Synthesis of 11,12-disubstituted 9,10-anthraquinodimethanes: The first dehydroxylation reaction by active magnesium

Article abstract of DOI:10.1016/S0040-4039(02)00304-0

The reaction of 9,10-diformylanthracene with Grignard reagents gave 11,12-disubstituted 9,10-anthraquinonemethane (1) in quantitative to excellent yields. The formation of these quinodimethanes caused by the active magnesium generated from the Grignard re

Full text of DOI:10.1016/S0040-4039(02)00304-0

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 43 (2002) 2623–2625
Synthesis of 11,12-disubstituted 9,10-anthraquinodimethanes:
the first dehydroxylation reaction by active magnesium
Shaheen M. I. Shah, Shigeyasu Kuroda,* Mitsunori Oda,* Tokiko Tanaka, Ryuta Miyatake and
Mayumi Izawa
Department of Applied Chemistry, Faculty of Engineering, Toyama University, Gofuku 3190, Toyama 930-8555, Japan
Received 27 December 2001; revised 4 February 2002; accepted 8 February 2002
Abstract—The reaction of 9,10-diformylanthracene with Grignard reagents gave 11,12-disubstituted 9,10-anthraquinonemethane
(1) in quantitative to excellent yields. The formation of these quinodimethanes caused by the active magnesium generated from
the Grignard reagents was revealed. © 2002 Elsevier Science Ltd. All rights reserved.
9,10-Anthraquinodimethane and its derivatives have
been widely and actively investigated from the view-
point of organic superconductors and as the synthetic
intermediate of [2.2]cyclophanes.1 Although 11,12-
diaryl substituted 9,10-anthraquinodimethanes have
been synthesized as stable compounds,2 the parent
11,12-dialkyl substituted quinodimethanes have been
left unknown so far because of their highly reactive
properties to polymerize.3 Only 1,4,11,12-tetramethyl-
9,10-anthraquinodimethane has been synthesized and
isolated.3 During the course of our research on the
synthesis of new conjugated aromatic compounds con-
taining an anthracene moiety, we found a new method
for the first synthesis of 11,12-dialkyl and 11,12-diaryl
substituted 9,10-anthraquinodimethanes (1a–f) in one
step by the reaction of 9,10-diformylanthracene (2) with
the Grignard reagent (RMgX) under ambient condi-
tions in quantitative to excellent yields. Also, we suc-
ceeded in the first isolation of 11,12-dimethyl and
11,12-diethyl compounds at ambient temperature. Fur-
thermore, the diol (3a) with the Grignard reagent
(MeMgI) also gave the corresponding 11,12-disubsti-
tuted 9,10-anthraquinodimethanes under similar condi-
tions. The mechanistic experiments revealed that the
formation of quinodimethanes by dehydroxylation took
place by the action of the active magnesium generated
not only from the Grignard reagents but also from
other methods.
The reaction of 2 with freshly prepared methylmagne-
sium iodide (60 equiv.) in dry THF–ether (ca. 1:1 in
volume) solution at 40°C for 8 h gave 1a quantitatively.
Some preliminary experiments revealed that the com-
plete quinodimethane formation requires a large excess
amount of the Grignard reagent and reaction tempera-
ture above 40°C; otherwise, the reaction gave diols
(3a–f) or their mixture at under that temperature. The
reaction of 2 with other Grignard reagents (R=Et, Ph,
etc.) also afforded the corresponding 11,12-disubsti-
tuted quinodimethanes in excellent to reasonable yields
as shown in Table 1.
Table 1. The results of one-pot synthesis of 1 from 2
H
R
CHO
RMgX
CHO
R
1a~fH
2
Entry
Products
Yielda (%)
Ratio (E/Z)c
1
2
3
4
5
6
1a: R=Me
1b: R=Et
1c: R=Ph
1d: R=o-MeC6H4
1e: R=p-MeC6H4
98b
90b
61
47
42
1:1
1:1
1:1.29
1:1.96
1:1.04
1:1.28
1f: R=p-MeOC6H4 40
a Yields after chromatographic purification.
b Yields were determined by 1H NMR analysis.
c Ratio refers to the isomer mixture characterized by 1H NMR
spectrum.
Keywords: Grignard reagent; dehydroxylation; active magnesium.
* Corresponding author. E-mail: kuro@eng.toyama-u.ac
0040-4039/02/$ - see front matter © 2002 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(02)00304-0

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S. M. I. Shah et al. / Tetrahedron Letters 43 (2002) 2623–2625
The structures of these new compounds were confirmed
by their physical properties. The stereochemistry
between the substituents of these quinodimethanes was
determined by the 1H NMR spectra. The 1H NMR
spectrum of 1a showed that the methine protons
appeared at l 6.19 and 6.16 ppm as quartets (J=7.19
Hz), and the methyl groups at l 2.12 and 2.13 ppm as
two doublets, indicating a mixture of syn and anti
forms. The structure of 1b was determined in a similar
way,4 and the other known compounds (1c–f) were
identified by comparison of the physical properties.2 To
examine the effects of the solvent and the molar ratios
of the reagents, the reactions were performed under
various conditions by using MeMgI as a typical Grig-
nard reagent. The reaction does not depend upon the
solvent, either THF or ether. The reaction of 2 with the
use of a lesser molar ratio than 60 equiv. of the
cially available MeMgI (Aldrich Chemical Co.) gave
only diol (3a) and no quinodimethane (1a) was
obtained. These results suggested that the formation of
quinodimethane was due to the active magnesium metal
generated from the MeI or the MeMgI in solution.5
This was confirmed by the use of active magnesium
prepared by alternative methods as follows (Table 2).
The entrainment reagent,6 that is, the reaction of 1,2-
dibromoethane with Mg (20 equiv.), of 3a exclusively
gave quinodimethane in 94% yield, entry 4. Further-
more, entries 5–7 show that less molar of reagents
effective for dehydroxylation, e.g. the treatment of 5
equiv. of active Mg* generated by the reaction of
Li+[naphthalene]− with MgCl2, also gave quinodi-
methane quantitatively.
Based upon the above results, this reaction path is
proposed to proceed as follows. The reaction of Grig-
nard reagents with 2 gave halomagnesium salt of the
corresponding diols (4), which were also generated by
the reaction of 3 with any R%MgX. These complexes
were dehydroxylated by the action of an excess of
active magnesium, as shown in Scheme 1.
Grignard reagent gave
a
mixture of diol and
quinodimethane depending on the ratio. Furthermore,
treatment of diol (3a) with 60 equiv. of methylmagne-
sium iodide under the same conditions also gave 1a
quantitatively. The reaction of 2 and 3a with the use of
the same equiv. of filtered MeMgI or that of commer-
Table 2. The actions of the Grignard reagents and active Mg* on 3a to formation of 1a
Entry
Reagents and conditions
Molar ratio (equiv.)
Ratio (%)
Total yield (%)
3a
1a
1
2
3
4
5
6
7
MeMgI, THF–ether, 8 h, 40°C
MeMgI, THF–ether, 8 h, 40°C
30
60
10
20
0.5
2
58
–
21
–
81
19
–
42
100
75
100
19
90
98
95
94
98
99
98
Br(CH2)2Br, Mg, THF–ether, 8 h, 40°C
Br(CH2)2Br, Mg, THF–ether, 8 h, 40°C
Naphthalene–Li, MgCl2, THF, 8 h, 40°C
Naphthalene–Li, MgCl2, THF, 8 h, 40°C
Naphthalene–Li, MgCl2, THF, 8 h, 40°C
81
100
5
Scheme 1.

S. M. I. Shah et al. / Tetrahedron Letters 43 (2002) 2623–2625
2625
Acknowledgements
over anhydrous MgSO4. The solvent was evaporated and
chromatographed on silica gel (eluting with benzene/hex-
ane, 2:1) and gave 1a–f, respectively.
We gratefully acknowledge financial support by a
Grant-in-Aid for Scientific Research (No. 10640513)
from the Ministry of Education, Science, Sport, Cul-
ture, and Technology, Japan.
Compound 1a: Colorless oil, 1H NMR (400 MHz, CDCl3–
TMS) l 7.58–7.54 (m, 2H), 7.52–7.49 (m, 2H), 7.31–7.22
(m, 4H), 6.19 (q, J=7.19 Hz, 2H, methine–H, E or Z),
6.16 (q, J=7.19 Hz, 2H, methine-H, Z or E), 2.13 (d,
J=8.39 Hz, 6H, CH3, E or Z), 2.12 (d, J=8.39 Hz, 6H,
CH3, Z or E); 13C NMR (100 MHz, CDCl3–TMS) l
139.47, 136.97, 135.92, 135.89, 134.85, 132.49, 127.69,
127.20, 127.07, 126.73, 126.03, 125.61, 123.86, 123.81,
123.53, 123.11, 16.01; UV–vis (MeOH) wmax/nm (log m) 213
(4.65), 227 (4.48), 261 (4.21), 283 (4.30); IR (film) 1632,
1600 cm−1 (CꢀC); MS (EI, 70 eV): m/z (%)=232 (M+,
100), 217 (77), 202 (58), 101 (21); HRMS calcd for C18H16:
232.1252, found 232.1265.
References
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4. General procedure: A solution of alkyl halide (60 equiv.)
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continued for 1.5 h at room temperature. Then, to this
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combined organic layer was washed with brine and dried
Compound 1b: Colorless oil, 1H NMR (400 MHz, CDCl3–
TMS) l 7.58–7.45 (m, 4H), 7.30–7.23 (m, 4H), 6.03 (t,
J=7.59 Hz, 2H, methine-H, E or Z), 6.01 (t, J=7.59 Hz,
2H, methine-H, Z or E), 2.58 (quin., J=7.19 Hz, 4H,
CH2, E or Z), 2.56 (quin, J=7.59 Hz, 4H, CH2, Z or E),
1.15 (t, J=7.19 Hz, 6H, CH3, E or Z), 1.146 (t, J=7.59
Hz, 6H, CH3, Z or E); 13C (100 MHz, CDCl3–TMS) l
139.37, 137.02, 135.06, 134.37, 134.33, 132.87, 131.75,
131.47, 127.50, 127.10, 127.03, 126.74, 126.11, 125.65,
123.85, 123.15, 23.33, 14.79; UV–vis (MeOH) wmax/nm
(log m) 211 (4.71), 252 (4.18), 261 (4.19), 285 (4.22); IR
(film) 1633, 1593 cm−1 (CꢀC); MS (EI, 70 eV): m/z (%)=
260 (M+, 64), 245 (25), 231 (100), 215 (41), 203 (50);
HRMS calcd for C20H20: 260.1565, found 260.1584.
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38, 4761–4767; (b) Rieke, R. D.; Hanson, M. V. Tetra-
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