Functionalization of sterically hindered o-benzoquinones: Amino-substituted 3,6-di(tert-butyl)-o-benzoquinones

Article abstract of DOI:10.1007/s11172-007-0287-6

New sterically hindered functionalized o-quinones were synthesized by the 1,4-nucleophilic addition of secondary cyclic amines to 3,6-di(tert-butyl)-o- benzoquinone. The ability of these o-quinones to form o-semiquinone complexes with transition and main-

Full text of DOI:10.1007/s11172-007-0287-6

Russian Chemical Bulletin, International Edition, Vol. 56, No. 9, pp. 1849—1856, September, 2007
1849
Functionalization of sterically hindered oꢀbenzoquinones:
aminoꢀsubstituted 3,6ꢀdi(tertꢀbutyl)ꢀoꢀbenzoquinones
G. A. Abakumov, V. K. Cherkasov,ꢀ T. N. Kocherova, N. O. Druzhkov, Yu. A. Kurskii, M. P. Bubnov,
G. K. Fukin, and L. G. Abakumova
G. A. Razuvaev Institute of Organometallic Chemistry, Russian Academy of Sciences,
49 ul. Tropinina, 603950 Nizhny Novgorod, Russian Federation.
Fax: +7 (831 2) 12 7497. Eꢀmail: tanya@iomc.ras.ru
New sterically hindered functionalized oꢀquinones were synthesized by the 1,4ꢀnucleoꢀ
philic addition of secondary cyclic amines to 3,6ꢀdi(tertꢀbutyl)ꢀoꢀbenzoquinone. The ability of
these oꢀquinones to form oꢀsemiquinone complexes with transition and mainꢀgroup metals was
studied by ESR spectroscopy in solution.
Key words: oꢀquinones, amines, piperazines, nucleophilic addition, oꢀsemiquinone metal
complexes, charge transfer band, ESR spectroscopy.
Sterically hindered oꢀbenzoquinones have attracted
interest due to their wide use as the starting compounds
in the synthesis of metal complexes with freeꢀradical
ligands.1—3 The introduction of an additional reactive
group into oꢀbenzoquinone (the functionalization of
oꢀbenzoquinone)4—11 extends the coordination potential
of the oꢀsemiquinone ligand. The synthesis of highꢀspin
polynuclear compounds12 and coordination polymers13,14
containing paramagnetic metal ions along with radical
oꢀsemiquinone ligands is one of the promising applications
of such functionalized oꢀquinones (including diꢀoꢀquinoꢀ
nes). The use of functionalized oꢀquinones for the design
of paramagnetic probes and labels, which are introduced
into systems by reactions leaving intact the paramagnetic
center,15,16 is another remaining undeveloped field of apꢀ
plication of these compounds.
Amines belong to one of the largest classes of ligands
used in coordination and organometallic chemistry.17 In
addition, amines can form adducts with simple acids as
well as with Lewis acids. oꢀQuinones functionalized by
amino groups are of obvious interest as the starting comꢀ
pounds for the synthesis of metal complexes with freeꢀ
radical ligands.
thesize new bifunctional oꢀquinones. The synthesis of
morpholine and piperidine derivatives of unsubstituꢀ
ted oꢀbenzoquinone is based on the reaction of pyroꢀ
catechol with the corresponding amines in the presence
of copper(II) salts. However, 4,5ꢀdiaminoꢀsubstituted
oꢀquinones thus prepared exist as zwitterionic structures
and do not have properties characteristic of oꢀquinones
(oneꢀelectron reduction and the formation of oꢀsemiꢀ
quinone complexes).19
The reactions of quinone 1 with a series of amines
(morpholine, 1ꢀphenylpiperazine, and 1ꢀdiphenylmethylꢀ
piperazine) in acetonitrile at room temperature followed
by oxidation of the reaction mixture with an alkali soluꢀ
tion of potassium ferricyanide afford 4ꢀaminoꢀ3,6ꢀdi(tertꢀ
butyl)ꢀoꢀbenzoquinones 2a—c in high yields (Scheme 1).
Scheme 1
Earlier,18 we have reported that the reactions of
3,6ꢀdi(tertꢀbutyl)ꢀoꢀbenzoquinone (1) with primary aroꢀ
matic amines afford the corresponding 2ꢀhydroxyꢀpꢀ
quinone imines. pꢀQuinone imine, which is produced in
the reactions of primary aliphatic amines, exists in soluꢀ
tion in equilibrium with tautomeric 4ꢀaminoꢀoꢀquinone.
The reaction with secondary aliphatic amine (piperidine),
whose addition product contains no protons capable of
migration, yielded new substituted oꢀquinone.
The aim of the present study was to investigate the
reactions of 1 with secondary cyclic amines and to synꢀ
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1786—1793, September, 2007.
1066ꢀ5285/07/5609ꢀ1849 © 2007 Springer Science+Business Media, Inc.

1850
Russ.Chem.Bull., Int.Ed., Vol. 56, No. 9, September, 2007
Abakumov et al.
Scheme 2
Unsubstituted piperazine contains two reaction cenꢀ
ters due to which its reaction with quinone 1 does not
stops at 4ꢀpiperazinylꢀsubstituted oꢀquinone; instead, it
affords, depending on the reaction conditions, two differꢀ
ent products (Scheme 2). The reaction of equimolar
amounts of the reagents in acetonitrile involves the second,
intramolecular nucleophilic addition, reaction giving rise
finally to tricyclic 5,8ꢀdi(tertꢀbutyl)ꢀ2,3ꢀdihydroꢀ1,4ꢀ
ethanoquinoxalineꢀ6,7ꢀdione (4).
by the chlorine atom. The molecular structure of pyroꢀ
catechol salt 5 was confirmed by Xꢀray diffraction
(Fig. 1). The subsequent oxidation of compound 5 affords
5ꢀtertꢀbutylꢀ8ꢀchloroꢀ2,3ꢀdihydroꢀ1,4ꢀethanoquinoxaꢀ
lineꢀ6,7ꢀdione (6).
The structures of all new oꢀquinones were confirmed
by elemental analysis, IR spectroscopy, and 1H and
13C NMR spectroscopy. The molecular structures of comꢀ
pounds 2a, 4, 5, and 7 were established by Xꢀray difꢀ
fraction.
The structures of oꢀbenzoquinones 2a, 4, and 7 are
characterized by the noncoplanarity of the cyclohexaꢀ
dienone ring. The OCCO torsion angles are 26.4, 43.7,
and 12.8° for oꢀbenzoquinones 2a, 4, and 7, respectively.
As opposed to compounds 2a, 4, and 7, the correspondꢀ
ing angle in 5 is 1.4°. Therefore, the introduction of a
bulky substituent at position 4 of the ring adjacent to the
tertꢀbutyl group in compounds 2a, 4, and 7 leads to a
substantial distortion of the geometry of the OCCO fragꢀ
ment. In the absence of bulky substituents in the adjacent
positions of quinone, the OCCO torsion angles are
2.40—6.54°.21—24 Apparently, the minimization of nonꢀ
bonded interactions between the substituent at position 4
of the ring and the tertꢀbutyl group is responsible for a
deviation of the oxygen atoms from the plane of the
molecule.
In compound 4, the piperazine rings adopts a rigid
boat conformation. Four protons of this ring are conꢀ
stantly in axial positions, and the other four protons are in
equatorial positions. In the 1H NMR spectrum, two
NCH2CH2N fragments are manifested as an AA´BB´ sysꢀ
tem. The HA and HB (HA´ and HB´) protons are geminal,
the HA and HA´ (HB and HB´) protons are in a synꢀ
periplanar conformation, and the HA and HB´ (HA´ and
HB) protons are in an anticlinal conformation. The chemiꢀ
cal shifts are δA = 2.89 and δB = 3.04. The spinꢀspin
3
2
coupling constants are JAA´ = JBB´ = 9.6 Hz, JA´B´
=
JAB = –12.9 Hz, and 3JAB´ = JA´B = 6.5 Hz.
In the reaction of piperazine with an excess of
quinone 1 in chloroform, the intramolecular cyclization
slows down (the yield of tricyclic product 4 is at most
15—20%), and the competitive reaction of the free NH
group of the piperazine fragment with the second molꢀ
ecule 1 becomes predominant, resulting in the formation
of bisꢀoꢀquinone 7 in 50—55% yield based on consumed
piperazine.
The C—C and C—O bond lengths in the quinone
fragment are typical of oꢀbenzoquinones21—25 (Table 1).
The electronic absorption spectrum of the
starting oꢀquinone 1 (Table 2) in dichloromethane at
290 K shows two absorption bands26 with maxima
at 415 nm (ε = 2500 L mol–1 cm–1) and 584 nm
The treatment of quinone 4 with concentrated hydroꢀ
chloric acid involves the reduction20 giving rise to a salt
accompanied by the replacement of one tertꢀbutyl group

Aminoꢀsubstituted 3,6ꢀdi(tertꢀbutyl)ꢀoꢀbenzoquinones Russ.Chem.Bull., Int.Ed., Vol. 56, No. 9, September, 2007 1851
C(9)
C(8)
C(10)
C(7)
C(9)
C(10)
C(4)
C(7)
C(8)
O(2)
C(3)
C(3)
O(2)
N(1)
N(2)
C(17)
C(18)
C(15)
C(4)
C(2)
C(1)
C(2)
C(1)
C(18)
C(16)
C(15)
O(3)
C(5)
O(1)
C(5)
C(6)
O(1)
N(1)
C(6)
C(17)
C(16)
C(14)
C(13)
C(11)
C(11)
C(12)
C(12)
C(13)
C(14)
2a
4
C(12)
C(11)
C(13)
C(14)
O(2)
C(4)
C(7)
H(6)
C(8)
C(9)
H(1a)
C(5)
C(6)
C(3)
C(2)
N(1)
C(1)
C(15)
N(2)
C(10)
C(6)
C(5)
O(1A)
O(2A)
Cl(1)
N(1A)
N(1)
C(16)
O(1)
C(1)
C(7)
C(13)
C(2)
C(9)
C(8)
C(3)
C(10)
C(12)
C(11)
H(1)
C(4)
O(2)
O(1)
C(14)
H(2)
7
Fig. 1. Molecular structures of compounds 2a, 4, 5, and 7.
5
(ε = 100 L mol–1 cm–1). Under analogous conditions, the
electronic absorption spectra of 4ꢀNꢀsubstituted oꢀquinoꢀ
nes 2a—c and 7 contain, along with absorption bands
characteristic of oꢀquinones, an electron transfer band
with a maximum at 500 nm corresponding to the inꢀ
tramolecular charge transfer between the electronꢀdonatꢀ
ing (piperidine) fragment and the electronꢀwithdrawing
(quinone) fragment of the molecule (Fig. 2, Scheme 3).
D
1.0
0.8
0.6
0.4
0.2
3
1
2
Scheme 3
300
400
500
600
λ/nm
Fig. 2. Electronic absorption spectra of compounds 1 (1), 2a (2),
and 4 (3) (dichloromethane).
To the contrary, the electronic absorption spectra of
4,5ꢀN,Nꢀdisubstituted oꢀquinones 4 and 6, like that

1852
Russ.Chem.Bull., Int.Ed., Vol. 56, No. 9, September, 2007
Abakumov et al.
Table 1. Selected bond lengths (d), bond angles (ω), and torsion angles (θ) in molecules 2a, 4,
5, and 7
Parameter
Value
Parameter
Value
Molecule 2а
Molecule 4
Bond
d/Å
Bond
d/Å
O(1)—C(1)
O(2)—C(2)
N(1)—C(5)
C(1)—C(6)
C(1)—C(2)
C(2)—C(3)
C(3)—C(4)
C(4)—C(5)
C(5)—C(6)
1.217(2)
1.215(2)
1.437(2)
1.479(2)
1.547(2)
1.472(2)
1.341(2)
1.474(2)
1.357(2)
O(1)—C(1)
N(1)—C(4)
C(1)—C(6)
C(1)—C(2)
N(2)—C(5)
O(2)—C(2)
C(2)—C(3)
C(3)—C(4)
C(4)—C(5)
C(5)—C(6)
Angle
1.213(2)
1.438(2)
1.477(2)
1.550(2)
1.444(2)
1.212(2)
1.477(2)
1.351(2)
1.495(2)
1.353(2)
ω/deg
Angle
ω/deg
O(1)—C(1)—C(2)
O(2)—C(2)—C(1)
C(6)—C(5)—N(1)
N(1)—C(5)—C(4)
116.38(14)
117.22(14)
120.93(13)
116.26(13)
O(1)—C(1)—C(2)
O(2)—C(2)—C(1)
C(3)—C(4)—N(1)
N(1)—C(4)—C(5)
C(6)—C(5)—N(2)
N(2)—C(5)—C(4)
Angle
116.54(12)
116.51(12)
122.68(12)
112.20(11)
122.96(12)
111.93(11)
θ/deg
Angle
θ/deg
O(1)—C(1)—C(2)—O(2)
26.4
O(1)—C(1)—C(2)—O(2)
43.7
Molecule 5
Bond
Molecule 7
d/Å
Bond
d/Å
Cl(1)—C(2)
N(1)—C(1)
N(2)—C(6)
O(1)—C(3)
O(2)—C(4)
C(1)—C(6)
C(1)—C(2)
C(2)—C(3)
C(3)—C(4)
C(4)—C(5)
Angle
O(1)—C(3)—C(4)
O(2)—C(4)—C(3)
C(2)—C(1)—N(1)
C(5)—C(6)—N(2)
Angle
1.735(1)
1.462(2)
1.450 (2)
1.357(2)
1.361(2)
1.377(2)
1.381(2)
1.385(2)
1.405(2)
1.408(2)
ω/deg
115.60(12)
116.17(13)
124.20(12)
124.71(12)
θ/deg
O(1)—C(3)
O(2)—C(4)
N(1)—C(1)
C(1)—C(2)
C(1)—C(6)
C(2)—C(3)
C(3)—C(4)
C(4)—C(5)
C(5)—C(6)
1.221(2)
1.218(2)
1.399(2)
1.376(2)
1.481(2)
1.464(2)
1.557(2)
1.469(2)
1.340(2)
Angle
ω/deg
122.81(12)
115.85(11)
115.30(12)
117.13(13)
θ/deg
C(2)—C(1)—N(1)
N(1)—C(1)—C(6)
O(1)—C(3)—C(4)
O(2)—C(4)—C(3)
Angle
O(1)—C(3)—C(4)—O(2)
1.4
O(1)—C(3)—C(4)—O(2)
12.8
of 1, show only two absorption bands with maxima at
395 and 545 nm (ε = 2100 L mol–1 cm–1 and ε =
230 L mol–1 cm–1) for 4 and at 420 and 560 nm (ε =
2300 L mol–1 cm–1 and ε = 260 L mol–1 cm–1) for 6. The
charge transfer band in the spectra of these compounds is
absent, because the rigid molecular structure strictly deꢀ
termines the orientation of the lone electron pair of the
nitrogen atom, thus excluding the possibility of its conjuꢀ
gation with the quinone ring.
All new oꢀquinones can undergo oneꢀelectron reducꢀ
tion to form radical anions and, consequently, they are
potential ligands for freeꢀradical metal complexes. The
ESR spectra of potassium oꢀsemiquinolates 2a—c and 7
in THF are doublets due to the hyperfine coupling beꢀ
tween the unpaired electron and the hydrogen atom
nucleus at position 5 of the semiquinone ring (Table 3).
The hyperfine coupling with other magnetic nuclei is
not observed in the ESR spectra; however, it makes a
contribution to the widths of individual components
of the spectra. The ESR spectrum of potassium oꢀsemiꢀ
quinolate 4 (gi = 2.0048) has a more complex strucꢀ
ture (Fig. 3) and shows the hyperfine coupling of the
unpaired electron with two nitrogen atom nuclei (14N,
I = 1, ai(2N) = 0.040 mT) and four equivalent protons of
the αꢀmethylene groups of the piperazine fragment
(ai(4Hα) = 0.115 mT).

Aminoꢀsubstituted 3,6ꢀdi(tertꢀbutyl)ꢀoꢀbenzoquinones Russ.Chem.Bull., Int.Ed., Vol. 56, No. 9, September, 2007 1853
Table 2. Spectroscopic characteristics of oꢀquinones, the posiꢀ
tions of absorption maxima (λ/nm), and the corresponding exꢀ
The formation of paramagnetic complexes was deꢀ
tected in the reactions of oꢀquinones with Mn2(CO)10
performed under visible light irradiation in toluene
(Scheme 4). The ESR spectra of chelate oꢀsemiquinone
manganese tetracarbonyl complexes 2a—c show the
hyperfine coupling of the unpaired electron with magꢀ
netic isotopes of one manganese atom (55Mn, I = 5/2,
100% (see Ref. 29)), the amino nitrogen atom, the proton
at position 5 of the quinone ring, and two αꢀmethylene
protons of the substituent (Table 4).
tinction coefficients (ε/L mol–1 cm–1
)
oꢀQuiꢀ
λππ* (ε)
λ (ε)ꢀ
λ nπ* (ε)
q
none
Hexane CH2Cl2 Hexane CH2Cl2 Hexane CH2Cl2
1
397
(3000) (2500)
366 355
(2200) (2700)
365 347
(2150) (2800)
358 349
415
—
—
595
(80)
597
(140)
600
(140)
603
(190)
551
584
(100)
590
(600)
602
(850)
596
(1300)
545
2а
2b
2c
4
470
(780)
495
(650)
468
500
(1550)
507
(1800)
515
Scheme 4
(2500) (3600) (1200) (2400)
377
(2800) (2100)
405 420
395
—
—
(180)
579
(230)
560
6
—
—
(3200) (2300)
(160)
ꢀꢀ
(260)
598
ꢀꢀ
ꢀꢀ
7
354
502
(5700)
(3700)
(1300)
ꢀ λ is the charge transfer band.
q
ꢀꢀ Insoluble.
Table 3. ESR parameters of radical anions 2a—c and 7
(THF, 290 K)
Due to the replacement of the tertꢀbutyl group in
oꢀquinone 6 by the chlorine atom, the molecule becomes
asymmetric, and the corresponding ESR spectra have a
more complex hyperfine structure compared to that of its
symmetric analog 4. The isotropic ESR spectrum of poꢀ
tassium oꢀsemiquinolate 6 is presented in Fig. 4. Its hyperꢀ
fine coupling constant is determined by interactions of
the unpaired electron with two nonequivalent nitrogen
atoms (ai(14N) = 0.040 mT and ai(14N) = 0.035 mT) and
two pairs of equivalent protons in the α position of
the piperazine substituent (ai(21H) = 0.130 mT and
ai(21H) = 0.102 mT). The ESR spectrum of the paramagꢀ
netic complex prepared by the reaction of oꢀquinone 6
with Mn2(CO)10 has six groups of lines as a consequence
of the hyperfine coupling of the unpaired electron with
the magnetic isotope 55Mn of one manganese atom
Radical anion
gi
ai (1H)
Linewidth
mT
2a–•
2b–•
2c–•
7–•
2.0047 0.0002
2.0050 0.0002
2.0050 0.0002
2.0052 0.0002
0.340
0.340
0.340
0.334
0.050
0.065
0.060
0.075
The diquinone nature of compound 7 is manifested in
the course of its chemical reduction with mercury in the
presence of lithium chloride in THF.27 The ESR spectral
pattern in a frozen solvent matrix (130 K) is typical of
biradical species with an axial symmetry of the D tensor.
The zeroꢀfield splitting parameter D is 3.5 mT. This D
parameter corresponds to the distance between the paraꢀ
magnetic centers r = 11.6 Å,28 which agrees well with the
Xꢀray diffraction data.
Table 4. ESR parameters of the chelate complexes formed by the
reactions of oꢀquinones 2a—c and 4 with manganese pentaꢀ
carbonyl (toluene, 290 K)
a
0.5 mT
Starting
gi
аi (Mn) аi (H5) аi (N) аi (2Hα)
oꢀquinone
b
mT
2а
2b
2c
4
2.0034 0.0002 0.690 0.340
2.0036 0.0002 0.680 0.340
2.0031 0.0002 0.680 0.340
0.050
0.040
0.050
0.035
(2N)
0.040
0.040
0.060
0.105
(4Hα)
Fig. 3. Isotropic ESR spectrum of manganese tetracarbonyl
oꢀsemiquinolate 4 in toluene at 290 K: a, experimental;
b, simulated.
2.0037 0.0002 0.712
—

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Russ.Chem.Bull., Int.Ed., Vol. 56, No. 9, September, 2007
Abakumov et al.
resolved spectrum with potassium. The constants ai(14N)
and ai(1H) were not precisely determined because of large
linewidths.
a
Experimental
The NMR spectra were recorded on a Bruker Avance
1
DPXꢀ200 spectrometer (200 MHz for H and 50 MHz for 13C)
with Me4Si as the internal standard. The ESR spectra were
measured on a Bruker ER 200 DꢀSRC spectrometer equipped
with an ER 4105 DR double resonator operating at 9.5 GHz.
The spectra were simulated with the use of the WinESR
SimFonia v1.25 Bruker software. The g factors were measured
using diphenylpicrylhydrazyl as the standard. The electronic abꢀ
sorption spectra were recorded on a Perkin—Elmer Lambdaꢀ25
spectrophotometer. The IR spectra were measured on a Specord
Mꢀ80 spectrometer. Xꢀray diffraction data sets were collected
on an automated Smart APEX diffractometer (graphite monoꢀ
chromator, MoKα radiation, ω—ϕꢀscanning technique, the exꢀ
posure time per frame was 10 s) at 100 K for all compounds. The
Xꢀray data collection and refinement statistics are given in
Table 5. All structures were solved by direct methods and refined
b
0.1 mT
Fig. 4. Isotropic ESR spectrum of potassium oꢀsemiquinolate 6
(THF, 290 K, gi = 2.0047): a, experimental; b, simulated.
(ai(55Mn) = 0.768 mT), each group of lines having a
by the fullꢀmatrix leastꢀsquares method based on F 2 with
hkl
quintet structure analogous to that observed in the poorly
anisotropic displacement parameters for all nonhydrogen atoms.
Table 5. Xꢀray data collection and refinement statistics for compounds 2a, 4, 5, and 7
Compound
2а
4
5
7
Molecular formula
Molecular weight
Crystal dimension/mm
Crystal system
Space group
a/Å
b/Å
c/Å
α/deg
β/deg
С18H27NO3
305.41
0.22×0.19×0.10
Monoclinic
С2/с
C18H26N2O2
302.41
C17H28Cl2N2O4
395.31
0.50×0.10×0.10
Triclinic
P–1
C32H46N2O4
522.71
0.27×0.19×0.12
Monoclinic
P2(1)/с
10.121(6)
10.940(6)
13.491(8)
90
103.015(1)
90
0.34×0.16×0.16
Monoclinic
P2(1)/n
11.478(8)
8.7182(6)
16.823(1)
90
18.786(1)
18.819(1)
20.349(1)
90
94.02(2)
90
7176.4(9)
16
1.131
7.359(6)
8.748(8)
15.769(14)
96.126(2)
101.849(2)
99.418(2)
969.79(15)
2
90.014(2)
90
1683.4(2)
4
1.193
0.078
γ/deg
V/Å3
1455.30(15)
2
Z
dcalc/g cm–3
1.354
0.358
1.192
0.078
µ/mm–1
0.076
F(000)
2656
656
420
568
Т/К
100(2)
100(2)
100(2)
100(2)
θꢀScan range/deg
Index ranges
1.76—26.50
–23 ≤ h ≤ 17,
–23 ≤ k ≤ 23,
–25 ≤ l ≤ 25
22010
2.15—25.99
–14 ≤ h ≤ 14,
–9 ≤ k ≤ 10,
–17 ≤ l ≤ 20
9632
2.39—26.00
–8 ≤ h ≤ 9,
–10 ≤ k ≤ 7,
–18 ≤ l ≤ 19
5845
2.07—26.00
–12 ≤ h ≤ 12,
–13 ≤ k ≤ 13,
–16 ≤ l ≤ 16
12371
Number of measured reflections
Number of independent reflections (Rint
Number of variables
)
7435 (0.0552)
613
3309 (0.0319)
303
3779 (0.0159)
338
2877 (0.0299)
264
R1 (I ≥ 2σ(I ))
0.0447
0.0405
0.0409
0.0420
wR2 (based on all reflections)
Goodnessꢀofꢀfit on F 2
Residual electron density (max/min)
/e Å–3
0.0898
0.951
0.254/–0.193
0.0943
1.025
0.283/–0.164
0.0910
1.063
0.376/–0.232
0.1005
1.042
0.345/–0.153
CCDC number
645416
645417
645418
645419

Aminoꢀsubstituted 3,6ꢀdi(tertꢀbutyl)ꢀoꢀbenzoquinones Russ.Chem.Bull., Int.Ed., Vol. 56, No. 9, September, 2007 1855
The H atoms in all structures were located in difference electron
density maps and refined isotropically. All calculations were
carried out with the use of the SHELXTL v. 6.10 program
package.30
The solvents were purified and dried according to stanꢀ
dard procedures.31 3,6ꢀDi(tertꢀbutyl)ꢀoꢀbenzoquinone was synꢀ
thesized according to a known procedure.32 Morpholine
(Khimreaktiv), piperazine (Fluka), 1ꢀ(diphenylmethyl)piperꢀ
azine (Fluka), and 1ꢀphenylpiperazine (Acros) are commerꢀ
cially available reagents.
3,6ꢀDi(tertꢀbutyl)ꢀ4ꢀ(morpholinꢀ4ꢀyl)ꢀ1,2ꢀbenzoquinone (2a).
3,6ꢀDi(tertꢀbutyl)ꢀoꢀbenzoquinone (1 g, 4.5 mmol) and morphoꢀ
line (0.3 mL, 4.5 mmol) were dissolved in MeCN (50 mL). The
reaction mixture was magnetically stirred at ~20 °C for 3 h.
Then the mixture was oxidized by adding it to a vigorously
stirred solution of potassium ferricyanide (10 g), Na2CO3 (3 g),
and KOH (0.2 g) in water (100 mL). After completion of the
reaction, water (300 mL) was added, and the quinone that preꢀ
cipitated was filtered off, washed, and dried. After recrystallizaꢀ
tion from hexane, cherryꢀcolored crystals were obtained in a
yield of 1.14 g (82%), m.p. 135—137 °C. Found (%): C, 71.05;
H, 8.74. C18H27NO3. Calculated (%): C, 70.79; H, 8.91.
IR (Nujol mulls), ν/cm–1: 1690, 1685, 1670, 1625, 1565, 1490,
1395, 1365, 1320, 1300, 1265, 1225, 1200, 1115, 1065, 1035,
1025, 1000, 920, 910, 805, 610. 1H NMR (CDCl3, 200 MHz), δ:
1.24 and 1.36 (both s, 9 H each, But); 2.96—3.01 (m, 4 H,
N—CH2); 3.79—3.84 (m, 4 H, O—CH2); 6.91 (s, 1 H, H(5)).
13C NMR (CDCl3, 50 MHz), δ: 29.1 and 30.8 (C(CH3)3);
35.2 and 36.0 (C(CH3)3); 51.3 (CH (N—CH2)); 66.5
(CH (O—CH2)); 132.8 (CH(5)); 140.0, 148.4, and 156.0 (C(3),
C(4) and C(6)); 182.4 and 185.2 (C=O).
tion from hexane, crystals were isolated in a yield of 1.34 g
(68%), m.p. 151—152 °C. Found (%): C, 78.89; H, 8.03.
C31H38N2O2. Calculated (%): C, 79.11; H, 8.14. IR (Nujol
mulls), ν/cm–1: 1685, 1670, 1620, 1565, 1500, 1470, 1395, 1365,
1290, 1275, 1205, 1135, 1075, 10005, 850, 765, 750, 730, 710,
1
695. H NMR (CDCl3, 200 MHz), δ: 1.23 and 1.30 (both s,
9 H each, But); 2.48—2.52 (m, 4 H, CH2); 3.11—3.16 (m, 4 H,
CH2); 4.25 (s, 1 H, CH—Ph2); 6.91 (s, 1 H, H(5)); 7.19—7.33
(m, 6 H, mꢀ, pꢀPh); 7.44 (d, 4 H, oꢀPh) . 13C NMR (CDCl3,
50 MHz), δ: 29.1 and 30.5 (CH3 (But)); 34.9 and 35.7
(CMe3 (But)); 52.1 (N—CH2); 76.3 (Ph—CH2—N) 127.2
(CH (pꢀPh)); 127.8 and 128.7 (CH (oꢀ, mꢀPh)); 133.0 (CH(5));
135.6 (C—N (Ph)); 142.2, 147.3, and 156.9 (C(3), C(4), C(6));
182.1 and 183.5 (C=O).
5,8ꢀDi(tertꢀbutyl)ꢀ2,3ꢀdihydroꢀ1,4ꢀethanoquinoxalineꢀ6,7ꢀ
dione (4). 3,6ꢀDi(tertꢀbutyl)ꢀoꢀbenzoquinone (1 g, 4.5 mmol)
and piperazine (0.4 g, 4.5 mmol) were dissolved in MeCN
(50 mL). The reaction mixture was magnetically stirred at ~20 °C
for 3 h. Then the mixture was oxidized by adding it to a vigorꢀ
ously stirred solution of potassium ferricyanide (10 g), Na2CO3
(3 g), and KOH (0.2 g) in water (100 mL). After completion of
the reaction, water (300 mL) was added, and the quinone that
precipitated was filtered off, washed, and recrystallized from
petroleum ether. Darkꢀred crystals were obtained in a yield of
1.24 g (91%), m.p. 188—190 °C. Found (%): C, 71.63; H, 8.51.
C18H26N2O2. Calculated (%): C, 71.49; H, 8.67. IR (Nujol
mulls), ν/cm–1: 1675, 1565, 1490, 1395, 1365, 1350, 1300, 1280,
1230, 1145, 1065, 1000, 980, 865, 845, 825, 775, 650, 545.
1H NMR (CDCl3, 200 MHz), δ: 1.32 (s, 18 H, But); 2.87—3.06
(m, 8 H, N—CH2, JAA´ = JBB´ = 9.6 Hz, JA´B´ = JAB = –12.9 Hz,
JAB´ = JA´B = 6.5 Hz). 13C NMR (CDCl3, 50 MHz), δ: 30.4
(C(CH3)3); 34.8 (C(CH3)3); 47.1 (N—CH2); 142.4 and 158.6
(C (3), C(4), C(5), and C(6)); 190.6 (C=O).
5ꢀtertꢀButylꢀ8ꢀchloroꢀ2,3ꢀdihydroꢀ1,4ꢀethanoquinoxalineꢀ
6,7ꢀdione (6). 5,8ꢀDi(tertꢀbutyl)ꢀ2,3ꢀdihydroꢀ1,4ꢀethanoquinꢀ
oxalineꢀ6,7ꢀdione (1 g, 3.3 mmol) was dissolved in concentrated
HCl (50 mL). The reaction mixture was magnetically stirred at
80 °C for 1 h. Then the mixture was neutralized with an aqueous
alkali solution, extracted with diethyl ether, and dried. After
recrystallization from acetone, compound 5 was obtained as
white crystals. Compound 5 was oxidized with a solution of
potassium ferricyanide (10 g), Na2CO3 (3 g), and KOH (0.2 g)
in water (100 mL), extracted with diethyl ether, and washed to
neutral pH. After the removal of diethyl ether, the dry residue
was crystallized from petroleum ether. Darkꢀcherryꢀcolored crysꢀ
tals were obtained in a yield of 0.8 g (86%), m.p. 184—185 °C.
Found (%): C, 60.09; H, 5.99; Cl, 12.57. C14H17ClN2O2. Calꢀ
culated (%): C, 59.89; H, 6.10; Cl, 12.63. IR (Nujol mulls),
ν/cm–1: 1700, 1680, 1655, 1625, 1565, 1365, 1335, 1280, 1250,
1225, 1170, 1150, 1055, 995, 985, 840, 815, 765, 685, 555.
1H NMR (CDCl3, 200 MHz), δ: 1.37 (s, 9 H, But); 2.89—3.26
(m, 8 H, N—CH2). 13C NMR (CDCl3, 50 MHz), δ: 30.7
(C(CH3)3); 35.8 (C(CH3)3); 47.2 and 47.3 (N—CH2); 122.9;
142.7; 156.5; 159.7; 177.3, and 183.2 (C=O).
4ꢀ(4ꢀPhenylpiperazinꢀ1ꢀyl)ꢀ3,6ꢀdi(tertꢀbutyl)ꢀ1,2ꢀbenzoꢀ
quinone (2b). 3,6ꢀDi(tertꢀbutyl)ꢀoꢀbenzoquinone (1 g, 4.5 mmol)
and 1ꢀphenylpiperazine (0.7 mL, 4.5 mmol) were dissolved in
MeCN (50 mL). The reaction mixture was magnetically stirred
at ~20 °C for 2 h. Then the mixture was oxidized by adding it to
a vigorously stirred solution of potassium ferricyanide (10 g),
Na2CO3 (3 g), and KOH (0.2 g) in water (100 mL). After compleꢀ
tion of the reaction, water (300 mL) was added, and the quinone
that precipitated was filtered off, washed, and recrystallized from
petroleum ether. Crystals were obtained in a yield of 1.34 g
(78%), m.p. 132—135 °C. Found (%): C, 75.49; H, 8.53.
C24H32N2O2. Calculated (%): C, 75.75; H, 8.48. IR (Nujol
mulls), ν/cm–1: 1685, 1650, 1610, 1550, 1510, 1365, 1330, 1285,
1
1275, 1235, 1200, 1145, 930, 835, 755, 690. H NMR (CDCl3,
200 MHz), δ: 1.24 and 1.37 (both s, 9 H each, But); 3.20—3.30
(m, 8 H, N—CH2); 6.89—6.99 (m, 4 H, mꢀ, pꢀPh, H(5));
7.26—7.35 (m, 2 H, oꢀPh). 13C NMR (CDCl3, 50 MHz), δ: 29.1
and 30.8 (C(CH3)3); 35.1 and 36.0 (C(CH3)3); 49.6 and 51.5
(N—CH2); 116.7 (CH (oꢀPh)); 120.8 (CH (pꢀPh)); 129.4
(CH (mꢀPh)); 132.9 (CH(5)); 138.7, 148.0, and 156.5 (C(3),
C(4), C(6)); 151.2 (C—N (Ph)); 182.4 and 184.7 (C=O).
4ꢀ(4ꢀDiphenylmethylpiperazinꢀ1ꢀyl)ꢀ3,6ꢀdi(tertꢀbutyl)ꢀ1,2ꢀ
benzoquinone (2c). 3,6ꢀDi(tertꢀbutyl)ꢀoꢀbenzoquinone (1 g,
4.5 mmol) and 1ꢀ(diphenylmethyl)piperazine (1.13 g, 4.5 mmol)
were dissolved in MeCN (50 mL). The reaction mixture was
magnetically stirred at ~20 °C for 5 h. Then the mixture was
oxidized by adding it to a vigorously stirred solution of potasꢀ
sium ferricyanide (10 g), Na2CO3 (3 g), and KOH (0.2 g) in
water (100 mL). After 1 h, the product was extracted with diꢀ
ethyl ether, washed to neutral pH, and dried. After recrystallizaꢀ
4,4´ꢀ(Piperazineꢀ1,4ꢀdiyl)ꢀbis[3,6ꢀdi(tertꢀbutyl)ꢀ1,2ꢀbenzoꢀ
quinone] (7). 3,6ꢀDi(tertꢀbutyl)ꢀoꢀbenzoquinone (2.2 g,
10 mmol) and piperazine (0.6 g, 7 mmol) were dissolved in
CHCl3 (60 mL). The reaction mixture was magnetically stirred
at ~20 °C for 24 h. Then PbO2 (4.5 g) was added, the mixture
was kept for 2 h, and unconsumed PbO2 was filtered off. The
solvent was removed, and the dry residue was recrystallized from

1856
Russ.Chem.Bull., Int.Ed., Vol. 56, No. 9, September, 2007
Abakumov et al.
a mixture of CH2Cl2 and MeCN. Darkꢀcherryꢀcolored crystals
were obtained in a yield of 1.89 g (52%), m.p. 181—182 °C.
Found (%): C, 73.65; H, 8.83. C32H46N2O4. Calculated (%):
C, 73.53; H, 8.87. IR (Nujol mulls), ν/cm–1: 1685, 1675, 1630,
1535, 1490, 1465, 1405, 1365, 1350, 1285, 1275, 1210, 1140,
1055, 1030, 1015, 940, 925, 885, 840, 725, 685, 655, 600.
1H NMR (CDCl3, 200 MHz), δ: 1.25 and 1.38 (both s,
18 H each, But); 3.11 (s, 8 H, CH2); 6.88 (s, 2 H, H(5)).
13C NMR (CDCl3, 50 MHz), δ: 29.1 and 30.9 (CH3 (But));
35.2 and 36.1 (CMe3 (But)); 51.0 (N—CH2); 132.6 (CH(5));
140.0 (br, C—N); 148.5 and 155.8 (C(3), C(6)); 182.3 and
185.1 (C=O).
14. G. A. Abakumov, V. K. Cherkasov, A. V. Piskunov, N. O.
Druzhkov, and V. N. Ikorskii, Izv. Akad. Nauk, Ser. Khim.,
2005, 1580 [Russ. Chem. Bull., Int. Ed., 2005, 54, 1627].
15. A. L. Buchachenko and A. M. Vasserman, Stabil´nye radikaly
[Stable Radicals], Khimiya, Moscow, 1973 (in Russian).
16. E. G. Rozantsev, Svobodnye iminoksil´nye radikaly [Free
Iminoxyl Radicals], Khimiya, Moscow, 1970 (in Russian).
17. G. Wilkinson, Comprehensive Coordination Chemistry,
Pergamon, 1987, v. 2.
18. G. A. Abakumov, V. K. Cherkasov, T. N. Kocherova, N. O.
Druzhkov, Yu. A. Kurskii, and L. G. Abakumova, Izv. Akad.
Nauk, Ser. Khim., 2006, 1151 [Russ. Chem. Bull., Int. Ed.,
2006, 55, 1195].
oꢀQuinone semiquinolates with potassium and magnesium
were generated according to known procedures.33,34
19. W. Brackman and E. Havinga, Rec. Trav. Chim. PaysꢀBas,
1955, 74, 937.
This study was financially supported by the Russian
Foundation for Basic Research (Project Nos 07ꢀ03ꢀ00711
and 07ꢀ03ꢀ00819) and the Council on Grants of the Presiꢀ
dent of the Russian Federation (Program for State Supꢀ
port of Leading Scientific Schools of the Russian Federaꢀ
tion, Grant NShꢀ4947.2006.3).
20. I. A. Novikova, V. B. Vol´eva, N. L. Komissarova, I. S.
Belostotskaya, and V. V. Ershov, Izv. Akad. Nauk SSSR, Ser.
Khim., 1981, 2110 [Bull. Acad. Sci. USSR, Div. Chem. Sci.,
1997, 46, 2093 (Engl. Transl.)].
21. A. L. Macdonald and J. Trotter, J. Chem. Soc., Perkin
Trans. 2, 1973, 476.
22. J. S. Edmonds, M. Nomachi, M. Terasaki, M. Morita, B. W.
Skelton, and A. H. White, Biochem. Biophys. Res. Commun.
2004, 319, 556.
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Received May 30, 2007;
in revised form September 6, 2007