Selective reduction of carbonyl amides: Toward the first unsymmetrical bischelating N-substituted 1,2-diamino-4,5-diamidobenzene

Article abstract of DOI:10.1002/ejoc.200800087

Selective reduction of carbonyl amides from key tetraamido intermediate 12 afforded an unprecedented N-substituted 1,2-diamino-4,5-diamidobenzene (13) and/or the first member (14) of a new family of unsymmetrical 12π-electron quinonediimines. Wiley-VCH Ve

Full text of DOI:10.1002/ejoc.200800087

FULL PAPER
DOI: 10.1002/ejoc.200800087
Selective Reduction of Carbonyl Amides: Toward the First Unsymmetrical
Bischelating N-Substituted 1,2-Diamino-4,5-diamidobenzene
Claire Seillan,[a] Pierre Braunstein,[b] and Olivier Siri*[a]
Keywords: Reduction / N ligands / Amides
Selective reduction of carbonyl amides from key tetraamido
intermediate 12 afforded an unprecedented N-substituted
1,2-diamino-4,5-diamidobenzene (13) and/or the first
member (14) of a new family of unsymmetrical 12π-electron
quinonediimines.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2008)
chemically connected by two single C–C bonds but each
unit is electronically independent (no conjugation).[5]
As an extension of these studies, it appeared very attract-
ive to develop the synthesis of new N-substituted p-benzo-
quinonediimines such as 4, for which a fine tuning of the
substituents in the two different, potentially bischelating
sites would allow new developments in quinoid and coordi-
nation chemistry.
During the course of this work, we developed access to
N-substituted 1,2-diamino-4,5-diamidobenzenes such as 5,
which were hitherto unknown. Note that only the unsubsti-
tuted amino analog was recently described [molecule 5 with
R1 = H and R2 = C(O)OEt] as an intermediate in the prep-
aration of ligands containing salophen and bis(oxamato)
cavities.[18,19]
Introduction
p-Benzoquinonediimines constitute a large and impor-
tant class of organic compounds that display interesting
colors and are endowed with very rich chemical and physi-
cal properties.[1,2] They can be classified under three major
categories, namely, I, II, and III.[1] Class I molecules (1)
contain no substituent attached to the benzoquinoid ring
and have been described mainly with electron-withdrawing
R groups that stabilize the systems.[2] Class II (2) contains
amino substituents at the 2- and 5-positions of the benzo-
quinoid ring (R1 = or ϶ R2 = or ϶ R3).[1,3–11] Class III
derivatives (3) contains all other 1,4-benzoquinonediimines
(X = or ϶ Y, but both are different from N).[1]
The second class of quinonediimines is the largest owing
to easy access to symmetrical systems (R1 = R2 = R3) and
a high stability, which have allowed their use in different
fields ranging from hair coloring[12] and biosensors[13] to
supramolecular[14] and coordination chemistry.[15] This high
stability is explained by the coupling principle[16,17] of the
12π-electron system of the quinoid skeleton, which is best
described as being constituted of two 6π-electron subunits
Systems of type 5 combine the structural elements of 6
and 7, which have generated much interest in organic,[20–22]
organometallic,[23–28] and/or supramolecular chemistry[29,30]
owing to the ability of the amino and/or amido groups to
act as nucleophiles, coordinating moieties, or H-donor sites.
The preparation of N-substituted aromatic amide amines
has mainly involved a strategy based on the selective
monoacylation of one of the amino groups.[31–36] The devel-
opment of new procedures is thus still of great interest.
Herein, we report a rare example of selective reduction
of carbonyl amides from key tetraamido intermediate 12,
which allows access to unprecedented N-substituted 1,2-di-
amino-4,5-diamidobenzene 13 and the first member (14) of
a new family of unsymmetrical 12π-electron quinonediimines.
[a] Centre Interdisciplinaire de Nanoscience de Marseille (CINaM),
UPR 3118 CNRS, Aix Marseille Université,
Campus de Luminy, case 913, 13288 Marseille Cedex 09, France
Fax: +33-4-91829580
E-mail: siri@univmed.fr
[b] Laboratoire de Chimie de Coordination, Institut de Chimie
(UMR 7177 CNRS), Université Louis Pasteur,
4, rue Blaise Pascal, 67070 Strasbourg Cedex, France
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the alkyl and aryl substituents. However, the chemoselectiv-
ity in the reduction of 12 to 13 is limited, probably by the
presence of competing reaction sites in the intermediates
involved in the formation of 13 and 14.
Results and Discussion
Nitration of 1,2-diaminobenzene 8 itself is not feasible
and N,NЈ-protected derivatives have been used for the prep-
aration of 1,2-diamino-4,5-dinitrobenzene 9 bearing two
amino groups (Scheme 1).[37] After treatment of 9 with
tBuC(O)Cl in MeCN in the presence of NEt3, compound
10 was isolated in 95% yield. The reduction of the nitro
groups was performed with SnCl2·2H2O in MeOH to afford
11 (80% yield), which was further treated with PhC(O)Cl
in MeCN to give 12 in 85% yield (Scheme 1).
Direct reduction of the four amido functionalities of 12
results in the formation of the corresponding electron-rich
tetraamino derivative A (not isolated), which in air sacri-
fices its aromatic character in favor of quinoid structure
14 (Scheme 1). Isolation of A should be possible under an
atmosphere of nitrogen, as described for the symmetrical
1,2,4,5-tetrakis-N-tert-butylaminobenzene analog.[4] De-
spite difficult purifications due to its high solubility and its
presence among a mixture of compounds with similar po-
larities, molecule 14 could be isolated pure as an orange
solid. The use of a large excess of LiAlH4 (18 equiv.) for the
reduction of 12 led only to the formation of 14 with a sim-
ilar yield (5%). The low yield may be due to partial decom-
position of 14 during its isolation as a result of possible side
reactions (hydrolysis, co-condensation), which lead to the
presence of a large number of unidentified compounds (the
remaining 65% of the reaction products). However, once
isolated pure, 14 appears to be stable in solution or in the
solid state for weeks. Note that access to 14 can also be
achieved by reduction of 13 with LiAlH4.
1
The H NMR spectrum of 13 shows the presence of a
signal at δ = 2.61 ppm, which is in agreement with the pres-
ence of a methylenic HN–CH2–tBu group (i.e., methylenic
HN–CH2–Ph groups are downfield shifted up to 4.30 ppm
approx.). In addition, a broad signal at δ = 9.06 ppm is
consistent with the presence of two equivalent amido N–H
protons and confirms the selective reduction.
As a white powder, molecule 13 exhibits an expected ab-
sorption band in the UV region centered at 326 nm (ε =
5200 Lmol–1 cm–1) (Figure 1).
Scheme 1. Synthesis of molecules 13 and 14.
The 1H NMR spectrum of 12 revealed two NH reso-
nances at δ = 9.03 and 9.98 ppm and a signal at δ =
7.84 ppm (aromatic C–H of the central ring), which is con-
sistent with the structure drawn. This tetraamido com-
pound appeared to be a key intermediate for the prepara-
tion of two new classes of organic systems. Reduction of 12
with LiAlH4 in refluxing THF afforded 13 and 14 as the
Figure 1. UV/Vis absorption spectrum of compound 13 in CHCl3
at room temperature.
The cyclic voltammogram of 13 in anhydrous CH2Cl2
major (30% yield) and minor (5% yield) products, respec- showed two poorly reversible waves (oxidative potentials at
tively. 0.54 and 0. 77 V vs. Ag/AgCl) resulting from two successive
The selective reduction of 12 with LiAlH4 into 1,2-di- oxidation processes (Figure 2). When the cyclic voltammog-
amino-4,5-diamidobenzene 13 could be achieved as a result ram was recorded by starting in negative potentials, no re-
of the different reactivities of the carbonyl amides, which duction peak was observed. In contrast, three new re-
originates from the different steric and electronic effects of duction peaks appeared at –0.03, –0.69, and 0.83 V vs. Ag/
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Selective Reduction of Carbonyl Amides
Scheme 2. Tautomeric equilibrium of 14 in solution.
AgCl when the experiment was started in positive poten- available 1,2,4-triaminobenzene dihydrochloride with
tials. This result is consistent with chemical evolution of the tBuC(O)Cl in MeCN in the presence of NEt3. As expected,
oxidized species as observed for aromatic amines.[38]
molecule 16 is well soluble in organic solvents such as ace-
tone and CH2Cl2.
Conclusions
We described a rare example of selective reduction of car-
bonyl amides from key tetraamido intermediate 13, which
afforded unprecedented N-substituted 1,2-diamino-4,5-di-
amidobenzene 12 that might be used in different areas of
chemistry. In addition, we could isolate the first member
(14) of a new family of 12π-electron quinonediimines, for
which a fine tuning of the N-substituents in the two dif-
ferent potentially chelating sites opens new opportunities in
coordination chemistry.
Figure 2. Cyclic voltammogram of compound 13 in CH2Cl2 [0.1 
N(nBu)4PF6] starting in oxidation (···) and in reduction (Ϫ).
Experimental Section
General: Commercial analytical-grade reagents were obtained from
commercial suppliers and used directly without further purifica-
tion. Solvents were distilled under an atmosphere of argon prior to
use and dried by standard methods. 1H and 13C NMR spectra were
The 1H NMR spectrum of 14 showed two singlets at δ =
2.92 and 4.50 ppm, which is characteristic of the methylenic
protons N–CH2–tBu and N–CH2–Ph, respectively. The recorded in CDCl3, [D6]acetone, and [D6]DMSO with a AC250
Bruker spectrometer operating at 250 MHz. Chemical shifts are re-
ported in δ units in parts per million (ppm). Splitting patterns are
designed as s, singlet; d, doublet; m, multiplet; br., broad. Elemen-
tal and MS analyses were performed by the Spectropole of Mar-
seille. ESI mass spectral analyses were recorded with a 3200
QTRAP (Applied Biosystems SCIEX) mass spectrometer. The
HRMS mass spectral analysis was performed with a QStar Elite
(Applied Biosystems SCIEX) mass spectrometer. Cyclic voltam-
metric (CV) data were acquired by using a BAS 100 Potentiostat
(Bioanalytical Systems) and a PC computer containing BAS100W
presence of two magnetically equivalent olefinic protons
and neopentyl and benzyl groups is consistent with a fast
intramolecular double proton transfer involving two tauto-
mers and generating in solution an average structure of
higher symmetry (Scheme 2). This phenomenon has been
described previously but only for symmetrical quinone-
diimines.[5,11,39]
The poor solubility of 12 suggests the formation in the
solid state of an H-bonded supramolecular network involv-
ing the four amido functionalities, as observed for symmet- software (v2.3). A three-electrode system with a Pt working elec-
rical analog 15.[5] The fact that diamino–diamido analog 13
is much more soluble in organic solvents supports the view
that the four amido groups of 15 are involved in this H-
trode (diameter 1.6 mm), a platinum counter electrode, and an Ag/
AgCl (with 3  NaCl filling solution) reference electrode was used.
Tetrabutylammonium hexafluorophosphate (Fluka) was used as re-
ceived. Anhydrous CH2Cl2 with electronic-grade purity was used.
bonded network.
The compound was studied at 1ϫ10–3  in CH2Cl2/TBHP 0.1 ,
and the cyclic voltammogram was recorded at a scan rate of
250 mV·s–1. Ferrocene was used as an internal standard.
1,2-Bis(2,2-dimethylpropanamido)-4,5-dinitrobenzene (10): Triethyl-
amine (1.4 mL, 4 equiv.) was added dropwise to a solution of 1,2-
diamino-4,5-dinitrobenzene 9 (0.50 g, 2.53 mmol, 1 equiv.) in anhy-
drous acetonitrile (80 mL) under an atmosphere of argon at room
temperature. The mixture was then stirred at room temperature for
5 min and trimethyl acetyl chloride (625 µL, 6.90 mmol, 2 equiv.)
In order to confirm this hypothesis, we realized the
was added dropwise. The reaction mixture was heated under reflux
synthesis of compound 16 by reaction of commercially for 6 h, and the reaction was monitored by TLC (cyclohexane/ethyl
Eur. J. Org. Chem. 2008, 3113–3117
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C. Seillan, P. Braunstein, O. Siri
FULL PAPER
acetate, 5:5). The solvent was then evaporated under reduced pres-
sure. The residue was taken up in water (50 mL), and the insoluble
product was isolated by filtration. This latter was purified by
chromatography on silica gel (cyclohexane/ethyl acetate, 8:2, 7:3,
6:4) to afford 10 (0.88 g, 95% yield) as a beige solid. 1H NMR
(250 MHz, [D6]acetone): δ = 1.34 (s, 18 H, CH3), 8.43 (s, 2 H,
sure. The crude product was then taken up in acetonitrile (2 mL).
The solid in suspension was isolated by filtration and washed with
diethyl ether (3 mL) to afford 13 (0.06 g, 30% yield) as a white
1
solid. H NMR (250 MHz, CDCl3): δ = 0.91 (s, 18 H, CH3), 2.61
(s, 4 H, N-CH2-tBu), 3.04 (br. s, 2 H, HN-CH2-tBu), 6.72 (s, 2 H,
aromatic CH), 7.51 (t, Jortho = 7.5 Hz, 6 H, aromatic CH), 8.02 (d,
aromatic CH), 9.35 (br. s, 2 H, NH) ppm. 13C{1H} NMR (62 MHz, Jortho = 7.5 Hz, 4 H, aromatic CH), 9.06 [s, 2 H, HN-C(O)Ph] ppm.
[D6]acetone): δ = 27.5 (CH3), 40.5 [-C(CH3)3], 122.3 (aromatic
CH), 136.0, 139.6 (aromatic C), 178.9 (C=O) ppm. MS (ESI): m/z
= 367 [M + H]+. C16H22N4O6 (366.15): calcd. C 52.45, H 6.05, N
15.26; found C 52.18, H 6.03, N 15.09.
13C{1H} NMR (62 MHz, CDCl3): δ = 27.8 (CH3), 31.3 [-C-
(CH3)3], 56.2 (N-CH2-tBu), 109.2, 122.5, 127.6, 128.6, 131.7, 134.3,
137.2 (aromatic CH), 166.1 (C=O) ppm. MS (MALDI-TOF+): m/z
= 487 [M + H]+, 509 [M + Na]+. C30H38N4O2·H2O (504.31): calcd.
C 71.40, H 7.99, N 11.10, found C 71.90, H 7.32, N 11.62.
4,5-Diamino-1,2-bis(2,2-dimethylpropanamido)benzene (11): SnCl2·
2H2O (12.00 g, 53.38 mmol, 14 equiv.) was quickly added to a solu-
tion of 10 (1.40 g, 3.82 mmol, 1 equiv.) in methyl alcohol (100 mL)
under reflux. The solution was then stirred for 17 h in refluxing
methyl alcohol. The end of the reaction was monitored by TLC
(cyclohexane/ethyl acetate, 5:5). The solvent was evaporated under
reduced pressure, and the residue was taken up in a mixture of
EtOH/H2O (20:50). The mixture was neutralized by the addition
of a saturated solution of NaHCO3. Tin salts were removed by
filtration. The filtrate was then extracted by ethyl acetate. The or-
ganic layer was dried with anhydrous MgSO4, filtered, and evapo-
rated under reduced pressure. The residue was purified by flash
chromatography on silica gel (ethyl acetate then ethyl acetate/
methyl alcohol, 99:1, 98:2, 95:5, 90:10). Expected compound 11
(0.93 g, 80% yield) was obtained as an orange solid. 1H NMR
(250 MHz, [D6]acetone): δ = 1.25 (s, 18 H, CH3), 4.06 (br. s, 4 H,
NH2), 6.70 (s, 2 H, aromatic CH), 8.46 [br. s, 2 H, NH-C(O)] ppm.
13C{1H} NMR (62 MHz, [D6]acetone): δ = 28.0 (CH3); 39.7
[-C(CH3)3]; 105.3 (aromatic CH); 123.3, 139.2 (aromatic C); 177.1
(C=O) ppm. MS (ESI): m/z = 307 [M + H]+. C16H26N4O2 (306.20):
calcd. C 62.30, H 8.72, N 17.87; found C 62.50, H 8.75, N 17.92.
N-Benzyl-2-(benzylamino)-NЈ-neopentyl-5-(neopentylamino)-1,4-
benzoquinonediimine (14): The filtrate obtained from the synthesis
of 13 was evaporated under reduced pressure and taken up in pen-
tane. The insoluble solid was then isolated by filtration and washed
with pentane to afford compound 14 (0.01 g, 5% yield) as an
orange amorphous solid. 1H NMR (250 MHz, [D6]acetone): δ =
0.97 (s, 18 H, CH3), 2.92 (s, 4 H, N-CH2-tBu), 4.50 (s, 4 H, N-
CH2-Ph), 5.29 (s, 2 H, quinoid CH), 6.80 (br. s, 2 H, NH), 7.35
(m, 10 H, aromatic CH) ppm. HRMS (ESI): calcd. for C30H40N4
[M + H]+ 457.3326; found 457.3312.
1,2,4-Tris(2,2-dimethylpropanamido)benzene (16): Triethylamine
(57 µL, 4.09 mmol, 3 equiv.) was added dropwise to a solution of
1,2,4-triaminobenzene dihydrochloride (0.21 g, 1.02 mmol,
1 equiv.) in anhydrous acetonitrile (30 mL) under an atmosphere of
argon at room temperature. The mixture was then stirred at room
temperature for 5 min and trimethyl acetyl chloride (38 µL,
3.09 mmol, 2 equiv.) was added dropwise. The reaction mixture was
heated under reflux for 4 h, and the reaction was monitored by
TLC (cyclohexane/ethyl acetate, 5:5). The solvent was then evapo-
rated under reduced pressure. The residue was taken up in water
(30 mL), and insoluble product 16 (0.34 g, 89% yield) was isolated
4,5-Dibenzamido-1,2-bis(2,2-dimethylpropanamido)benzene
(12):
1
by filtration as a purple solid. H NMR (250 MHz, [D6]acetone):
Triethylamine (1 mL, 7.17 mmol, 4 equiv.) was added dropwise to
a solution of 11 (0.56 g, 1.83 mmol, 1 equiv.) in acetonitrile (60 mL)
under an atmosphere of argon at room temperature. The mixture
was then stirred at room temperature for 5 min and benzoyl chlo-
ride (640 µL, 5.51 mmol, 3 equiv.) was added dropwise. The reac-
tion mixture was heated under reflux for 26 h, and the reaction was
monitored by TLC (cyclohexane/ethyl acetate, 5:5). The solution
was cooled down to room temperature, and the white precipitate
was isolated by filtration and washed with water to afford 12
δ = 1.29 (br. s, 27 H, CH3), 7.31 (d, Jortho = 8.5 Hz, 1 H, aromatic
CH), 7.52 (dd, Jortho = 8.5 Hz, Jpara = 2.5 Hz, 1 H, aromatic CH),
7.75 (d, Jpara = 2.5 Hz, 1 H), 8.74 (br. s, 1 H, NH), 8.82 (br. s, 1
H, NH), 8.88 (br. s, 1 H, NH) ppm. 13C{1H} NMR (62 MHz,
[D6]acetone): δ = 27.75, 27.76, 27.77 (CH3); 39.48, 39.57, 39.62
[-C(CH3)3]; 117.17, 118.04, 125.39, 126.91, 131.31, 135.57 (aro-
matic CH); 177.07, 178.10, 178.24 (C=O) ppm. MS (ESI): m/z =
376 [M + H]+. C21H33N3O3·1/2H2O (384.25): calcd. C 65.81, H
8.80, N 11.29; found C 65.60, H 8.91, N 10.93.
1
(0.81 g, 85% yield) as a white solid. H NMR (250 MHz, [D6]ace-
tone): δ = 1.33 (s, 18 H, CH3), 7.55 (m, 6 H, aromatic CH), 7.84
(s, 2 H, aromatic CH), 8.06 (dd, Jortho = 8.0 Hz, Jmeta = 1.5 Hz, 4
H, aromatic CH), 9.03 [br. s, 2 H, NH-C(O)-tBu], 9.98 [br. s, 2 H,
NH-C(O)-Ph] ppm. 13C{1H} NMR spectroscopic data of com-
pound 12 are not reported owing to its lack of solubility. MS
(MALDI-TOF): m/z = 513 [M – H]+. C30H34N4O4 (514.25): calcd.
C 70.02, H 6.66, N 10.89; found C 69.71, H 6.72, N 10.92.
Acknowledgments
This work in Marseille and Strasbourg was supported by the Cen-
tre National de la Recherche Scientifique, the Ministère de l’Enseig-
nement Supérieur et de la Recherche, and the Provence Alpes Côte
d’Azur Region (PhD grant of C. S.). We thank Dr. Hugues Brisset
for fruitful discussions and electrochemical studies.
4,5-Dibenzamido-1,2-bis(neopentylamino)benzene (13): Compound
12 (0.21 g, 0.41 mmol, 1 equiv.) was added in small portions to a
stirred suspension of LiAlH4 (0.10 g, 2.63 mmol, 6 equiv.) in anhy-
drous THF (30 mL) under an atmosphere of argon. The reaction
mixture was stirred in refluxing THF under an atmosphere of ar-
gon for 6 h. The total consumption of reactive 12 was monitored
by TLC. The mixture was cooled down to room temperature and
hydrolyzed with water/methyl alcohol (3:1, 8 mL). The solvents
were evaporated under reduced pressure, and the residue was taken
up in dichloromethane. The insoluble aluminate salts were removed
by filtration, and the filtrate was washed with water, dried with
anhydrous MgSO4, filtered, and evaporated under reduced pres-
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Received: January 24, 2008
Published Online: May 8, 2008
Eur. J. Org. Chem. 2008, 3113–3117
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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