Structure and electronic properties of quinone dimers connected with acetylene and diacetylene linkages

Article abstract of DOI:10.1016/j.tet.2009.03.001

Quinone dimers connected with acetylene (QAQ) and diacetylene linkages (QAAQ) have been synthesized and their structure and electronic properties studied. X-ray analysis, DFT calculations, and UV-vis measurements showed that, unlike directly connected qui

Full text of DOI:10.1016/j.tet.2009.03.001

Tetrahedron 65 (2009) 3639–3644
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Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Structure and electronic properties of quinone dimers connected with acetylene
and diacetylene linkages
,
a
a
a
b
Naoto Hayashi a , Takahiro Ohnuma , Yoko Saito , Hiroyuki Higuchi , Keiko Ninomiya
*
a Graduate School of Science and Engineering, University of Toyama, Gofuku, Toyama 9308555, Japan
b Graduate School of Engineering, Kyoto University, Katsura, Kyoto 6158510, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Quinone dimers connected with acetylene (QAQ) and diacetylene linkages (QAAQ) have been synthe-
sized and their structure and electronic properties studied. X-ray analysis, DFT calculations, and UV–vis
measurements showed that, unlike directly connected quinone dimers (QQ), they had planar and thus
Received 28 January 2009
Received in revised form 27 February 2009
Accepted 1 March 2009
efficiently extended
considerably raised, and QAQ thereby behaved as a mild oxidizing agent.
Ó 2009 Elsevier Ltd. All rights reserved.
p conjugation systems. The respective reduction potentials of QAQ and QAAQ were
Available online 6 March 2009
1. Introduction
These findings prompted us to investigate quinone dimers
connected with acetylene and diacetylene linkages, denoted as
Quinones have been widely employed in various fields of
chemistry, including reaction chemistry, medicinal chemistry,
biochemistry, and material chemistry.1 As the usefulness of qui-
nones is based on their strong electron acceptor characters, a sig-
nificant number of studies have been conducted with the aim of
modulating or enhancing these characters. It is well known that
QAQ and QAAQ, respectively. It was expected that the
p systems in
those compounds would be more efficiently conjugated since the
linkages would reduce the steric repulsion in order to enhance the
planarity of the
additional p atomic orbitals would contribute to the extension of
p
system,4 as well as that two (QAQ) or four (QAAQ)
the
p
systems. In fact, there are several compounds in which TTF,5
such characters can be enhanced by the extension of the
p
system2
porphyrin,6,7 anthraquinone,8 and dendrimeric moieties9 are con-
nected by acetylene and/or diacetylene linkages, exhibiting re-
markable photochemical and electrochemical properties due to
or by the substitution of electron-withdrawing groups. In addition,
we recently reported that a covalent linkage between quinone
moieties significantly enhances their electron acceptor characters;
covalently connected quinone dimers (QQ) and trimers (QQQ) were
observed to have considerably higher reduction potentials as
compared to quinone monomers.3 The enhanced electron acceptor
characters of QQ and QQQ are likely to be largely attributable to the
‘substituent effect’ of the quinone moiety; the contribution of the
their extended
p systems. Acetylene and diacetylene linkages are
also advantageous in view of the rigidity of the molecular structure
and the facileness of the synthesis, which determines their com-
mon use in material chemistry.10 Quinones connected with diac-
etylene linkages were previously prepared as partial structures of
p-quinone-fused hexadehydro[18]annulenes,11 although the effects
of the diacetylene linkages could not be examined due to the lack of
analogues, which are connected either directly or with acetylene
linkages.12 Herein, QAQ and QAAQ were synthesized, their elec-
tronic and structural properties were investigated by means of
X-ray diffraction, Raman and UV–vis spectra, DFT calculations, and
cyclic voltammetry (CV), and the results were compared with those
for QQ. Additionally, the capabilities of QAQ and QAAQ as oxidizing
agents were studied.
extension of the
p system appeared to be small since the X-ray
structure and the electronic absorption spectra of QQ and QQQ
indicated that quinone moieties were highly twisted owing to the
steric repulsion between the hydrogen and the oxygen atoms, and
as a result the
p
systems were not fully conjugated.
O
O
O
O
O
O
O
O
QQQ
O
O
QQ
2. Results and discussion
QAQ and QAAQ were synthesized as shown in Scheme 1. Similarly
to QQ, tert-butyl groups were substituted into QAQ and QAAQ
in order to increase their solubility and stability. 2-tert-Butyl-5-
iododimethoxybenzene (1) was subjected to Sonogashira coupling13
* Corresponding author. Fax: þ81 76 445 6613.
E-mail address: nhayashi@sci.u-toyama.ac.jp (N. Hayashi).
0040-4020/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2009.03.001

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N. Hayashi et al. / Tetrahedron 65 (2009) 3639–3644
with trimethylsilylacetylene to give 2, followed by the removal of the
TMS protections under basic conditions to give 3, which was in turn
subjected to Sonogashira coupling with 1 to afford MAM, while the
Eglinton coupling14 of 3 gave MAAM. By oxidation using cerium(IV)
ammonium nitrite (CAN), MAM and MAAM yielded QAQ and QAAQ
as thermally stable, deep red powders, respectively.
(left), the molecule was centrosymmetric, situated on the inversion
center of the crystal, with a nearly planar conformation. As seen in
the X-ray structures of several other oligoyne compounds,15 the
diacetylene moiety was found to bear a slight deviation from lin-
earity. It is noteworthy that while the quinone ring of QQ was in the
boat form due to the steric repulsion between the oxygen atoms in
the crystalline,3 no structural distortion of the quinone moieties
was found in QAQ and QAAQ. The values of the structural param-
eters of QAQ and QAAQ (bond lengths, bond angles, and dihedral
angles) were virtually identical to the standard values of these
parameters for quinone and acetylene moieties within errors, in-
dicating that there is no influence from the acetylene moiety on the
structural parameters of the quinone moieties, and vice versa. On
the other hand, nC^C of QAQ (2203 cmꢀ1) was observed to shift
bathochromically as compared to those of diphenylacetylene
OCH3
OCH3
PdCl2(PPh3)2, CuI
I
(H3C)3Si
H
Si(CH3)3
iso-Pr2NH
(95%)
H3CO
OCH3
1
2
K2CO3
CH3OH/H2O (4:1)
(88%)
(2226 cmꢀ1 16 and MAM (2220 cmꢀ1), while nC^C of QAAQ was
)
found to be 2215 cmꢀ1, which is comparable to that of MAAM
OCH3
(2217 cmꢀ1).
H
The potential energy curves for the –C^C– and ^C–C^ bond
rotations were calculated by means of the B3LYP/6-311þG(d,p)
method for model compounds bearing no tert-butyl groups,
denoted as QAQ0 and QAAQ0. It was revealed that QAQ0 and QAAQ0
had three and four potential minima, respectively, among which
H3CO
3
PdCl2(PPh3)2, CuI, 1
iso-Pr2NH
(quant.)
Cu(OAc)2
Pyridine
(60%)
the anti conformers (
the syn conformers (
f
w180ꢁ) represented the global minima and
w0ꢁ) represented one of the next energy
OCH3
OCH3
OCH3
OCH3
f
levels (Fig. 3). The potential energies of the anti and syn conformers
of QAQ0 and QAAQ0, together with those of MAM0 and MAAM0, are
compared as shown in Table 1. QAQ0, QAAQ0, and MAM0 prefer anti
to syn conformations, while those two conformations are ener-
getically comparable for MAAM0. It should be noted that the ener-
getic difference between the anti and syn conformers is
1.5 kcal molꢀ1 for QAQ0, which is more significant than that for
MAM0. This cannot be explained in terms of different magnitudes of
the steric repulsion between the oxygen atoms since those atoms
are well separated even in the syn conformers: the oxygen–oxygen
distance is 4.26 Å in the syn conformer of QAQ0, which is consid-
erably larger than the sum of van der Waals radii (3.18 Å).17 The
larger disadvantage of the syn conformer of QAQ0 probably arises
from the more significant electrostatic repulsion between the oxy-
gen atoms in QAQ0, since the C]O bond of QAQ0 is more polarized
H3CO
H3CO
MAAM
H3CO
H3CO
MAM
CAN
CH3CN
(90%)
CAN
CH3CN
(91%)
O
O
O
O
O
O
O
O
QAQ
QAAQ
Scheme 1. Synthesis of QAQ and QAAQ.
An X-ray analysis of QAQ was performed using a good crystal
prepared by slow evaporation from a 1,2-dimethoxyethane solu-
tion. The X-ray structure of QAQ was revealed to be a centrosym-
metrical molecule (Fig. 1, left). While the two quinone moieties of
than the aryl–O bond of MAM0, which magnifies the
d- character of
the oxygen atom. On the other hand, the syn conformers are also
disfavored in QAAQ0, albeit more weakly than in QAQ0. This in-
dicates that the disadvantage of the syn conformers originates from
long-distance interactions, i.e., from Coulombic forces. Although
QAQ0 and QAAQ0 prefer anti conformations, the energy difference
between the syn and anti conformers appear to be relatively small.
QQ were considerably twisted in its X-ray structure, the
p system of
QAQ was found to be almost planar owing to the acetylene linkage.
An X-ray analysis was also conducted for a crystal of QAAQ
obtained from a dichloromethane solution. As shown in Figure 2
Figure 1. X-ray structure of QAQ. (left) ORTEP drawing (50% probability). (right) A top view of ribbon motif formed by CH/O interactions (represented by orange broken lines).

N. Hayashi et al. / Tetrahedron 65 (2009) 3639–3644
3641
Figure 2. X-ray structure of QAAQ. (left) ORTEP drawing (50% probability). (right) A top view of ribbon motif formed by CH/O interactions (represented by orange broken lines).
spectra of QAQ and QAAQ (570 nm, vs 390 nm in QQ). Additionally,
new absorption peaks appeared around 320, 380, and 470 nm. These
indicate the efficient extension of the
p conjugation system in QAQ
and QAAQ owing to the acetylene and diacetylene linkages. It is
noteworthy that the bathochromic shifts of the absorption peaks
were more significant for QQ, QAQ, and QAAQ than for MM, MAM,
and MAAM. On the other hand, although the bathochromic shift of
the absorption edge between MAM and MAAM was found to be
20 nm, no notable shift was observed between QAQ and QAAQ.
The redox behavior of 2,5-di-tert-butyl-1,4-benzoquinone (Q),
QQ, QAQ, and QAAQ was measured by means of CV (Table 2). In
a dichloromethane solution, QQ, QAQ, and QAAQ commonly
exhibited two reversible reduction waves (E11/2 and E12/2) corre-
sponding to the formation of radical anions and dianions, re-
spectively. The respective third waves (E3) were irreversible, and
were followed by the decay of the resultant species since the E3
waves appeared to be accompanied by small shoulder-like
Figure 3. Potential energy curves for the –C^C– (QAQ0, filled circles) and ^C–C^
(QAAQ0, open circles) bond rotation relative to the energy of the conformers (
calculated by B3LYP/6-311þG(d,p) methods.
f
¼180ꢁ)
Thus, planar conformations observed in the X-ray structure of QAQ
and QAAQ are due not only to intramolecular factors but also to
intermolecular interactions probably. In fact, Figures 1 (right) and 2
(right) show the presence of four-fold CH/O interactions18 between
the adjacent molecules in crystalline (dC/O¼3.367 and 3.387 Å for
QAQ and 3.367 and 3.371 Å for QAAQ), which may assist the con-
formations of QAQ and QAAQ to be planar. The stacking of the
ribbon motifs formed with the aid of CH/O interactions is also
shown in Figures 1 and 2, describing no significant overlapping of
the
p moieties between the layers (blue and green). Also, the
acetylene (QAQ) and diacetylene (QAAQ) moieties are far apart so
that neither photo-dimerization nor polymerization is likely to take
place in crystalline.
The electronic absorption spectra (1,4-dioxane) of 4,40-di-tert-
butyl-2,20,5,50-tetramethoxybiphenyl(MM), MAM, MAAM, QQ, QAQ,
and QAAQ are shown in Figure 4. Compared to QQ, substantial
bathochromic shifts of the absorption edge were observed in the
Table 1
Potential energies (kcal molꢀ1) and dihedral angles (ꢁ, in parentheses) of the syn and
anti conformers of QAQ0, QAAQ0, MAM0, and MAAM0 geometrically optimized using
the B3LYP/6-311þG(d,p) method
Compound
D
Ea (dihedral angle)
anti
syn
1.49 (0.0)
0.33 (0.2)
0.77 (0.2)
QAQ0
0.00 (179.7)
0.00 (179.5)
0.00 (179.6)
0.00 (177.7)
QAAQ0
MAM0
MAAM0
Figure 4. Electronic absorption spectra of MM (upper black), MAM (upper blue),
MAAM (upper red), QQ (lower black), QAQ (lower blue), and QAAQ (lower red) in 1,4-
dioxane.
ꢀ0.10 (12.9)
a
Relative to the energy of the anti conformer.

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N. Hayashi et al. / Tetrahedron 65 (2009) 3639–3644
Table 2
O
C
O
O
O
Reduction potentials for compounds Q, QQ, QAQ, and QAAQa
C
C
C
Compound
E11/2
E12/2
Ep3c
Q
QQ
QAQ
QAAQ
ꢀ1.06 (1e)
ꢀ0.73 (1e)
ꢀ0.63 (1e)
ꢀ0.60 (1e)
ꢀ1.78 (1e)
ꢀ1.07 (1e)
HO
O
C
HO
O
ꢀ1.54b
I
II
ꢀ0.80 (1e)
ꢀ0.73 (1e)
ꢀ1.58b
ꢀ1.61b
O
O
O
O
Electrode; Pt (working), Pt (counter), and Ag/Agþ (reference). Supporting elec-
a
C
trolyte n-Bu4NClO4. Solvent; CH2Cl2. Scan rate; 100 mV sꢀ1
.
b
HO
O
HO
O
Irreversible.
III
IV
O
O
O
O
extensions, as shown in Figure S1. The rise of the E11/2s of QAQ and
QAAQ as compared to QQ is indicative of the efficient extension of
the
p conjugation system by the acetylene and diacetylene linkages,
O
O
O
O
V
VI
although it was smaller than expected from the comparison with
the E11/2 of Q. This indicates that E11/2 can be significantly lowered by
any linkage of quinone moieties, as well as that the contribution of
O
O
O
O
the planarization of the
p
system to the lowering of E11/2 is relatively
small. On the other hand, E12/2s were considerably raised in the order
of QQ, QAQ, and QAAQ, which is explainable in terms of the re-
O
O
O
O
VII
VIII
Scheme 3.
duction of the on-site Coulombic repulsion in the extended
p sys-
tems of QAQ and QAAQ.
As QAQ and QAAQ were found to have strong electron acceptor
characters, their capabilities as oxidizing agents were examined.
When a tetralin (1,2,3,4-tetrahydronaphthalene) solution of QAQ
was heated at 100 ꢁC for 48 h, QAQ disappeared completely, and
This can be explained in terms of relative stability of the in-
termediate carbocations;21 benzylic cation generated from o-xylene
by hydride abstract is less stabilized than that from tetralon because
the former is a primary cation while the latter is a secondary one.
Next, as quinone is an electron-accepting moiety, QAQ wasexpected
to behave as a dienophile, similarly to acetylenedicarboxylic acid
diesters, and was thus subjected to Diels–Alder reactions with
tetraphenylcyclopentadienone, cyclopentadine, furan, and Dani-
shefsky’s diene (1-methoxyl-3-trimethylsiloxybutadiene).22 How-
ever, all attempts resulted in yielding inseparable complex mixtures.
nearly double the molar quantity of
obtained. When QAAQ was used instead of QAQ under the same
conditions, the -oxidation of tetralin proceeded, albeit rather
slowly: 32% of unreacted QAAQ was recovered, and ca. 1.8 times the
molar quantity of -tetralon based on the consumed QAAQ was
a-tetralon based on QAQ was
a
a
obtained (Scheme 2). The different behavior of QAQ and QAAQ
should be attributable to the different reaction rates of hydride ion
transfer from the 1-position of tetralin to the carbonyl oxygen of
QAQ and QAAQ, respectively, which is known to be the rate-de-
termining step in the general mechanism of benzylic oxidation by
quinones.19 The hydride ion transfer is likely to occur faster in QAQ
because of the higher stability of the phenoxide I compared to III
(Scheme 3). In the phenoxide compounds, the negative charges may
be regarded as being localized considerably as depicted in I and III
because of the intrinsically asymmetrical molecular structure.
Moreover, the contribution of the resonance formulae II and IV is
not important due to the lack of aromaticity. This indicates that the
quinone moieties in I and III should affect the phenoxide moieties
mainly in an inductive manner. Generally, the inductive effect is
greater when the substituent locates closely. Therefore, the stabi-
lization effects by the quinone moiety should be greater in I than in
III in order that the hydride transfer to QAQ occurred faster than
that to QAAQ. Note that the situation is thoroughly different in the
radical anions V and VII, the latter being more stabilized than the
former. This is due to highly delocalized characters of the radical
spins and negative charges as described by the resonance formulae
VI and VIII. As the stabilization effects would be generally larger in
3. Conclusions
We have described the synthesis and the properties of QAQ and
QAAQ, in which two quinone moieties are connected by acetylene
and diacetylene linkages, respectively. DFT calculations showed
that QAQ and QAAQ prefer the planar conformations, although
their planar structure observed in the X-ray structure should be due
not only to the intramolecular factors but also to intermolecular
CH/O interactions. The intrinsically planer character of the
p con-
jugation system of QAQ and QAAQ gives rise to the bathochromic
shift in their UV–vis spectra and the notable rise of the reduction
potentials as compared to QQ. It was also observed that both QAQ
and QAAQ behaved as mild oxidizing agents, while QQ decayed by
itself in the same conditions due to its thermal instability. Studies of
quinone trimers and higher oligomers linked directly or connected
with acetylene or diacetylene linkages are currently underway as
further exploration of co-oligomers consisting of quinone and
acetylene moieties.
the more extended
p compounds, VII would be more stabilized than
V. This is supported by the fact that the E11/2 of QAAQ was observed to
be lower than that of QAQ (Table 2). In contrast, heating a tetralin
solution of QQ yielded a complex mixture containing 18% of 3,7-di-
tert-butyl-8-hydroxydibenzofuran-1,4-dione20 and a trace amount
4. Experimental section
4.1. General
All commercially available chemicals were used without further
purification except pyridine, which was dried over KOH. All re-
actions were performed in standard glassware under an inert argon
atmosphere, unless otherwise stated. Melting points were de-
termined on microscopic thermometer without correction.
1H (600 MHz) and 13C NMR (150 MHz) spectra were recorded on
a JEOL JNM-ECP600 in CDCl3 with tetramethylsilane as internal
reference. Mass spectra were conducted on a JEOL MStation JMS-
of a-tetralon. On the other hand, products were not observed in hot
o-xylene solutions of any of the three dimers QQ, QAQ, and QAAQ.
O
QAQ or QAAQ
100 °C, 48 h
Scheme 2.

N. Hayashi et al. / Tetrahedron 65 (2009) 3639–3644
3643
700 (EI) and a JEOL JMS-SX102A (HRMS/EI). Raman spectra were
measured on a JASCO RFT-200. Electronic absorption spectra were
recorded on a SHIMADZU UV-2400PC. Cyclic voltammetry (CV) was
performed on an ALS model 600A in 1.0 mM of substrate. All
oxidation CV measurements were carried out in anhydrous
dichloromethane containing 0.1 M tetrabutylammonium perchlo-
rate (n-Bu4NClO4) as a supporting electrolyte, purging with argon
prior to conduct the experiment. Platinum electrode was used as
a working electrode and a platinum wire as a counter electrode. All
potentials were recorded versus Ag/Agþ electrode (in acetonitrile)
as a reference electrode. The redox processes were analyzed by
using semiderivative technique.
(cmꢀ1): 2218
(
nC^C). MS (EI): m/z¼410 (Mþ). HRMS (m/z):
410.2455 (Mþ, calcd 410.2457 for C26H34O4).
4.5. Synthesis of bis(5-tert-butyl-1,4-benzoquinon-2-yl)-
acetylene (QAQ)
To a solution of MAM (0.12 g, 0.3 mmol) in acetonitrile (5 mL)
was added cerium ammonium nitrite (CAN, 0.79 g, 1.5 mmol) at
ambient temperature in dark. After stirring for 4 h, the reaction
mixture was quenched with water, then subjected to supersonic
treatment until the solid was precipitated. The precipitate was
separated by suction filtration, washed with acetone/water (1:1
v/v), dried, and recrystallized from 1,2-dimethoxyethane to give
QAQ as a deep red powder (0.09 g, 90%). Mp 200–203 ꢁC. 1H NMR:
4.2. Synthesis of 2-tert-butyl-5-trimethylsilylethynyl-1,4-
dimethoxybenzene (2)
d
¼6.96 (2H, s, CH), 6.66 (2H, s, CH), 1.29 (18H, s, t-Bu). 13C NMR:
¼186.24, 183.34, 157.05, 140.50, 131.44, 129.60, 93.35, 35.45, 29.04.
d
A
solution of 2-tert-butyl-5-iodo-1,4-dimethoxybenzene (1)
IR (cmꢀ1): 1665, 1445 (nC]O). Raman (cmꢀ1): 2203 (nC^C). MS (EI):
m/z¼350 (Mþ). HRMS (m/z): 350.1520 (Mþ, calcd 350.1518 for
C22H22O4).
(3.73 g, 12 mmol) and CuI (56 mg, 0.29 mmol) in diisopropylamine
(40 mL) was degassed with argon. After dichlorobis-
(triphenylphosphine)palladium (0.41 g, 0.58 mmol) and trime-
thylsilylacetylene (2.5 mL, 17 mmol) was added, the reaction
mixture was stirred at ambient temperature for 4 h. After addition
of water, the reaction mixture was extracted with ethyl acetate.
Combined organic phase was washed with 3 mol Lꢀ1 HCl, brine,
dried over Na2SO4, and evaporated to dryness. From the crude
product, 2 (3.20 g, 95%) was isolated by preparative chromatog-
raphy (SiO2, n-hexane/EtOAc 9:1) as a brown powder. Mp 118–
4.6. Synthesis of bis(4-tert-butyl-2,5-dimethoxyphenyl)buta-
1,3-diyne (MAAM)
A solution of 3 (0.50 g, 2.3 mmol) and Cu(OAc)2 (0.83 mg,
4.6 mmol) in pyridine (50 mL) was stirred at 40 ꢁC for 3 h. After
addition of water, the reaction mixture was extracted with chloro-
form for three times. Combined organic phase was washed with
3 mol Lꢀ1 HCl, satd NaHCO3, brine, dried over Na2SO4, and evapo-
rated to dryness. From the crude product, MAAM (0.30 g, 60%) was
isolated by preparative chromatography (SiO2, n-hexane/EtOAc
120 ꢁC. 1H NMR:
–OCH3), 3.79 (3H, s, –OCH3), 1.35 (9H, s, t-Bu), 0.26 (9H, s, –SiMe3).
d
¼6.90 (1H, s, Ar), 6.81 (1H, s, Ar), 3.85 (3H, s,
13C NMR:
d
¼154.50, 152.30, 141.00, 116.65, 111.40, 109.91, 101.45,
97.79, 56.86, 55.62, 35.29, 29.53, 0.12. MS (EI): m/z¼290 (Mþ).
HRMS (m/z): 290.1698 (Mþ, calcd 290.1702 for C17H26SiO2).
9:1) as a light brown powder. Mp 200–203 ꢁC. 1H NMR:
s, Ar), 6.84 (2H, s, Ar), 3.88 (6H, s, –OCH3), 3.79 (6H, s, –OCH3), 1.37
(18H, s, t-Bu). 13C NMR:
¼155.51, 152.24, 141.71, 116.64, 110.86,
d¼6.95 (2H,
d
4.3. Synthesis of 2-tert-butyl-5-ethynyl-1,4-
dimethoxybenzene (3)
108.66, 78.79, 77.59, 56.61, 55.60, 35.44, 29.48. Raman (cmꢀ1): 2217
(
nC^C). MS (EI): m/z¼435 ([Mþ1]þ). HRMS (m/z): 434.2459 (Mþ,
calcd 434.2457 for C28H34O4).
A solution of 2 (3.20 g, 11 mmol) in methanol/hexane (4:1 v/v)
(200 mL) was degassed with argon. After K2CO3 (0.76 g, 5.5 mmol)
was added, the reaction mixture was stirred at ambient tempera-
ture for 3 h. After addition of water, organic layer was separated,
and aqueous layer was extracted with ethyl acetate. Combined
organic phase was washed with brine, dried over Na2SO4, and
evaporated to dryness to give 3 (2.11 g, 88%) as a brown solid. Mp
4.7. Synthesis of bis(5-tert-butyl-1,4-benzoquinon-2-yl)buta-
1,3-diyne (QAAQ)
To a solution of MAAM (0.51 g, 1.2 mmol) in acetonitrile
(30 mL) was added cerium ammonium nitrite (3.24 g, 5.9 mmol)
at ambient temperature in dark. After stirring for 4 h, the reaction
mixture was quenched with water, then subjected to supersonic
treatment until the solid was precipitated. The precipitate was
separated by suction filtration, washed with acetone/water (1:1
v/v), dried, and recrystallized from dichloromethane to give QAAQ
58–60 ꢁC. 1H NMR:
–OCH3), 3.79 (3H, s, –OCH3), 3.28 (1H, s, –C^CH), 1.37 (9H, s, t-Bu).
d¼6.94 (1H, s, Ar), 6.85 (1H, s, Ar), 3.88 (3H, s,
13C NMR:
d
¼154.71, 152.26, 141.31, 116.75, 110.84, 108.60, 80.47,
80.26, 56.59, 55.64, 35.34, 29.52. MS (EI): m/z¼218 (Mþ). IR (Nujol,
cmꢀ1): 3278 (nC–H), 2098 (nC^C). HRMS (m/z): 218.1305 (Mþ, calcd
218.1307 for C14H18O2).
as a deep red powder (0.40 g, 91%). Mp >300 ꢁC. 1H NMR:
(2H, s, CH), 6.65 (2H, s, CH), 1.28 (18H, s, t-Bu). 13C NMR:
183.14, 157.24, 141.39, 131.50, 129.45, 85.18, 77.79, 35.50, 29.02. IR
(cmꢀ1): 1658, 1447 (nC]O). Raman (cmꢀ1): 2215 (nC^C). MS (EI):
m/z¼374 (Mþ). HRMS (m/z): 374.1521 (Mþ, calcd 374.1518 for
C24H22O4).
d
¼6.92
d
¼186.01,
4.4. Synthesis of bis(4-tert-butyl-2,5-dimethoxyphenyl)-
acetylene (MAM)
A solution of 1 (2.35 g, 7.4 mmol) and CuI (35 mg, 0.18 mmol)
in diisopropylamine (40 mL) was degassed with argon. After
dichlorobis(triphenylphosphine)palladium (0.26 g, 0.36 mmol)
and 3 (2.41 g, 11 mmol) was added, the reaction mixture was
stirred at ambient temperature for 4 h. After addition of water, the
reaction mixture was extracted with ethyl acetate. Combined or-
ganic phase was washed with 3 mol Lꢀ1 HCl, brine, dried over
Na2SO4, and evaporated to dryness. From the crude product, MAM
(3.09 g, quant) was isolated by preparative chromatography (SiO2,
n-hexane/EtOAc 9:1) as a white powder. Mp 231–233 ꢁC. 1H NMR:
4.8. Oxidation of tetralin and o-xylene by QQ, QAQ,
and QAAQ
Typical procedure. A solution of QAQ (35 mg, 0.10 mmol) in
tetralin (2 mL) was heated at 100 ꢁC for 48 h. After cooling, the
reaction mixture was subjected to column chromatography (SiO2,
n-hexane/EtOAc 9:1) to give a-tetralon (28 mg, 0.19 mmol).
4.9. X-ray analysis
d
¼7.00 (2H, s, Ar), 6.86 (2H, s, Ar), 3.91 (6H, s, –OCH3), 3.82 (6H, s,
–OCH3), 1.37 (18H, s, t-Bu). 13C NMR:
¼154.02, 152.40, 140.36,
116.22, 111.47, 110.54, 89.38, 56.97, 55.68, 35.27, 29.58. Raman
d
X-ray diffraction data were collected on a four-circle diffrac-
tometer. Crystal parameters were determined by means of peak-

3644
N. Hayashi et al. / Tetrahedron 65 (2009) 3639–3644
search method, and all intensities were converted to structure
factors in a conventional manner. The crystal structure was solved
by direct methods and Fourier technique (SHELXL-9723 on PC-
Linux). All non-hydrogen atoms were refined with anisotropic pa-
rameters. All hydrogen atoms were found on a differential Fourier
map and refined isotropically. Crystallographic data (excluding
structure factors) for the structures in this paper have been de-
posited with the Cambridge Crystallographic Data Centre as sup-
plementary publication nos. CCDC 718053 and 718054. Copies of
the data can be obtained, free of charge, on application to CCDC, 12
Union Road, Cambridge CB2 1EZ, UK, (fax: þ44 (0)1223 336033 or
e-mail: deposit@ccdc.cam.ac.uk).
Acknowledgements
This work was supported by the Saneyoshi Scholarship Foun-
dation, Japan.
Supplementary data
Supplementary data associated with this article can be found in
the online version, at doi:10.1016/j.tet.2009.03.001.
References and notes
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Weinheim, 1988; Vol. 2; (b) Griesbeck, A. Science of Synthesis. Quinones and
Heteroatom Analogs; Thieme: New York, NY, 2006; Vol. 28.
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Lett. 2007, 36, 386; (b) Kawase, T.; Minami, Y.; Nishigaki, S.; Okano, H.; Kurata, H.;
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3. Hayashi, N.; Yoshikawa, T.; Ohnuma, T.; Higuchi, H.; Sako, K.; Uekusa, H. Org.
Lett. 2007, 9, 5417.
QAQ. C22H22O4, MW¼350.40, monoclinic, P21/c (no. 14),
a¼9.381(2), b¼6.775(3), c¼14.9256(18) Å,
b
¼93.443(15)ꢁ, Z¼2,
T¼200 K, Dcalcd¼1.229 g cmꢀ3, R1¼0.046 (I>2
(I)), wR2¼0.136 (all
s
data).
QAAQ. C24H22O4, MW¼374.42, monoclinic, C2/c (no. 15),
a¼22.685(4), b¼6.724(4), c¼17.703(5) Å,
b
¼131.021(10)ꢁ, Z¼4,
T¼200(2) K, Dcalcd¼1.221 g cmꢀ3, R1¼0.083 (I>2
(I)), wR2¼0.275
s
(all data).
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4.10. Molecular orbital (MO) calculations
8. van Dijk, E. H.; Myles, D. J. T.; van der Veen, M. H.; Hummelen, J. C. Org. Lett.
2006, 8, 2333.
Molecular orbital (MO) calculations were performed using
Spartan ’04 Windows (Wavefunction, Inc.) on Microsoft Windows
XP. All calculations were performed using B3LYP/6-311þG(d,p)
methods. Computational analysis was performed for the com-
pounds bearing no tert-butyl substituents, bis(1,4-benzoquinon-
2-yl)acetylene (QAQ0), bis(1,4-benzoquinon-2-yl)buta-1,3-diyne
(QAAQ0), bis(2,5-dimethoxyphenyl)acetylene (MAM0), and
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Doucet, H.; Hierso, J.-C. Angew. Chem., Int. Ed. 2007, 46, 834; (e) Diederich, F.;
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bis(2,5-dimethoxyphenyl)buta-1,3-diyne (MAAM0) as
a model
compound. Fully geometrical optimization was performed for
their anti and syn conformers. As to QAQ0 and QAAQ0, fully relaxed
triple-bond (QAQ0) or (central) single-bond (QAAQ0) torsional
potentials were also calculated; i.e., for each fixed torsional angle
(f
) around the triple (QAQ0) or single-bond (QAAQ0), all remaining
internal degrees of freedom were optimized. A 10ꢁ grid of points
18. Desiraju, G. R.; Steiner, T. The Weak Hydrogen Bond-In Structural Chemisty and
Biology; Oxford: New York, NY, 1999.
was applied. During calculations, C2 molecular symmetry was
postulated for all cases except QAAQ0 at
metrical optimization process of which did not converge by any
f
¼170ꢁ and 0ꢁ, geo-
19. Becker, H.-D.; Turner, A. B. In The Chemistry of Quinonoid Compounds; Patai, S.,
Rappoport, Z., Eds.; Wiley: Chichester, UK, 1988; Vol. II, Chapter 23, p 1351.
20. Hayashi, N.; Kanda, A.; Higuchi, H.; Ninomiya, K. Heterocycles 2008, 76, 1361.
21. (a) Lee, H.; Harvey, R. G. J. Org. Chem. 1983, 48, 749; (b) Lee, H.; Harvey, R. G.
J. Org. Chem. 1988, 53, 4587.
22. (a) Danishefsky, S.; Kitahara, T. J. Am. Chem. Soc. 1974, 96, 7807; (b) Danishefsky,
S.; Kitahara, T.; Yan, C. F.; Morris, J. J. Am. Chem. Soc. 1979, 101, 6996.
23. Sheldrick, G. M. Shelxl-97, Program Package for the Solution and Refinement of
Crystal Structures; University of Gottingen: Germany, 1997.
means. Thus, geometrical optimization of C1 symmetrical struc-
ture was conducted for QAAQ0 at
f
f
¼170ꢁ, while for QAAQ0 at
¼0ꢁ the forementioned syn conformer of QAAQ0 substituted,
because its
f was nearly equal to zero. The obtained total energies
appear in Table S1.