Facile Synthesis of Dibenzotetracenedione Derivatives by Rhodium-Catalyzed [2+2+2] Cycloaddition/Spontaneous Aromatization

Article abstract of DOI:10.1002/asia.201801670

It has been established that a cationic rhodium(I)/SEGPHOS complex catalyzes the [2+2+2] cycloaddition of biphenyl-linked 1,7-diynes with 1,4-naphthoquinone and anthracene-1,4-dione. Conveniently, spontaneous aromatization proceeded upon removal of the rhodium complex by passing the reaction mixture through an alumina column, to give the corresponding dibenzotetracenediones and dibenzopentacenediones, respectively, in good yields. The obtained dibenzotetracenedione could be readily transformed into the corresponding dibenzotetracene in good yield. This dibenzotetracene showed blue fluorescence with a good quantum yield, which was significantly higher than those of tetracene, tetrabenzotetracene, and hexabenzotetracene.

Full text of DOI:10.1002/asia.201801670

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Accepted Article
Title: Facile Synthesis of Dibenzotetracenedione Derivatives by
Rhodium-Catalyzed [2+2+2] Cycloaddition/Spontaneous
Aromatization
Authors: Yukimasa Aida, Yu Shibata, and Ken Tanaka
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10.1002/asia.201801670
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Facile Synthesis of Dibenzotetracenedione Derivatives by
Rhodium-Catalyzed [2+2+2] Cycloaddition/Spontaneous
Aromatization
Yukimasa Aida,[a] Yu Shibata,[a] and Ken Tanaka*[a]
Abstract: It has been established that a cationic rhodium(I)/segphos
complex catalyzes the [2+2+2] cycloaddition of biphenyl-linked 1,7-
diynes with 1,4-naphthoquinone and anthracene-1,4-dione.
Conveniently, spontaneous aromatization proceeded upon removal
of the rhodium complex by passing the reaction mixture through an
alumina column to give the corresponding dibenzotetracenediones
and dibenzopentacenediones, respectively, in good yields. The thus
obtained dibenzotetracenedione could be readily transformed into
the corresponding dibenzotetracene in good yield. This
dibenzotetracene showed blue fluorescence with a good quantum
yield, which is significantly higher than those of tetracene,
tetrabenzotetracene, and hexabenzotetracene.
On the other hand, cationic rhodium(I)/biaryl bisphosphine
complexes are highly active and selective catalysts for the
[2+2+2] cycloaddition[8] of α,ω-diynes with cyclic alkenes,[9] such
as
dihydrofuran,[9c]
norbornene,[9a]
benzothiophene
cyclopentene,[9c]
dioxides,[9b]
indene,[9c]
2,3-
and
acenaphthylene.[9d] In this paper, we found that a cationic
rhodium(I)/segphos complex is able to catalyze the [2+2+2]
cycloaddition of biphenyl-linked diynes with 1,4-naphthoquinone
and anthracene-1,4-dione (Scheme 1, bottom).[10] Interestingly,
in the presence of this rhodium complex, aromatization of the
cyclohexadiene products did not proceed, while spontaneous
aromatization proceeded to give dibenzotetracenediones and
dibenzopentacenediones upon removal of the rhodium complex
by passing the reaction mixture through an alumina column even
under an argon atmosphere. It is well known that acene-m,n-
diones are good precursors for the synthesis of acenes.[11]
Therefore, the present method is useful for the facile synthesis
of dibenzo-fused acene derivatives.
Introduction
The transition-metal-catalyzed [2+2+2] cycloaddition of three
alkynes is one of the most convenient methods for the synthesis
of substituted benzenes.[1] Instead, that of two alkynes with an
previous work (non-catalytic cycloaddition-aromatization reaction)
alkene
giving
1,3-cyclohexadienes[2]
followed
by
O
R5
dehydrogenation is sometimes advantageous for this purpose.
For example, the use of cyclohexene and dihydronaphthalene
derivatives[3] allows the synthesis of naphthalene and
R6
R1
O
O
R1
Cp2ZrCl2
nBuLi
O
R2
R3
R1
R4
R2
R3
R5
R6
R2
R3
CuCl
anthracene
derivatives
without
using
benzynes
and
ZrCp2
R4
naphthynes,[4] the preparation of which is troublesome due to
employing not readily available substrates and harsh reaction
conditions. As readily available dihydronaphthalene derivatives,
commercially available 1,4-naphthoquinone has been employed
for the convenient synthesis of anthraquinones. In 2006, the Xi
research group reported the [2+2+2] cycloaddition of two
alkynes with 1,4-naphthoquinone and anthracene-1,4-dione
giving multicyclic cyclohexadiene derivatives by using
stoichiometric amounts of zirconium and copper complexes.[5–7]
Subsequently, the thus obtained cyclohexadienes could be
transformed into the corresponding anthraquinones and
dibenzopentacenediones in good yields by spontaneous
aromatization or treatment with a stoichiometric amount of an
external oxidant (p-chloranil) (Scheme 1, top). However, a
catalytic variant of this [2+2+2] cycloaddition has not been
reported to date.
R4
up to 86% yield
with or without p-chloranil
R1
O
O
R2
R3
R5
R6
R4
up to 85% yield
this work (catalytic cycloaddition-aromatization reaction)
[Rh(cod)2]BF4/
segphos
R1
O
O
R1
catalyst
R2
R2
O
O
up to 79% yield
Scheme 1. Transition-metal-mediated [2+2+2] cycloaddition/aromatization of
two alkynes with 1,4-naphthoquinone (cod = 1,5-cyclooctadiene).
[a]
Y. Aida, Dr. Y. Shibata, Prof. Dr. K. Tanaka
Department of Chemical Science and Engineering
Tokyo Institute of Technology
O-okayama, Meguro-ku, Tokyo 152-8550 (Japan)
E-mail: ktanaka@apc.titech.ac.jp
Results and Discussion
Homepage: http://www.tuat.ac.jp/~tanaka-k/
We first investigated the reaction of biphenyl-linked diyne 1a,
possessing the n-butoxycarbonyl and methyl groups at the
alkyne termini, and 1,4-naphthoquinone (2a) (1.1 equiv) in the
Supporting information for this article is given via a link at the end of
the document.
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10.1002/asia.201801670
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[Rh(cod)2]BF4/
segphos
catalyst
R1
O
O
O
O
presence of a cationic rhodium(I)/H8-binap complex (20 mol %).
Pleasingly, spontaneous aromatization, as well as the desired
[2+2+2] cycloaddition, proceeded to give the corresponding
dibenzotetracenedione product 3aa in good yield (Table 1, entry
1). In order to improve the product yield, various biaryl
bisphosphine ligands (Figure 1) were screened (entries 1–5),
which revealed that the use of segphos afforded 3aa in the
highest yield (entry 3). In sharp contrast to our previously
reported [2+2+2] cycloadditions using cyclic alkenes, the use of
non-biaryl bisphosphine ligand (dppf, Figure 1) and PPh3 also
afforded 3aa, although the yields were moderate (entries 6 and
7). Increasing the steric bulk of the aryl groups on the
phosphorus atom of segphos was also tested, while the yields of
3aa decreased (entries 8–10). Thus, segphos was selected as
the best ligand. Finally, the catalyst loading could be reduced to
5 mol % without erosion of the product yield (entry 11).
R1
R2
R2
1
2 (5 equiv)
3
Me
O
Me
O
O
O
CO2n-Bu
CO2Me
3aa /
3ba / 78%
63% (2a: 1.1 equiv)
(5 mol % Rh, CH2Cl2, RT, 5 h)
65% (2a: 5 equiv)
(5 mol % Rh, CH2Cl2, RT, 5 h)
86%
(5 mol % Rh, CH2Cl2, RT, 5 h)[a]
(5 mol % Rh, CH2Cl2, RT, 5 h)
Me
O
Ph
O
Table 1. Optimization of reaction conditions for rhodium-catalyzed [2+2+2]
cycloaddition-spontaneous aromatization of 1a with 2a[a]
O
O
CO2Et
CO2Me
3ca / 65%
3da / 11%
5–20 mol %
[Rh(cod)2]BF4/
Ligand
(10 mol % Rh, CH2Cl2, RT, 5 h)
(20 mol % Rh, PhCl, 130 °C, 48 h)
Me
O
O
Me
Me
Ac
O
O
Me
O
CH2Cl2, RT, 5 h
CO2nBu
O
O
CO2nBu
Me
O
2a (1.1 equiv)
1a
3aa
3ea / 79%
3fa / 56%
(20 mol % Rh, CH2Cl2, RT, 5 h)
[20 mol % Rh, (CH2Cl)2, 80 °C, 24 h]
Catalyst
[mol %]
20
Entry
Ligand
Conv [%][b]
Yield [%][b]
CO2Me
O
Me
O
1
2
H8-binap
binap
100
100
100
100
100
100
77
61
55
66
45
32
44
46
29
50
38
63
20
O
O
CO2Me
CO2Me
3
20
segphos
difluorphos
biphep
3ga / 12%
[20 mol % Rh, (CH2Cl)2, 80 °C, 24 h]
3bb / 76%
(20 mol % Rh, CH2Cl2, RT, 5 h)
4
20
Me (CO2Me)
O
Me
O
5
20
O
6
20
dppf
7
20
2PPh3
Me
O
3fb / 24%
[20 mol % Rh, (CH2Cl)2, 80 °C, 24 h]
8
20
tol-segphos
xyl-segphos
dtbm-segphos
segphos
100
100
100
100
CO2Me (Me)
3bc / 0% [using 1,2-naphthoquinone (2c)]
[20 mol % Rh, (CH2Cl)2, 80 °C, 24 h]
9
20
10
11
20
5
Scheme 2. Substrate Scope. [Rh(cod)2]BF4 (0.0050–0.020 mmol), segphos
(0.0050–0.020 mmol), 1 (0.100 mmol), 2 (0.110–0.500 mmol), and solvents
(2.0 mL) were used. The cited yields were of isolated products. [a]
[Rh(cod)2]BF4 (0.025 mmol), segphos (0.025 mmol), 1b (0.500 mmol), 2a
(2.50 mmol), and CH2Cl2 (2.0 mL) were used.
[a] [Rh(cod)2]BF4 (0.0050–0.020 mmol), ligand (0.0050–0.020 mmol), 1a
(0.100 mmol), 2a (0.110 mmol), and CH2Cl2 (2.0 mL) were used. [b] Isolated
yield.
O
Z
O
The scope of biphenyl-linked diynes 1 was then examined
under the above-optimized reaction conditions as shown in
Scheme 2.[12] With respect to the substituents at the alkyne
termini, biphenyl-linked 1,7-diynes, possessing not only the n-
butoxycarbonyl group (1a) but also the methoxy- and
ethoxycarbonyl groups (1b and 1c), reacted with 2a to give the
corresponding dibenzotetracenediones 3aa–3ca with good
yields. Diyne 1d possessing the phenyl group also reacted with
2a to afford the desired product 3da in low yield, although
elevation of the reaction temperature (130 °C), high catalyst
loading (20 mol% Rh), and longer reaction time (48 h) were
required. Acetyl-substituted diyne 1e was also capable of
PPh2
PPh2
PAr2
PAr2
PPh2
PPh2
O
Z
O
H8-binap
binap
segphos (Z = CH2, Ar = Ph)
tol-segphos (Z = CH2, Ar = 4-MeC6H4)
xyl-segphos (Z = CH2, Ar = 3,5-Me2C6H3)
dtbm-segphos
(Z = CH2, Ar = 4-tBu-3,5-Me2C6H2)
difluorphos (Z = CF2, Ar = Ph)
PPh2
PPh2
PPh2
PPh2
Fe
dppf
biphep
Figure 1. Structures of bisphosphine ligands.
reacting
with
2a
to
give
the
corresponding
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dibenzotetracenedione 3ea with good yield. In addition to
unsymmetrical diynes, symmetrical one 1f could participate in
this reaction to give 3fa in good yield, but diyne 1g, possessing
two methoxycarbonyl groups at the alkyne termini, reacted with
2a to give 3ga in low yield. With respect to alkenes, not only 1,4-
naphthoquinone (2a) but also anthracene-1,4-dione (2b) could
participate in this cycloaddition-aromatization to give the
corresponding dibenzopentacenediones 3bb and 3fb in 76%
and 24% yields, respectively. However, unfortunately, no
substrate conversion was observed in the reaction of 1b and
1,2-naphthoquinone (2c) even at the elevated reaction
temperature of 80 °C.[13] Similarly, we previously reported that a
six-membered 1,2-dicarbonyl compound (phenanthrene-9,10-
dione) cannot be employed in the cationic rhodium(I) complex-
catalyzed [2+2+2] cycloaddition of 1,6- and 1,7-diynes with
carbonyl compounds.[14] The formation of stable and unreactive
cationic rhodium(I)/(2c)2 complex A from 2c and the cationic
rhodium(I)/bisphosphine complex may account for no substrate
conversion when using 2c (Figure 2).[15] 1,4-Benzoquinone was
also tested, but the corresponding cycloadducts were unstable
and decomposed upon isolation.
generated as a major product (Supporting Information, Scheme
S1). Therefore the alumina is not responsible for the
aromatization and the presence of a catalytic amount of the
rhodium complex with free coordination sites indeed inhibits
spontaneous aromatization even under air, although the
mechanism of this stabilization effect by the rhodium complex is
not clear at the present stage.
20 mol %
[Rh(cod)2]BF4/
O
Me
segphos
CH2Cl2, RT, 5 h
Ac
O
1e
2a (5 equiv)
Hd
Hf
O
O
O
O
Hb
Ha
O
O
Hc
He
(i) with Rh complex
4ea / 86%
3ea / 0%
(ii) without Rh complex
0%
84%
(i) 1H NMR spectrum of the reaction mixture after evaporation and exposure to
air (in CDCl3).
Hc, singlet
Me2SO2
O
Ha, doublet
Hd, doublet
O
O
P
P
J = 6.9 Hz
J = 1.6 Hz
RhI+
O
Hb, multiplet
P
P
A
= segphos
Figure 2. Structure of cationic rhodium(I)/(2c)2 complex A.
(ii) 1H NMR spectrum of the reaction mixture after passing through an alumina
column under argon followed by evaporation (in CDCl3).
The reaction of 2a with malonate-linked 1,6-diyne 1h,
instead of the biphenyl-linked 1,7-diyne, was also investigated.
However, the yield of the corresponding anthraquinone 3ha was
low (Scheme 3).
Me2SO2
He, singlet
Hf, singlet
10 mol %
[Rh(cod)2]BF4/
O
Me
O
MeO2C
MeO2C
segphos
Me
MeO2C
MeO2C
CH2Cl2, RT, 5 h
CO2Et
O
EtO2C
3ha / 28%
O
1h
2a (5 equiv)
Scheme
3.
Rhodium-catalyzed
[2+2+2]
cycloaddition-spontaneous
Scheme 4. 1H NMR analyses of the reaction of 1e with 2a. The reaction was
conducted using [Rh(cod)2]BF4 (0.020 mmol), segphos (0.020 mmol), 1e
(0.100 mmol), 2a (0.500 mmol), and CH2Cl2 (2.0 mL). The cited yields were
determined by 1H NMR using dimethyl sulfone (0.100 mmol) as an internal
standard. (i) The doublet peak at 4.66 ppm, the multiplet peak at 3.92–3.83
ppm, the singlet peak at 2.42 ppm, and the doublet peak at 2.03 ppm are
assigned to the protons Ha, Hb, Hc, and Hd of 4ea. (ii) The singlet peaks at 3.36
ppm and 2.66 ppm are assigned to the protons He and Hf of 3ea.
aromatization of 1,6-diyne 1h with 1,4-naphthoquinone (2a).
In order to ascertain at what stage aromatization proceeds,
1
we conducted H NMR analyses of the reaction mixtures before
1
and after removal of the rhodium complex (Scheme 4). The H
NMR spectrum of the reaction mixture after evaporation and
exposure to air in the presence of the rhodium complex revealed
that non-aromatized product 4ea is generated [Scheme 4, (i)].
However, the 1H NMR spectrum of the reaction mixture after
removal of the rhodium complex by passing through an alumina
column under argon followed by evaporation revealed that
aromatized product 3ea is solely generated [Scheme 4, (ii)].
Me
O
Me
NaBH4
iPrOH, reflux
Me
O
Me
3fa
5 / 64%
1
Additionally, we conducted the H NMR analysis of the reaction
UV-Vis absorption: !max = 322 nm
fluorescence: !max = 492 nm (excitated at 322 nm)
F = 66% (excitated at 330 nm)
mixture being stirred for 16 h under argon after the addition of an
excess amount of PPh3 (10 equiv relative to rhodium) followed
by evaporation, which revealed that aromatized product 3ea is
"
Scheme 5. Synthesis of dibenzotetracene derivative 5.
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As mentioned in the introduction, acene-m,n-dione is a good
quantum yields of tetracene, tetrabenzotetracene, and
hexabenzotetracene.
precursor for the synthesis of acene.[11] Indeed, reductive
[11e]
aromatization of 3fa with NaBH4
proceeded to give dimethyl-
substituted dibenzotetracene 5 as an air-stable solid in good
yield (Scheme 5).[16]
Experimental Section
Although several examples of the synthesis of dibenzo[a,c]-
fused tetracenes have been reported, their photophysical
properties including fluorescence quantum yields have not been
examined. Thus we briefly examined the photophysical
properties of the thus obtained dibenzotetracene 5. Absorption
and fluorescence spectra of 5 are shown in Figure 3. Pleasingly,
dibenzotetracene 5 showed blue fluorescence with a good
quantum yield of 66%. This value is significantly higher than
General
Anhydrous 1,4-dioxane (No. 042-31655), PhCl (No. 28,451-3), (CH2Cl)2
(No. 28,450-5), and iPrOH (No. 27,847-5) were obtained from Aldrich
and Wako, and used as received. Anhydrous and degassed CH2Cl2 (No.
041-32345), and THF (No. 209-18705) were obtained from Aldrich and
Wako, and used as received. iPr2NH was dried over KOH. Et3N was
dried over KOH and bubbling with nitrogen, and the other solvents except
for MeOH and 1,4-dioxane for the synthesis of substrates were dried
over Molecular Sieves 4Å (Wako) prior to use. H8-binap, segphos, tol-
segphos, xyl-segphos, and DTBM-segphos were obtained from
Takasago International Corporation. α,ω-Diynes 1b,[9d] 1c,[9d] 1e,[9d] 1f,[20]
1g,[9c] and 1h,[9d] and anthracene-1,4-dione (2b)[21] were prepared
according to the literatures. All other reagents were obtained from
commercial sources and used as received. 1H (400 MHz) and 13C (100
MHz) NMR data were collected on a Bruker AVANCE III HD 400 at
ambient temperature unless otherwise specified. HRMS data were
obtained on a Bruker micrOTOF Focus II. All reactions were carried out
under nitrogen or argon in oven-dried glassware with magnetic stirring
unless otherwise noted. The UV/Vis absorption of 5 in CHCl3 (0.5×10–5
M) was recorded on a JASCO V-630 spectrometer with a resolution of
1.0 nm. The emission spectra of 5 in CHCl3 (0.5×10–5 M) was recorded
on a JASCO FP-6200 spectrometer with a resolution of 1.0 nm upon
excitation at 322 nm. The fluorescence quantum yield was measured on
a Hamamatsu Photonics, Absolute PL Quantum Yield Measurement
System, C11347-01.
fluorescence
quantum
yields
of
tetracene
(6),[17]
tetrabenzotetracene (7),[18] and hexabenzotetracene (8)[19]
(Figure 4).
Figure 3. Absorption (solid line) and fluorescence (dashed line) spectra of 5.
Synthesis of Diynes
Butyl 3-(2'-(prop-1-yn-1-yl)-[1,1'-biphenyl]-2-yl)propiolate (1a)
The title compound was prepared according to the conditions of the
literature used in the synthesis of structurally related compounds.[9d] To a
stirred solution of ((2-bromophenyl)ethynyl)trimethylsilane[22] (1.75 g, 6.91
mmol) in MeOH/THF (5:1, 24 mL) was added K2CO3 (1.91 g, 13.8 mmol)
at room temperature under air. After being stirred at the same
temperature for 30 min, the reaction mixture was poured into H2O/n-
hexane. The aqueous phase was extracted with two portions of n-hexane.
The combined extract was washed with brine, dried over Na2SO4, and
concentrated. The residue was used for the next reaction without further
purification. To a stirred solution of iPr2NH (1.90 mL, 13.8 mmol) in THF
(14 mL) was added nBuLi (8.80 mL, 13.8 mmol, 1.57 mol/L in n-hexane)
at −78 °C and the resulting mixture was stirred at the same temperature
for 10 min. To this mixture was added a solution of the above residue in
THF (10 mL) at −78 °C and the resulting mixture was stirred at the same
temperature for 30 min. To the mixture was added ClCO2nBu (3.60 mL,
27.6 mmol) at −78 °C. After being stirred at room temperature for 1 h, the
reaction mixture was quenched with water and poured into saturated
aqueous NH4Cl/EtOAc. The aqueous phase was extracted with two
portions of EtOAc. The combined extract was washed with brine, dried
over Na2SO4, and concentrated. The residue was purified by a silica gel
column chromatography (n-hexane/CH2Cl2 = 85:15) to give crude butyl 3-
(2-bromophenyl)propiolate (1.60 g). To a stirred solution of this crude
6
7
8
!F = 16% (ref 16)
!
F = 28% (ref 17)
!
F = 31% (ref 18)
Figure 4. Structures and fluorescence quantum yields of tetracene (6),
tetrabenzotetracene (7), and hexabenzotetracene (8).
Conclusions
In conclusion, we have established that
a
cationic
rhodium(I)/segphos complex is able to catalyze the [2+2+2]
cycloaddition of biphenyl-linked 1,7-diynes with 1,4-
naphthoquinone and anthracene-1,4-dione. Interestingly, in the
presence of this rhodium complex, aromatization of the
cyclohexadiene products did not proceed, while spontaneous
aromatization proceeded to give dibenzotetracenediones and
dibenzopentacenediones in good yields upon removal of the
rhodium complex by passing the reaction mixture through an
alumina column even under an argon atmosphere. The thus
obtained dibenzotetracenedione could be readily transformed
into the corresponding dibenzotetracene in good yield. This
butyl
3-(2-bromophenyl)propiolate
(1.60
g),
(2-(prop-1-yn-1-
yl)phenyl)boronic acid[23] (1.00 g, 6.27 mmol), and Cs2CO3 (2.41 g, 7.41
mmol) in 1,4-dioxane (11 mL) was added Pd2dba3 (78.3 mg, 0.0855
mmol) and [(tBu3P)H]BF4 (59.5 mg, 0.205 mmol) at room temperature.
After being stirred at 80 °C for 13 h, the reaction mixture was filtered
dibenzotetracene showed blue fluorescence with
quantum yield, which is significantly higher than fluorescence
a good
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1
through a pad of Celite and concentrated. The residue was purified by a
Mp 182−184 °C; H NMR (CDCl3, 400 MHz) δ 8.54–8.42 (m, 3H), 8.31–
8.26 (m, 1H), 8.26–8.20 (m, 2H), 7.84–7.73 (m, 2H), 7.72–7.62 (m, 2H),
7.58–7.50 (m, 2H), 4.54 (t, J = 6.6 Hz, 2H), 3.35 (s, 3H), 1.81–1.72 (m,
2H), 1.38 (sext, J = 7.4 Hz, 2H), 0.93 (t, J = 7.4 Hz, 3H); 13C NMR (CDCl3,
100 MHz); HRMS (ESI) calcd for C32H24O4Na [M+Na]+ 495.1567, found
495.1556.
silica gel column chromatography (n-hexane/CH2Cl2 = 85:15) to give
crude 1a. This crude 1a was purified by
a
gel permeation
chromatography (GPC) to give 1a (0.612 g, 1.94 mmol, 34% yield in 3
steps from ((2-bromophenyl)ethynyl)trimethylsilane) as a pale yellow oil.
1H NMR (CDCl3, 400 MHz) δ 7.70–7.66 (m, 1H), 7.52–7.44 (m, 3H),
7.40–7.27 (m, 4H), 4.10 (t, J = 6.6 Hz, 2H), 1.85 (s, 3H), 1.64–1.55 (m,
2H), 1.41–1.30 (m, 2H), 0.92 (t, J = 7.4 Hz, 3H); 13C NMR (CDCl3, 100
MHz) δ 154.1, 144.9, 141.4, 133.6, 132.5, 130.6, 130.0, 129.7, 127.7,
127.3, 127.1, 123.3, 119.3, 89.3, 85.8, 83.2, 78.7, 65.7, 30.4, 19.0, 13.6,
4.3; HRMS (ESI) calcd for C22H20O2Na [M+Na]+ 339.1356 found
339.1345.
Lage-scale Procedure for the Rhodium-Catalyzed [2+2+2]
Cycloaddition-Aromatizaion
of
α,ω-dDyne
1b
with
1,4-
Naphthoquinone (2a) (Scheme 2, 3ba): Segphos (15.3 mg, 0.025
mmol) and [Rh(cod)2]BF4 (10.2 mg, 0.025 mmol) were dissolved in
CH2Cl2 (2.0 mL) and the mixture was stirred at room temperature for 10
min. H2 was introduced to the resulting solution in a Schlenk tube. After
being stirred at room temperature for 30 min, the resulting mixture was
concentrated to dryness and dissolved in CH2Cl2 (0.5 mL). To the residue
was added a CH2Cl2 (1.0 mL) solution of 2a (0.395 g, 2.50 mmol) and a
CH2Cl2 (0.5 mL) solution of 1b (0.137 g, 0.500 mmol) in this order at
room temperature. The mixture was stirred at room temperature for 5 h.
The resulting solution was concentrated and purified by a preparative
TLC (n-hexane/CH2Cl2 = 1:2) twice to give 3ba (0.186 g, 0.431 mmol,
86% yield) as a yellow solid.
Methyl 3-(2'-(phenylethynyl)-[1,1'-biphenyl]-2-yl)propiolate (1d)
The title compound was prepared according to the conditions of the
literature used in the synthesis of structurally related compounds.[9d] To a
stirred solution of 2,2'-diethynyl-1,1'-biphenyl[20] (0.809 g, 4.00 mmol) in
THF (80 mL) was added nBuLi (2.40 mL, 4.00 mmol; 1.64 mol/L in n-
hexane) at −78 °C and the resulting mixture was stirred at −78 °C for 30
min. To the resulting mixture was added ClCO2Me (0.37 mL, 4.80 mmol)
at −78 °C. After being stirred at room temperature for 1 h, the reaction
mixture was quenched with water and poured into saturated aqueous
NH4Cl/EtOAc. The aqueous phase was extracted with two portions of
EtOAc. The combined extract was washed with brine, dried over Na2SO4,
and concentrated. The residue was used for the next reaction without
further purification. To a solution of the residue in Et3N/THF (3.2:1, 21
mL) was added iodobenzene (0.89 mL, 8.0 mmol), Pd(PPh3)2Cl2 (0.169 g,
0.240 mmol), and CuI (91.4 mg, 0.480 mmol) at room temperature. After
being stirred at the same temperature for 17 h, the reaction mixture was
poured into saturated aqueous NH4Cl/CH2Cl2. The aqueous phase was
extracted with two portions of CH2Cl2. The combined extract was washed
with brine, dried over Na2SO4, and concentrated. The residue was
Methyl 16-methyl-10,15-dioxo-10,15-dihydrodibenzo[a,c]tetracene-9-
carboxylate (3ba, Scheme 2)
1
Mp 246−248 °C; H NMR (CDCl3, 400 MHz) δ 8.54–8.44 (m, 2H), 8.44–
8.37 (m, 1H), 8.31–8.26 (m, 1H), 8.26–8.20 (m, 2H), 7.83–7.73 (m, 2H),
7.72–7.62 (m, 2H), 7.60–7.50 (m, 2H), 4.09 (s, 3H), 3.35 (s, 3H); 13C
NMR (CDCl3, 100 MHz) δ 184.8, 183.9, 171.5, 140.0, 139.9, 135.2,
134.2, 133.7, 133.3, 132.9, 132.1, 131.9, 130.1, 130.0, 129.6, 129.3,
129.1, 128.5, 127.7, 127.2, 126.9, 126.8, 126.6, 123.81, 123.80, 53.3,
25.1; HRMS (ESI) calcd for C29H18O4Na [M+Na]+ 453.1097, found
453.1084.
purified by a silica gel column chromatography (n-hexane/CH2Cl2
=
50:50) to give 1d (0.420 g, 1.32 mmol, 31% yield in 2 steps from 2,2'-
diethynyl-1,1'-biphenyl) as a sticky brown oil. 1H NMR (CDCl3, 400 MHz)
δ 7.75–7.68 (m, 1H), 7.68–7.61 (m, 1H), 7.59–7.48 (m, 2H), 7.47–7.33
(m, 5H), 7.28–7.17 (m, 4H), 3.69 (s, 3H); 13C NMR (CDCl3, 100 MHz) δ
154.4, 144.7, 141.8, 133.8, 132.3, 131.4, 130.8, 130.0, 129.9, 128.2,
128.1, 127.98, 127.96, 127.6, 123.3, 122.6, 119.3, 92.8, 88.7, 86.0, 82.9,
52.6; HRMS (ESI) calcd for C24H16O2Na [M+Na]+ 359.1043, found
359.1044.
Ethyl 16-methyl-10,15-dioxo-10,15-dihydrodibenzo[a,c]tetracene-9-
carboxylate (3ca, Scheme 2)
29.0 mg, 65% yield, Yellow solid; Mp 233−235 °C; 1H NMR (CDCl3, 400
MHz) δ 8.56–8.45 (m, 3H), 8.34–8.28 (m, 1H), 8.28–8.21 (m, 2H), 7.85–
7.74 (m, 2H), 7.73–7.64 (m, 2H), 7.61–7.52 (m, 2H), 4.60 (q, J = 7.1 Hz,
2H), 3.37 (s, 3H), 1.41 (t, J = 7.2 Hz, 3H); 13C NMR (CDCl3, 100 MHz) δ
184.9, 184.0, 171.0, 139.88, 139.86, 135.2, 134.2, 133.6, 133.4, 132.9,
132.1, 131.9, 130.13, 130.07, 130.0, 129.3, 129.2, 129.1, 129.0, 128.5,
127.5, 127.19, 127.17, 126.7, 126.6, 123.8, 123.7, 62.4, 25.1, 13.8;
HRMS (ESI) calcd for C30H20O4Na [M+Na]+ 467.1254, found 467.1237.
Rhodium-Catalyzed
Aromatizaion
[2+2+2]
Cycloaddition/Spontaneous
Representative Procedure for the Rhodium-Catalyzed [2+2+2]
Cycloaddition-Aromatizaion of α,ω-Diynes with 1,4-
Methyl 10,15-dioxo-16-phenyl-10,15-dihydrodibenzo[a,c]tetracene-9-
carboxylate (3da, Scheme 2)
1
Naphthoquinone (2a) (Scheme 2, 3aa): Segphos (3.1 mg, 0.0050
mmol) and [Rh(cod)2]BF4 (2.0 mg, 0.0050 mmol) were dissolved in
CH2Cl2 (2.0 mL) and the mixture was stirred at room temperature for 10
min. H2 was introduced to the resulting solution in a Schlenk tube. After
being stirred at room temperature for 30 min, the resulting mixture was
concentrated to dryness and dissolved in CH2Cl2 (0.5 mL). To the residue
was added a CH2Cl2 (1.0 mL) solution of 2a (79.1 mg, 0.500 mmol) and a
CH2Cl2 (0.5 mL) solution of 1a (31.6 mg, 0.100 mmol) in this order at
room temperature. The mixture was stirred at room temperature for 5 h.
The resulting solution was concentrated and purified by a preparative
TLC (n-hexane/CH2Cl2 = 1:2) twice to give 3aa (30.6 mg, 0.0648 mmol,
65% yield) as a yellow solid.
1
5.3 mg, 11% yield, Yellow amorphous; H NMR (CDCl3, 400 MHz) δ 8.50
(d, J = 7.7 Hz, 1H), 8.48–8.44 (m, 1H), 8.41 (d, J = 7.6 Hz, 1H), 8.30–
8.25 (m, 1H), 8.11–8.06 (m, 1H), 7.83–7.67 (m, 3H), 7.63–7.56 (m, 1H),
7.52–7.39 (m, 5H), 7.35–7.27 (m, 2H), 7.05–6.96 (m, 1H), 4.10 (s, 3H);
13C NMR (CDCl3, 100 MHz) δ 184.4, 183.3, 171.0, 141.6, 141.5, 137.1,
135.3, 134.9, 134.5, 133.8, 133.3, 132.5, 132.1, 131.4, 130.9, 130.6,
130.5, 130.1, 129.6, 129.5, 129.2, 128.6, 128.5, 128.0, 127.6, 127.22,
127.18, 127.1, 126.0, 123.8, 123.6, 53.4; HRMS (ESI) calcd for
C34H20O4Na [M+Na]+ 515.1254, found 515.1231.
9-Acetyl-16-methyldibenzo[a,c]tetracene-10,15-dione (3ea, Scheme
2)
Butyl 16-methyl-10,15-dioxo-10,15-dihydrodibenzo[a,c]tetracene-9-
carboxylate (3aa, Scheme 2)
1
32.6 mg, 79% yield, Yellow solid; Mp 250 °C (dec.); H NMR (CDCl3, 400
MHz) δ 8.52 (t, J = 7.8 Hz, 2H), 8.43–8.37 (m, 1H), 8.31–8.24 (m, 2H),
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10.1002/asia.201801670
Chemistry - An Asian Journal
FULL PAPER
8.21–8.15 (m, 1H), 7.84–7.65 (m, 4H), 7.62–7.52 (m, 2H), 3.34 (s, 3H),
2.65 (s, 3H); 13C NMR (CDCl3, 100 MHz) δ 208.3, 185.2, 184.9, 139.9,
139.7, 139.2, 135.2, 134.3, 133.7, 133.3, 132.0, 131.9, 131.4, 130.6,
130.0, 129.53, 129.46, 129.3, 129.1, 128.3, 128.2, 127.9, 127.2, 126.74,
126.72, 123.9, 123.8, 32.7, 25.0; HRMS (ESI) calcd for C29H18O3Na
[M+Na]+ 437.1148, found 437.1167.
a solution of 3fa (52.8 mg, 0.137 mmol) in iPrOH (4 mL) was added
NaBH4 (103.4 mg, 2.73 mmol) at 0 °C and the resulting mixture was
stirred at reflux for 9 h. The mixture was cooled to room temperature and
stirred at the same temperature for 13 h. The mixture was heated to the
reflux point and stirred at the same temperature for 10 h. To the mixture
was added 2M aqueous HCl (4 mL) at room temperature. After being
stirred at the same temperature for 1 h, the reaction mixture was poured
into 2M aqueous HCl/CH2Cl2. The aqueous phase was extracted with two
portions of CH2Cl2. The combined extract was washed with saturated
aqueous NaHCO3 and brine, dried over Na2SO4, and concentrated. The
residue was purified by a preparative TLC (n-hexane/toluene = 3:1) to
9,16-Dimethyldibenzo[a,c]tetracene-10,15-dione (3fa, Scheme 2)
1
21.5 mg, 56% yield, Yellow solid; Mp 258 °C (dec.); H NMR (CDCl3, 400
MHz) δ 8.48 (d, J = 8.0 Hz, 2H), 8.28–8.21 (m, 4H), 7.79–7.73 (m, 2H),
7.69–7.63 (m, 2H), 7.60–7.53 (m, 2H), 3.30 (s, 6H); 13C NMR (CDCl3,
100 MHz) δ 186.6, 138.9, 136.4, 135.1, 133.3, 132.0, 130.5, 129.84,
129.82, 128.4, 126.50, 126.46, 123.7, 24.4; HRMS (ESI) calcd for
C28H18O2Na [M+Na]+ 409.1199, found 409.1199.
give crude 5. This crude
5 was purified by a gel permeation
chromatography (GPC) to give 5 (31.4 mg, 0.0881 mmol, 64% yield) as a
yellow solid. Mp 195 °C (dec.); 1H NMR (CDCl3, 400 MHz) δ 8.72 (s, 2H),
8.25 (dd, J = 7.9, 1.1 Hz, 2H), 8.08 (dd, J = 6.4, 3.2 Hz, 2H), 8.08 (d, J =
8.0 Hz, 2H), 7.53–7.37 (m, 6H), 3.28 (s, 6H); 13C NMR (CDCl3, 100 MHz)
δ 132.2, 132.1, 131.5, 131.1, 130.9, 129.7, 128.4 ,127.3, 126.9, 126.5,
125.5, 123.7, 123.6, 19.8; HRMS (APCI) calcd for C28H20 [M]+ 356.1560,
found 356.1552.
Dimethyl
10,15-dioxo-10,15-dihydrodibenzo[a,c]tetracene-9,16-
dicarboxylate (3ga, Scheme 2)
5.9 mg, 12% yield, Yellow solid; Mp >300 °C; 1H NMR (CDCl3, 400 MHz)
δ 8.56 (d, J = 8.1 Hz, 2H), 8.47 (d, J = 8.2 Hz, 2H), 8.30 (dd, J = 5.6, 3.3
Hz, 2H), 7.84 (dd, J = 5.7, 3.4 Hz, 2H), 7.77–7.70 (m, 2H), 7.62–7.56 (m,
2H), 4.11 (s, 6H); 13C NMR (CDCl3, 100 MHz) δ 182.6, 170.5, 134.8,
134.6, 133.6, 132.1, 132.0, 130.0, 129.8, 128.4, 127.8, 127.5, 127.1,
123.9, 53.5; HRMS (ESI) calcd for C30H18O6Na [M+Na]+ 497.0996, found
497.0991.
Acknowledgements
This work was supported by ACT-C (No. JPMJCR1122YR) from
Japan Science and Technology Agency (JST), Japan and a
Grant-in-Aid for Scientific Research (No. 26102004) from Japan
Society for the Promotion of Science (JSPS), Japan. Y.A. thanks
JSPS research fellowship for young scientists (No. 17J08763).
We thank Takasago International Corp. for the gift of H8-BINAP,
Segphos, tol-Segphos, xyl-Segphos, and DTBM-Segphos, and
Umicore for generous support in supplying the rhodium and
palladium complexes.
Methyl 18-methyl-10,17-dioxo-10,17-dihydrodibenzo[a,c]pentacene-
9-carboxylate (3bb, Scheme 2)
1
36.7 mg, 76% yield, Orange solid; Mp 292−292 °C; H NMR (CDCl3, 400
MHz) δ 8.79 (d, J = 11.5 Hz, 2H), 8.54–8.46 (m, 2H), 8.42 (d, J = 7.8 Hz,
1H), 8.26 (d, J = 8.2 Hz, 1H), 8.12–8.03 (m, 2H), 7.73–7.63 (m, 4H),
7.61–7.52 (m, 2H), 4.12 (s, 3H), 3.40 (s, 3H); 13C NMR (CDCl3, 100 MHz)
δ 184.8, 183.9, 171.7, 140.1, 140.0, 135.5, 135.0, 133.1, 132.1, 132.0,
131.4, 131.1, 130.1, 130.0, 129.8, 129.7, 129.4, 129.34, 129.30, 129.28,
129.1, 129.0, 128.5, 127.7, 127.0, 126.6, 123.82, 123.80, 53.3, 25.3;
HRMS (ESI) calcd for C33H20O4Na [M+Na]+ 503.1254, found 503.1260.
Keywords: alkynes • dibenzotetracenediones • quinones •
rhodium • [2+2+2] cycloaddition
[1]
For selected recent reviews of the transition-metal-catalyzed [2+2+2]
cycloaddition of alkynes, see: a) K. Tanaka, Y. Kimura, K. Murayama,
Bull. Chem. Soc. Jpn. 2015, 88, 375; b) S. Okamoto, Y. Sugiyama,
Synlett 2013, 24, 1044; c) Transition-metal-mediated Aromatic Ring
Construction, ed. by K. Tanaka, John Wiley & Sons: Hoboken, USA,
2013; d) D. L. J. Broere, E. Ruijter, Synthesis 2012, 44, 2639; e) G.
Domínguez, J. Pérez-Castells, Chem. Soc. Rev. 2011, 40, 3430; f) N.
Weding, M. Hapke, Chem. Soc. Rev. 2011, 40, 4525; g) M. R. Shaaban,
R. El-Sayed, A. H. M. Elwahy, Tetrahedron 2011, 67, 6095; h) S. Li, L.
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R. Hua, M. V. A. Abrenica, P. Wang, Curr. Org. Chem. 2011, 15, 712; j)
A. Pla-Quintana, A. Roglans, Molecules 2010, 15, 9230; k) D. Leboeuf,
V. Gandon, M. Malacria, in Handbook of Cyclization Reactions, Vol. 1,
ed by S. Ma, Wiley-VCH, Weinheim, 2010, p. 367; l) J. A. Varela, C.
Saá, J. Organomet. Chem. 2009, 694, 143; m) K. Tanaka, Chem. Asian
J. 2009, 4, 508; n) S. Kotha, E. Brahmachary, K. Lahiri, Eur. J. Org.
Chem. 2005, 4741.
9,18-Dimethyldibenzo[a,c]pentacene-10,17-dione (3fb, Scheme 2)
10.3 mg, 24% yield, Red solid; Mp 276 °C (dec.); 1H NMR (CDCl3, 400
MHz) δ 8.73 (s, 2H), 8.46 (d, J = 8.0 Hz, 2H), 8.25 (d, J = 8.1 Hz, 2H),
8.06 (dd, J = 6.2, 3.4 Hz, 2H), 7.68–7.59 (m, 4H), 7.55 (t, J = 7.6 Hz, 2H),
3.32 (s, 6H); 13C NMR (CDCl3, 100 MHz) δ 186.6, 138.9, 136.3, 135.1,
132.0, 131.7, 131.4, 129.9, 129.8, 128.9, 128.4, 128.2, 126.5, 123.7,
24.5; HRMS (ESI) calcd for C64H40O4Na [2M+Na]+ 895.2819, found
895.2776.
4-Ethyl 2,2-dimethyl 11-methyl-5,10-dioxo-1,3,5,10-tetrahydro-2H-
cyclopenta[b]anthracene-2,2,4-tricarboxylate (3ha, Scheme 3)
12.8 mg, 28% yield, White solid; Mp 204−206 °C; 1H NMR (CDCl3, 400
MHz) δ 8.24–8.15 (m, 2H), 7.81–7.70 (m, 2H), 4.54 (q, J = 7.1 Hz, 2H),
3.78 (s, 6H), 3.75 (s, 2H), 3.73 (s, 2H), 2.78 (s, 3H), 1.44 (t, J = 7.1 Hz,
3H); 13C NMR (CDCl3, 100 MHz) δ 184.9, 182.9, 171.2, 168.9, 147.8,
142.9, 139.0, 134.5, 134.3, 133.6, 132.5, 131.9, 131.1, 129.6, 127.2,
126.8, 61.8, 58.9, 53.3, 40.6, 39.4, 19.1, 14.1; HRMS (ESI) calcd for
C25H22O8Na [M+Na]+ 473.1207, found 437.1215.
[2]
For selected recent reviews of the transition-metal-catalyzed [2+2+2]
cycloaddition involving alkenes, see: a) G. Domínguez, J. Pérez-
Castells, Chem. Eur. J. 2016, 22, 6720; b) Y. Satoh, Y. Obora, Eur. J.
Org. Chem. 2015, 2015, 5041; c) M. Amatore, C. Aubert, Eur. J. Org.
Chem. 2015, 2015, 265; d) G. Domínguez, J. Pérez-Castells, [2 + 2 +
2] cycloadditions. In Comprehensive Organic Synthesis II, 2nd ed, ed
by P. Knochel, Elsevier: Amsterdam, 2014; Vol. 5, p. 1537; e) N. Saito,
D. Tanaka, M. Mori, Y. Sato, Chem. Rec. 2011, 11, 186; f) T. Shibata,
K.Tsuchikama, Org. Biomol. Chem. 2008, 6, 1317; g) P. R. Chopade, J.
Louie, Adv. Synth. Catal. 2006, 348, 2307.
9,16-Dimethyldibenzo[a,c]tetracene (5, Scheme 5)
The title compound was prepared according to the conditions of the
literature used in the synthesis of structurally related compounds.[11e] To
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10.1002/asia.201801670
Chemistry - An Asian Journal
FULL PAPER
[3]
[4]
Although the catalytic [2+2+2] cycloaddition of two alkynes with one
cyclohexene or dihydronaphthalene derivative has not been reported,
the cobalt(I)-mediated reactions using cyclohexene were reported. See:
a) V. Gandon, D. Leboeuf, S. Amslinger, K. P. C. Vollhardt, M. Malacria,
C. Aubert, Angew. Chem. Int. Ed. 2005, 44, 7114; b) A, Geny, D.
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Aubert, Chem. Eur. J. 2007, 13, 5408.
[13] Elevation of the reaction temperature (130 °C in PhCl) and extension of
the reaction time (72 h) resulted in a complex mixture of decomposition
products.
[14] For an example of the synthesis of rhodium(I)-semiquinonato
complexes, see: M. Mitsumi,; S. Umebayashi, Y. Ozawa, M. Tadokoro,
H. Kawamura, K. Toriumi, Chem. Lett. 2004, 33, 970.
[15] For an example of the unsuccessful use of a six-membered 1,2-
dicarbonyl compound (phenanthrene-9,10-dione) in the cationic
rhodium(I) complex-catalyzed [2+2+2] cycloaddition of 1,6- and 1,7-
diynes with carbonyl compounds, see: Y. Otake, R. Tanaka, K. Tanaka,
Eur. J. Org. Chem. 2009, 2009, 2737.
For selected recent reviews of the synthesis of anthracene derivatives
using benzynes and naphthynes, see: a) S. Zade, S. M. Bendikov,
Angew. Chem. Int. Ed. 2010, 49, 4012; b) C. Tönshoff, H. F. Bettinger,
in Polyacenes I, ed. by J. S. Siegel, Y.-T. Wu, Top. Curr. Chem. Vol.
349, Springer, Berlin, Heidelberg, 2013, p. 1; c) D. Pérez, D. Peña, E.
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[5]
[6]
C. Chen, C. Xi, Z. Ai, X. Hong, Org. Lett. 2006, 8, 4055.
The [2+2+2] cycloaddition of two alkynes with dimethyl fumarate by
using stoichiometric amounts of zirconium and copper complexes was
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[7]
For examples of the transition-metal-catalyzed [2+2+2] cycloaddition of
two alkynes with acyclic 2-butene-1,4-dione derivatives, see: a) A. J.
Chalk, J. Am. Chem. Soc. 1972, 94, 5928; b) Z. Zhou, L. P. Battaglia, G.
P. Chiusoli, M. Costa, M. Nardelli, C. Pelizzi, G. J. Predieri, Chem. Soc.,
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Sagae, M. Hirano, Synlett 2007, 2007, 1426; h) L. X. Alvarez, B.
Bessières, J. Einhorn, Synlett 2008, 2008, 1376. In some of the above
examples, subsequent aromatization was also demonstrated. See: refs
7a–c, 7e, and 7f.
[22] T. Ishida, S. Kikuchi, T. Tsubo, T. Yamada, Org. Lett. 2013, 15, 848.
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[8]
For reviews of the rhodium-catalyzed [2+2+2] cycloaddition, see: a) K.
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Metal-Mediated Aromatic Ring Construction; ed by K. Tanaka, Wiley:
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Rhodium(I)-Catalyzed Cycloisomerization and Cyclotrimerization
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a) T. Shibata, A. Kawachi, M. Ogawa, Y. Kuwata, K. Tsuchikama, K.
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[12] Dimerization and trimerization of diynes 1 proceeded as side reactions.
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10.1002/asia.201801670
Chemistry - An Asian Journal
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R1
O
O
RhI+/segphos
catalyst
Yukimasa Aida, Yu Shibata, and Ken
Tanaka*
R1
R2
O
R2
O
O
O
O
Page No. – Page No.
PPh2
PPh2
up to 86% yield
[2+2+2] Cycloaddition
&
Facile Synthesis of
O
Spontaneous Aromatization
segphos
Dibenzotetracenedione Derivatives by
Rhodium-Catalyzed [2+2+2]
Cycloaddition/Spontaneous
Aromatization
It has been established that a cationic rhodium(I)/Segphos complex catalyzes the
[2+2+2] cycloaddition of biphenyl-linked 1,7-diynes with 1,4-naphthoquinone and
anthracene-1,4-dione. Conveniently, spontaneous aromatization proceeded upon
removal of the rhodium complex by passing the reaction mixture through an
alumina column to give the corresponding dibenzotetracenediones and
dibenzopentacenediones, respectively, in good yields.
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