M.; Meewan, M.; Baker,
S. J.; Lux, S.; Ding, C. Z.; Jia, G.; Kully, M.; Plattner, J. J. Synthesis
and SAR of Novel Benzoxaboroles as a New Class of β-lactamase
Inhibitors. Bioorg. Med. Chem. Lett. 2011, 21, 2533. (d) Huang, X.-P.;
Karpiak, J.; Kroeze, W. K.; Zhu, H.; Chen, X.; Moy, S. S.; Saddoris, K.
A.; Nikolova, V. D.; Farrell, M. S.; Wang, S.; Mangano, T. J.;
Deshpande, D. A.; Jiang, A.; Penn, R. B.; Jin, J.; Koller, B. H.;
Kenakin, T.; Shoichet, B. K.; Roth, B. L. Allosteric Ligands for the
Pharmacologically Dark Receptors GPR68 and GPR65. Nature 2015,
527, 477.
(9) (a) Xia, Y.; Alley, M. R. K.; Zhou, Y.; Singh, R.; Ding, C.; Cao,
K.; Plattner, J. J.; Ou, L.; Jia, G.; Saraswat, N.; Ramachandran, S.;
Zhou, D. Trisubstituted Benzoxaborole Compounds as Antibacterial
Agents, Their Preparation, and Use in the Treatment of Bacterial
Infection. PCT Int. Appl. 2011/017125 A1, February 10, 2011.
(b) McKinney, D. C.; Zhou, F.; Eyermann, C. J.; Ferguson, A. D.;
Prince, D. B.; Breen, J.; Giacobbe, R. A.; Lahiri, S.; Verheijen, J. C.
4,5-Disubstituted 6-Aryloxy-1,3-dihydrobenzo[c][1,2]oxaboroles Are
Broad-Spectrum Serine β-Lactamase Inhibitors. ACS Infect. Dis. 2015,
1, 310.
(10) (a) Liu, Y. E.; Lu, Z.; Li, B.; Tian, J.; Liu, F.; Zhao, J.; Hou, C.;
Li, Y.; Niu, L.; Zhao, B. Enzyme-Inspired Axially Chiral Pyridox-
amines Armed with a Cooperative Lateral Amine Chain for
Enantioselective Biomimetic Transamination. J. Am. Chem. Soc.
2016, 138, 10730. (b) Basak, S.; Mal, D. Intramolecular Carbonyl-
ene Reactions in the Synthesis of peri-Oxygenated Hydroaromatics.
Tetrahedron 2016, 72, 1758.
1990
https://dx.doi.org/10.1021/acs.orglett.1c00032
Org. Lett. 2021, 23, 1986−1990