Palladium-Catalyzed Annulation of 2,2 ′ -Dibromobiphenyls with Alkynes: Synthesis of Functionalized Phenanthrenes and Dibenzochrysenes

Article abstract of DOI:10.1055/s-0034-1378726

A palladium-catalyzed annulation process of 2,2′-dibromobiphenyls with alkynes for the synthesis of functionalized phenanthrenes has been realized. The methodology provides an efficient approach to dibenzochrysene derivatives starting from simple reactants in two steps.

Full text of DOI:10.1055/s-0034-1378726

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© Georg Thieme Verlag Stuttgart · New York
2015, 26, 1991–1996
letter
1991
J. Ma et al.
Letter
Synlett
Palladium-Catalyzed Annulation of 2,2′-Dibromobiphenyls with
Alkynes: Synthesis of Functionalized Phenanthrenes and Diben-
zochrysenes
Jun Ma
Br
Pd(PPh3)2Cl2 (5 mol%)
Gaoqiang Li*
Yan Qiao
Xantphos (5.5 mol%)
R1
R2
+
K2CO3 (3 equiv)
mesitylene, 150 °C
R1
R2
Jingxuan Tu
Sha Liu
Br
up to 78%
Feng Xu*
Key Laboratory of Macromolecular Science of Shaanxi Province,
School of Chemistry and Chemical Engineering, Shaanxi Normal
University, Xi’an, Shaanxi 710062, P. R. of China
gqli@snnu.edu.cn
S
S
S
N
fengxu@snnu.edu.cn
Cl
57% yield; 37 h
63% yield; 38 h
61% yield; 38 h
57% yield; 40 h
Received: 20.03.2015
Accepted after revision: 10.05.2015
Published online: 15.07.2015
Although a number of efficient synthetic methodologies
have been developed for the preparation of π-conjugated
phenanthrenes,10–15 the recently reported transition-metal-
catalyzed annulations of biphenyl derivatives,14,15 especially
using 2,2′-diiodobiphenyls15 with alkynes are the most eco-
nomic and synthetically most attractive for the easily pre-
pared or commercially available substances, low reaction
cost, high efficiency and widespread functional group toler-
ance. However, only iodobiphenyls showed unique reactivi-
ty towards alkynes and successfully afforded the phenan-
threnes; attempts of using their analogues such as 2-bro-
mobiphenyl and 2,2′-dibromobiphenyl failed to promote
the annualtion.15b To realize the annulation of bromobiphe-
nyls and alkynes is still a great challenge and has become
an urgent issue for the generality of this kind of methodolo-
gy.
We previously reported that 1,8-dibromonaphthalene
effectively underwent the annulation reaction with alkynes
in the presence of a palladium catalyst to afford the corre-
sponding annulated acenaphthylenes.16 It may be conceived
that the phenanthrene ring would be generated when 2,2′-
dibromobiphenyl was used instead of 1,8-dibromonaph-
thalene under the similar reaction conditions. Indeed, it
worked well under the optimized reaction conditions. We
report herein a palladium-catalyzed annulation reaction of
2,2′-dibromobiphenyl and alkynes to synthesize function-
alized phenanthrenes.
DOI: 10.1055/s-0034-1378726; Art ID: st-2015-w0198-l
Abstract A palladium-catalyzed annulation process of 2,2′-dibromobi-
phenyls with alkynes for the synthesis of functionalized phenanthrenes
has been realized. The methodology provides an efficient approach to
dibenzochrysene derivatives starting from simple reactants in two
steps.
Key words alkynes, annulations, domino reaction, fused-ring sys-
tems, palladium
Because of the advances in organic electronics such as
light emitters, semiconductors, liquid crystals, and solar
cells, the chemistry of polycyclic aromatic hydrocarbons
(PAHs) has attracted a great deal of attention and they have
become increasingly important for the development of su-
perior organic materials.1 Phenanthrene is one of the most
stable fused aromatics.2 Its high resonance energy and high
energy gap qualify it as a highly attractive building block
for conjugated systems. Many π-conjugated functional ma-
terials such as picene3 and carbon nanotubes4 contain a
core of phenanthrene motif. Some phenanthrene deriva-
tives have exhibited excellent photoconductivity,5 super-
conductivity3 and electroluminescent6 properties as well as
interesting biological activities such as antitumor, anti-im-
mune and anti-inflammatory properties.7 Phenanthrene
oligomers are useful stable p-type semiconductors for or-
ganic field-effect transistors (OFETs)8 and 9,10-diaryl-
phenanthrenes can be converted into photoluminescent
blue-emitting polyphenanthrenes.9 Based on these promis-
ing features, development of efficient synthetic routes to
the phenanthrenes bearing appropriate functional group,
especially incorporating heteroatom is highly valuable for
the control of the optical and electronic properties of mate-
rials.
Initially, we chose 2,2′-dibromobiphenyl (1a) and di-
phenylacetylene (2a) as model substrates to screen the re-
action (Table 1). We found that
a combination of
tetrakis(triphenylphosphine)palladium (5 mol%), triphenyl-
phosphine (5.5 mol%), and potassium carbonate (3.0 equiv)
in toluene at reflux successfully gave the desired annulation
product 9,10-diphenylphenanthrene (3aa) in 20% isolated
yield (Table 1, entry 1).
© Georg Thieme Verlag Stuttgart · New York — Synlett 2015, 26, 1991–1996

1992
J. Ma et al.
Letter
Synlett
The screening of palladium source revealed that
bis(triphenylphosphine)palladium(II) dichloride showed
the best catalytic ability and enhanced the yield to 37% (Ta-
ble 1, entry 4). On further examination of various bases and
phosphine ligands i.e., tricyclohexylphosphine (PCy3; Table
1, entry 8), dicyclohexyl(2′,6′-dimethoxybiphenyl-2-
yl)phosphine (S-Phos; Table 1, entry 9), dicyclohex-
yl(2′,4′,6′-triisopropylbiphenyl-2-yl)phosphine (X-Phos; Ta-
ble 1, entry 10) and (9,9-dimethyl-9H-xanthene-4,5-di-
yl)bis(diphenylphosphine) (Xantphos; Table 1, entry 11),
the combination of potassium carbonate and Xantphos ex-
hibited the highest performance and improved the yield to
59% (Table 1, entry 11). The strong base, potassium tert-
butoxide was ineffective in this transformation and only
trace product was formed (monitored by TLC plate; Table 1,
entry 6). A higher reaction temperature is generally benefi-
cial to the annulation process, especially for the synthesis of
PAHs. Therefore, we used mesitylene as a solvent instead of
toluene and increased the reaction temperature to 150 °C.
withdrawing acetyl group (2k) and nitro group (2l) and
electron-donating methoxy group (2c and 2g) all smoothly
underwent the annualtions with 2,2′-dibromobiphenyls to
produce the functionalized phenanthrenes in good yields.
Electron-deficient alkynes were less reactive and gave a
slightly lower yield even with a longer reaction time. Note
that diarylalkynes with halo substituents such as fluoro
(2e) and chloro (2p) on the benzene ring were well tolerat-
ed. The functionalized phenanthrenes containing halo at-
oms are very useful for they can be easily further derivat-
ized by means of simple coupling strategies and the likes.
Diarylalkyne with sterically demanding ortho substituent
still successfully afforded the corresponding phenanthrenes
(3ad and 3bd) even though with sharply decreased yields.
2,2′-Dibromo-4,4′,5,5′-tetramethylbiphenyl (1b) furnished
the annulations process in a shorter reaction time but with
slightly lower yields than 2,2′-dibromobiphenyl (1a). Addi-
tionally, 1-aryl-2-alkyl substituted acetylenes also success-
fully reacted with 2,2′-dibromobiphenyl to give the corre-
sponding phenanthrenes in high yield (3h and 3i). More
importantly, electron-deficient acetylenes with heteroaro-
matic substituents such as 1-phenyl-2-(2-thienyl)acetylene
(2m), di(2-thienyl)-substituted acetylenes (2n) and 1-phe-
nyl-2-(4-pyridyl)acetylene (2o) were still capable of the an-
nulations with 2,2′-dibromobiphenyl and generated the
functionalized phenanthrenes with heteroaromatics in fair
yields. The synthesis of 9,10-disubstituted phenanthrene
derivatives containing heteroaromatics has seldom been re-
ported before using electron-deficient heteroaromatic-sub-
stituted acetylenes, especially when the heteroatom exists
ortho to the substituted position of heteroaromatic ring.
The successful incorporation of heteroaromatic rings in
PAHs is highly valuable to the electronic and optical proper-
ties of organic materials. In fact, the incorporation of het-
eroaromatic rings and the fusion of bridging heteroatoms
may tune the molecular and electronic structures of PAHs,
which are closely related to the electronic properties of ma-
terials.
The dibenzochrysene (DBC) is a twisted polycyclic aro-
matic hydrocarbon. Its derivatives can be applied to the
preparation of sensors, nonlinear optical and liquid-crystal-
line materials, etc. The preparation of parent dibenzochry-
sene and its derivatives generally requires multistep syn-
theses.17 The Scholl reaction18 is one of the most famous C–
C bond-forming reactions and has been extensively utilized
for intramolecular oxidative cyclodehydrogenation of vari-
ous polybenzenoid hydrocarbons to prepare the corre-
sponding planar polyaromatic hydrocarbons.1a,b To illus-
trate the potential application of 9,10-diarylphenanthrenes,
we investigated the synthesis of dibenzochrylsenes by the
Scholl reaction using 3aa and 3ab (Scheme 1). The diben-
zochrylsenes 4aa and 4ab were readily synthesized with
yields of 70% and 82%, respectively, using CuCl2 and AlCl3 as
an oxidant.
Table 1 Screen of Reaction Conditionsa
Br
[Pd], [P]
+
Ph
Ph
base, toluene
reflux
Ph
Ph
Br
1a
[Pd]
Pd(PPh3)4
3aa
2a
Entry
[P]
Ph3P
Base
K2CO3
T (h)
Yield (%)b
1
2
48
48
48
48
48
48
48
48
48
48
48
36
20
30
10
37
32
trace
8
Pd(OAc)2
Pd2(dba)3
Ph3P
K2CO3
K2CO3
K2CO3
Cs2CO3
t-BuOK
Et3N
3
Ph3P
4
Pd(PPh3)Cl2
Pd(PPh3)Cl2
Pd(PPh3)Cl2
Pd(PPh3)Cl2
Pd(PPh3)Cl2
Pd(PPh3)Cl2
Pd(PPh3)Cl2
Pd(PPh3)Cl2
Pd(PPh3)Cl2
Ph3P
5
Ph3P
6
Ph3P
7
Ph3P
8
Cy3P
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
12
15
19
59
78
9
S-Phos
X-Phos
10
11
12c
Xantphos
Xantphos
a Reaction conditions: 1 (0.3 mmol), 2a (0.33 mmol), [Pd] (5.0 mol%), li-
gand (5.5 mol%), base (3.0 equiv), toluene (5 mL), reflux.
b Isolated yield.
c Mesitylene was used as a solvent and the reaction temperature was in-
creased to 150 °C (bath temp.).
As we expected, the corresponding 9,10-diphenyl-
phenanthrene was finally obtained in 78% yield (Table 1,
entry 12).
With the optimal reaction conditions in hand, we next
investigated the substrate scope of the annulation reaction
(Table 2). Diarylalkynes with substituent such as methyl
(2b), ethyl (2f), sterically bulky tert-butyl (2j), electron-
© Georg Thieme Verlag Stuttgart · New York — Synlett 2015, 26, 1991–1996

1993
J. Ma et al.
Letter
Synlett
Table 2 (continued)
Table 2 Palladium-Catalyzed Annulations of 2,2′-Dibromobiphenyls
with Alkynes
Entry
Product
Time (h) Yield (%)
Br
R1
R1
R1
R1
R1
7
3ag
28
61
R1
Br
1a: R1 = H
R1
R1
Pd(PPh3)2Cl2 (5 mol%)
Xantphos (5.5 mol%)
1b: R1 = Me
+
O
R2
R3
K2CO3 (3 equiv)
mesitylene, 150 °C
R3
R2
2
3
Entry
Product
Time (h) Yield (%)
8
9
3ah
33
33
69
66
1
3aa
36
78
3ai
2
3ab
30
69
10
3aj
35
60
3
4
3ac
30
48
58
21
O
11
3ak
40
59
3ad
O
O
12
3al
40
43
5
3ae
38
53
NO2
F
13
3am
38
63
S
6
3af
30
72
© Georg Thieme Verlag Stuttgart · New York — Synlett 2015, 26, 1991–1996

1994
J. Ma et al.
Letter
Synlett
Table 2 (continued)
CuCl2 (5.0 equiv)
AlCl3 (5.0 equiv)
Entry
14
Product
Time (h) Yield (%)
CS2, r.t.
3an
38
40
61
57
S
S
R
R
3aa, R = H
3ab, R = Me
4aa, R = H: 46 h, 70%
4ab, R = Me: 40 h, 82%
Scheme 1 Synthesis of dibenzochrysene derivatives
15
3ao
In conclusion, we have developed a palladium-catalyzed
annulation process of 2,2′-dibromobiphenyls with alkynes
for the synthesis of functionalized phenanthrenes.19,20 The
electron-deficient heteroaromatic-substituted acetylenes
are capable of the annulation process. Thiophene-fused and
pyridine-fused PAHs can also be synthesized easily. This
methodology also provides a highly efficient and low-cost
approach to dibenzochrysene derivatives starting from
simple, commercially available reactants in two steps.
N
16
3ap
37
57
Cl
Acknowledgment
We are grateful for the financial support from the National Natural
Science Foundation of China (21302117 and 21172138), the Natural
Science Foundation of Shaanxi Province (2013JQ2008) and the Funda-
mental Research Funds for the Central Universities (GK201402060).
17
3ba
18
60
Supporting Information
Supporting information for this article is available online at
http://dx.doi.org/10.1055/s-0034-1378726.
S
u
p
p
ortiInfogrmoaitn
S
u
p
p
o
nrtogI
f
rmoaitn
18
3bb
14
50
References and Notes
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19
3bc
24
34
O
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3bd
36
10
O
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(0.3 mmol), alkyne (0.33 mmol), Pd(PPh3)2Cl2 (11 mg, 5 mol%),
Xantphos (10 mg, 5.5 mol%) and K2CO3 (124 mg, 0.9 mmol)
under N2. Mesitylene (5 mL) was added from a syringe, and the
mixture was stirred at 150 °C until the reaction was complete
(TLC). The mixture was cooled to r.t., and H2O (10 mL) was
added. The resulting mixture was extracted with EtOAc (3 × 15
mL). The organic layers were combined, dried over anhyd
Na2SO4, and concentrated to give a residue that was purified by
column chromatography (silica gel, PE–EtOAc).
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9-(3-Methoxyphenyl)-10-phenylphenanthrene (3ac): white
solid; yield: 63 mg (58%); mp189.8–191.1 °C. 1H NMR (400
MHz, CDCl3): δ = 8.81 (d, J = 8.3 Hz, 2 H), 7.60–7.68 (m, 3 H),
7.54–7.57 (m, 1 H), 7.46–7.51 (m, 2 H), 7.26–7.29 (m, 1 H),
7.18–7.25 (m, 3 H), 7.13–7.16 (m, 2 H), 6.70–6.79 (m, 3 H), 3.68
(s, 3 H). 13C NMR (101 MHz, CDCl3): δ = 158.9, 140.9, 139.5,
137.0, 137.0, 131.9, 131.7, 131.0, 131.0, 130.0, 130.0, 128.5,
127.9, 127.7, 127.6, 126.6, 126.6, 126.5, 126.4, 123.8, 122.5,
122.5, 116.6, 112.4, 55.2. HRMS (ESI): m/z calcd for
[C27H20ONa]+: 383.1412; found: 383.1418.
9-(2-Methoxyphenyl)-10-phenylphenanthrene (3ad): faint
yellow solid; yield: 23 mg (21%); mp 198.9–191.1 °C. 1H NMR
(400 MHz, CDCl3): δ = 8.71 (dd, J = 8.3, 4.0 Hz, 2 H), 7.53–7.58
(m, 2 H), 7.47–7.50 (m, 1 H), 7.36–7.41 (m, 3 H), 7.07–7.16 (m, 6
H), 6.93 (dd, J = 7.4, 1.7 Hz, 1 H), 6.68–6.77 (m, 2 H), 3.49 (s, 3
H). 13C NMR (101 MHz, CDCl3): δ = 156.2, 138.8, 136.5, 133.0,
131.3, 131.0, 130.7, 129.7, 129.1, 128.9, 127.5, 127.5, 126.7,
126.4, 126.2, 125.6, 125.5, 125.4, 125.2, 125.2, 121.5, 121.5,
119.0, 109.3, 54.1. HRMS (ESI): m/z calcd for [C27H20ONa]+:
383.1412; found: 383.1407.
9-(4-Fluorophenyl)-10-phenylphenanthrene (3ae): white
solid; yield: 55 mg (53%); mp 256.8–257.9 °C. 1H NMR (400
MHz, CDCl3): δ = 8.80 (d, J = 8.4 Hz, 2 H), 7.64–7.68 (m, 2 H),
7.47–7.56 (m, 4 H), 7.20–7.26 (m, 3 H), 7.08–7.14 (m, 4 H),
6.90–6.95 (m, 2 H). 13C NMR (101 MHz, CDCl3): δ = 162.8, 160.3,
139.5, 137.7, 136.1, 135.5, 132.6, 132.5, 131.8, 131.0, 130.1,
127.9, 127.7, 127.6, 126.7, 126.6, 126.6, 126.5, 122.6, 122.5,
114.7, 114.5. HRMS (ESI): m/z calcd for [C26H17FNa]+: 371.1212;
found: 371.1225.
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9-(4-Ethylphenyl)-10-phenylphenanthrene
(3af):
white
solid; yield: 77 mg (72%); mp 163.3–164.5 °C. 1H NMR (400
MHz, CDCl3): δ = 8.80 (d, J = 8.3 Hz, 2 H), 7.54–7.67 (m, 4 H),
7.45–7.50 (m, 2 H), 7.18–7.26 (m, 3 H), 7.14–7.16 (m, 2 H), 7.05
(s, 4 H), 2.61 (q, J = 7.6 Hz, 2 H), 1.21 (t, J = 7.6 Hz, 3 H). 13C NMR
(101 MHz, CDCl3): δ = 142.2, 141.6, 139.7, 137.3, 137.2, 136.7,
132.1, 132.0, 131.1, 130.9, 130.0, 129.0, 128.0, 127.8, 127.6,
127.2, 127.0, 126.6, 126.3, 126.3, 122.5, 122.4, 28.5, 15.4. HRMS
(ESI): m/z calcd for [C28H22Na]+: 381.1620; found: 381.1629.
9,10-Bis(4-tert-butylphenyl)phenanthrene (3aj): white solid;
yield: 80 mg (60%); mp 279.9–281.0 °C. 1H NMR (400 MHz,
CDCl3): δ = 8.80 (d, J = 8.2 Hz, 2 H), 7.71 (dd, J = 8.2, 0.9 Hz, 2 H),
7.63–7.67 (m, 2 H), 7.48–7.51 (m, 2 H), 7.17–7.20 (m, 4 H),
7.01–7.03 (m, 4 H), 1.27 (s, 18 H). 13C NMR (101 MHz, CDCl3):
δ = 149.0, 137.6, 136.6, 132.0, 130.7, 129.9, 128.0, 126.5, 126.2,
124.1, 122.5, 34.4, 31.3. HRMS (ESI): m/z calcd for [C34H34Na]+:
465.2559; found: 465.2572.
9-Phenyl-10-(2-thienyl)phenanthrene (3am): yellow solid;
yield: 64 mg (63%); mp 214.5–215.3 °C. 1H NMR (400 MHz,
CDCl3): δ = 8.79 (d, J = 8.3 Hz, 2 H), 7.78–7.80 (m, 1 H), 7.65–
7.70 (m, 2 H), 7.52–7.56 (m, 2 H), 7.46–7.50 (m, 1 H), 7.22–7.33
(m, 6 H), 6.92–6.95 (m, 1 H), 6.84–6.86 (m, 1 H). 13C NMR (101
MHz, CDCl3): δ = 140.1, 139.9, 139.5, 132.5, 131.7, 130.7, 130.4,
(18) (a) Scholl, R.; Mansfeld, J. J. Ber. Dtsch. Chem. Ges. 1910, 43, 1734.
(b) Kovacic, P.; Jones, M. B. Chem. Rev. 1987, 87, 357.
© Georg Thieme Verlag Stuttgart · New York — Synlett 2015, 26, 1991–1996

1996
J. Ma et al.
Letter
Synlett
129.9, 129.6, 129.2, 128.2, 127.6, 127.6, 126.9, 126.9, 126.8,
126.7, 126.6, 126.3, 126.0, 122.5, 122.4. HRMS (ESI): m/z calcd
for [C24H16SNa]+: 359.0871; found: 359.0872.
9-(2-Methoxyphenyl)-2,3,6,7-tetramethyl-10-phenyl-
phenanthrene (3bd): faint yellow solid; yield: 12 mg (10%); mp
203.5–204.8 °C. 1H NMR (400 MHz, CDCl3): δ = 8.50 (d, J = 5.4
Hz, 2 H), 7.12–7.21 (m, 8 H), 7.01 (dd, J = 7.4, 1.7 Hz, 1 H), 6.82–
6.84 (m, 1 H), 6.75 (d, J = 8.2 Hz, 1 H), 3.56 (s, 3 H), 2.53 (s, 3 H),
2.52 (s, 3 H), 2.30 (s, 6 H). 13C NMR (101 MHz, CDCl3): δ = 157.4,
140.4, 136.2, 135.3, 135.2, 135.1, 135.0, 132.6, 132.5, 130.9,
130.2, 130.1, 129.1, 128.3, 128.2, 128.1, 127.6, 127.3, 127.2,
127.1, 126.2, 122.7, 119.9, 110.3, 55.2, 20.5, 20.4, 20.2, 20.1.
HRMS (ESI): m/z calcd for [C31H28ONa]+: 439.2038; found:
439.2036.
4-(10-Phenylphenanthren-9-yl)pyridine (3ao): faint yellow
solid; yield: 57 mg (57%); mp 235.8–236.8 °C. 1H NMR (400
MHz, CDCl3): δ = 8.75 (dd, J = 8.3, 4.9 Hz, 2 H), 8.42 (dd, J = 4.5,
1.4 Hz, 2 H), 7.60–7.65 (m, 2 H), 7.37–7.50 (m, 4 H), 7.16–7.22
(m, 3 H), 7.01–7.08 (m, 4 H). 13C NMR (101 MHz, CDCl3): δ =
149.2, 148.2, 138.6, 137.3, 134.4, 131.5, 130.8, 130.5, 130.2,
128.1, 128.0, 127.9, 127.1, 127.1, 127.0, 127.0, 126.9, 126.8,
126.3, 122.8, 122.6. HRMS (ESI): m/z calcd for [C25H17NNa]+:
354.1259; found: 354.1265.
9-(p-Tolyl)-2,3,6,7-tetramethyl-10-phenylphenanthrene
(3bb): faint yellow solid; yield: 60 mg (50%); mp 249.9–251.1
°C. 1H NMR (400 MHz, CDCl3): δ = 8.50 (s, 2 H), 7.11–7.24 (m, 7
H), 7.00 (s, 4 H), 2.52 (s, 6 H), 2.31 (s, 3 H), 2.30 (s, 6 H). 13C NMR
(101 MHz, CDCl3): δ = 140.3, 136.9, 135.9, 135.9, 135.5, 135.3,
135.3, 135.2, 131.2, 131.0, 130.3, 130.2, 128.2, 128.1, 128.1,
127.8, 127.7, 127.4, 126.1, 122.7, 29.7, 21.3, 20.4, 20.2, 20.2.
HRMS (ESI): m/z calcd for [C31H28Na]+: 423.2089; found:
423.2089.
9-(3-Methoxyphenyl)-2,3,6,7-tetramethyl-10-phenyl-
phenanthrene (3bc): faint yellow solid; yield: 42 mg (34%); mp
149.1–150.3 °C. 1H NMR (400 MHz, CDCl3): δ = 8.56 (s, 2 H),
7.37 (s, 1 H), 7.23–7.31 (m, 7 H), 6.72–6.82 (m, 3 H), 3.72 (s, 3
H), 2.58 (s, 6 H), 2.36 (d, J = 6.0 Hz, 6 H). 13C NMR (101 MHz,
CDCl3): δ = 158.8, 141.4, 140.1, 135.7, 135.7, 135.4, 135.4, 135.3,
131.1, 131.1, 130.1, 129.9, 128.4, 128.1, 128.1, 127.8, 127.8,
127.6, 127.4, 126.3, 123.9, 122.7, 116.6, 112.2, 55.2, 21.6, 20.5,
20.2, 15.4. HRMS (ESI): m/z calcd for [C31H28ONa]+: 439.2038;
found: 439.2035.
(20) Dibenzochryenes 4aa and 4ab; General Procedure: A dried
flask was charged with 9,10-disubstituted phenanthrene (0.4
mmol), CuCl2 (270 mg, 2.0 mmol) and AlCl3 (267 mg, 2.0 mmol)
under argon, and CS2 (5 mL) was added by a syringe. The
mixture was stirred at r.t. until the reaction was complete. The
mixture was diluted with CH2Cl2 and filtered through a plug of
silica gel. The solvents were then removed under reduced pres-
sure to provide a crude product, which was further purified by
silica gel column chromatography (silica gel, PE–EtOAc).
Palladium-Catalyzed Annulation of 2,2′-Dibromobiphenyls
with Alkynes; Synthesis of Functionalized Phenanthrenes
and Dibenzochrysenes:
A palladium-catalyzed annulation
process of 2,2′-dibromobiphenyls with alkynes for the synthesis
of functionalized phenanthrenes was realized. The electron-
deficient heteroaromatic-substituted acetylenes are capable of
the annulation process. Thiophene-fused and pyridine-fused
PAHs can also be synthesized easily. This methodology also pro-
vides a highly efficient and low-cost approach to dibenzochry-
sene derivatives starting from simple commercially available
reactants in two steps.
© Georg Thieme Verlag Stuttgart · New York — Synlett 2015, 26, 1991–1996