Synthesis and first characterization of N-alkyldiaminoresorcinols

Article abstract of DOI:10.1016/j.tetlet.2006.06.025

We report the synthesis and first characterization of N-alkyldiaminoresorcinols (or 4,6-bis-dialkylaminobenzene-1,3-diols C₆H₂(NHR)₂(OH)₂) (10a, R = CH₂-2-Py; 10b, R = CH₂-3-Py; 10c, R = CH

Full text of DOI:10.1016/j.tetlet.2006.06.025

Tetrahedron Letters 47 (2006) 5727–5731
Synthesis and first characterization of
N-alkyldiaminoresorcinols
b
a,
*
Qing-Zheng Yang,a Olivier Siri,a,b, Hugues Brisset and Pierre Braunstein
*
aLaboratoire de Chimie de Coordination, UMR 7177 CNRS, Universite´ Louis Pasteur, 4, rue Blaise Pascal,
67070 Strasbourg Cedex, France
bGroupe de Chimie Organique et Mate´riaux Mole´culaires, UMR 6114 CNRS, Universite´ de la Me´diterrane´e Faculte´ des Sciences de
Luminy, case 901, 163 avenue de Luminy, 13288 Marseille Cedex 09, France
Received 9 March 2006; accepted 2 June 2006
Available online 27 June 2006
Abstract—We report the synthesis and first characterization of N-alkyldiaminoresorcinols (or 4,6-bis-dialkylaminobenzene-1,3-diols
C6H2(NHR)2(OH)2) (10a, R = CH2-2-Py; 10b, R = CH2-3-Py; 10c, R = CH2-4-Py) which result from one-pot stepwise reactions: (i)
air–oxidation of diaminoresorcinol 3, (ii) transamination reaction leading to the corresponding functional 6p+6p quinonemo-
noimine zwitterions C6H2( NHR)2( O)2 (9a, R = CH2-2-Py; 9b, R = CH2-3-Py; 9c, R = CH2-4-Py), (iii) reduction and re-aroma-
tization in the presence of the corresponding primary amine bearing a pyridine moiety.
Ó 2006 Elsevier Ltd. All rights reserved.
Introduction of substituent(s) on the benzene ring1,2 has
led to hundreds of compounds showing dramatic
changes of their properties depending on the nature of
the substituent(s).3 Amino and/or hydroxy benzene
derivatives have attracted considerable interest in
organic,3 colour (cosmetic),4 inorganic5 and supramo-
lecular chemistry6,7 owing to the ability of the NH2
and/or OH groups to act as nucleophiles, coordinating
moieties or H-donor sites. Resorcinol 1 and 1,3-diami-
nobenzene 2 have been the object of 21,416 and 12,999
references (Scifinder source, June 2006), respectively.
Therefore, it is surprising that the aromatic system 3,
which combines the structural elements of 1 and 2 and
is commercially available, has been much less explored
(635 references), although the substitution pattern of
its amino and hydroxy groups would allow bis-ortho-
condensation reactions by analogy with those involving
1,2,4,5-tetraaminobenzene,8–15 metal complexation (bis-
chelation),16,17 or supramolecular interactions18,19 by
analogy with other N2O2 donor systems.
HO
OH
HO
OH
H2N
NH2
H2N
NH2
1
2
3
are much more stable and used as Schiff bases in coordi-
nation chemistry.20,21
HO
OH
HO
OH
N
N
HN
R
NH
R
R
R
4
5
To the best of our knowledge, only seven molecules of
type 4 have been described in the literature: compound
622 for which R is a triazine group and six compounds
of type 7 for which R1 = aryl,23,24 alkyl,25,26 carbonyl11
or –NHTs (Ts = tosyl) groups.27
N-substituted diaminoresorcinol derivatives 4 are very
few, compared to the diiminoresorcinol analogs 5 which
Although molecules of type 4 with N-alkyl substituent
have been proposed as reactive intermediates in different
reactions,19,28 none of them has been isolated and struc-
turally characterized owing to their high instability. A
fine-tuning of the N-substituent R could be attractive
for applications in organic, organometallic and/or
Keywords: Zwitterions; Aromatic; Diaminoresorcinols; Ligand;
Reduction.
*
Corresponding authors. Tel.: +33 491 829 588; fax: +33 491 829 580
(Q.-Z.Y.); e-mail: siri@luminy.univ-mrs.fr
0040-4039/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2006.06.025

5728
Q.-Z. Yang et al. / Tetrahedron Letters 47 (2006) 5727–5731
HO
HN
OH
NH
HO
OH
HN
NH
R1
R1
N
N
N
N
O
O
R1
7
R1
N
N
Cl
Cl
6
supramolecular chemistry, in particular because the
reactivity of the N–H groups (i.e., their basicity and/or
nucleophilic character) would be strongly modified by
the presence of a more electron-donating moiety.
Figure 1. ORTEP view of the crystal structure of the zwitterionic
compound 9b in 9bÆ4H2O. Displacement parameters include 50%
of the electron density. Selected bond distances (A) and angles (°):
O(1)–C(2) = 1.259(2), C(2)–C(1) = 1.390(3), C(1)–C(6) = 1.392(2),
C(6)–O(2) = 1.257(2), N(1)–C(3) = 1.313(2), C(3)–C(4) = 1.390(2),
C(4)–C(5) = 1.384(3), C(5)–N(2) = 1.321(2), C(2)–C(3) = 1.526(2),
˚
Herein, we report the high yield synthesis and first isola-
tion of N-alkyl diaminoresorcinol derivatives—or 4,6-
bisdialkylaminobenzene-1,3-diols C6H2(NHR)2(OH)2
(10a, R = CH2-2-Py; 10b, R = CH2-3-Py; 10c, R =
CH2-4-Py)—from the parent diaminoresorcinol C6H2-
(NH2)2(OH)2 (3) via 6p+6p zwitterionic intermediates.
C(6)–C(5) = 1.521(2);
O(1)–C(2)–C(1) = 125.83(15),
O(1)–C(2)–
C(3) = 116.25(17), N(1)–C(3)–C(4) = 124.25(16), N(1)–C(3)–C(2) =
114.83(15).
The easy access to a family of functional 6p+6p
quinonemonoimine zwitterions of the type C6H2-
( NHR)2( O)2 (9) has recently become possible by a
transamination reaction of the parent molecule
C6H2( NH2)2( O)2 (8), the oxidized form of 3, with
primary amines.29,30 In the course of these studies, we
realized that primary amines bearing a pyridine moiety
behaved differently. When an excess of 2-, 3-, or 4-picol-
ylamine was added in air to an aqueous solution of
3Æ2HCl, the formation of purple intermediates was ob-
served, consistent with the expected zwitterions 9a–c,
respectively, the amine acting simultaneously as a base
(deprotonation of the salt) and a nucleophile (Scheme
1).
identified as 10a–c.31 The purple intermediates 9a–c
could be isolated independently and fully character-
ized,32 including by X-ray diffraction analysis of mole-
cule 9bÆ4H2O (Fig. 1).33 Examination of the bond
distances within the N(1)–C(3)–C(4)–C(5)–N(2) and
O(1)–C(2)–C(1)–C(6)–O(2) moieties shows an equaliza-
tion of the C–C, C–O and C–N distances which is con-
sistent with a complete electronic delocalization of the p
system.
There is no conjugation between these two moieties
since the C(2)–C(3) and C(6)–C(5) distances of
˚
1.526(2) and 1.521(2) A, respectively, correspond to typ-
ical single bonds.19 This bonding situation is similar to
that encountered in other, related 6p+6p zwitteri-
ons.19,29,30 Compounds 9a and 9b are soluble in MeOH,
CH2Cl2, DMSO and slightly soluble in acetone and H2O
and give purple solutions whereas 9c is only soluble in
CH2Cl2, acetone or DMSO. In contrast, only 10a could
be characterized in solution owing to its slight solubility
in DMSO and relative stability compared to 10b and
10c. The formation of 10c, the most unstable in the ser-
ies, was indicated by the colour and solubility changes.
The difference of solubility between 10a–c may be due
to the strength of the H-bonding interactions in the solid
state depending on the position of the pyridyl nitrogen.
However, after a few minutes, we observed the forma-
tion of grey green precipitates which were almost insol-
uble in all solvents. These new compounds were then
O
O
HO
OH
RNH2
2 Cl
+
air / H2O
H2N
NH2
H3N
NH3
3·2HCl
8
RNH2
1
The H NMR spectrum of 10a revealed the presence of
Excess
RNH2
two –OH (d = 8.30) and two –NH (d = 8.50) groups,
and of two signals at d 5.85 and 6.31 that would suggest
its aromatic character (compared with d = 5.04 and 5.62
for the potentially antiaromatic system 9a).19b This was
further confirmed by X-ray diffraction on a single crystal
obtained from the reaction mixture kept under nitrogen
(Fig. 2).33 The C–C distances within the C6 ring are in
O
O
HO
OH
+
air
HN
R
NH
R
HN
R
NH
R
9a R = CH2-2-Py
9b R = CH2-3-Py
9c R = CH2-4-Py
9d R = CH2-Ph
10a R = CH2-2-Py
10b R = CH2-3-Py
10c R = CH2-4-Py
˚
the range 1.383(4)–1.392(4) A, which reveals their equal-
ization compared to the situation in 8ÆH2O where they
29
˚
range from 1.382(3) to 1.520(3) A. Together with the
presence of a hydrogen atom on each oxygen, this is
consistent with a re-aromatization of the system.
Scheme 1. Synthesis of 9a–c and 10a–c.

Q.-Z. Yang et al. / Tetrahedron Letters 47 (2006) 5727–5731
5729
HO
N
OH
N
t-BuC(O)Cl
O
O
10a
THF
t-Bu
t-Bu
N
N
11
Scheme 2. Synthesis of 11.
3.30,35,36 In order to demonstrate the potential of the
N-alkyl diaminoresorcinols in organic chemistry, we
have used 10a as precursor for the preparation of a
new N4O4-type ligand, molecule 11, which was obtained
as a white powder by reaction of a suspension of 10a in
dry THF with 2 equiv of t-BuC(O)Cl (Scheme 2).37
Figure 2. ORTEP view of the crystal structure of the aromatic
compound 10a. Displacement parameters include 50% of the electron
density. Selected bond distances (A) and angles (°): O(1)–
C(2) = 1.378(3), C(2)–C(1) = 1.383(4), C(1)–C(6) = 1.384(4), C(6)–
O(2) = 1.386(3), N(1)–C(3) = 1.405(4), C(3)–C(4) = 1.392(4), C(4)–
C(5) = 1.391(4), C(5)-N(2) = 1.404(4), C(2)–C(3) = 1.386(4), C(6)–
˚
In conclusion, we have described the synthesis and first
characterization of N-alkyl diaminoresorcinols, 10a–c,
by using a one-pot stepwise preparation: (i) oxidation
of diaminoresorcinol 3, (ii) transamination reaction
leading to the corresponding functional quinonemono-
imine zwitterions 9a–c, (iii) reduction and re-aromatiza-
tion in the presence of primary amines bearing a
pyridine moiety. Molecules 9b and 10a have been fully
characterized, including by X-ray diffraction analysis.
The use of compounds 10 (N4O2 donor set) as well as
that of the acylated derivative 11 (N4O4 donor set) in
coordination chemistry is under investigation.
C(5) = 1.388(4);
O(1)–C(2)–C(1) = 123.4(3),
O(1)–C(2)–C(3) =
116.7(3), N(1)–C(3)–C(4) = 123.2(3), N(1)–C(3)–C(2) = 117.9(3).
Since quinonoid compounds form a long-known class of
redox-active molecules owing to their strong electron
acceptor ability,34 one could envisage that formation
of 10a–c resulted from the reduction of 9a–c by the
excess of n-picolylamine (n = 2, 3 or 4) needed to
achieve initial transamination. Although the synthesis
of molecules 10 was performed in water, electrochemical
studies could not be carried out in this medium owing to
the insolubility of the zwitterionic precursors 9 and of
the final aromatic products. The electrochemical proper-
ties of 9b and 3-picolylamine have therefore been
studied by cyclic voltammetry in anhydrous CH2Cl2
containing N(n-Bu)4PF6 as supporting electrolyte (scan
rate of 250 mV sÀ1). The cyclic voltammogram (CV) of
9b showed two monoelectronic reversible waves at very
low reduction potential (i.e., À1.234 V and À1.833 V vs
Fc+/Fc) indicating that 9b is also difficult to reduce. The
CV of pure 3-picolylamine shows only an irreversible
wave at 1.081 V versus Fc+/Fc indicating its high oxida-
tion potential. These values obtained in CH2Cl2 suggest
that formation of 10b cannot result from a redox reac-
tion between 9b and 3-picolylamine. Interestingly, the
use of benzylamine instead of picolylamines only led
to the formation of zwitterion 9d29 (i.e., no re-aromati-
zation was observed), which indicates the key role
played by the pyridine moiety, probably as a base.
Water is likely to have a significant effect on the redox
potential of the compounds involved (presence of Lewis
basic function) so that the formation of molecules 10 in
aqueous solution may thus involve other intermediate
species which would form only in the presence of
picolylamines.
Acknowledgements
This work was supported by the Centre National de la
`
Recherche Scientifique and the Ministere de la Recher-
che et des Nouvelles Technologies (Post-doctoral Grant
to Q.-Z.Y.). We also thank Professor R. Welter (ULP
Strasbourg) for the X-ray structure determinations.
References and notes
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When the grey/green precipitates of 10a–c are dried in
air, their colour turns to purple. This indicates their easy
oxidation in the solid state to form compounds 9a–c, as
observed in solution for the parent diaminoresorcinol

5730
Q.-Z. Yang et al. / Tetrahedron Letters 47 (2006) 5727–5731
12. Kobayashi, T.; Kobayashi, S. Eur. J. Org. Chem. 2002,
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Chem 2003, 1, 1216.
Compound 9a: Yield: 70%. MS (MALDI-TOFÀ): m/z:
319.1 [MÀ1]À, 228.1 [MÀ1ÀCH2Py]À; 1H NMR
(300 MHz, DMSO-d6) d = 4.73 (s, 4H, CH2), 5.04 (s,
1H, N
C CH), 5.62 (s, 1H, O C CH), 7.30 (m, 4H,
3 4
NCHCH and NCCH), 7.78 (td, J = 7.7 Hz, J = 1.8 Hz,
2H, NCHCHCH), 8.51 (ddd, 3J = 4.8 Hz, 4J = 1.8 Hz,
5J = 0.9 Hz, 2H, NCH), 9.53 (br s, 2H, NH); 13C NMR
(75 MHz, DMSO-d6) d = 47.72 (s, CH2), 83.71 (s,
15. Reddy, T. I.; Iwama, T.; Halpern, H. J.; Rawal, V. H. J.
Org. Chem. 2002, 67, 4635.
16. Siri, O.; Braunstein, P. Chem. Commun. 2000, 2223.
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18. Braunstein, P.; Siri, O.; Taquet, J.-p.; Yang, Q.-Z. Chem.
Eur. J. 2004, 10, 3817.
N C C), 98.00 (s, O C C), 122.16 (s, NCHCH),
123.22 (s, NCCH), 137.58 (s, NCHCHCH), 149.53 (s,
NCH), 155.48 (s, NC), 157.17 (s, N C), 172.38 (s, O C).
Anal. Calcd for C18H16N4O2Æ4H2O: C, 55.09; H, 6.16; N,
14.28. Found: C, 55.43; H, 5.61; N, 15.23.
19. (a) Siri, O.; Braunstein, P. Chem. Commun. 2002, 208; (b)
Braunstein, P.; Siri, O.; Taquet, J.-P.; Rohmer, M.-M.;
Compound 9b: Yield: 73%. MS (MALDI-TOFÀ): m/z:
319.1 [MÀ1]À, 228.1 [MÀ1ÀCH2Py]À; 1H NMR
(300 MHz, DMSO-d6) d = 4.69 (s, 4H, CH2), 5.00 (s,
´
Benard, M.; Welter, R. J. Am. Chem. Soc. 2003, 125,
12246.
1H, N C CH), 5.72 (s, 1H, O C CH), 7.31 (ddd,
20. Manecke, V. G.; Wille, W. E. Makromolekulare Chemie
1970, 133, 61.
21. Manecke, V. G.; Wille, W. E.; Kossmehl, G. Mak-
romolekulare Chemie 1972, 160, 111.
22. Matzuzaki, Y.; Fujii, K.; Kohgo, O.; Naruse, H.; Misawa,
T.; WO 2002006409, 2002.
3J = 7.8 Hz, 3J = 4.8 Hz, 5J = 0.66 Hz, 2H, NCHCH),
7.64 (dt, 3J = 7.8 Hz, 4J = 1.8 Hz, 2H, NCHCHCH), 8.49
(dd, 3J = 4.8 Hz, 4J = 1.8 Hz, 2H, NCHCH), 8.54 (d,
4J = 1.8 Hz, 2H, NCHC), 9.63 (br, 2H, NH); 13C
NMR(75 MHz, DMSO-d6) d = 43.75 (s, CH2), 82.95 (s,
N
C C), 98.19 (s, O C C), 124.09 (s, NCHCH),
23. Schab-Balcerzak, E.; Jikei, M.; Kakimoto, M. Polymer J.
2003, 35, 208.
24. Evstafev, V. P.; Braz, G. I.; Yakubovich, A. Y. Khim. Get.
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25. Kawashi, J.; Matsubara, H.; Nakahara, Y. Jpn Koka¨ı
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26. Heller, G.; Sourlis, A. Chem. Ber. 1910, 43, 2581.
27. Fukuoka, T.; Hota, H. Jpn Koka¨ı Tokkyo Koho; JP
10044619, 1998.
132.76 (s, NCHC), 135.71 (s, NCHCHCH), 149.19
(s, NCHCH), 149.48 (s, NCHC), 157.12 (s, N C),
172.32 (s, O C). Anal. Calcd for C18H16N4O2Æ4H2O: C,
55.09; H, 6.16; N, 14.28. Found: C, 54.73; H, 6.05; N,
14.61.
Compound 9c: Yield: 76%. Ms (MALDI-TOF+): m/z:
1
321.1 [M+1]+; H NMR (300 MHz, DMSO-d6) d = 4.64
(s, 4H, CH2), 5.02 (s, 1H, N
C CH), 5.50 (s, 1H,
3
O
C CH), 7.18 (d, J = 5.6 Hz, 4H, NCHCH), 8.45 (d,
28. Lee, Y.; Sayre, L. M. J. Am. Chem. Soc. 1995, 117,
3096.
3J = 5.6 Hz, 4H, NCH), 9.78 (br s, 2H, NH); 13C NMR
(75 MHz, DMSO-d6) d = 45.08 (s, CH2), 83.51 (s,
29. Yang, Q.-Z.; Siri, O.; Braunstein, P. Chem. Eur. J. 2005,
11, 7237.
30. Yang, Q. Z.; Siri, O.; Braunstein, P. Chem. Commun. 2005,
2660.
N
C
C), 98.21 (s, O
145.73 (s, NCHCHCH), 150.20 (s, NCH), 157.56 (s,
C), 172.26 (s, O C). Anal. Calcd for C18H16N4O2Æ
C C), 122.72 (s, NCHCH),
N
H2O: C, 63.89; H, 5.36; N, 16.56. Found: C, 64.05; H,
31. Typical procedure for the synthesis of compounds 10: An
excess of picolylamine (2.033 g, 18.8 mmol) was added to
an aqueous solution of 3Æ2HCl (0.500 g, 2.35 mmol) and
the mixture allowed to stand for 2–3 h. The green
precipitate was isolated by filtration, washed with cold
water, then with acetone and dried in vacuo.
Compound 10a: Yield: 86%. MS (MALDI-TOF+): m/z
5.18; N, 16.87.
ꢀ
33. Crystal data for 9bÆ4H2O: triclinic, space group P1 with
a = 9.577(5), b = 10.207(5), c = 10.644(5), a = 96.663(5),
b = 97.473(5), c = 109.794(5) at 173(2) K with Z = 2.
Refinement of 12,090 reflections (2964 reflections with
I > 2r(I)), R = 0.0577, Rw = 0.1418, GOF = 0.948.
For 10a: orthorhombic, space group Pbcn with a =
13.4520(10), b = 15.3120(10), c = 15.3470(10), a = b =
c = 90.00 at 293(2) K with Z = 8. Refinement of 6804
reflections (3636 reflections with I > 2r(I)), R = 0.0676,
Rw = 0.620, GOF = 0.913. Crystallographic data for the
structures 9bÆ4H2O and 10a have been deposited at the
Cambridge Crystallographic Data Centre (CCDC 283397
and 283398, respectively). Copies of the data can be
obtained, free of charge, on application to CCDC, 12
Union Road, Cambridge CB2 1EZ, UK [fax: +40 (0)1223
336033 or e-mail: deposit@ccdc.cam.ac.uk].
1
323.1 [M+1]+. H NMR (300 MHz, DMSO-d6) d = 4.21
(d, 3J = 6.0 Hz, 4H, NHCH2), 4.81 (t, 3J = 6.0 Hz, 2H,
NHCH2), 5.85 (s, 1H, NHCCH), 6.31 (s, 1H, OCCH),
3
7.24 (m. 4H, NCHCH and NCCH), 7.68 (td, J = 7.7 Hz,
4J = 1.8 Hz, 2H, NCHCHCH), 8.30 (br s, 2H, OH), 8.50
(br d, 3J = 4.8 Hz, 2H, NCH); 13C NMR (75 MHz,
DMSO-d6) d = 50.07 (s, CH2), 98.12 (s, NHCCH),
104.34 (s, HOCCH), 121.86 (s, NCHCH), 122.30 (s,
NCCH), 130.21 (s, NCHCHCH), 135.34 (s, NCH), 136.87
(s, NC), 149.16 (s, NHC), 172.38 (s, HOC). Despite several
attempts, no satisfactory elemental analysis could be
obtained owing to the sensitivity of 10a.
34. Sawyer, D. T.; Sobkowiak, A. J. L.; Roberts, J. Electro-
chemistry for Chemists, 2nd ed.; Wiley & Sons: New York,
1995.
35. Typke, P. G. W. Chem. Ber. 1883, 551.
36. Beaugeard, N. H.; Matti, J. Bull. Soc. Chim. Fr. 1956,
1612.
Compound 10b: Yield: ꢀ78% (calculated immediately
after its isolation because of its high unstability). MS
(MALDI-TOF+): m/z: 323.2 [M+1]+. Despite several
attempts, no satisfactory elemental analysis could be
obtained owing to the sensitivity of 10b.
37. Synthesis of 11: To
a suspension of 10a (0.466 g,
32. Typical procedure for the synthesis of zwitterions 9: An
excess of picolylamine (1.730 g, 16.0 mmol) was added
to an aqueous solution of 3Æ2HCl (0.426 g, 2.00 mmol)
and the mixture was allowed to stand for 2–3 h. The
green precipitate was isolated by filtration, washed with
cold water and slowly dried in air to afford a purple
powder.
1.45 mmol) in dry THF (80 mL) was added an excess of
NEt3 (1.0 mL) and then 2 equiv CH3C(O)C1 (0.349 g,
2.90 mmol). The mixture was stirred at room temperature
for 24 h. After removal of HNEt3Cl by filtration and
evaporation of the filtrate to 5 mL, pentane was added to
precipitate 11 which was isolated by filtration. Yield:
0.433 g, 61%. MS (MALDI-TOF+): m/z 491.3 [M+1]+. 1H

Q.-Z. Yang et al. / Tetrahedron Letters 47 (2006) 5727–5731
5731
NMR (300 MHz, CDCl3) d = 1.04 (s, 18H, CH3), 3.97 (d,
2J = 15.0 Hz, 2H, CHaHb), 5.37 (d, 2J = 15.0 Hz, 2H,
CHaHb), 6.65 (s, 1H, NHCCH), 6.99 (s, 1H, OCCH), 7.27
(s, overlap with solvent peak, 2H, NCHCH), 7.40 (d,
3J = 7.8 Hz, 2H, NCCH), 7.77 (td, 3J = 7.7 Hz,
4J = 1.7 Hz, 2H, NCHCHCH), 8.50 (br d, 3J = 4.7 Hz,
2H, NCH); 13C NMR (75 MHz, CDCl3) d = 28.67 (s,
CH3), 40.55 (s, C(CH3)3), 59.60 (s, CH2), 107.00 (s,
NCCH), 122.68 (s), 122.98 (s), 123.66 (s), 138.28 (s),
147.16 (s), 156.87 (s), 157.43 (s), 178.47 (s, C@O). Anal.
Calcd for C28H34N4O4: C, 68.55; H, 6.99; N, 11.42.
Found: C, 68.47; H, 6.93; N, 11.59.