Unusual oxidative cleavage of the aryl-ethynyl bonds in (arylethynyl)polymethylbenzenes with iodine in dimethyl sulfoxide

Article abstract of DOI:10.1023/A:1011329621330

While heating 1,2,4,5-tetramethyl-3,6-bis(phenylethynyl)benzene, 1,3,5-trimethyl-2,4-bis(phenylethynyl)benzene, and 1,2,4,5-tetramethyl-3-(phenylethynyl)benzene with iodine in DMSO in the absence of oxygen, the triple bonds are oxidized to give the corresponding 1,2-diketones. In the presence of oxygen, the previously unknown competitive oxidative process causes the cleavage of the aryl-ethynyl bonds so that duroquinone and the corresponding 4-hydroxybenzils are formed. This cleavage is produced by oxygen only in the presence of iodine and DMSO. It was shown that the key stage of the process is the formation of intermediate charge-transfer complexes between polymethylbenzene rings and iodine.

Full text of DOI:10.1023/A:1011329621330

Russian Chemical Bulletin, International Edition, Vol. 50, No. 6, pp. 1051—1055, June, 2001
1051
Unusual oxidative cleavage of the aryl—ethynyl bonds
in (arylethynyl)polymethylbenzenes with iodine in dimethyl sulfoxide
M. S. Yusubov,a G. A. Zholobova,a I. L. Filimonova,a V. P. Vasil´eva,b V. D. Filimonov,b and Ki-Whan Chic
aSiberian State Medical University,
2 Moskovskii Trakt, 634050 Tomsk, Russian Federation.
E-mail: yusubov@mail.ru
bTomsk Polytechnic University,
30 prosp. Lenina, 634004 Tomsk, Russian Federation.
E-mail: filim@org.chtd.tpu.edu.ru
cUniversity of Ulsan,
680-749, Ulsan, Republic of Korea
While heating 1,2,4,5-tetramethyl-3,6-bis(phenylethynyl)benzene, 1,3,5-trimethyl-2,4-
bis(phenylethynyl)benzene, and 1,2,4,5-tetramethyl-3-(phenylethynyl)benzene with iodine in
DMSO in the absence of oxygen, the triple bonds are oxidized to give the corresponding
1,2-diketones. In the presence of oxygen, the previously unknown competitive oxidative
process causes the cleavage of the aryl—ethynyl bonds so that duroquinone and the corre-
sponding 4-hydroxybenzils are formed. This cleavage is produced by oxygen only in the
presence of iodine and DMSO. It was shown that the key stage of the process is the formation
of intermediate charge-transfer complexes between polymethylbenzene rings and iodine.
Key words: alkynes, oxidation, iodine, dimethyl sulfoxide, 1,2-diketones.
Iodine and PdCl2 in DMSO are among the mildest
and most selective oxidants of internal alkynes to 1,2-di-
ketones.1—3 A fundamental advantage of these reagents
is that they cause no cleavage of the carbon—carbon
bonds in substrates or reaction products. However, we
reported previously4 that the reaction of I2 with
1,2,4,5-tetramethyl-3,6-bis(phenylethynyl)benzene (1) in
DMSO mainly gives duroquinone (2) and 1-(4-hydroxy-
2,3,5,6-tetramethylphenyl)-2-phenylethanedione (3). In
the present work, we extensively studied the influence of
the reaction conditions on this new oxidative transfor-
mation of alkyne 1 and illustrated the general character
of this process with other polymethylated diaryl-
acetylenes.
It was shown that heating of alkyne 1 with iodine in
DMSO initiates two competing reactions, which domi-
nate each other depending on the reaction conditions
(Scheme 1, Table 1):
(1) oxidation in an atmosphere of oxygen or in air to
duroquinone 2 and 4-hydroxyphenyldiketone 3 and
(2) oxidation in an atmosphere of argon to diketone
(4) and predominantly to tetraketone (5).
The yields of products 2—5 depend on the amount
of iodine and the temperature. Thus, the yield of
duroquinone 2 at 110 °C was higher than at 145 °C
under the conditions of oxygen bubbling, probably, be-
cause of a decreased solubility of the latter in DMSO. At
145 °C, the yield of duroquinone 2 is independent of the
Table 1. Oxidation of 1,2,4,5-tetramethyl-3,6-bis(phenylethynyl)benzene (1) (1 mmol) with I2 in DMSO
I2
Ò
t
Yield (%)
Conditions
/mmol /°Ñ
/h
2
3
4
5
1.0
1.0
1.0
1.0
1.0
0.25
0.25
1.0
—*
145
145
145
145
110
145
110
135
110
3.5
5.5
5.5
2.0
42.0
7.0
42.0
18.0
50.0
32
21
14
26
20
13
18
18
14
—
Trace amounts
7
Contact with air
In an atmosphere of argon
Argon bubbling
Oxygen bubbling
Oxygen bubbling
Oxygen bubbling
Oxygen bubbling
Sealed tube with air
Oxygen bubbling
Trace amounts
Trace amounts
7
6.5
3
10
77
66
10
16
10
4
43
60
44
3
70
Trace amounts
—
7
Trace amounts
—
55
—
* The starting alkyne 1 was recovered.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1007—1011, June, 2001.
1066-5285/01/5006-1051 $25.00 © 2001 Plenum Publishing Corporation

1052
Russ.Chem.Bull., Int.Ed., Vol. 50, No. 6, June, 2001
Yusubov et al.
Scheme 1
Table 2. Oxidation of 1,3,5-trimethyl-2,4-bis(phenylethynyl)ben-
zene (6) (1.0 mmol) with I2 in DMSO
Me
Me
I2
Ò
t
Yield (%)
/mmol
/°C
/h
7
8
9
Ph
Ph
0.25*
0.5*
1.0**
105
105
130
40
41
4
11
<1
26
<1
9
<1
21
21
20
Me
Me
1
I —Me SO
* In an atmosphere of oxygen.
** In an atmosphere of argon.
2
2
O2
Ar
O
diketone 4 at 110 °C in the presence of oxygen gives
hydroxyphenyldiketone 3 (40%) and tetraketone 5 (28%).
Because of these circumstances, the yields of diketone 4
are low (3—10%) in all the cases studied (see Table 1),
indicating that hydroxyphenyldiketone 3 and quinone 2
result from the cleavage of the aryl—alkynyl rather than
aryl—CO bonds in products 3—5.
The oxidation of 1,3,5-trimethyl-2,4-bis(phenyl-
ethynyl)benzene (6) in air is accompanied by resini-
fication, yielding several products. The major products
were diketone 7 (1—11%), tetraketone 8 (1—9%) as
products of normal oxidation of the triple bonds and
diketone 9 (21%) as a product of oxidative cleavage of
the aryl—ethynyl bond (Table 2). Under argon, the
major oxidation products were diketones 7 (26%) and 9
(20%) (Scheme 2). In this case, no quinones are formed
in an atmosphere of oxygen or in air, as distinct from
the oxidation of alkyne 1. Apart from the aforemen-
tioned products, the reaction mixture also contains
benzoic acid (up to 16%).
At the same time, the oxidation of 1,4-bis(phenyl-
ethynyl)benzene (10) (a methyl-free structural analog of
compound 1) with I2—DMSO under the conditions of
oxygen bubbling involves only the triple bonds to give
1,4-bis(1,2-dioxo-2-phenylethyl)benzene (11) (yield
88%), i.e., the reaction outcome only slightly differ
from that in the oxidation with the same system simply
in the air2 (yield 90%).
The study of the oxidation of tolan derivatives 12
and 13 with I2/DMSO gave the following results. In the
case of 1,2,4,5-tetramethyl-3-(phenylethynyl)benzene
(12), oxygen bubbling through the reaction mixture
Me
Me
Me
Me
Me
Ph
O
O
Ph
O
Me
Me
Me
Me
2
4
+
+
O
Me
Me
Me
Me
Ph
O
O
OH
O
Ph
Ph
Me
Me
Me
O
O
3
5
amount of iodine, whereas its yield at 110 °C increases
from 60 to 70% with a fourfold reduction in the iodine
amount (see Table 1). Thus, the results in Table 1
indicate the dominant role of oxygen in the formation of
quinone 2 and hydroxyphenyldiketone 3 and the domi-
nant role of iodine in the formation of diketone 4 and
tetraketone 5. It was also found experimentally that
alkyne 1 in an iodine-free atmosphere of oxygen in
DMSO remains unchanged at 110 °C for 50 h. Thus,
both the components (iodine and oxygen) are necessary
to form quinone 2. The formation of compounds 2 and
3 is also accompanied by the generation of benzoic acid
from the eliminated phenylethynyl group.
It was found that hydroxyphenyldiketone 3 and
tetraketone 5 remain inert to I2 in DMSO. By contrast,
Scheme 2
O
O
O
Ph
Ph
Ph
Me
Me
Me
Me
Ph
I —Me SO
O
2
2
O
O
+
+
105—130 °C
Me
Me
Me
O
Me
Me
Me
Me
Me
OH
O
Ph
Ph
Ph
6
7
8
9

Unusual oxidative cleavage of aryl—ethynyl bonds
Russ.Chem.Bull., Int.Ed., Vol. 50, No. 6, June, 2001
1053
affords duroquinone 2 (66%) and benzoic acid (54%),
while the reaction in an atmosphere of oxygen-free
argon yields diketone 14 (77%). It should be noted that
the use of commercial, oxygen-containing argon results
not only in diketone 14 but also in noticeable amounts
of duroquinone 2 (5—6%). Diketone 14 does not fur-
ther oxidize to duroquinone 2 or hydroxyphenyldiketone
3 (Scheme 3).
camphor into camphorquinone when air is passed through
a solution of a substrate and NaI in DMSO. The most
essential statement8 says that DMSO does not oxidize
bromocamphor according to the Kornblum reaction
mechanism (as could be expected), but the process
involving oxygen and DMSO proceeds through inter-
mediate free radicals of unidentified structures.
Semiempirical PM3 optimization of the geometry of
alkyne 12 and tolan shows that the triple bond lengths
are nearly equal in both acetylene derivatives (1.196 and
1.195 Å, respectively) and that the duryl—alkynyl bond is
slightly longer (1.418 Å) than the phenyl—alkynyl bond
in tolan (1.415 Å). Therefore, the quantum-chemical
calculations of the ground state of the sterically hindered
alkyne do not predict easy or, moreover, spontaneous
cleavage of the aryl—phenylethynyl bond in any way.
At the same time, we can advance the following
hypothesis that does not contradict the experimental
data. It is well known that iodine as an electron accep-
tor can form charge-transfer complexes with arenes; the
latter, in the case of complete electron transfer, decom-
pose into the corresponding radical cations and anions.9
The stability of charge-transfer complexes increases
with an increase in the electron-donating properties of
arenes.9 From this point of view, polymethylbenzene
rings in compounds 1, 4, 6, and 12 should be a pre-
ferred site for the formation of charge-transfer com-
plexes with iodine. Indeed, the PM3 calculations show
that both highest-energy occupied molecular orbitals
(HOMO) of compound 12 (7B1, 8.73 and 4A2, 9.05 eV)
has a lower energy than the HOMO of tolan (3B3u, 8.89
and 1A2, 9.88 eV), which makes it a stronger electron
donor. The electron for the lowest-energy unoccupied
orbital of iodine has to be delivered from HOMO2 of
compound 12 (9.05 eV), which is localized on the
durene ring and has the fit type of symmetry.
Scheme 3
O
Me
Me
Me
Ph
Ar
Me
Me
Me
Me
O
I —Me SO
2
2
Me
Ph
14
O2
2
12
Previously,5 it was also shown that the action of
iodine on 2,4,6-trimethyltolan 13 in DMSO with access
for atmospheric oxygen at a low conversion of the
substrate causes the oxidation of only the triple bond to
give diketone 15 in 33% yield (Scheme 4). No carboxy-
lic acids were detected in the reaction mixture.
Scheme 4
O
Me
Me
Me
Me
Ph
I2—Me2SO
135 °C
Me
Ph
Me
O
After the radical cation of compound 12 is formed
(A), it can be attacked by oxygen according to the
radical ion mechanism to follow the transformations
presented in Scheme 5.
This scheme can also be valid for the stepwise
cleavage of the aryl—ethynyl bonds in compounds 1, 4,
6, and 7. The advanced hypothesis also correlates with
the fact that, if the para-position in intermediate C is
occupied by the noneliminable group, the reaction stops
at the stage of formation of the corresponding phenol
(compounds 3 and 9).
13
15
To sum up the results obtained, one can conclude
that quinone 2 and hydroxyphenyldiketones 3 and 9
result from the elimination of the phenylethynyl rather
than COCOPh fragment and that duroquinone 2 is
formed in noticeable amounts only upon oxidation in
an atmosphere of oxygen. Under argon, the triple bonds
of the substrates are normally oxidized with I2 and
DMSO to give 1,2-diketones.
We found no reported analogs of oxidative cleavage
of the aryl—phenylethynyl bonds under the action of
either DMSO or other reagents, which were discovered
for compounds 1, 4, 6, and 12. As far as we know,
DMSO neither alone nor in combination with oxygen
or halogens was referred to as an oxidant of arenes to
quinones. Among a number of methods for the synthesis
of quinones from arenes, oxygen is used in the presence
of catalytic amounts of nitrogen-containing oxidants.6,7
A certain specific effect of oxygen and DMSO as oxi-
dants was noted earlier8 for the oxidation of 3-bromo-
To estimate the probability of forming the hypotheti-
cal radical cation B and determine its spatial and elec-
tronic structure, the potential energy surface for a sys-
tem composed of intermediate A and the oxygen mol-
ecule was calculated by the PM3 method. The mini-
mum found corresponds to structure B; its enthalpy of
formation is lower by ∆∆H = 120.6 kcal mol–1 than that
of the isolated oxygen molecules and species A. Struc-
ture B is schematically displayed in Fig. 1 (its selected
geometrical parameters and effective charges are given
in Table 3).

1054
Russ.Chem.Bull., Int.Ed., Vol. 50, No. 6, June, 2001
Yusubov et al.
Scheme 5
bond
lengths
in
O(10)
O(11)
6
dicarbonyl compounds.
It should be specially
stressed that the C(1)—
C(7) bond becomes sig-
nificantly longer, which
can cause its cleavage. In
5
7
8
9
Me
Me
Me
Me
Me
1
•
O
O
4
2
•
3
•
•
Ph
O
O
Ph
+
+
+
Me
Me
Me
addition, the total spin density in intermediate A is
distributed over the whole aromatic system, including
both rings and the triple bond, whereas in radical cation
B it is localized only on the durene fragment and the
O(11) atom. This fact is an additional piece of evidence
in favor of the formation of radical C through the
cleavage of the C(1)—C(7) bond.
B
A
Me
Me
O
O
•
B
+
+
Ph
Thus, the scheme proposed for oxidative cleavage of
the bonds between the ethynyl groups and polymethylated
aromatic rings upon the action of iodine and oxygen in
DMSO correlates with the experimental facts and is not
contradictory to our quantum-chemical results.
Me
Me
C
D
O
H2O
–H+
O2
–CO2
OH
D
PhCOOH
Experimental
Ph
O
IR spectra were recorded on a Mattson 5000 spectropho-
tometer (thin films or pellets with KBr). 1H and 13C NMR
spectra were recorded on a Bruker DRX 500 spectrometer
(500.13 and 125 MHz, respectively) in CDCl3, acetone-d6, or
CCl4 with Me4Si as the internal standard. Elemental analysis
was carried out on an E.A. 1106 Carlo Erba CHNS-O instru-
ment. The melting point was measured on an Electrothermal-
9100 instrument. Column chromatography used L 40/100 µm
(Chemapol) and Silica gel 60 G (Merck) silica gels; TLC was
carried out on Silufol UV-254 (Kavalier) and Silica gel 60 F254
(Merck) plates with hexane, hexane—benzene (3 : 1 and 3 : 2),
or hexane—ethyl acetate (9 : 1) as eluents. The structures of the
compounds described in the literature were confirmed by ana-
lytical and spectral data and compared with the characteristics
of the authentic samples.
Me
Me
Me
Me
O
O2
•
C
O
•
Me
Me
Me
O2
Me
Me
Me
O
O
Oxidation of 1,2,4,5-tetramethyl-3,6-bis(phenylethynyl)ben-
zene (1). Iodine (64 mg, 0.25 mmol) was added to a solution of
compound 1 (334 mg, 1.0 mmol) in 10 mL of DMSO, and
oxygen was bubbled through the reaction mixture stirred with a
magnetic stirrer at 110 °C for 42 h. The resulting solution was
poured into 30 mL of a 5% aqueous solution of Na2S2O3, and
the products were extracted with ether (3½30 mL). the extract
was washed with water and brine and dried with Na2SO4. The
ether was removed, and the residue was dissolved in 3.0 mL of
benzene and chromatographed on silica gel. Elution with hex-
ane gave 6-(1,2-dioxo-2-phenylethyl)-1,2,4,5-tetramethyl-
Me
Me
Analysis of the calculated geometrical and charge pa-
rameters leads one to the conclusion that there is a strong
bonding between the C(7)—O(10) and C(8)—O(11) at-
oms in intermediate B, and the C(7)—C(8) bond is no
longer a triple one. The length of this bond (1.543 Å)
and the C(7)—O(10) and C(8)—O(11) interatomic dis-
tances are very close to the normal CO—CO and C=O
Table 3. PM3-calculated effective charges (q), interatomic distances (d), and
bond angles (ω) in radical cation B
Atom
q/au
Bond
d/Å
Angle
ω/deg
Ñ(1)
Ñ(7)
Ñ(8)
Î(10)
Î(11)
–0.21
0.27
0.33
–0.22
–0.30
Ñ(1)—Ñ(7)
Ñ(1)—Î(10)
Ñ(7)—Ñ(8)
Ñ(8)—Ñ(9)
Î(10)—Î(11)
Ñ(7)—Î(10)
Ñ(8)—Î(11)
1.508
2.376
1.543
1.474
3.237
1.208
1.221
Î(10)—Ñ(1)—Ñ(7)
Ñ(1)—Ñ(7)—Ñ(8)
Ñ(7)—Ñ(8)—Ñ(9)
25.6
115.6
119.8
Ñ(1)—Î(10)—Î(11) 64.19

Unusual oxidative cleavage of aryl—ethynyl bonds
Russ.Chem.Bull., Int.Ed., Vol. 50, No. 6, June, 2001
1055
3-(phenylethynyl)benzene (4) (26 mg, 7%), m.p. 154—156 °C
(from ethanol) (cf. Ref. 10: 159—160 °C). Further elution with
hexane—benzene (3 : 1) gave 3,6-bis(1,2-dioxo-2-phenyl-
ethynyl)-1,2,4,5-tetramethylbenzene (5) (16 mg, 4%), m.p.
202—204 °C (from ethyl acetate) (cf. Ref. 10: 203—204 °C) and
2 (52 mg, 63%), m.p. 110—112 °C. Final elution with hex-
ane—ethyl acetate (9 : 1) gave benzoic acid (23 mg, 48%), m.p.
122—123 °C (cf. Ref. 12: 122.5 °C).
Oxidation of 6-(1,2-dioxo-2-phenylethyl)-1,2,4,5-tetra-
methyl-3-(phenylethynyl)benzene (4). Iodine (38 mg, 0.15 mmol)
was added to a solution of compound 4 (55 mg, 0.15 mmol) in
2.0 mL of DMSO. Oxygen was bubbled through the reaction
mixture with stirring at 110 °C for 23 h. The resulting solution
was treated as described above and chromatographed on silica
gel. Elution with hexane—benzene (3 : 1) gave tetraketone 5
(15.5 mg, 26%), m.p. 202—204 °C (from ethyl acetate). Fur-
ther elution with hexane—benzene (3 : 2) gave diketone 3
(17 mg, 40%), m.p. 164—166 °C (from ethanol). Final elution
gave benzoic acid (5.0 mg, 25%), m.p. 122—123 °C (cf.
Ref. 12: 122.5 °C).
Oxidation of 1,4-bis(phenylethynyl)benzene (10). Iodine
(127 mg, 0.5 mmol) was added to a solution of compound 10
(140 mg, 0.5 mmol) in 4.0 mL of DMSO. Oxygen was bubbled
through the reaction mixture stirred at 135 °C for 11 h. The
resulting solution was poured into 15 mL of 5% Na2S2O3. The
yellow acicular crystals that formed were filtered off and recrys-
tallized from ethanol to give 1,4-bis(1,2-dioxo-2-phenyl-
ethyl)benzene (11) (151 mg, 88%), m.p. 125—126 °C (from
ethanol) (cf. Ref. 2: 124—125 °C).
duroquinone
2 (115 mg, 70%) as yellow needles, m.p.
110—112 °C (from hexane) (cf. Ref. 11: 110—112 °C). The
residue was eluted with hexane—benzene (3 : 2) to give
3-(1,2-dioxo-2-phenylethyl)-6-hydroxy-1,2,4,5-tetramethyl-
benzene (3) (51 mg, 18%), m.p. 164—166 °C (from ethanol)
(cf. Ref. 4: 164—166 °C). IR (KBr), ν/cm–1: 3530 (O—H),
1680 (C=O), 1140 (C—O). 1H NMR (acetone-d6—CCl4),
δ: 2.10 (s, 6 H, 2 Me); 2.15 (s, 6 H, 2 Me); 7.58 (m,
2 H arom); 7.70 (m, 1 H arom); 8.10 (d, 2 H arom, J = 7.6 Hz);
8.60 (s, 1 H, OH). 13C NMR (acetone-d6—CCl4), δ: 12.23 and
17.72 (Me), 121.41, 129.43, 130.86, 133.07, 133.57, 134.72,
155.34 (C arom), 191.48 and 199.12 (C=O). Final elution gave
benzoic acid (60 mg, 25%), m.p. 122—123 °C (cf. Ref. 12:
122.5 °C).
Oxidation of 1,3,5-trimethyl-2,4-bis(phenylethynyl)benzene
(6). Iodine (127 mg, 0.5 mmol) was added to a solution of
compound 6 (162 mg, 0.5 mmol) in 5.0 mL of DMSO. The
reaction mixture was stirred with access for atmospheric oxygen
at 105 °C for 4 h and treated as described above. The product
was chromatographed on silica gel. Elution with hexane recov-
ered the starting alkyne 6 (30 mg). Further elution with hex-
ane—ethyl acetate (9 : 1) gave 4-(1,2-dioxo-2-phenylethyl)-
1,3,5-trimethyl-2-phenylethynylbenzene (7) (46 mg, 26%),
m.p. 90—92 °C (from propanol) (cf. Ref. 10: 91—92 °C);
2,4-bis(1,2-dioxo-2-phenylethyl)-1,3,5-trimethylbenzene (8)
(1.5 mg), m.p. 126—127 °C (from ethanol) (cf. Ref. 10); and
1-(3-hydroxy-2,4,6-trimethylphenyl)-2-phenylethanedione (9)
(27 mg, 20%), m.p. 132—133 °C (from hexane—benzene,
3 : 1). IR, ν/cm–1: 3497 (O—H), 1670 (C=O), 1217 (C—O).
1H NMR (CDCl3), δ: 2.16 (s, 3 H, Me); 2.17 (s, 3 H, Me);
2.23 (s, 3 H, Me); 4.62 (s, 1 H, OH); 6.84 (s, 1 H arom); 7.51
(m, 2 H arom); 7.65 (m, 1 H arom); 8.13 (d, 2 H arom).
13C NMR (acetone-d6—CCl4), δ: 13.35, 16.01 and 19.76 (Me),
122.13, 126.42, 128.20, 128.81, 130.42, 130.66, 132.00, 134.35,
135.04, 155.34 (C arom), 191.06 and 197.50 (C=O). Found (%):
C, 75.74; H, 5.96. C17H16O3. Calculated (%): C, 76.10; H, 6.01.
Final elution gave benzoic acid (10 mg, 16%), m.p. 122—123 °C
(cf. Ref. 12: 122.5 °C).
Oxidation of 1,2,4,5-tetramethyl-3-(phenylethynyl)benzene
(12). A. In an atmosphere of argon. Iodine (254 mg, 1.0 mmol)
was added to a solution of compound 12 (234 mg, 1.0 mmol) in
5.0 mL of DMSO. Argon was bubbled through the reaction
mixture stirred at 115 °C for 11 h. The resulting solution was
treated as described above and chromatographed on silica gel.
Elution with hexane gave 3-(1,2-dioxo-2-phenylethyl)-1,2,4,5-
tetramethylbenzene (14) (205 mg, 77%), m.p. 61.5—62.5 °C
(from methanol). 1H NMR (CDCl3), δ: 2.11 (s, 6 H, 2 Me);
2.22 (s, 6 H, 2 Me); 7.05 (s, 1 H arom); 7.54 (m, 2 H arom);
7.65 (d, 1 H arom); 8.22 (d, 2 H arom, J = 7.5 Hz). 13C NMR
(CDCl3), δ: 16.54 and 19.40 (Me), 128.75, 130.50, 131.14,
131.99, 133.58, 134.25, 134.29, 137.53 (C arom), 190.26 and
199.42 (C=O). Found (%): C, 81.28; H, 6.97. C18H18O2.
Calculated (%): C, 81.17; H, 6.81.
This work was financially supported by the Russian
Foundation for Basic Research (Project No. 00-03-
32812a).
References
1. V. D. Filimonov, M. S. Yusubov, and Ki-Whan Chi, Usp.
Khim., 1998, 67, 803 [Russ. Chem. Rev., 1998, 67, 725
(Engl. Transl.)].
2. M. S. Yusubov and V. D. Filimonov, Synthesis, 1991, 131.
3. M. S. Yusubov, V. D. Filimonov, V. P. Vasilyeva, and
Ki-Whan Chi, Synthesis, 1995, 1234.
4. M. S. Yusubov, G. A. Zholobova, V. P. Vasil´eva,
V. Habicher, and V. D. Filimonov, Zh. Org. Khim., 1996,
32, 1276 [Russ. J. Org. Chem., 1996, 32 (Engl. Transl.)].
5. M. S. Yusubov, Ki-Whan Chi, E. A. Krasnokutskaya, V. P.
Vasil´eva, and V. D. Filimonov, Zh. Org. Khim., 1995, 31,
1675 [Russ. J. Org. Chem., 1995, 31 (Engl. Transl.)].
6. A. Haines, Methods for Oxidation of Organic Compounds,
Academic Press, London, 1985.
7. M. Hudlicky, Oxidations in Organic Chemistry, a.c.s.
Washington, 1990, 94.
8. K. Hattori, T. Yoshida, K. Rikuta, and T. Miyakoshi,
Chem. Lett., 1994, 1885.
9. E. N. Gur´yanova, I. P. Gol´dshtein, and I. P. Romm,
Donorno-aktseptornaya svyaz´ [Donor-Acceptor Bonding],
Khimiya, Moscow, 1973, 397 pp. (in Russian).
10. L. G. Karpitskaya, V. P. Vasil´eva, and E. B. Merkushev,
Zh. Org. Khim., 1991, 27, 1961 [J. Org. Chem. USSR, 1991,
27 (Engl. Transl.)].
11. W. J. Burke, I. L. Bishop, and J. A. Warbunton, J. Org.
Chem., 1962, 27, 4003.
B. In an atmosphere of oxygen. Iodine (127 mg, 0.5 mmol)
was added to a solution of compound 12 (117 mg, 0.5 mmol) in
3.0 mL of DMSO. Oxygen was bubbled through the reaction
mixture stirred at 115 °C for 8 h. The resulting solution was
treated as described above and chromatographed on silica gel.
Elution with hexane recovered the starting alkyne 12 (22 mg).
Further elution with hexane—benzene (3 : 1) gave duroquinone
12. Svoistva organicheskikh soedinenii [The Properties of Organic
Compounds], Ed. A. A. Potekhin, Khimiya, Leningrad,
1984, 520 pp. (in Russian).
Received October 9, 2000;
in revised form January 30, 2001