Palladium-Catalyzed Amide Synthesis via Aminocarbonylation of Arylboronic Acids with Nitroarenes

Article abstract of DOI:10.1021/acs.orglett.9b01772

A palladium-catalyzed aminocarbonylation of aryl boronic acids with nitroarenes for the synthesis of amides has been developed. A wide range of substrates were well-tolerated and gave the corresponding amides in moderate to good yields. No external oxidant or reductant was needed in this procedure. This procedure provides a redox-economical process for the synthesis of amides.

Full text of DOI:10.1021/acs.orglett.9b01772

Letter
pubs.acs.org/OrgLett
Cite This: Org. Lett. XXXX, XXX, XXX−XXX
Palladium-Catalyzed Amide Synthesis via Aminocarbonylation of
Arylboronic Acids with Nitroarenes
Jin-Bao Peng,† Da Li,† Hui-Qing Geng,† and Xiao-Feng Wu*,†,‡
†Department of Chemistry, Zhejiang Sci-Tech University, Hangzhou, Zhejiang 310018, China
‡Leibniz-Institut fu
̈
r Katalyse e.V. an der Universitat Rostock, Albert-Einstein-Straße 29a, Rostock 18059, Germany
̈
S
* Supporting Information
ABSTRACT: A palladium-catalyzed aminocarbonylation of
aryl boronic acids with nitroarenes for the synthesis of amides
has been developed. A wide range of substrates were well-
tolerated and gave the corresponding amides in moderate to
good yields. No external oxidant or reductant was needed in
this procedure. This procedure provides a redox-economical
process for the synthesis of amides.
a
Table 1. Optimization of the Reaction Conditions
mide is one of the most essential structural motifs in life
Ascience and also widely exists in natural products and
pharmaceutical compounds as well as organic materials.1,2
Traditionally, amides are synthesized by the reaction between
carboxylic acids and amines. Although this reaction is
thermodynamically favorable, it suffers from the high activation
energy due to the formation of the ammonium salt. Thus the
direct amidation of acid with amine usually requires a high
reaction temperature. To drive the equilibrium to the right,
three strategies were usually used: (1) using an activated
carboxylic acid derivative such as acid chloride or anhydride;
(2) using an additional reagents such as HATU, HOBt, or
PyBOP as the catalyst; and (3) transamidation with the other
amides.3 An alternative strategy for amide synthesis is the
transition-metal-catalyzed aminocarbonylation of aryl halides
with amines as the nucleophile.4 Compared with amines, the
direct use of nitroarenes as nitrogen sources is more attractive
because nitroarenes are generally less expensive than the
corresponding anilines. Several research groups, including
Beller, Driver, Hu, and us, have demonstrated that nitroarenes
could serve as an alternate nitrogen source in amino-
carbonylation reactions.5 For example, Hu and coworkers
developed a nickel-catalyzed reductive aminocarbonylation of
aryl halides with nitroarenes using Co2(CO)8 as a CO
surrogate.6 Both aryl iodides and bromides were tolerated,
and a broad substrate scope had been achieved. Herein we
report a new palladium-catalyzed aminocarbonylation of aryl
boronic acids with nitroarenes for the synthesis of amides.7 No
external reductant or oxidant was needed in this procedure.
Initially, phenylboronic acid 1a and 4-nitrotoluene 2a were
selected as the model substrates for this aminocarbonylation
reaction. To our delight, using Mo(CO)6 as a solid CO source
and K2CO3 as the base, the desired amide 3aa was successfully
obtained in 50% yield using the Pd(acac)2/DPPP catalyst
system in 1,4-dioxane (Table 1, entry 1). Subsequently, a series
of acidic and basic additives were tested in this reaction, and it
was found that K2CO3 was optimal. Acidic additive PTS·H2O
b
entry
1
2
palladium
ligand
DPPP
1a/2a
solvent
yield (%)
Pd(acac)2
Pd(acac)2
Pd(TFA)2
PdCl2
1:2
1:2
1:2
1:2
1:2
1:1.5
1:1
1.5:1
2:1
1:2
1:2
1:2
1:2
1:2
1:2
dioxane
dioxane
dioxane
dioxane
dioxane
dioxane
dioxane
dioxane
dioxane
dioxane
DME
50
17
29
18
trace
17
trace
7
14
62
54
74(70)
46
15
18
c
DPPP
DPPP
DPPP
DPPP
DPPP
DPPP
DPPP
DPPP
DPPP
DPPP
DPPP
DPPF
DPEphos
Xantphos
3
4
5
6
7
8
9
10
11
12
13
Pd(OAc)2
Pd(acac)2
Pd(acac)2
Pd(acac)2
Pd(acac)2
Pd(acac)2
Pd(acac)2
Pd(acac)2
Pd(acac)2
Pd(acac)2
Pd(acac)2
d
d
d
e
CH3CN
CH3CN
CH3CN
CH3CN
d
d
14
15
d
a
Reaction conditions: 1a (0.5 mmol), 2a (1 mmol), palladium
catalyst (5 mol %), ligand (5 mol %), Mo(CO)6 (1 equiv), K2CO3 (2
equiv), solvent (1 mL), 20 h. Yields were determined by GC using
dodecane as an internal standard. PTS·H2O (20 mol %) was used
instead of K2CO3. H2O (5 equiv) was added. Isolated yield. DME:
dimethoxyethane.
b
c
d
e
resulted in a lower yield of 3aa (Table 1, entry 2). Only a trace
amount of product 3aa was detected when another base such
as Cs2CO3, K3PO4, or NEt3 was used (see Table S1). Then,
various palladium catalysts were screened for this reaction.
Unfortunately, reduced yields were observed with these
Received: May 21, 2019
© XXXX American Chemical Society
A
DOI: 10.1021/acs.orglett.9b01772
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
catalysts (see Table S2). When Pd(TFA)2, PdCl2, and
Pd(OAc)2 were used as the catalysts, 3aa was obtained in
29%, 18%, and trace yields, respectively (Table 1, entries 3−5).
The ratio of phenylboronic acid and nitroarene played an
important role in this reaction. Reducing the amount of
nitroarene to 1.5 equiv decreased the yield of 3aa to 17%
(Table 1, entry 6). Only a trace amount of 3aa was obtained
when 1 equiv of nitroarene was used (Table 1, entry 7). When
excess phenylboronic acid against nitroarene was used, the
amide product 3aa could also be obtained, albeit in lower
yields (Table 1, entries 8 and 9). In our experience, the
addition of water usually plays a significant role in the
reduction of nitroarenes because it serves as the hydrogen
source.8 Indeed, the yield of 3aa was improved to 62% when 5
equiv of water was added in the reaction (Table 1, entry 10).
Subsequently, various solvents were examined in this reaction.
Ether solvent such as dimethoxyethane was effective and
provided the product 3aa in 54% yield (Table 1, entry 11).
CH3CN was found out to be the optimal solvent and produced
3aa in 74% yield (Table 1, entry 12). Screening of the
bidentate phosphine ligands revealed that DPPP was optimal.
When DPPF, DPEphos, or Xantphos was used as the ligand,
3aa was obtained in 46, 15, or 18% yield, respectively (Table 1,
entries 13−15). Notably, 55% of the desired amide can still be
obtained by decreasing the loading of palladium catalyst to 2
mol %.
and produced the corresponding product in 62% yield (3ha).
In addition, heteroaryl boronic acids were also suitable
substrates for this transformation. For example, thiophen-3-
ylboronic acid 1i and furan-3-ylboronic acid 1j reacted
successfully with 4-nitrotoluene 2a and provided the
corresponding products 3ia and 3ja in 43 and 48% yield,
respectively.
Subsequently, we turned our attention to examine the
generality of this aminocarbonylation reaction with respect to
nitroarenes. As illustrated in Scheme 2, a range of nitro-
a
Scheme 2. Substrate Scope of Nitroarenes
With the optimized conditions in hand (Table 1, entry 12),
we began to investigate the substrate scope of this trans-
formation with various arylboronic acids and nitroarenes. First,
as summarized in Scheme 1, we investigated the substrate
a
Scheme 1. Substrate Scope of Arylboronic Acids
a
Reaction conditions: phenylboronic acid 1a (0.5 mmol), nitroarenes
(1 mmol), Pd(acac)2 (5 mol %), DPPP (5 mol %), Mo(CO)6 (1
mmol), K2CO3 (2 equiv), MeCN (1 mL), 110 °C, 20 h, isolated
yields.
benzenes with various substitutions at different positions of the
benzene ring were applied under the optimized conditions
(Table 1, entry 12). The corresponding amides were
successfully prepared in moderate to good yield (Scheme 2).
The electronic properties of the substituents on the benzene
ring did not significantly affect the reaction yields. Both
electron-donating and electron-withdrawing groups substituted
nitrobenzene at the para position were well tolerated and
produced the corresponding products in good to excellent
yield (Scheme 2, 3ab, 3ac, 3ad, and 3ag). The steric effect of
the substituents dramatically affected the yields (Scheme 2,
3ah vs 3ai). Moreover, this aminocarbonylation reaction also
works well for nitroheteroarene. For instance, 8-nitroquinoline
2m smoothly reacted with phenylboronic acid 1a and
produced the corresponding amide 3am in 72% yield.
On the basis of these results and previous literature, a
plausible catalytic cycle for this aminocarbonylation reaction is
proposed, as shown in Scheme 3. Initially, the transmetalation
of phenylboronic acid with Pd(II) gives a phenyl−palladium
complex, which is transformed into an acyl−palladium
intermediate after the coordination and insertion of CO
a
Reaction conditions: arylboronic acid (0.5 mmol), 4-nitrotoluene 2a
(1 mmol), Pd(acac)2 (5 mol %), DPPP (5 mol %), Mo(CO)6 (1
mmol), K2CO3 (2 equiv), MeCN (1 mL), 110 °C, 20 h, isolated
yields.
scope of the arylboronic acids. A series of different substituted
phenylboronic acids were successfully applied under our
standard reaction conditions, and the corresponding amides
were obtained in moderate to good yield (Scheme 1, 3ba−ha).
Both electron-donating-group- and electron-withdrawing-
group-substituted phenylboronic acids were well tolerated.
Fluoride was compatible in this aminocarbonylation reaction
B
DOI: 10.1021/acs.orglett.9b01772
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
coupling reagents for the synthesis of pharmaceuticals. Org. Process
Res. Dev. 2016, 20, 140−177. (e) Carey, J. S.; Laffan, D.; Thomson,
C.; Williams, M. T. Analysis of the reactions used for the preparation
of drug candidate molecules. Org. Biomol. Chem. 2006, 4, 2337−2347.
(f) Roughley, S. D.; Jordan, A. M. The medicinal chemist’s toolbox:
an analysis of reactions used in the pursuit of drug candidates. J. Med.
Chem. 2011, 54, 3451−3479.
Scheme 3. Plausible Catalytic Cycle
(2) For recent reviews on amide N−C acyl cleavage, see: (a) Shi, S.;
Nolan, S. P.; Szostak, M. Well-Defined Palladium(II)-NHC
Precatalysts for Cross-Coupling Reactions of Amides and Esters by
Selective N−C/O−C Cleavage. Acc. Chem. Res. 2018, 51, 2589−
2599. (b) Meng, G.; Szostak, M. N-Acyl-Glutarimides: Privileged
Scaffolds in Amide N-C Bond Cross-Coupling. Eur. J. Org. Chem.
2018, 2018, 2352−2365. (c) Liu, C.; Szostak, M. Twisted Amides:
From Obscurity to Broadly Useful Transition-Metal-Catalyzed
Reactions by N-C Amide Bond Activation. Chem. - Eur. J. 2017, 23,
7157−7173.
(3) (a) Valeur, E.; Bradley, M. Amide bond formation: beyond the
myth of coupling reagents. Chem. Soc. Rev. 2009, 38, 606−631. (b) Li,
G.; Szostak, M. Highly selective transition-metal-free transamidation
of amides and amidation of esters at room temperature. Nat. Commun.
2018, 9, 4165. (c) Zhou, T.; Li, G.; Nolan, S. P.; Szostak, M.
[Pd(NHC)(acac)Cl]: Well-Defined, Air-Stable, and Readily Available
Precatalysts for Suzuki and Buchwald-Hartwig Cross-coupling
(Transamidation) of Amides and Esters by N-C/O-C Activation.
Org. Lett. 2019, 21, 3304−3309.
from Mo(CO)6. At the same time, the nitroarene is reduced by
Mo(CO)6 in the presence of water to give aromatic amine.8
The nucleophilic attack of amine on the acyl−palladium
intermediate releases the desired product and Pd(II) for the
next catalytic cycle.
(4) (a) de Figueiredo, R. M.; Suppo, J. S.; Campagne, J. M.
Nonclassical Routes for Amide Bond Formation. Chem. Rev. 2016,
116, 12029−12122. (b) Pattabiraman, V. R.; Bode, J. W. Rethinking
amide bond synthesis. Nature 2011, 480, 471−479. (c) Allen, C. L.;
Williams, J. M. Metal-catalysed approaches to amide bond formation.
Chem. Soc. Rev. 2011, 40, 3405−3415. (d) Guo, X.; Facchetti, A.;
Marks, T. J. Imide-and amide-functionalized polymer semiconductors.
In summary, we have developed a palladium-catalyzed
aminocarbonylation of aryl boronic acids with nitroarenes for
the synthesis of amides. A range of substituted amides were
prepared in moderate to good yield from easily available aryl
boronic acids and nitroarenes. No external reductant or
oxidant is needed in this procedure. The reaction proceeded in
a CO-gas-free and redox-economic manner, where Mo(CO)6
was used as a solid CO source and nitroarene was used as a
cheap and abundant nitrogen source.
Chem. Rev. 2014, 114, 8943−9021. (e) Brennfuhrer, A.; Neumann,
̈
H.; Beller, M. Palladium-catalyzed carbonylation reactions of aryl
halides and related compounds. Angew. Chem., Int. Ed. 2009, 48,
4114−4133. (f) Friis, S. D.; Skrydstrup, T.; Buchwald, S. L. Mild Pd-
catalyzed aminocarbonylation of (hetero) aryl bromides with a
palladacycle precatalyst. Org. Lett. 2014, 16, 4296−4299. (g) Xu, T.;
Alper, H. Pd-catalyzed chemoselective carbonylation of aminophenols
with iodoarenes: alkoxycarbonylation vs aminocarbonylation. J. Am.
Chem. Soc. 2014, 136, 16970−16973. (h) Skogh, A.; Friis, S. D.;
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.9b01772.
̈
Skrydstrup, T.; Sandstrom, A. Palladium-Catalyzed Aminocarbonyla-
tion in Solid-Phase Peptide Synthesis: A Method for Capping,
Cyclization, and Isotope Labeling. Org. Lett. 2017, 19, 2873−2876.
(i) Zhang, J.; Ma, Y.; Ma, Y. Synthesis of Secondary Amides through
the Palladium(II)-Catalyzed Aminocarbonylation of Arylboronic
Acids with Amines or Hydrazines and Carbon Monoxide. Eur. J.
Org. Chem. 2018, 2018, 1720−1725. (j) Zhang, J.; Hou, Y.; Ma, Y.;
Szostak, M. Synthesis of Amides by Mild Palladium-Catalyzed
Aminocarbonylation of Arylsilanes with Amines Enabled by Copper-
(II) Fluoride. J. Org. Chem. 2019, 84, 338−345.
General comments, general procedure, optimization
details, analytic data, and NMR spectra (PDF)
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: xiao-feng.wu@catalysis.de
ORCID
(5) For selected examples on aminocarbonylation reactions with
nitro compounds, see: (a) Peng, J.-B.; Geng, H.-Q.; Li, D.; Qi, X.;
Ying, J.; Wu, X.-F. Palladium-Catalyzed Carbonylative Synthesis of
α,β-Unsaturated Amides from Styrenes and Nitroarenes. Org. Lett.
2018, 20, 4988−4993. (b) Cheung, C. W.; Leendert Ploeger, M.; Hu,
X. Amide Synthesis via Nickel-Catalysed Reductive Aminocarbony-
lation of Aryl Halides with Nitroarenes. Chem. Sci. 2018, 9, 655−659.
(c) Peng, J.-B.; Geng, H.-Q.; Wang, W.; Qi, X.; Ying, J.; Wu, X.-F.
Palladium-catalyzed four-component carbonylative synthesis of 2,3-
disubstituted quinazolin-4(3H)-ones: Convenient methaqualone
preparation. J. Catal. 2018, 365, 10−13. (d) Zhou, F.; Wang, D. S.;
Guan, X.; Driver, T. G. Nitroarenes as the Nitrogen Source in
Intermolecular Palladium-Catalyzed Aryl C-H Bond Aminocarbony-
lation Reactions. Angew. Chem., Int. Ed. 2017, 56, 4530−4534.
(e) Jana, N.; Zhou, F.; Driver, T. G. Promoting Reductive Tandem
Reactions of Nitrostyrenes with Mo(CO)6 and a Palladium Catalyst
to Produce 3H-indoles. J. Am. Chem. Soc. 2015, 137, 6738−6741.
Xiao-Feng Wu: 0000-0001-6622-3328
Funding
We acknowledge the financial supports from NSFC
(21801225, 21772177).
Notes
The authors declare no competing financial interest.
REFERENCES
■
(1) For selected recent reviews, see: (a) Roy, S.; Roy, S.; Gribble, G.
W. Metal-catalyzed amidation. Tetrahedron 2012, 68, 9867−9923.
(b) Pattabiraman, V. R.; Bode, J. W. Rethinking amide bond
synthesis. Nature 2011, 480, 471−479. (c) de Figueiredo, R. M.;
Suppo, J. S.; Campagne, J. M. Nonclassical routes for amide bond
formation. Chem. Rev. 2016, 116, 12029−12122. (d) Dunetz, J. R.;
Magano, J.; Weisenburger, G. A. Large-scale applications of amide
C
DOI: 10.1021/acs.orglett.9b01772
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
(f) Zhou, F.; Wang, D. S.; Driver, T. G. Palladium-Catalyzed
Formation of N-Heteroarenes from Nitroarenes using Molybdenum
Hexacarbonyl as the Source of Carbon Monoxide. Adv. Synth. Catal.
2015, 357, 3463−3468. (g) Fang, X.; Jackstell, R.; Beller, M. Selective
Palladium-Catalyzed Aminocarbonylation of Olefins with Aromatic
Amines and Nitroarenes. Angew. Chem., Int. Ed. 2013, 52, 14089−
14093. (h) Wang, X.; Li, P.; Yuan, X.; Lu, S. Selenium-Catalyzed
Carbonylation of Nitroarenes to Symmetrical 1, 3-Diarylureas under
Solvent-Free Conditions. J. Mol. Catal. A: Chem. 2006, 253, 261−264.
(i) Ragaini, F.; Ghitti, A.; Cenini, S. Mechanistic Study of the
Ru3(CO)12/Tetraalkylammonium Chloride Catalyzed Carbonylation
Reactions of Nitroarenes to Carbamates and Ureas: A Completely
Revised Picture. Organometallics 1999, 18, 4925−4933. (j) Islam, S.
M.; Mal, D.; Palit, B. K.; Saha, C. R. Reductive Carbonylation of
Nitroaromatics using RhA (CO)2. J. Mol. Catal. A: Chem. 1999, 142,
169−181. (k) Wehman, P.; Borst, L.; Kamer, P. C.; van Leeuwen, P.
W. Influence of an Aromatic Carboxylic Acid as Cocatalyst in the
Palladium-Catalysed Reductive Carbonylation of Aromatic Nitro
Compounds. J. Mol. Catal. A: Chem. 1996, 112, 23−36. (l) Bassoli, A.;
Rindone, B.; Cenini, S. Polar Effects in the Ruthenium (0)-Catalysed
Reductive Carbonylation of Aromatic Nitro Derivatives to Give Ureas
and Amines. J. Mol. Catal. 1991, 66, 163−170. (m) Tafesh, A. M.;
Weiguny, J. A Review of the Selective Catalytic Reduction of
Aromatic Nitro Compounds into Aromatic Amines, Isocyanates,
Carbamates, and Ureas Using CO. Chem. Rev. 1996, 96, 2035−2052.
(n) Yang, Y.; Lu, S. Selenium-Catalyzed Reductive Carbonylation of
Nitrobenzene with Amines as Coreagents to Give Unsymmetric
Phenylureas. Tetrahedron Lett. 1999, 40, 4845−4846. (o) Chen, J.;
Ling, G.; Lu, S. Synthesis of New Unsymmetric N, N′-Dipyridylurea
Derivatives by Selenium and Selenium Dioxide-Catalyzed Reductive
Carbonylation of Substituted Nitropyridines. Tetrahedron 2003, 59,
8251−8256. (p) Chen, J.; Lu, S. Synthesis of Substituted Pyridyl
Ureas by Selenium Dioxide-Catalyzed Carbonylation. Appl. Catal., A
2004, 261, 199−203. (q) Ling, G.; Chen, J.; Lu, S. Selenium-
Catalyzed Carbonylation of Substituted Nitrobenzenes with Amino-
methylpyrimidines as Co-Reagents to Synthesize N-phenyl-N′-
methylpyrimidylurea Derivatives. J. Mol. Catal. A: Chem. 2003, 202,
23−29. (r) Mei, J.; Yang, Y.; Xue, Y.; Lu, S. Selective Formation of
Unsymmetric Ureas by Selenium-Catalyzed Oxidative-Reductive
Carbonylation with CO. J. Mol. Catal. A: Chem. 2003, 191, 135−139.
(6) For selected reviews on carbonylation using CO surrogates, see:
(a) Morimoto, T.; Kakiuchi, K. Evolution of Carbonylation Catalysis:
No Need for Carbon Monoxide. Angew. Chem., Int. Ed. 2004, 43,
5580−5588. (b) Odell, L. R.; Russo, F.; Larhed, M. Molybdenum
Hexacarbonyl Mediated CO Gas-Free Carbonylative Reactions.
Synlett 2012, 23, 685−698. (c) Konishi, H.; Manabe, K. Formic
Acid Derivatives as Practical Carbon Monoxide Surrogates for Metal-
Catalyzed Carbonylation Reactions. Synlett 2014, 25, 1971−1986.
(d) Peng, J.-B.; Qi, X.; Wu, X.-F. Recent Achievements in
Carbonylation Reactions: A Personal Account. Synlett 2017, 28,
175−194. (e) Gautam, P.; Bhanage, B. M. Recent Advances in the
Transition Metal Catalyzed Carbonylation of Alkynes, Arenes and
Aryl Halides using CO Surrogates. Catal. Sci. Technol. 2015, 5, 4663−
4702. (f) Sam, B.; Breit, B.; Krische, M. J. Paraformaldehyde and
Methanol as C1 Feedstocks in Metal-Catalyzed C-C Couplings of π-
Unsaturated Reactants: Beyond Hydroformylation. Angew. Chem., Int.
Ed. 2015, 54, 3267−3274. (g) Friis, S. D.; Lindhardt, A. T.;
Skrydstrup, T. The Development and Application of Two-Chamber
Reactors and Carbon Monoxide Precursors for Safe Carbonylation
Reactions. Acc. Chem. Res. 2016, 49, 594−605. (h) Åkerbladh, L.;
Odell, L. R.; Larhed, M. Palladium-Catalyzed Molybdenum
Hexacarbonyl-Mediated Gas-Free Carbonylative Reactions. Synlett
2019, 30, 141−155.
of Boronic Acids with Nitro Compounds. Angew. Chem., Int. Ed. 2019,
58, 2129−2133. (d) Nykaza, T. V.; Yang, J.; Radosevich, A. T. PEt3-
Mediated Deoxygenative C-N Coupling of Nitroarenes and Boronic
Acids. Tetrahedron 2019, 75, 3248.
(8) He, L.; Sharif, M.; Neumann, H.; Beller, M.; Wu, X.-F. A
Convenient Palladium-Catalyzed Carbonylative Synthesis of 4(3H)-
Quinazolinones from 2-Bromoformanilides and Organo Nitros with
Mo(CO)6 as a Multiple Promoter. Green Chem. 2014, 16, 3763−
3767.
(7) (a) Newhouse, T.; Baran, P. S.; Hoffmann, R. W. The
Economies of Synthesis. Chem. Soc. Rev. 2009, 38, 3010−3021.
(b) Burns, N. Z.; Baran, P. S.; Hoffmann, R. W. Redox Economy in
Organic Synthesis. Angew. Chem., Int. Ed. 2009, 48, 2854−2867.
́
́
(c) Suarez-Pantiga, S.; Hernandez-Ruiz, R.; Virumbrales, C.; Pedrosa,
M. R.; Sanz, R. Reductive Molybdenum-Catalyzed Direct Amination
D
DOI: 10.1021/acs.orglett.9b01772
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