Exclusive 1,2-aryl shift in platinum(II) chloride-catalyzed cyclization of 1-(indol-2-yl)-2,3-allenols

Article abstract of DOI:10.1002/adsc.201100935

An efficient cyclization of 1-(indole-2-yl)-2,3-allenols in the presence of platinum(II) chloride leading to polysubstituted carbazoles via 1,2-methyl or an exclusive 1,2-aryl migration of the metal-carbene intermediate was observed. The reaction proceeds via the intermediacy of a metal carbene intermediate, which induces the carbon-carbon bond cleavage via 1,2-migration to afford the products. Copyright

Full text of DOI:10.1002/adsc.201100935

UPDATES
DOI: 10.1002/adsc.201100935
Exclusive 1,2-Aryl Shift in Platinum(II) Chloride-Catalyzed
Cyclization of 1-(Indol-2-yl)-2,3-allenols
Wangqing Kong,a Youai Qiu,a Xue Zhang,b Chunling Fu,a and Shengming Maa,b,*
a
Laboratory of Molecular Recognition and Synthesis, Department of Chemistry, Zhejiang University, Hangzhou 310027,
Peopleꢀs Republic of China
b
State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of
Sciences, 345 Lingling Lu, Shanghai 200032, Peopleꢀs Republic of China
Fax : (+86)-21-6260-9305; e-mail: masm@sioc.ac.cn
Received: November 30, 2011; Revised: May 1, 2012; Published online: July 29, 2012
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/adsc.201100935.
Abstract: An efficient cyclization of 1-(indole-2-yl)-
2,3-allenols in the presence of platinum(II) chloride
leading to polysubstituted carbazoles via 1,2-methyl
or an exclusive 1,2-aryl migration of the metal-car-
bene intermediate was observed. The reaction pro-
ceeds via the intermediacy of a metal carbene inter-
mediate, which induces the carbon-carbon bond
cleavage via 1,2-migration to afford the products.
nescent,[11] hole-transporting, and light-emitting prop-
erties.[12] The important potentials of these carbazole
derivatives have made them attractive targets for or-
ganic synthesis.[13]
Despite the fact that there are many useful synthet-
ic procedures to prepare carbazoles, there remain
some limitations:[14] (a) the yields usually are not very
good, (b) harsh reaction conditions are usually
needed and some processes cannot tolerate functional
groups, (c) the starting materials are not readily avail-
able, (d) the atom economy is rather poor, and (e) it
is non-regioselective in some of the well-recognized
protocols. Thus, the development of mild, efficient
and regiocontrolled diversified method for the prepa-
ration of carbazole alkaloids, which is suitable for in-
troduction of specific substituent(s) to any position of
Keywords: allenes; carbenes; cyclization; platinum
Introduction
[1]
À
Selective C C bond cleavage, which is synthetically the captioned skeleton is still of high current interest.
attractive, poses a great challenge due to the inherent Recently, we have described an approach to the car-
À
strength of the C C bond as well as the selectivity bazole skeleton through a Pt-catalyzed cyclization of
over the often accompanying C H bond activation.
[2]
1-(indol-2-yl)-2,3-allenols.[15] According to our own
À
As we know, there are three major approaches for the observations and literature data, a possible mechanis-
cleavage of carbon-carbon bonds with transition tic pathway involving a Pt-carbene intermediate
metals: (i) direct oxidative addition of carbon-carbon M[6,16] has been proposed for this transformation
bonds with low-valent transition metals or their com- (Scheme 1). We reasoned that 4,4-disubstitution of
plexes;[3] (ii) b-carbon elimination of carbon-metal carbon groups may be implemented to check the in-
À À À
species such as M C C C or heteroatom-metal spe- termediacy of the metal carbene M and the subse-
[4]
À À À
cies such as M O C C; (iii) rearrangement via the quent carbon-carbon single bond cleavage via 1,2-mi-
intermediacy of such carbocations.[5] To the best our gration. If it is operative, this protocol may provide
knowledge, examples of highly selective cleavage re- a method to introduce the substituent to any location
À
actions of C C bonds via the 1,2-carbon migration of of the carbazole skeleton providing that the selective
metal-carbene intermediates are still quite limited.[6]
carbon-carbon bond cleavage may be realized
On the other hand, tricyclic carbazole derivatives (Scheme 1).
are well-known alkaloids present in plants, and many
of these compounds show biological activities, such as
antioxidative, antitumor, antibacterial, antimicrobial, Results and Discussion
psychotropic, antihistaminic, antiinflammatory, and
antibiotic activities.[7] In addition, carbazole deriva- To this end, we have tested the cyclization of 4,4-di-
tives are also widely used as organic materials with methyl-substituted 2,3-allenol 5a to avoid the issue of
special thermal,[8] electrical,[9] optical,[9,10] electrolumi- selectivity in the first place (Table 1). The reaction
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Wangqing Kong et al.
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Scheme 1.
Table 1. Optimization of the reaction conditions for the reaction of 4,4-dimethyl-substituted 2,3-allenol 5a.
Entry
Catalyst
AuCl3
Solvent
NMR yield of 6a [%][a]
Recovery of 5a [%]
1
2
3
4
5
6
7
8
toluene
toluene
toluene
toluene
xylenes
DCE
20
11
43
86
74
22
47
8
40
–
69
14
49
–
–
–
–
AuCl
PtCl4
PtCl2
PtCl2
PtCl2
PtCl2
PtCl2
PtCl2
PtCl2
PtCl2
PtCl2
PtCl2
(PPh3) (5 mol%)/AgOTf (5 mol%)
–
44
15
46
16
–
–
73
15
CH2Cl2
THF
9
dioxane
acetonitrile
toluene
toluene
toluene
10
11[b]
12[c]
13[d]
[a]
1H NMR yield of 6a and recovery of 5a obtained by using CH2Br2 as internal standard.
The reaction temperature was 408C.
The reaction temperature was 58C.
[b]
[c]
[d]
PtCl2 (3 mol%) was used.
with AuCl3 or AuClACHTNURTGENUNG(PPh3) (5 mol%)/AgBF4 (5 mol%) and the reaction at 58C led to incomplete conversion
afforded carbazole 6a in a very low yield (entries 1 (entries 11 and 12, Table 1). When 3 mol% PtCl2 was
and 2, Table 1). Interestingly, PtCl4 catalyzed this used, the yield of 6a was only 49% with 5a being re-
transformation affording 6a in 43% yield (entry 3, covered in 15% (entry 13, Table 1).
Table 1). Then, it was observed that the reaction of 5a
However, the reaction of 4,4-dialkyl-substituted al-
with PtCl2 (5 mol%) in toluene afforded carbazole 6a lenols 5b and 5c afforded a mixture of two regio-
in a surprising 86% NMR yield as the only product
indicating the smooth 1,2-methyl migration (entry 4,
Table 1), which is different from the previous re-
port.[16f] Next, several solvents were tested for the
PtCl2-catalyzed reaction of 5a at room temperature:
xylenes was also effective affording 6a in 74% NMR
yield (entry 5, Table 1); other solvents failed to afford
better yields (entries 6–10, Table 1). At a higher tem-
ACHTUNGTRENNiUNG somers with very low yields (Scheme 2).
perature (408C), the yield of 6a was slightly lower Scheme 2.
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Exclusive 1,2-Aryl Shift in Platinum(II) Chloride-Catalyzed Cyclization of 1-(Indol-2-yl)-2,3-allenols
Table 2. PtCl2-catalyzed cyclization reaction of 4-aryl-4-
methyl-substituted 1-(indol-2-yl)-2,3-allenols via an aryl-
carbon bond cleavage.[a]
Entry Ar
Time [h] Isolated yield of 6 [%]
1
2
3
4
5
6
7
Ph (5d)
p-MeOC6H4 (5e)
m-MeOC6H4 (5f) 12
p-ClC6H4 (5g)
p-FC6H4 (5h)
2-furyl (5i)
24
6
67 (6d)
87 (6e)
75 (6f)
72 (6g)
77 (6h)
61 (6i)
83 (6j)
24
25
4
Figure 1. ORTEP representation of 6m.
2-thienyl (5j)
13
blue light-emitting materials.[18] In addition, it is capa-
ble of exhibiting the bifunctional properties of light
emission and hole transport, which is potentially
useful for highly efficient non-doped light-emitting
diodes (OLEDs).[18c]
[a]
Reaction conditions: mixture of 0.4 mmol of 5 and PtCl2
(5 mol%) in 2 mL of toluene under N2.
After some trials, we were able to establish the
The migration for the aryl group and that for the
highly selective carbon-carbon single bond cleavage methyl group from Pt-carbene intermediate M has
reaction of 4-aryl-4-alkyl-substitued allenols with the been studied with DFT calculations. As a visual pre-
results shown in Table 2. Different carbazoles were af- sentation of the data, the energy barrier of aryl migra-
forded in moderate to good yields with the aromatic tion is found to be lower than that of the competing
group serving as the 1,2-migration group exclusively, methyl migration by 4.2 kcalmolÀ1, thus, correctly ac-
which was established by the X-ray diffraction study counting for the observed exclusive formation of 6d
of 6m[17] (Figure 1). Electronic effects of substituents as the final product in the experiment. Although the
on the phenyl ring showed no obvious impact on the methyl migration product is computed to be thermo-
yields (entries 2–5, Table 1): both meta and para sub- dynamically more stable, its formation is kinetically
stituted substrates such as 5e–h afforded the corre- less favorable.
sponding products 6e–h (entries 2–5, Table 2). It is
Substituents may also be introduced to 1- or 2-posi-
worthy of note that the Ar group could also be a het- tion of the carbazole ring in 6k and 6l by installing R1
erocyclic group such as 2-furyl or 2-thienyl (entries 6 and/or R2 groups in the starting allenols. Moreover,
and 7, Table 2). The thienyl-substituted carbazoles different substituents may also be introduced to the
such as 6j are particularly useful in the generation of original indole part by using 1-(poly-substituted indol-
short-wavelength absorption or emission for designing 2-yl)-2,3-allenols. Thus, it was clearly demonstrated
Scheme 3. Methyl migration vs. phenyl migration: energies are relative to M.
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Wangqing Kong et al.
UPDATES
cations in organic synthesis, in projects oriented to-
wards drug discovery and new organic materials
based on carbazoles due to the mild reaction condi-
tions, easy availability of the starting materials, and
the potential of the products. Further studies on the
scope, selectivity, and synthetic applications of this re-
action are being carried out in our laboratory.
Experimental Section
Toluene and THF were refluxed in the presence of sodium
using diphenyl ketone as indicator and distilled right before
use. PtCl2 was purchased from Alfa. Compounds 5a–f, 5h,
5k, 5m–5p, and 5r were prepared as described below.
Scheme 4. Synthesis of differently poly-substituted carb-
ACHTUNGTRENNUNGazoles
that this method allows, in principle, the assembly of
substituent(s) to any location of the carbazole
(Scheme 4).
1-(1-Ethyl-1H-indol-2-yl)-4-methylpenta-2,3-dien-1-ol
(5a); Typical Procedure[15,19]
The reactions of 5p–5r were tested. However, no
reaction occurred (Scheme 5). Furthermore, the reac-
tion of substrate 5s afforded 6p in a very low yield
(3%). The major product is the cycloisomerization
product 8 (55%). In order to prevent the cycloisome-
rization involving the hydroxy group, this functionali-
ty was protected with a methyl group. However, the
yield of 6p was still low (5%) with 9 being recovered
in 63%.
Conclusions
We have reported a new modular synthesis of carba-
zoles via the Pt-catalyzed cyclization of poly- substi-
tuted 1-(indol-2-yl)-2,3-allenols. Through these experi-
ments, it is further confirmed that the reaction pro-
ceeds through a unique metal carbene intermediate.
To a solution of 1a (1.0901 g, 6.5 mmol) and THF (25 mL)
was added dropwise n-BuLi (2.6 mL, 2.5M in hexane,
6.5 mmol) at À788C with stirring under a nitrogen atmos-
phere within 10 min. After being stirred for 1 h at À788C,
a solution of 1-ethyl-1H-indole-2-carbaldehyde (1.2101 g,
7.0 mmol) in anhydrous THF (5 mL) was added dropwise at
this temperature within 10 min. Then the mixture was al-
À
Selective C C bond cleavage has been realized: com-
pared with the methyl group, aryl groups migrate ex-
clusively. The new methodology may find wide appli- lowed to warm up to room temperature, quenched with a sa-
Scheme 5.
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Exclusive 1,2-Aryl Shift in Platinum(II) Chloride-Catalyzed Cyclization of 1-(Indol-2-yl)-2,3-allenols
turated aqueous solution of NH4Cl (20 mL), and extracted
with diethyl ether (20 mLꢂ3). The ether layer was dried
over anhydrous Na2SO4, filtered, and concentrated under
vacuum. The product 7a was then used without further pu-
rification.
lowed to warm up to room temperature, quenched with the
addition a saturated aqueous solution of NH4Cl (20 mL),
and extracted with diethyl ether (25 mLꢂ3). The ether layer
was dried over anhydrous Na2SO4, filtered, concentrated
under vacuum. Column chromatography on silica gel (petro-
leum ether/ethyl acetate=20/1) afforded 7g that was used as
such in the next step.
To an ice-cold suspension of LiAlH4 (0.2501 g, 6.5 mmol)
in dry Et2O (15 mL) under N2 was added dropwise a solution
of 7a prepared in the previous step in Et2O (5 mL) within
5 min. Then the mixture was allowed to warm up to room
temperature. After being stirred for 4.5 h, the resulting mix-
ture was quenched with water. The aqueous layer was ex-
tracted with diethyl ether (15 mLꢂ3), washed with water
(20 mLꢂ3) and dried over anhydrous Na2SO4. Filtration,
evaporation, and column chromatography on silica gel (pe-
troleum ether/ethyl acetate=10/1) gave 5a; as a solid; yield:
0.7995 g (combined yield from 1a to 5a is 51%); mp 98–
To a solution of CuBr (0.7524 g, 5 mmol) and 7g prepared
above in Et2O (20 mL) was added dropwise a solution of
EtMgBr (70 mL, 0.71M in Et2O, 50 mmol) at À308C with
stirring under a nitrogen atmosphere within 25 min. After
the addition, the reaction mixture was stirred for 11 h as
monitored by TLC at this temperature, quenched with satu-
rated ammonium chloride solution (30 mL), extracted with
ether (3ꢂ30 mL), washed with water, and dried over anhy-
drous Na2SO4. Fifration, evaporation and column chroma-
tography on silica gel (petroleum ether/ethyl acetate=20/1~
10/1) afforded 5g as a solid; yield: 1.3587 g (combined yield
from 1g to 5g is 40%); mp 122–1238C (ethyl acetate/n-
hexane). 1H NMR (300 MHz, CDCl3): d=7.70 (d, J=
7.5 Hz, 1H, ArH), 7.52–7.26 (m, 6H, ArH), 7.25–7.13 (m,
1H, ArH), [(6.69, s), (6.62, s), 1H, ArH], 6.10–5.97 (m, 1H,
CH=), 5.62–5.48 (m, 1H, CH), 4.48–4.13 (m, 2H, NCH2),
2.52–2.30 (m, 1H, OH), [2.25 (d, J=2.4 Hz), 2.20 (d, J=
2.4 Hz), 3H, CH3], 1.45 (t, J=7.1 Hz, 3H, CH3); IR (neat):
n=3531, 3410, 3055, 2981, 2933, 2899, 1951, 1657, 1611,
1592, 1537, 1489, 1460, 1409, 1347, 1315, 1267, 1221, 1165,
1128, 1094, 1062, 1012 cmÀ1; MS (70 eV, EI): m/z (%)=339
1
998C (ethyl acetate/n-hexane). H NMR (300 MHz, CDCl3):
d=7.60 (dt, J=7.8 and 1.1 Hz, 1H, ArH), 7.34 (dd, J=8.3
and 0.80 Hz, 1H, ArH), 7.25–7.17 (m, 1H, ArH), 7.13–7.05
(m, 1H, ArH), 6.50 (s, 1H, ArH), 5.55–5.44 (m, 1H, CH=),
5.38 (t, J=5.9 Hz, 1H, CH), 4.42–4.18 (m, 2H, NCH2), 2.07
(d, J=6.0 Hz, 1H, OH), 1.81 [d, J=3.0 Hz, 3H, one CH3
from (CH3)2C=], 1.77 [d, J=0.9 Hz, 3H, one CH3 from
(CH3)2C=], 1.42 (t, J=7.2 Hz, 3H, CH3); 13C NMR
(75 MHz, CDCl3): d=199.9, 140.4, 137.0, 127.3, 121.7, 120.9,
119.4, 109.3, 100.8, 100.0, 92.3, 65.4, 38.4, 20.6, 20.5, 15.4; IR
(KBr): n=3356, 3045, 2979, 2934, 2901, 1967, 1612, 1537,
1460, 1347, 1315, 1221, 1164, 1129, 1075 cmÀ1; MS (70 eV,
EI): m/z (%)=242 (M+ +1, 13.80), 241 (M+, 77.84), 118
(100); anal. calcd. for C16H19NO: C 79.63, H 7.94, N 5.80,
found: C 79.74, H 8.07, N 5.73.
[M CTHNUGTRENNGNU CHTUNGTRENNUGN
+A(37Cl), 33.68], 337 [M+A(35Cl), 100]; anal. calcd. for
C21H20NClO: C 74.66, H 5.97, N 4.15; found: C 74.74, H
5.96, N 4.07.
4-(4-Chlorophenyl)-1-(1-ethyl-1H-indol-2-yl)penta-
2,3-dien-1-ol (5g); Typical Procedure
1-(1-Ethyl-1H-indol-2-yl)-2,4-dimethylpenta-2,3-dien-
1-ol (5l);[20] Typical Procedure
To a solution of 1g (1.9419 g, 10 mmol) and THF (25 mL)
was slowly added dropwise n-BuLi (4.0 mL, 2.5M in hexane,
10 mmol) at À788C with stirring under a nitrogen atmos-
phere within 5 min. After being stirred for 55 min at À788C,
a solution of 1-ethyl-1H-indole-2-carbaldehyde (1.7319 g,
10 mmol) in anhydrous THF (5 mL) was added dropwise at
this temperature within 10 min. Then the mixture was al-
To a solution of 1l (1.1210 g, 10 mmol) in Et2O (50 mL) was
added dropwise n-BuLi (4 mL, 2.5M in hexane, 10 mmol) at
À788C with stirring under a nitrogen atmosphere within
10 min. After being stirred for 45 min at À788C, a solution
of 1-ethyl-1H-indole-2-carbaldehyde (1.7352 g, 10 mmol) in
anhydrous Et2O (10 mL) was added dropwise at this temper-
ature within 5 min. Then the mixture was allowed to warm
up to À408C within 2 h. CuCN (52.5 mg, 0.58 mmol) was
then added at À608C, followed by the addition of a solution
of CH3MgBr (10 mL, 3M in Et2O, 30 mmol) dropwise at
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Wangqing Kong et al.
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À608C with stirring under a nitrogen atmosphere within
30 min. After the addition was over, the reaction mixture
was stirred for 14 h at À308C as monitored by TLC,
quenched with a saturated ammonium chloride solution
(30 mL), extracted with ether (3ꢂ30 mL), washed with
water, and dried over anhydrous Na2SO4. Filtration, evapo-
ration and column chromatography on silica gel (petroleum
ether/ethyl acetate=10/1) afforded 5l as a liquid; yield:
1.0203 g (combined yield from 1l to 5l is 40%). 1H NMR
(300 MHz, CDCl3): d=7.61 (dt, J=7.8 and 0.9 Hz, 1H,
ArH), 7.32 (d, J=8.3 and 0.8 Hz, 1H, ArH), 7.24–7.15 (m,
1H, ArH), 7.12–7.03 (m, 1H, ArH), 6.45 (s, 1H, ArH), 5.18
(s, 1H, CH), 4.38–4.20 (m, 2H, NCH2), 2.27 (bs, 1H, OH),
1.80 (s, 3H, CH3), 1.78 (s, 3H, CH3), 1.64 (s, 3H, CH3), 1.38
(t, J=7.2 Hz, 3H, CH3); 13C NMR (75 MHz, CDCl3): d=
196.5, 138.9, 137.0, 127.3, 121.5, 120.7, 119.2, 109.2, 101.0,
100.1, 68.3, 38.3, 20.84, 20.78, 16.3, 15.3; IR (neat): n=3405,
3050, 2980, 2930, 2898, 2870, 1974, 1654, 1611, 1541, 1461,
0.30 mmol) in toluene (1.5 mL) at room temperature for 6 h
afforded 6e (silica gel, petroleum ether/ethyl acetate=40:1)
as a solid; yield: 80.4 mg (87%); mp 136–1388C (ethyl ace-
1
tate/n-hexane). H NMR (300 MHz, CDCl3): d=8.20 (d, J=
8.1 Hz, 1H, ArH), 7.50–7.10 (m, 7H, ArH), 6.98–6.88 (m,
2H, ArH), 4.32 (q, J=7.2 Hz, 2H, NCH2), 3.80 (s, 3H,
OCH3), 2.75 (s, 3H, ArCH3), 1.37 (t, J=7.1 Hz, 3H, CH3);
13C NMR (75 MHz, CDCl3): d=158.2, 140.2, 139.0, 134.8,
132.8, 131.2, 130.9, 127.9, 125.0, 123.8, 123.0, 121.8, 118.7,
113.4, 108.2, 105.6, 55.3, 37.4, 18.2, 13.8; IR (KBr): n=3039,
2974, 2943, 1603, 1591, 1515, 1484, 1470, 1382, 1333, 1277,
1245, 1176, 1156, 1106, 1038 cmÀ1; MS (70 eV, EI): m/z
(%)=316 (M+ +1, 24.94), 315 (M+, 100); anal. calcd. for
C22H21NO: C 83.78, H 6.71, N 4.44; found: C 83.82, H 6.72,
N 4.39.
9-Ethyl-4-methyl-3-(m-tolyl)-9H-carbazole (6f): The reac-
tion of PtCl2 (2.8 mg, 0.01 mmol) and 5f (61.2 mg,
0.19 mmol) in toluene (1.0 mL) at room temperature for
12 h afforded 6f (silioca gel, petroleum ether/ethyl acetate=
1413, 1363, 1346, 1316, 1221, 1164, 1125, 1077, 1038 cmÀ1
;
MS (70 eV, EI): m/z (%)=256 (M+, 7.59), 255 (M+, 36.58),
118 (100); HR-MS: m/z=255.1618, calcd. for C17H21NO
(M+): 255.1623.
1
50/1) as a liquid; yield: 43.2 mg (75%). H NMR (300 MHz,
CDCl3): d=8.27 (d, J=8.1 Hz, 1H, ArH), 7.55–7.12 (m, 9H,
ArH), 4.40 (q, J=7.2 Hz, 2H, NCH2), 2.82 (s, 3H, ArCH3),
2.43 (s, 3H, ArCH3), 1.45 (t, J=7.1 Hz, 3H, CH3); 13C NMR
(75 MHz, CDCl3): d=142.4, 140.2, 139.1, 137.5, 133.3, 131.0,
130.7, 127.8, 127.4, 127.0, 125.0, 123.8, 123.1, 121.8, 118.7,
108.2, 105.6, 37.4, 21.5, 18.2, 13.8; IR (neat): n=3047, 2971,
2917, 2866, 1692, 1622, 1594, 1480, 1467, 1449, 1382, 1344,
1333, 1257, 1154, 1100 cmÀ1; MS (70 eV, EI): m/z (%)=300
(M+ +1, 24.39), 299 (M+, 99.80), 284 (100); HR-MS: m/z=
299.1674, calcd. for C22H21N (M+): 299.1674.
Synthesis of Carbazoles;[15] Typical Procedure for 9-
Ethyl-3,4-dimethyl-9H-carbazole (6a)
To
a dry Schlenk tube were added PtCl2 (5.2 mg,
0.02 mmol), 5a (96.0 mg, 0.40 mmol), and toluene (2 mL) se-
quentially under N2. After continuous stirring for 10 h at
room temperature, the reaction was complete as monitored
by TLC. Evaporation and column chromatography on silica
gel (petroleum ether/ethyl acetate=100/1) afforded 6a as
3-(4-Chlorophenyl)-9-ethyl-4-methyl-9H-carbazole (6g):
The reaction of PtCl2 (4.0 mg, 0.015 mmol) and 5g (98.5 mg,
0.29 mmol) in toluene (1.5 mL) at room temperature for
24 h afforded 6g (silica gel, petroleum ether/ethyl acetate=
40/1) as a solid; yield: 67.2 mg (72%); mp 175–1768C (ethyl
1
a liquid; yield: 64.5 mg (73%). H NMR (300 MHz, CDCl3):
d=8.26 (d, J=8.1 Hz, 1H, ArH), 7.50–7.31 (m, 2H, ArH),
7.30–7.09 (m, 3H, ArH), 4.30 (q, J=7.2 Hz, 2H, NCH2),
2.80 (s, 3H, ArCH3), 2.47 (s, 3H, ArCH3), 1.37 (t, J=7.4 Hz,
3H, CH3); 13C NMR (75 MHz, CDCl3): d=140.1, 138.6,
131.5, 127.7, 126.2, 124.7, 123.5, 122.9, 121.7, 118.3, 108.0,
105.4, 37.2, 19.5, 16.5, 13.6; IR (neat): n=3049, 2974, 2932,
2859, 1618, 1596, 1492, 1470, 1460, 1381, 1343, 1331, 1317,
1
acetate/n-hexane). H NMR (300 MHz, CDCl3): d=8.27 (d,
J=7.5 Hz, 1H, ArH), 7.55–7.20 (m, 9H, ArH), 4.40 (q, J=
7.2 Hz, 2H, NCH2), 2.80 (s, 3H, ArCH3), 1.45 (t, J=7.2 Hz,
3H, CH3); 13C NMR (75 MHz, CDCl3): d=140.8, 140.2,
139.2, 132.2, 131.8, 131.5, 130.7, 128.1, 127.5, 125.1, 123.7,
123.0, 121.8, 118.8, 108.3, 105.8, 37.4, 18.1, 13.7; IR (KBr):
n=3051, 2967, 1618, 1591, 1478, 1382, 1332, 1253, 1155,
1290, 1267, 1244, 1173, 1150, 1116, 1099, 1079, 1028 cmÀ1
;
MS (70 eV, EI): m/z (%)=224 (M+ +1, 13.30), 223 (M+,
70.45), 208 (100); HR-MS: m/z=223.1365, calcd. for
C16H17N (M+): 223.1361.
CHTUNGTRENNUNG
1085 cmÀ1; MS (70 eV, EI): m/z (%)=321 [M (37Cl), 29.74],
319 [M
G
3ACHTUNGTRENNUNG
[M+ÀCH
9-Ethyl-4-methyl-3-phenyl-9H-carbazole (6d): The reac-
tion of PtCl2 (4.0 mg, 0.015 mmol) and 5d (91.0 mg,
0.30 mmol) in toluene (1.4 mL) at room temperature for
24 h afforded 6d (silica gel, petroleum ether/ethyl acetate=
20/1) as a solid; yield: 57.6 mg (67%); mp 126–1278C (ethyl
5.67, N 4.38; found: C 78.71, H 5.45, N 4.38.
9-Ethyl-3-(4-fluorophenyl)-4-methyl-9H-carbazole
(6h):
The reaction of PtCl2 (4.4 mg, 0.017 mmol) and 5h (97.1 mg,
0.30 mmol) in toluene (1.5 mL) at room temperature for
25 h afforded 6h (silica gel, petroleum ether/ethyl acetate=
40/1) as a solid; yield: 70.2 mg (77%); mp 160–1618C (ethyl
1
acetate/n-hexane). H NMR (300 MHz, CDCl3): d=8.28 (d,
J=8.1 Hz, 1H, ArH), 7.55–7.20 (m, 10H, ArH), 4.40 (q, J=
7.2 Hz, 2H, NCH2), 2.83 (s, 3H, ArCH3), 1.46 (t, J=7.1 Hz,
3H, CH3); 13C NMR (75 MHz, CDCl3): d=142.4, 140.2,
139.1, 133.1, 130.7, 130.3, 127.9, 127.8, 126.2, 125.0, 123.7,
123.0, 121.8, 118.7, 108.2, 105.7, 37.4, 18.2, 13.7; IR (KBr):
n=3053, 2975, 2925, 1621, 1591, 1479, 1470, 1447, 1383,
1344, 1332, 1298, 1254, 1191, 1156, 1106, 1083, 1027,
1011 cmÀ1; MS (70 eV, EI): m/z (%)=286 (M+ +1, 20.93),
285 (M+, 91.60), 270 (100); anal. calcd. for C21H19N: C 88.38,
H 6.71, N 4.91; found: C 88.45, H 6.80, N 5.02.
1
acetate/n-hexane). H NMR (300 MHz, CDCl3): d=8.27 (d,
J=7.8 Hz, 1H, ArH), 7.56–7.42 (m, 2H, ArH), 7.41–7.20
(m, 5H, ArH), 7.13 (t, J=8.7 Hz, 2H, ArH), 4.40 (q, J=
7.3 Hz, 2H, NCH2), 2.80 (s, 3H, ArCH3), 1.45 (t, J=7.2 Hz,
3H, CH3); 19F NMR (282 MHz, CDCl3): d=À117.0;
13C NMR (75 MHz, CDCl3): d=161.7 (d, J=243.3 Hz),
140.2, 139.2, 138.3 (d, J=4.0 Hz), 132.0, 131.6 (d, J=7.5 Hz),
130.8, 127.7, 125.1, 123.7, 123.0, 121.8, 118.8, 114.7 (d, J=
21.2 Hz), 108.3, 105.7, 37.4, 18.1, 13.7; IR (KBr): n=3051,
2967, 1591, 1478, 1462, 1382, 1332, 1323, 1290, 1253, 1185,
1155, 1085, 1014 cmÀ1; MS (70 eV, EI): m/z (%)=304 (M+ +
9-Ethyl-3-(4-methoxyphenyl)-4-methyl-9H-carbazole (6e):
The reaction of PtCl2 (4.1 mg, 0.015 mmol) and 5e (98.1 mg,
2344
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Adv. Synth. Catal. 2012, 354, 2339 – 2347

Exclusive 1,2-Aryl Shift in Platinum(II) Chloride-Catalyzed Cyclization of 1-(Indol-2-yl)-2,3-allenols
1, 18.10), 303 (M+, 81.52), 288 (100); anal. calcd. for
C21H18FN: C 83.14, H 5.98, N 4.62; Found: C 83.34, H 5.88,
N 4.49.
8.4 Hz, 1H, ArH), 7.50–7.30 (m, 2H, ArH), 7.26–7.15 (m,
1H, ArH), 7.10 (s, 1H, ArH), 4.32 (q, J=7.2 Hz, 2H,
NCH2), 2.85 (s, 3H, ArCH3), 2.50 (s, 3H, ArCH3), 2.37 (s,
3H, ArCH3), 1.39 (t, J=7.4 Hz, 3H, CH3); 13C NMR
(75 MHz, CDCl3): d=139.9, 138.1, 134.7, 131.4, 125.4, 124.2,
123.7, 122.5, 119.9, 118.2, 107.9, 106.9, 37.1, 22.3, 17.0, 15.0,
13.7; IR (neat): n=3044, 3973, 2936, 2873, 1621, 1599, 1470,
1464, 1376, 1348, 1330, 1311, 1288, 1265, 1207, 1181, 1139,
1098, 1029 cmÀ1; MS (70 eV, EI): m/z (%)=238 (M+ +1,
12.57), 237 (M+, 66.11), 222 (100); HR-MS: m/z=237.1519,
calcd. for C17H19N (M+): 237.1517.
9-Ethyl-3-(2-furyl)-4-methyl-9H-carbazole (6i): The reac-
tion of PtCl2 (4.9 mg, 0.018 mmol) and 5i (88.0 mg,
0.30 mmol) in toluene (1.5 mL) at room temperature for 4 h
afforded 6i (silica gel, petroleum ether/ethyl acetate=40/1)
as a liquid; yield: 50.7 mg (61%). 1H NMR (300 MHz,
CDCl3): d=8.36 (d, J=7.8 Hz, 1H, ArH), 7.74 (d, J=
8.7 Hz, 1H, ArH), 7.61 (dd, J=1.8 and 0.9 Hz, 1H, ArH),
7.58–7.45 (m, 2H, ArH), 7.38–7.28 (m, 2H, ArH), 6.59 (dd,
J=3.6 and 1.8 Hz, 1H, ArH), 6.52 (dd, J=3.3 and 0.9 Hz,
1H, ArH), 4.39 (q, J=7.1 Hz, 2H, NCH2), 3.05 (s, 3H,
ArCH3), 1.46 (t, J=7.4 Hz, 3H, CH3); 13C NMR (75 MHz,
CDCl3): d=154.7, 141.3, 140.2, 139.4, 131.6, 126.5, 125.1,
123.8, 123.1, 122.2, 122.0, 118.9, 111.0, 108.3, 107.8, 105.9,
37.4, 18.1, 13.7; IR (neat): n=3051, 2975, 2931, 1618, 1592,
1485, 1471, 1384, 1345, 1331, 1319, 1291, 1252, 1194, 1152,
1106, 1079, 1026, 1003 cmÀ1; MS (70 eV, EI): m/z (%)=276
(M+ +1, 20.99), 275 (M+, 100); HR-MS: m/z=275.1311,
calcd. for C19H17NO (M+): 275.1310.
9-Ethyl-4,6-dimethyl-3-(p-tolyl)-9H-carbazole (6m): The
reaction of PtCl2 (3.9 mg, 0.015 mmol) and 5m (99.4 mg,
0.30 mmol) in toluene (1.5 mL) at room temperature for
16 h afforded 6m (silica gel, petroleum ether/ethyl acetate=
100/1) as a solid; yield: 77.8 mg (83%); mp 128–1298C
1
(CH2Cl2/n-hexane). H NMR (300 MHz, CDCl3): d=8.05 (s,
1H, ArH), 7.41–7.20 (m, 8H, ArH), 4.35 (q, J=7.2 Hz, 2H,
NCH2), 2.81 (s, 3H, ArCH3), 2.56 (s, 3H, ArCH3), 2.43 (s,
3H, ArCH3), 1.42 (t, J=7.2 Hz, 3H, CH3); 13C NMR
(75 MHz, CDCl3): d=139.5, 139.3, 138.5, 135.7, 132.8, 130.7,
130.2, 128.7, 127.8, 127.7, 126.2, 124.0, 123.1, 121.6, 107.9,
105.6, 37.4, 21.6, 21.2, 18.3, 13.7; IR (KBr): n=3020, 2974,
2919, 2865, 1624, 1595, 1573, 1489, 1474, 1449, 1382, 1345,
1308, 1257, 1226, 1154, 1112, 1010 cmÀ1; MS (70 eV, EI): m/z
(%)=314 (M+ +1, 25.61), 313 (M+, 100); anal. calcd. for
C23H23N: C 88.13, H 7.40, N 4.47; found: C 88.18, H 7.42, N
4.38.
9-Ethyl-4-methyl-3-(thiophen-2-yl)-9H-carbazole (6j): The
reaction of PtCl2 (4.1 mg, 0.015 mmol) and 5j (91.2 mg,
0.30 mmol) in toluene (1.5 mL) at room temperature for
13 h afforded 6j (silica gel, petroleum ether/ethyl acetate=
100/1) as
a
liquid; yield: 71.3 mg (83%). 1H NMR
(300 MHz, CDCl3): d=8.35 (d, J=7.8 Hz, 1H, ArH), 7.65–
7.46 (m, 3H, ArH), 7.45–7.39 (m, 1H, ArH), 7.38–7.29 (m,
2H, ArH), 7.25–7.15 (m, 1H, ArH), 7.14–7.10 (m, 1H,
ArH), 4.42 (q, J=7.2 Hz, 2H, NCH2), 3.01 (s, 3H, ArCH3),
1.49 (t, J=7.2 Hz, 3H, CH3); 13C NMR (75 MHz, CDCl3):
d=144.0, 140.2, 139.4, 132.1, 128.6, 126.9, 126.8, 125.1, 125.0,
124.8, 123.7, 123.0, 121.9, 118.9, 108.3, 105.7, 37.4, 18.1, 13.7;
IR (neat): n=3051, 2975, 2925, 1618, 1589, 1485, 1470, 1424,
1383, 1330, 1288, 1269, 1248, 1221, 1153, 1105, 1078,
1027 cmÀ1; MS (70 eV, EI): m/z (%)=292 (M+ +1, 21.45),
291 (M+, 100); HR-MS: m/z=291.1083, calcd. for C19H17NS
(M+): 291.1082.
9-Ethyl-6-methoxy-3,4-dimethyl-9H-carbazole (6n): The
reaction of PtCl2 (4.1 mg, 0.015 mmol) and 5n (82.0 mg,
0.30 mmol) in toluene (2.0 mL) at room temperature for
12 h afforded 6n (silica gel, petroleum ether/ethyl acetate=
1
40/1) as a liquid: yield: 53.6 mg (70%). H NMR (300 MHz,
CDCl3): d=7.86 (d, J=2.1H, 1H, ArH), 7.38–7.27 (m, 2H,
ArH), 7.23–7.11 (m, 2H, ArH), 4.33 (q, J=7.2 Hz, 2H,
NCH2), 3.99 (s, 3H, ArOCH3), 2.86 (s, 3H, ArCH3), 2.53 (s,
3H, ArCH3), 1.41 (t, J=7.1 Hz, 3H, CH3); 13C NMR
(75 MHz, CDCl3): d=153.0, 139.3, 135.4, 131.4, 127.8, 125.7,
123.9, 121.6, 113.0, 108.3, 107.2, 105.5, 56.3, 37.3, 19.5, 16.4,
13.6; IR (neat): n=2973, 2933, 2829, 1625, 1602, 1575, 1494,
1476, 1379, 1321, 1306, 1269, 1225, 1209, 1164, 1149,
1040 cmÀ1; MS (70 eV, EI): m/z (%)=253 (M+, 74.52), 238
(100); HR-MS: m/z=253.1471, calcd. for C17H19NO (M+):
253.1467.
9-Ethyl-1,4-dimethyl-3-phenyl-9H-carbazole (6k): The re-
action of PtCl2 (4.2 mg, 0.016 mmol) and 5k (96.2 mg,
0.30 mmol) in toluene (1.5 mL) at room temperature for
24 h afforded 6k (silica gel/petroleum ether/ethyl acetate=
1
40/1) as a liquid; yield: 75.6 mg (83%). H NMR (300 MHz,
CDCl3): d=8.43 (d, J=7.8 Hz, 1H, ArH), 7.66–7.55 (m, 6H,
ArH), 7.54–7.45 (m, 1H, ArH), 7.44–7.35 (m, 1H, ArH),
7.30 (s, 1H, ArH), 4.72 (q, J=7.2 Hz, 2H, NCH2), 2.95 (s,
6H, ArCH3), 1.56 (t, J=7.2 Hz, 3H, CH3); 13C NMR
(75 MHz, CDCl3): d=142.3, 140.9, 137.8, 133.2, 131.1, 130.2,
128.3, 127.9, 126.2, 124.9, 124.1, 123.0, 122.6, 118.8, 116.8,
108.4, 39.2, 20.0, 18.1, 15.5; IR (neat): n=3052, 3018, 2972,
2926, 2870, 1601, 1575, 1484, 1463, 1396, 1377, 1340, 1308,
1244, 1155, 1105, 1074, 1028, 1005 cmÀ1; MS (70 eV, EI): m/z
(%)=300 (M+ +1, 22.16), 299 (M+, 91.39), 284 (M+ÀCH3,
100); HR-MS: m/z=299.1674, calcd. for C22H21N (M+):
299.1674.
9-Ethyl-1,5,6-trimethyl-9H-carbazole (6o): The reaction of
PtCl2 (5.4 mg, 0.02 mmol) and 5o (101.1 mg, 0.40 mmol) in
toluene (2.0 mL) at room temperature for 16 h afforded 6o
(by double chromatography on silica gel: first round eluent
petroleum ether/ethyl acetate=50/1, second round eluent:
petroleum ether/ethyl acetate=100/1) as a liquid; yield:
1
68.1 mg (72%). H NMR (300 MHz, CDCl3): d=8.17 (d, J=
7.8H, 1H, ArH), 7.30 (d, J=8.1 Hz, 1H, ArH), 7.19 (d, J=
8.1 Hz, 2H, ArH), 7.16–7.08 (m, 1H, ArH), 4.60 (q, J=
7.1 Hz, 2H, NCH2), 2.85 (s, 3H, ArCH3), 2.83 (s, 3H,
ArCH3), 2.50 (s, 3H, ArCH3), 1.41 (t, J=7.2 Hz, 3H, CH3);
13C NMR (75 MHz, CDCl3): d=139.5, 138.9, 131.2, 128.1,
127.7, 126.4, 124.5, 122.0, 120.9, 119.5, 118.5, 105.6, 39.3,
20.4, 19.6, 16.6, 15.5; IR (neat) n=2967, 2931, 2866, 1587,
1494, 1485, 1460, 1404, 1378, 1327, 1310, 1281, 1263, 1243,
1176, 1120, 1047 cmÀ1; MS (70 eV, EI): m/z (%)=238 (M+ +
1, 10.80), 237 (M+, 57.23), 222 (M+ÀCH3, 100); HR-MS:
m/z=237.1519, calcd. for C17H19N (M+): 237.1517.
9-Ethyl-2,3,4-trimethyl-9H-carbazole (6l): The reaction of
PtCl2 (4.1 mg, 0.015 mmol) and 5l (78.5 mg, 0.30 mmol) in
toluene (1.5 mL) at room temperature for 12 h afforded 6l
(by double chromatography on silica gel: first round eluent
petroleum ether/ethyl acetate=10/1, second round eluent:
petroleum ether/ethyl acetate=200/1) as a liquid; yield:
1
40.3 mg (55%). H NMR (300 MHz, CDCl3): d=8.25 (d, J=
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Wangqing Kong et al.
UPDATES
zu, Y. Harada, H. Mishima, A. Suzuki, Synlett 2000,
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A. M. Echavarren, Chem. Rev. 2008, 108, 3326; k) V.
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Supporting Information
The preparations of compounds 5d–5f, 5h, 5k, 5m–5s, 5i, 5j,
1
6p, 8, and 9 and H and 13C NMR spectra of all starting ma-
terials and products are given in the Supporting Informa-
tion.
Acknowledgements
Financial support from the National Basic Research Program
of China (2009CB825300) is greatly appreciated. Shengming
Ma is a Qiu Shi Adjunct Professor at Zhejiang University.
We thank Mr. J. Liu in our group for reproducing the results
presented in entry 3 of Scheme 3.
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2s(I)], R1=0.0414, wR2=0.1222, R indices (all data)
R1=0.0471,
wR2=0.1313,
a=5.9542(3) Š,
a=908,
b=
b=
15.7895(8) Š,
c=19.0069(9) Š,
96.3270(10)8, g=908, V=1776.03(15) Š3, T=296 (2) K,
Z=4, reflections collected/unique: 20239/3114 (Rint
=
0.0205), number of observations [>2s(I)] 2702, param-
eters: 218. CCDC 737002 contains the supplementary
crystallographic data for this paper. These data can be
obtained free of charge from The Cambridge Crystallo-
graphic Data Centre via www.ccdc.cam.ac.uk/data_re-
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Adv. Synth. Catal. 2012, 354, 2339 – 2347
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asc.wiley-vch.de
2347