A fully palladium-mediated construction of phenanthrenes and naphthoxindoles

Article abstract of DOI:10.1002/ejoc.201100477

A fully palladium-catalyzed synthesis of unusual naphthoxindole alkaloids through a key intramolecular direct C-H arylation step leading to the formation of the phenanthrene core is described. The three-step process involves a highly efficient Heck coupli

Full text of DOI:10.1002/ejoc.201100477

FULL PAPER
DOI: 10.1002/ejoc.201100477
A Fully Palladium-Mediated Construction of Phenanthrenes and
Naphthoxindoles
Luma Nassar-Hardy,[a] Christophe Deraedt,[a] Eric Fouquet,[a] and François-Xavier Felpin*[a]
Keywords: C-H activation / Cyclization / Fused-ring systems / Heck reaction / Palladium
A fully palladium-catalyzed synthesis of unusual naphth-
oxindole alkaloids through a key intramolecular direct C–H
arylation step leading to the formation of the phenanthrene
core is described. The three-step process involves a highly
efficient Heck coupling of aryl diazonium salts with phenyl-
acrylates, giving the corresponding cis-stilbenes. Cyclization
of stilbenes into phenanthrenes through a direct intramolecu-
lar C–H arylation, followed by a palladium-mediated cycliza-
tion of an amino ester, led to the formation of novel naphth-
oxindoles.
Introduction
The phenanthrene nucleus constitutes an important class
of polycyclic aromatic hydrocarbons that is extensively
found in natural products and biologically active com-
pounds.[1] It has also been widely used in material science
with photophysical applications.[2] As a consequence, there
are a variety of available methods for the preparation of
phenanthrene-based compounds.[3] Among these strategies,
the cyclization of stilbene derivatives into the corresponding
phenanthrenes is currently the preferred approach. For in- Scheme 1. General strategy for the preparation of naphthoxindoles.
stance, oxidative cyclizations have been widely described,
but most require electron-rich substrates.[4] Photocycliza-
tions in the presence of an oxidant such as iodine have also
been reported; however, this approach suffers from modest
group compatibility, although an improved protocol has re-
cently been published that overcomes this lack of general-
ity.[5] Wang and co-workers also recently reported an ele-
gant total synthesis of papilistatin that involved the radical
cyclization of a bromostilbene intermediate with a modest
yield (30%).[6] In contrast, until now, cyclization of stilbenes
by direct C–H arylation has mostly been overlooked.[7] In
the context of a medicinal chemistry project, we wish to
Figure 1. Natural products related to the target naphthoxindoles.
report our latest investigations, which ultimately led to the
preparation of naphthoxindoles E through a fully palla- Results and Discussion
dium-catalyzed, three-step process, as illustrated in
Our studies started with the preparation of a variety of
Scheme 1. Naphthoxindoles are unusual tetracyclic con-
bromo-stilbenes 4–12 by the coupling of aryl diazonium
structions that are structurally related to various biolo-
salts with (2-nitrophenyl)acrylates (Table 1),[8] according to
gically active natural products (Figure 1).
our recently published procedure.[9] The reaction, which
was carried out in MeOH at room temperature, proceeds
with good to excellent yields under ligand-free and base-
free conditions. The simplicity and the robustness of the
catalytic system makes this protocol highly reproducible,
even for non-specialized chemists. We also prepared stilb-
[a] Université de Bordeaux, CNRS-UMR 5255, Institut des
Sciences Moléculaires (ISM),
351, Cours de la Libération, 33405 Talence, France
Fax: +33-5-40006286
E-mail: fx.felpin@ism.u-bordeaux1.fr
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© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Phenanthrenes and Naphthoxindoles
enes 10–12, which do not bear a nitro group, to evaluate were ineffective for the desired transformation (Table 2, En-
the scope of the direct C–H arylation, although these com- tries 1–5).[11] Even the use of Pearlman’s catalyst [Pd(OH)2/
pounds could not be further transformed into the target C], which has previously been successfully used for the C–
naphthoxindoles. It was observed that the preparation of H arylation of heterocycles,[12] was inactive with this sub-
cyano-stilbene 10 required higher palladium loading. We strate. In contrast, the use of Pd(OAc)2 (10 mol-%) fur-
assumed that strong complexation of cationic palladium in- nished phenanthrene 13 with good yield in dimethylacet-
termediates with the cyano group could explain this lower amide (DMAc) with K2CO3 as base at 130 °C (Table 2, En-
activity. As expected, complete control of the olefin geome- try 6). Decreasing the palladium loading to 2 mol-% slightly
try in favor of the cis-stilbenes was consistently obtained, improved the yield, but a lower loading (1 mol-%) was det-
1
and the trans-stilbenes were never observed by H NMR rimental for the conversion (Table 2, Entry 9). A large im-
analysis of the crude reaction mixture. The E geometry of pact of the base on the reaction outcome was observed;
cis-stilbenes prepared in this study was assigned by analyz- K2CO3 was by far superior to AcOK, Na2CO3, and tBuOK
1
ing the H NMR shift of the olefinic proton (ca. 8 ppm vs. (Table 2, Entries 8 vs. 10–12). The choice of solvent was
ca. 7 ppm for the Z isomer) and by analogy with structur- also found to be critical; DMAc proved to be more effective
ally related stilbenes previously prepared in our laboratory. than both N-methyl-2-pyrrolidinone (NMP) and N,N-di-
This behavior was rationalized by DFT calculations[9] that methylformamide (DMF), whereas no conversion was ob-
showed that a lower activation barrier is predicted for struc- served with either xylene or dioxane (Table 2, Entries 13–
tures having the two phenyl groups in a cis relation in the 16). The temperature also considerably impacted the reac-
transition state, which leads to the corresponding cis-stilb- tion outcome and the reagent stability; at 150 °C, extensive
ene.
decomposition products were observed (Table 2, Entry 17),
whereas at 90 °C the conversion was rather low (Table 2,
Entry 19). After careful optimization, we found that, for
this substrate, the reaction was best performed at 110 °C
(Table 2, Entry 17). Because we were still interested in per-
forming this transformation with a heterogeneous catalyst,
Table 1. Preparation of stilbenes by Heck coupling.
Table 2. Optimization studies of the intramolecular direct C–H
arylation.
Entry
Palladium Loading Solvent
[mol-%]
Base
(3 equiv.) [°C]
T
Yield
[%][a]
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20[c]
21[d]
PII/Ceggshell
PII/Cuniform
P0/Ceggshell
P0/Cuniform
Pd(OH)2
10
10
10
10
10
10
5
2
1
2
2
2
2
2
2
2
2
2
2
DMAc
DMAc
DMAc
DMAc
DMAc
DMAc
DMAc
DMAc
DMAc
DMAc
DMAc Na2CO3 130
DMAc
DMF
Xylene
Dioxane K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
AcOK
130
130
130
130
130
130
130
130
130
130
(Ͻ5)
0
0
0
(Ͻ5)
70
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
72
74
(50)
63
(32)
(98)[b]
(72)
66
0
0
31
75
tBuOK
K2CO3
K2CO3
130
130
130
130
130
150
110
90
With a set of bromo-stilbenes 4–12 in hand, the direct
C–H arylation step was then studied. The optimization tri-
als were conducted with stilbene 4 as the model substrate
(Table 2). Because direct C–H arylation of non-heterocyclic
substrates frequently require high palladium loading (typi-
cally more than 5 mol-%),[10] we initially screened hetero-
geneous palladium sources so that the palladium metal
could be recovered after completion (Table 2). Unfortu-
DMAc
DMAc
DMAc
DMAc
DMAc
DMAc
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
(38)
78
86
2
2
110
110
[a] Yield of isolated product. Conversion in parentheses, estimated
by H NMR spectroscopic analysis. [b] The starting material was
completely degraded. [c] Charcoal was added. [d] Charcoal and
1
nately, all the charcoal-supported palladium catalysts tested PCy3 were added.
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F.-X. Felpin et al.
FULL PAPER
we added charcoal to the reaction mixture and found that tilled DMAc was used, only the unexpected and highly un-
the yield was slightly improved (Table 2, Entry 20). Interest- stable quinone 21 was observed (52% yield) along with de-
ingly, the use of PCy3 as ligand, in the presence of charcoal, gradation products. On the other hand, with twice-distilled
led to a much cleaner crude reaction mixture and to the DMAc we were able to isolate the target phenanthrene 22
isolation of 13 in 86% yield (Table 2, Entry 21). We believe with modest yield (33%) along with a trace of quinone 21.
that charcoal acts as a stabilizer for active palladium species The mode of formation of quinone 21 is still unclear at this
and as a sponge for inactive species that would otherwise time; however, in the absence of palladium we did not ob-
form palladium black. ICP-MS analysis of the crude mix- serve its formation. We assume that a push–pull effect
ture after simple filtration showed that at least 80% of the would give a highly hydrolyzable intermediate 23, which
palladium initially introduced was adsorbed on the char- would ultimately furnish quinone 21 in the presence of
coal, allowing its recovery for further reprocessing.
water (Scheme 3).
We then applied the optimized conditions to the set of
bromo-stilbenes 4–12 (Table 3). A higher palladium loading
was required for the intramolecular C–H arylation of stil-
bene 6 leading to phenanthrene 15 due to the competitive
palladium-mediated debromination reaction that was ob-
served at a lower loading. In the absence of phosphane, the
protocol was found to be selective for reaction at the bro-
mine atom; no reaction occurred at the chlorine atom on
substrate 8. However, it should be noted that the use of
PCy3 with stilbene 8 led to a much lower yield of 17 (56 vs.
80%) due to side-reactions at the chlorine atom. As already
noted for the Heck reaction, the cyano-substituted stilbene
10 was much less reactive and required a higher palladium
loading for optimal conversion and good yield of 18. The
case of the methoxylated stilbene 9 was quite interesting,
because the major reaction product was highly dependent
on the quality of the DMAc used (Scheme 2). When undis-
Scheme 2. Unexpected formation of quinone 21 in undistilled
DMAc.
Table 3. Scope of the intramolecular direct C–H arylation.
Scheme 3. Mechanistic rationale for the formation of quinone 21.
Lastly, phenanthrenes 13–17 and 22 were converted with
good yields into the target naphthoxindoles 24–29 through
a palladium-mediated reductive cyclization (Table 4). This
step was conducted according to an extension of our re-
cently published procedure for the hydrogenation of olefins
and the hydrogenolysis of benzyl ethers.[13] The catalytic
system proceeds through the formation of a highly active
Pd0/C catalyst that was prepared in situ from Pd(OAc)2 and
charcoal. This strategy allows the use of low palladium
loadings and avoids the need to handle pyrophoric Pd/C
catalysts. ICP-MS analyses of the crude mixtures after a
single filtration showed only trace amounts (2–3 ppb) of re-
sidual palladium species in the supernatant, which means
that more than 99.9% of the palladium initially introduced
was adsorbed on the charcoal.
[a] PCy3 was omitted.
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Phenanthrenes and Naphthoxindoles
Methyl (E)-3-(2-Bromophenyl)-2-(2-nitrophenyl)acrylate (4): Purifi-
Table 4. Preparation of naphthoxindoles.
cation by flash chromatography (15% EtOAc/petroleum ether) gave
the desired product 4 as a white solid (300 mg, 83%). M.p. 143 °C.
1
IR (KBr): ν = 1527, 1709, 2956, 3064 cm–1. H NMR (300 MHz,
˜
CDCl3): δ = 3.77 (s, 3 H), 6.39 (dd, J = 1.1, 7.56 Hz, 1 H), 6.95 (t,
J = 7.9 Hz, 1 H), 7.01–7.09 (m, 2 H), 7.38–7.48 (m, 2 H), 7.56 (d,
J = 7.9 Hz, 1 H), 8.05 (s, 1 H), 8.16 (dd, J = 2.3, 6.8 Hz, 1 H) ppm.
13C NMR (75 MHz, CDCl3): δ = 52.5, 124.6, 127.0, 129.1, 130.1,
130.8, 131.2, 132.6, 132.9, 133.6, 135.2, 139.5, 149.0, 165.6 ppm.
HRMS (ESI): calcd. for C16H12NO4NaBr [M + Na]+ 383.9841;
found 383.9848.
Methyl (E)-3-(2-Bromo-5-methylphenyl)-2-(2-nitrophenyl)acrylate
(5): Purification by flash chromatography (20% EtOAc/petroleum
ether) gave the desired product 5 as a yellow solid (371 mg, 99%).
M.p. 103–104 °C. IR (KBr): ν = 1526, 1718, 2923, 2952, 3031,
˜
3066 cm–1. 1H NMR (300 MHz, CDCl3): δ = 2.24 (s, 3 H), 3.76 (s,
3 H), 6.61 (d, J = 7.9 Hz, 1 H), 6.75 (d, J = 7.9 Hz, 1 H), 7.03–
7.06 (m, 1 H), 7.40–7.49 (m, 3 H), 8.04 (s, 1 H), 8.16 (m, 1 H) ppm.
13C NMR (75 MHz, CDCl3): δ = 20.9, 52.5, 124.7, 124.8, 128.0,
129.2, 130.6, 131.5, 131.9, 132.1, 133.0, 133.2, 133.7, 139.5, 140.9,
149.1, 165.9 ppm. HRMS (ESI): calcd. for C17 H14NO4NaBr [M +
Na]+ 397.9998; found 397.9999.
Methyl (E)-3-(2-Bromo-4-isopropylphenyl)-2-(2-nitrophenyl)acrylate
(6): Purification by flash chromatography (20% EtOAc/petroleum
ether) gave the desired product 6 as a yellow solid (315 mg, 78%).
M.p. 125 °C. IR (KBr): ν = 1526, 1717, 2870, 2962, 3030,
˜
Conclusions
1
3066 cm–1. H NMR (200 MHz, CDCl3): δ = 1.16 (d, J = 6.9 Hz,
We have reported a novel route to naphthoxindole alka-
loids. Our approach entails a fully palladium-catalyzed,
three-step sequence composed of a Heck coupling of diazo-
nium salts, direct C–H arylation, and a reductive cycliza-
tion. The direct C–H arylation was carried out in the pres-
ence of charcoal, which stabilizes active palladium species
and adsorbs unstable palladium particles that would other-
wise form palladium black. Such a protocol allows the
preparation of naphthoxindoles with only parts-per-billion
levels of palladium contamination. We believe that this
study would be of interest to synthetic chemists involved in
palladium catalysis as well as to medicinal chemists con-
cerned by the contamination of biologically active com-
pounds with palladium residues. Moreover, this study pro-
vides access to structurally intriguing naphthoxindoles.
6 H), 2.78 (sept, J = 6.9 Hz, 1 H), 3.76 (s, 3 H), 6.64 (d, J = 8.1 Hz,
1 H), 6.80 (dd, J = 1.7, 8.1 Hz, 1 H), 7.05–7.09 (m, 1 H), 7.40–7.50
(m, 3 H), 8.06 (s, 1 H), 8.13–8.21 (m, 1 H) ppm. 13C NMR
(75 MHz, CDCl3): δ = 23.5, 33.6, 52.5, 124.6, 125.0, 125.4, 129.1,
130.6, 130.7, 131.5, 131.7, 132.2, 132.9, 133.6, 139.4, 149.0, 151.7,
165.8 ppm. HRMS (ESI): calcd. for C19H18NO4NaBr [M + Na]+
426.0311; found 426.0317.
Methyl (E)-3-[2-Bromo-5-(trifluoromethyl)phenyl]-2-(2-nitrophenyl)-
acrylate (7): Purification by flash chromatography (20% EtOAc/
petroleum ether) gave the desired product 7 as a yellow solid
(417 mg, 97%). M.p. 104–105 °C. IR (KBr): ν = 1550, 1605, 1723,
˜
1
2955, 3072 cm–1. H NMR (300 MHz, CDCl3): δ = 3.79 (s, 3 H),
6.95 (s, 1 H), 6.99–7.02 (m, 1 H), 7.30 (dd, J = 2.2, 8.4 Hz, 1 H),
7.44–7.49 (m, 2 H), 7.70 (d, J = 8.3 Hz, 1 H), 8.03 (s, 1 H), 8.17
(dd,
J = 1.8, 7.4 Hz, 1 H) ppm. HRMS (ESI): calcd. for
C17H11NO4F3NaBr [M + Na]+ 451.9715; found 451.9713.
Methyl (E)-3-(2-Bromo-4-chlorophenyl)-2-(2-nitrophenyl)acrylate
(8): Purification by flash chromatography (20% EtOAc/petroleum
ether) gave the desired product as a yellow solid 8 (356 mg, 90%).
Experimental Section
M.p. 91–93 °C. IR (KBr): ν = 1527, 1580, 1719, 2952, 3068 cm–1.
˜
1H NMR (200 MHz, CDCl3): δ = 3.75 (s, 3 H), 6.68 (d, J = 8.4 Hz,
1 H), 6.92–7.04 (m, 2 H), 7.41–7.51 (m, 2 H), 7.57 (s, 1 H), 7.97 (s,
1 H), 8.13–8.18 (m, 1 H) ppm. 13C NMR (75 MHz, CDCl3): δ =
52.6, 124.7, 125.0, 127.4, 129.4, 131.8, 131.4, 132.3, 132.7, 133.1,
133.7, 135.2, 138.1, 149.0, 165.4 ppm. HRMS (ESI): calcd. for
C16H11NO4NaClBr [M + Na]+ 417.9452; found 419.9428.
General Remarks: NMR chemical shifts are reported in ppm rela-
tive to CDCl3 at δ = 7.26 ppm (1H) or 77.0 ppm (13C). IR spectra
were recorded as neat samples on NaCl plates or with KBr pellets.
Yields refer to isolated material determined to be pure by NMR
spectroscopy and thin layer chromatography (TLC), unless speci-
fied otherwise in the text. Diazonium salts used in this study are all
known compounds and were prepared as described in the literature.
DARCO G-60 activated charcoal with a 100 mesh particle size, pro-
duced from lignin, was used.
Methyl (E)-3-(2-Bromo-4-methylphenyl)-2-(4,5-dimethoxy-2-nitro-
phenyl)acrylate (9): Purification by flash chromatography (20%
EtOAc/petroleum ether) gave the desired product 9 as a brown solid
General Procedure for the Preparation of Stilbenes 4–12: Acrylate
(1 mmol) and Pd(OAc)2 (0.25–3.5 mol-%, see Table 1) were added
(384 mg, 88%). M.p. 128–129 °C. IR (KBr): ν = 1520, 1573, 1604,
˜
1629, 1714, 2837, 2954, 3005, 3065, 3093 cm–1. 1H NMR
to a solution of diazonium salt (1.3–1.5 mmol) in MeOH (6 mL) (300 MHz, CDCl3): δ = 2.11 (s, 3 H), 3.54 (s, 3 H), 3.64 (s, 3 H),
at 25 °C. The resulting mixture was stirred for 18 h and then con-
centrated under reduced pressure. The crude product was purified
by flash chromatography to give the corresponding product.
3.83 (s, 3 H), 6.32 (s, 1 H), 6.53 (d, J = 8.1 Hz, 1 H), 6.68 (d, J =
8.5 Hz, 1 H), 7.26 (s, 1 H), 7.65 (s, 1 H), 7.83 (s, 1 H) ppm. 13C
NMR (75 MHz, CDCl3): δ = 20.4, 52.0, 55.9, 107.2, 113.5, 123.8,
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F.-X. Felpin et al.
FULL PAPER
125.4, 127.8, 130.0, 132.1, 132.5, 132.6, 138.1, 140.3, 141.0, 148.2,
152.8, 165.5 ppm. HRMS (ESI): calcd. for C19H18NO6NaBr [M +
Na]+ 458.0209; found 458.0217.
(dd, J = 7.9, 8.3 Hz, 1 H), 7.81 (d, J = 8.1 Hz, 1 H), 8.07 (dd, J =
1.3, 7.7 Hz, 1 H), 8.32 (s, 1 H), 8.33 (s, 1 H), 8.80 (dd, J = 1.0,
8.5 Hz, 1 H) ppm. 13C NMR (75 MHz, CDCl3): δ = 22.3, 51.9,
120.8, 122.7, 123.9, 124.2, 125.5, 127.6, 128.0, 129.7, 130.1, 130.4,
132.1, 134.0, 140.1, 148.5, 167.7 ppm. HRMS (ESI): calcd. for
C17H13NO4Na [M + Na]+ 318.0736; found 318.0732.
Methyl (E)-3-(2-Bromophenyl)-2-(2-cyanophenyl)acrylate (10): Puri-
fication by flash chromatography (30% EtOAc/petroleum ether)
gave the desired product 10 as a yellow solid (335 mg, 98%). M.p.
75–76 °C. IR (KBr): ν = 1631, 1714, 2225, 2955, 3009, 3065,
˜
Methyl 3-Isopropyl-8-nitrophenanthrene-9-carboxylate (15): Purifi-
cation by flash chromatography (20% EtOAc/petroleum ether) gave
the desired product 15 as a white solid (249 mg, 77%). M.p. 155 °C.
3408 cm–1. 1H NMR (300 MHz, CDCl3): δ = 3.85 (s, 3 H), 6.63
(dd, J = 1.7, 7.9 Hz, 1 H), 6.95 (dt, J = 1.1, 7.9 Hz, 1 H), 7.07 (dt,
J = 1.9, 7.5 Hz, 1 H), 7.21 (dd, J = 1.1, 7.2 Hz, 1 H), 7.39 (dt, J =
1.5, 7.7 Hz, 1 H), 7.48 (dt, J = 1.5, 7.6 Hz, 1 H), 7.56 (dd, J = 1.1,
7.9 Hz, 1 H), 7.65 (dd, J = 1.1, 7.5 Hz, 1 H), 8.21 (s, 1 H) ppm.
13C NMR (75 MHz, CDCl3): δ = 52.4, 113.3, 117.1, 124.8, 126.6,
128.2, 130.2, 130.3, 130.9, 131.0, 132.4, 132.6, 132.6, 134.1, 138.7,
142.5, 165.8 ppm. HRMS (ESI): calcd. for C17H12NO2NaBr [M +
Na]+ 363.9943; found 365.9939.
IR (KBr): ν = 1529, 1718, 2927, 2962, 3055 cm–1. 1H NMR
˜
(300 MHz, CDCl3): δ = 1.42 (d, J = 7.0 Hz, 6 H), 3.22 (sept, J =
7.0 Hz, 1 H), 3.91 (s, 3 H), 7.63 (dd, J = 1.5, 8.3 Hz, 1 H), 7.74
(dd, J = 7.7, 8.3 Hz, 1 H), 7.94 (d, J = 8.1 Hz, 1 H), 8.15 (dd, J =
1.3, 7.7 Hz, 1 H), 8.42 (s, 1 H), 8.47 (s, 1 H), 8.97 (d, J = 8.5 Hz,
1 H) ppm. 13C NMR (75 MHz, CDCl3): δ = 24.0, 35.0, 52.0, 120.2,
121.0, 124.0, 124.4, 125.7, 127.7, 128.6, 130.1, 130.6, 132.5, 134.1,
148.7, 150.9, 167.7 ppm. HRMS (ESI): calcd. for C19H17NO4Na
[M + Na]+ 346.1049; found 346.1047.
Methyl (E)-3-(2-Bromo-4-methylphenyl)-2-o-tolylacrylate (8): Puri-
fication by flash chromatography (10% EtOAc/petroleum ether)
gave the desired product 8 as a pale-yellow oil (331 mg, 96%). IR
Methyl 8-Nitro-2-(trifluoromethyl)phenanthrene-9-carboxylate (16):
Purification by flash chromatography (10% EtOAc/petroleum
ether, then 20% EtOAc/petroleum ether) gave the desired product
16 as a white powder (269 mg, 77%). M.p. 204–205 °C. IR (KBr):
(NaCl): ν = 1598, 1622, 1714, 2953, 3021, 3060 cm–1. 1H NMR
˜
(300 MHz, CDCl3): δ = 2.22 (s, 3 H), 2.25 (s, 3 H), 3.83 (s, 3 H),
6.65 (d, J = 8.1 Hz, 1 H), 6.76 (d, J = 8.1 Hz, 1 H), 7.11–7.28 (m,
4 H), 7.44 (s, 1 H), 8.22 (s, 1 H) ppm. 13C NMR (75 MHz, CDCl3):
δ = 19.3, 20.5, 52.0, 125.1, 125.7, 127.5, 129.7, 129.9, 131.7, 132.9,
132.9, 134.6, 136.3, 139.2, 140.3, 167.5 ppm. HRMS (ESI): calcd.
for C18H17NO2NaBr [M + Na]+ 367.0304; found 367.0310.
ν = 1523, 1725, 2925, 2957, 3078 cm–1. 1H NMR (300 MHz,
˜
CDCl3): δ = 3.93 (s, 3 H), 7.85 (dd, J = 7.7, 8.3 Hz, 1 H), 8.02 (dm,
J = 8.7 Hz, 1 H), 8.25–8.30 (m, 2 H), 8.49 (s, 1 H), 8.80 (d, J =
8.7 Hz, 1 H), 8.99 (dd, J = 1.1, 8.6 Hz, 1 H) ppm. HRMS (ESI):
calcd. for C17H10NO4F3Na [M + Na]+ 372.0454; found 372.0453.
Methyl (E)-3-(2-Bromophenyl)-2-o-tolylacrylate (9): Purification by
flash chromatography (10% EtOAc/petroleum ether) gave the de-
Methyl 3-Chloro-8-nitrophenanthrene-9-carboxylate (17): Purifica-
tion by flash chromatography (20% EtOAc/petroleum ether) gave
the desired product 17 as a white solid (252 mg, 80%). M.p. 204–
sired product 9 as a pale-yellow oil (328 mg, 99%). IR (NaCl): ν =
˜
1625, 1716, 2924, 2950, 3020, 3063 cm–1. 1H NMR (200 MHz,
CDCl3): δ = 2.13 (s, 3 H), 3.82 (s, 3 H), 6.67 (dd, J = 1.6, 7.6 Hz,
1 H), 6.91 (dt, J = 1.3, 7.6 Hz, 1 H), 6.99–7.26 (m, 6 H), 7.56 (dd,
J = 1.4, 8.1 Hz, 1 H), 8.10 (s, 1 H) ppm. 13C NMR (75 MHz,
CDCl3): δ = 19.6, 52.5, 125.3, 125.9, 126.7, 128.1, 129.9, 130.0,
130.1, 130.5, 132.7, 133.9, 134.6, 135.0, 136.6, 139.6, 167.8 ppm.
HRMS (ESI): calcd. for C17H15O2NaBr [M + Na]+ 353.0147;
found 353.0161.
205 °C. IR (KBr): ν = 1531, 1615, 1709, 1730, 2924, 3098 cm–1. 1H
˜
NMR (300 MHz, CDCl3): δ = 3.92 (s, 3 H), 7.67 (dd, J = 1.9,
8.5 Hz, 1 H), 7.77 (dd, J = 7.9, 8.3 Hz, 1 H), 7.93 (d, J = 8.5 Hz,
1 H), 8.20 (dd, J = 1.1, 7.7 Hz, 1 H), 8.38 (s, 1 H), 8.59 (t, J =
1.1 Hz, 1 H), 8.83 (dd, J = 1.3, 8.8 Hz, 1 H) ppm. 13C NMR
(75 MHz, DMSO): δ = 52.0, 119.9, 123.4, 125.0, 125.4, 127.2,
128.2, 129.2, 129.5, 131.1, 131.3, 132.0, 133.2, 135.3, 147.7,
166.8 ppm. HRMS (ESI): calcd. for C16H10NO4NaCl [M + Na]+
338.0190; found 338.0186.
General Procedure for the Preparation of Phenanthrenes 13–22 from
Stilbenes 4–12: Stilbene 1–9 (1 mmol), K2CO3 (2 mmol), Pd-
(OAc)2 (2–10 mol-%), charcoal [90 wt.-%/Pd(OAc)2], and
HPCy3BF4 (4–20 mol-%) were mixed in anhydrous DMAc (6 mL).
The reaction mixture was stirred at 110 °C in a sealed tube for 15 h
and then concentrated under reduced pressure. The crude product
was purified by flash chromatography to give the corresponding
product.
Methyl 8-Cyanophenanthrene-9-carboxylate (18): Purification by
flash chromatography (20% EtOAc/petroleum ether) gave the de-
sired product 18 as a white solid (183 mg, 70%). M.p. 129–130 °C.
1
IR (KBr): ν = 1726, 2221, 2923, 2953, 3003, 3039 cm–1. H NMR
˜
(300 MHz, CDCl3): δ = 4.1 (s, 3 H), 7.67–7.80 (m, 3 H), 7.93 (d, J
= 7.8 Hz, 1 H), 8.02 (d, J = 7.4 Hz, 1 H), 8.15 (s, 1 H), 8.61 (d, J
= 8.3 Hz, 1 H), 8.92 (d, J = 8.5 Hz, 1 H) ppm. 13C NMR (75 MHz,
CDCl3): δ = 52.7, 109.8, 118.3, 122.7, 126.4, 127.7, 127.8, 128.2,
128.3, 129.2, 129.6, 130.2, 130.5, 131.3, 132.1, 134.9, 168.9 ppm.
HRMS (ESI): calcd. for C17H11NO2Na [M + Na]+ 284.0681; found
284.0677.
Methyl 8-Nitrophenanthrene-9-carboxylate (13): Purification by
flash chromatography (25% EtOAc/petroleum ether) gave the de-
sired product 13 as a yellow solid (241 mg, 86%). M.p. 140 °C. IR
(KBr): ν = 1523, 1712, 2942, 2993, 3040 cm–1. 1H NMR (300 MHz,
˜
CDCl3): δ = 3.92 (s, 3 H), 7.63–7.76 (m, 3 H), 7.92 (d, J = 7.9 Hz,
1 H), 8.10 (d, J = 7.7 Hz, 1 H), 8.37 (s, 1 H), 8.54 (d, J = 8.3 Hz,
1 H), 8.83 (d, J = 8.5 Hz, 1 H) ppm. 13C NMR (75 MHz, CDCl3):
δ = 52.0, 120.6, 122.8, 124.0, 125.2, 125.9, 127.7, 128.4, 129.6,
129.8, 130.0, 130.2, 132.4, 134.0, 148.5, 167.5 ppm. HRMS (ESI):
calcd. for C16H11NO4Na [M + Na]+ 304.0580; found 304.0581.
Methyl 3,8-Dimethylphenanthrene-9-carboxylate (19): Purification
by flash chromatography (5% EtOAc/petroleum ether) gave the de-
sired product 19 as a white solid (185 mg, 70%). M.p. 116–117 °C.
IR (KBr): ν = 1710, 2948, 2970, 3018, 3058 cm–1. 1H NMR
˜
(300 MHz, CDCl3): δ = 2.63 (s, 6 H), 4.00 (s, 3 H), 7.42–7.48 (m,
2 H), 7.57 (dd, J = 7.1, 8.1 Hz, 1 H), 7.78 (d, J = 8.1 Hz, 1 H),
7.90 (s, 1 H), 8.46 (s, 1 H), 8.62 (d, J = 8.3 Hz, 1 H) ppm. 13C
NMR (75 MHz, CDCl3): δ = 22.1, 22.3, 52.6, 121.1, 122.7, 126.6,
Methyl 3-Methyl-8-nitrophenanthrene-9-carboxylate (14): Purifica-
tion by flash chromatography (20% EtOAc/petroleum ether, then
30% EtOAc/petroleum ether) gave the desired product 14 as a yel-
low solid (278 mg, 94%). M.p. 180–181 °C. IR (KBr): ν = 1512, 127.5, 127.6, 128.6, 128.7, 128.8, 129.0, 130.2, 131.1, 131.6, 134.5,
˜
1526, 1708, 1733, 2923, 2950 cm–1. 1H NMR (300 MHz, CDCl3):
δ = 2.61 (s, 3 H), 3.91 (s, 3 H), 7.49 (dd, J = 1.1, 8.1 Hz, 1 H), 7.62 [M + Na]+ 287.1042; found 287.1051.
138.1, 171.9 ppm. HRMS (ESI): calcd. for C18H16O2Na
4620
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© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2011, 4616–4622

Phenanthrenes and Naphthoxindoles
Methyl 8-Nitrophenanthrene-9-carboxylate (20): Purification by
flash chromatography (5% EtOAc/petroleum ether, then 10%
EtOAc/petroleum ether) gave the desired product 20 as a white so-
δ = 1.43 (d, J = 7.0 Hz, 6 H), 3.22 (sept, J = 7.0 Hz, 1 H), 7.11 (d,
J = 7.3 Hz, 1 H), 7.56–7.61 (m, 2 H), 8.07 (d, J = 8.5 Hz, 1 H),
8.12 (d, J = 8.3 Hz, 1 H), 8.42 (s, 1 H), 8.45 (s, 1 H), 9.28 (s, 1
lid (150 mg, 60%). M.p. 70 °C. IR (KBr): ν = 1712, 2942, 2968, H) ppm. 13C NMR (75 MHz, CDCl3): δ = 24.0, 34.7, 106.9, 115.9,
˜
3058 cm–1. 1H NMR (200 MHz, CDCl3): δ = 2.66 (s, 3 H), 4.02 (s, 120.5, 122.9, 124.3, 126.4, 126.9, 127.3, 128.6, 131.7, 131.9, 132.5,
3 H), 7.48 (dm, J = 6.5 Hz, 1 H), 7.56–7.74 (m, 3 H), 7.89 (dd, J
= 1.6, 7.6 Hz, 1 H), 7.94 (s, 1 H), 8.65 (app. t, J = 8.1 Hz, 2 H) ppm.
13C NMR (75 MHz, CDCl3): δ = 22.0, 52.6, 121.1, 122.9, 126.8,
127.0, 127.3, 128.1, 128.9, 129.0, 129.6, 129.7, 130.3, 131.4, 131.6,
171.8 ppm. HRMS (ESI): calcd. for C17H14O2Na [M + Na]+
273.0886; found 273.0895.
137.5, 150.4, 170.2 ppm. HRMS (ESI): calcd. for C18H15NONa [M
+ Na]+ 284.1045; found 284.1046.
8-(Trifluoromethyl)naphtho[3,2,1-cd]indol-5(4H)-one (27): Purifica-
tion by flash chromatography (5% EtOAc/CH2Cl2) gave the desired
product 27 as a yellow powder (241 mg, 84%). M.p. 234–235 °C.
1
IR (KBr): ν = 1624, 1701, 2924, 3025, 3072, 3172 cm–1. H NMR
˜
(200 MHz, [D8]THF): δ = 7.07 (d, J = 7.3 Hz, 1 H), 7.63 (app. t, J
= 7.3 Hz, 1 H), 8.03 (dd, J = 1.8, 8.5 Hz, 1 H), 8.21 (d, J = 8.4 Hz,
1 H), 8.54 (s, 1 H), 8.63 (s, 1 H), 8.92 (d, J = 8.7 Hz, 1 H), 9.89
Methyl 6-Methoxy-3-methyl-5,8-dioxo-5,8-dihydrophenanthrene-9-
carboxylate (21): Purification by flash chromatography (40%
EtOAc/petroleum ether) gave the desired product 21 as a very un-
1
(br. s,
1 H) ppm. HRMS (ESI): calcd. for C16H8NONaF3
stable yellow solid (161 mg, 52%). H NMR (200 MHz, CDCl3): δ
[M + Na]+ 288.0630; found 288.0593.
= 2.60 (s, 3 H), 3.90 (s, 3 H), 4.06 (s, 3 H), 7.48 (d, J = 8.1 Hz, 1
H), 7.81 (d, J = 7.9 Hz, 1 H), 7.87 (s, 1 H), 8.24 (s, 1 H), 9.37 (s,
1 H) ppm. MS (ESI): m/z = 310 [M]+, 296 [M – CH2]+.
9-Chloronaphtho[3,2,1-cd]indol-5(4H)-one (28): Purification by
flash chromatography (10% EtOAc/CH2Cl2), gave the desired
product 28 as a yellow powder (225 mg, 89%). M.p. 301 °C (dec.).
Methyl 5,6-Dimethoxy-3-methyl-8-nitrophenanthrene-9-carboxylate
(22): Purification by flash chromatography (20% EtOAc/petroleum
ether) gave the desired product 22 as a white solid (117 mg, 33%
IR (KBr): ν = 1603, 1630, 1717, 3093, 3186 cm–1. 1H NMR
˜
(200 MHz, DMSO): δ = 7.11 (d, J = 7.2 Hz, 1 H), 7.64 (dd, J =
7.3, 8.4 Hz, 1 H), 7.81 (dd, J = 2.0, 8.5 Hz, 1 H), 8.32 (d, J =
8.4 Hz, 1 H), 8.38 (d, J = 8.7 Hz, 1 H), 8.56 (s, 1 H), 8.91 (d, J =
2.0 Hz, 1 H), 10.9 (br. s, 1 H) ppm. 13C NMR (75 MHz DMSO):
δ = 107.3, 115.8, 122.4, 123.3, 125.7, 125.9, 125.9, 127.6, 129.7,
131.7, 132.7, 133.7, 134.4, 138.6, 168.2 ppm. HRMS (ESI): calcd.
for C15H8NONaCl [M + Na]+ 276.0186; found 276.0180.
yield). M.p. 173–175 °C. IR (KBr): ν = 1514, 1526, 1705, 2955,
˜
3091 cm–1. 1H NMR (200 MHz, CDCl3): δ = 2.63 (s, 3 H), 3.89 (s,
3 H), 3.99 (s, 3 H), 4.09 (s, 3 H), 7.53 (d, J = 8.1 Hz, 1 H), 7.84 (d,
J = 7.9 Hz, 1 H), 7.94 (s, 1 H), 8.24 (s, 1 H), 9.42 (s, 1 H) ppm.
13C NMR (75 MHz, CDCl3): δ = 22.7, 52.0, 56.8, 60.3, 110.6,
117.5, 124.1, 126.6, 127.8, 128.9, 129.7, 129.8, 130.0, 133.3, 139.9,
144.1, 150.2, 151.1, 167.7 ppm. HRMS (ESI): calcd. for
C19H17NO6Na [M + Na]+ 378.0948; found 378.0955.
1,2-Dimethoxy-9-methylnaphtho[3,2,1-cd]indol-5(4H)-one (29): Pu-
rification by flash chromatography (40% EtOAc/petroleum ether,
then 10% EtOAc/CH2Cl2), gave the desired product 29 as a yellow
General Procedure for the Preparation of the Naphthoxindoles 21–
26: Phenanthrene 10–19 (1 mmol), Pd(OAc)2 (0.5–1.5 mol-%), and
charcoal [90 wt.-%/Pd(OAc)2] were mixed in MeOH (6 mL). The
reaction mixture was stirred at 40 °C under H2 for 18 h, then con-
centrated under reduced pressure, and the crude product was puri-
fied by flash chromatography to give the corresponding product.
powder (208 mg, 71%). M.p. 219–221 °C. IR (KBr): ν = 1635,
˜
1701, 2939, 3061, 3088, 3191 cm–1. 1H NMR (300 MHz, CDCl3):
δ = 2.67 (s, 3 H), 4.02 (s, 3 H), 4.05 (s, 3 H), 6.94 (s, 1 H), 7.53
(dm, J = 8.1 Hz, 1 H), 8.02 (d, J = 8.3 Hz, 1 H), 8.18 (br. s, 1 H),
8.29 (s, 1 H), 9.20 (s, 1 H) ppm. 13C NMR (75 MHz DMSO): δ =
22.1, 57.0, 59.8, 96.9, 116.4, 120.1, 124.7, 126.6, 128.7, 130.9, 131.7,
131.8, 134.9, 139.1, 140.5, 153.4, 168.8 ppm. HRMS (ESI): calcd.
for C18H15NO3Na [M + Na]+ 316.0944; found 316.0949.
Naphtho[3,2,1-cd]indol-5(4H)-one (24): Purification by flash
chromatography (silica gel; 15% EtOAc/CH2Cl2), gave the desired
product 24 (195 mg, 89%) as yellow powder. M.p. 230–231 °C. IR
(KBr): ν = 1628, 1707, 2929, 3031, 3069, 3192 cm–1. 1H NMR
˜
(300 MHz, DMSO): δ = 7.09 (d, J = 7.1 Hz, 1 H), 7.63 (dd, J =
7.4, 8.3 Hz, 1 H), 7.76 (app. t, J = 8.1 Hz, 1 H), 7.87 (app. t, J =
7.1 Hz, 1 H), 8.25 (d, J = 8.3 Hz, 1 H), 8.34 (d, J = 8.0 Hz, 1 H),
8.52 (s, 1 H), 8.80 (d, J = 8.1 Hz, 1 H) ppm. 13C NMR (75 MHz
DMSO): δ = 106.6, 115.5, 122.0, 123.7, 125.4, 126.4, 126.5, 127.2,
129.3, 129.4, 131.4, 131.9, 133.1, 138.4, 168.3 ppm. HRMS (ESI):
calcd. for C15H9NONa [M + Na]+ 242.0576; found 242.0575.
Acknowledgments
We gratefully aknowledge the “Université de Bordeaux”, the “Cen-
tre National de la Recherche Scientifique (CNRS)”, and the “Ag-
ence Nationale de la Recherche” (ANR JCJC 7141) for the finan-
cial support of this project. We thank M. Olivier Bruguier (Uni-
versité de Montpellier) for ICP-MS analyses.
9-Methylnaphtho[3,2,1-cd]indol-5(4H)-one (25): Purification by
flash chromatography (30% EtOAc/petroleum ether) gave the de-
sired product 25 as yellow powder (172 mg, 74%). M.p. 255–
[1] For recent examples, see: a) T.-S. Wu, L.-F. Ou, C.-M. Teng,
Phytochemistry 1994, 36, 1063–1068; b) T.-H. Chuang, S.-J.
Lee, C.-W. Yang, P.-L. Wu, Org. Biomol. Chem. 2006, 4, 860–
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256 °C. IR (KBr): ν = 1606, 1629, 1688, 2921, 3020, 3093,
˜
3184 cm–1. 1H NMR (300 MHz, DMSO): δ = 2.60 (s, 3 H), 7.05
(d, J = 7.1 Hz, 1 H), 7.54–7.62 (m, 2 H), 8.18 (d, J = 8.5 Hz, 2 H),
8.44 (s, 1 H), 8.56 (s, 1 H), 10.82 (s, 1 H) ppm. 13C NMR (75 MHz
DMSO): δ = 21.6, 106.5, 115.4, 122.3, 123.2, 124.5, 126.1, 126.3,
128.9, 129.1, 131.0, 131.6, 138.5, 139.4, 168.5 ppm. HRMS (ESI):
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9-Isopropylnaphtho[3,2,1-cd]indol-5(4H)-one (26): Purification by
flash chromatography (20% EtOAc/petroleum ether, then 30%
EtOAc/petroleum ether) gave the desired product 26 as a yellow
solid (183 mg, 70%). M.p. 180–181 °C. IR (KBr): ν = 1608, 1631,
˜
1707, 2954, 3023, 3071, 3173 cm–1. 1H NMR (300 MHz, CDCl3):
Eur. J. Org. Chem. 2011, 4616–4622
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
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F.-X. Felpin et al.
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Received: April 4, 2011
Published Online: June 21, 2011
4622
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© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2011, 4616–4622