Synthesis of aromatic ring fused pyrrole derivatives by palladium-catalyzed annulation of o-iodoarylamines with allyl acetate

Article abstract of DOI:10.3987/com-03-9965

Indoles, azaindoles, and pyrroloquinolines were obtained by palladium-catalyzed annulation of o-iodoarylamines with allyl acetate under 5 mol percent Pd(OAc)₂, 1 equiv. LiCl, 3 equiv. K₂CO₃, and 2 equiv. allyl acetate in DMF at 120°C.

Full text of DOI:10.3987/com-03-9965

HETEROCYCLES, Vol. 63, No. 3, 2004, pp. 631 - 639
Received, 19th November, 2003, Accepted, 9th January, 2004, Published online, 19th January, 2004
SYNTHESIS OF AROMATIC RING FUSED PYRROLE DERIVATIVES
BY PALLADIUM-CATALYZED ANNULATION OF o-IODOARYL-
AMINES WITH ALLYL ACETATE
Chang Sung Hong, Jae Yong Seo, Eul Kgun Yum,* and Nack-Do Sunga
Department of Chemistry, Chungnam National University, Yusung, Daejon
305-764, Korea
aDivision of Applied Biology and Chemistry, Chungnam National University,
Yusung, Daejon 305-764, Korea
Abstract – Indoles, azaindoles, and pyrroloquinolines were obtained by
palladium-catalyzed annulation of o-iodoarylamines with allyl acetate under 5
mol % Pd(OAc)2, 1 equiv. LiCl, 3 equiv. K2CO3 , and 2 equiv. allyl acetate in DMF
at 120°C.
π-Allylpalladium complexes are some of the most widely used synthetic intermediates in organic
synthesis.1 π-Allylpalladium complexes can be formed in several different ways from various organic
substrates, such as allylic alcohols, halides, carboxylates, phosphates, vinylepoxides, etc.1b Catalytic
transformation via π–allylpalladium intermediates has found widespread use in a number of important
chemical processes, including allylic substitution with soft or hard nucleophiles, bis-oxidation of
conjugated dienes, hydrogenolysis, transmetallation, and carbonylation.1a Specifically, the cyclization of a
π–allylpalladium intermediate with soft or hard nucleophiles has been used to synthesize various
carbocycles and heterocycles.2 Larock and coworkers also reported intermolecular ring formation with
1,2-dienes,3 1,3-dienes,4 1,4-dienes,5 and vinylic cyclopropane6 using aromatic halides bearing functional
groups in the ortho position to synthesize heterocycles. However, one-pot formation of heterocycles by
intermolecular ring formation with allyl acetate is extremely rare. Recently, many intermolecular reactions
with allyl acetate have been reported for the formation of carbon-carbon bonds,7 carbon-nitrogen bonds,8
and cycloaddition.9 As part of our continuing interest in developing new synthetic methods for
heterocycles,10,11 we examined palladium-catalyzed annulation of various ortho iodoarylamines with

allylic substrates to synthesize various indole analogues. Indole analogues have attracted considerable
attention in recent years, since indole is the core structure of many biologically active compounds.12-14
Initially, we chose the palladium-catalyzed reaction of N-acetyl-2-iodoaniline with various allylic
substrates to optimize the reaction conditions. The results are summarized in Table 1.
Table 1. Optimization of indole synthesis by palladium-catalyzed annulation with allylic substrates.
I
5 mol % Pd, 1 eq. LiCl
3 eq. Base, DMF, 120 oC
+
2 eq. Allylic substrate
CH3
N
H
NHAc
Reaction
Time (h)
Entrya
Pd Source
Allylic Substrate
Base
Yields (%)
1
2
Pd(OAc)2
〃
CH2=CH-CH2OAc
K2CO3
KOAc
K2CO3
KOAc
K2CO3
〃
13
〃
15
〃
12
48
〃
〃
〃
〃
67
63
〃
〃
〃
〃
〃
〃
3
PdCl2
60
〃
4
65
5
Pd(dba)2
Pd(Ph3P)2Cl2
Pd(Ph3P)4
Pd(OAc)2
〃
40
6
<10
<10
45
〃
7
〃
8
CH2=CH-CH2CO2CH3
CH2=CH-CH2OC6H4-4-NO2
CH2=CH-CH2OC6H4-4-Cl
〃
〃
9
40
10
〃
25
a All reactions were run on a 0.5 mmol scale in 10 mL DMF.
First, we examined the effect of palladium species using 1 equiv. of LiCl and potassium bases (Entries 1-7).
The reactions using Pd(OAc)2 or PdCl2 provided higher yields of deacetylated 2-methylindole than the
other palladium species (Entries 1-4). We also examined the effects of several allylic substrates under
K2CO3. The reaction using allyl acetate gave a higher yield of the desired product than the reactions using
other allylic substrates (Entries 8-10). From these results, we decided that the optimum reaction conditions
consisted of 5 mol % Pd(OAc)2, 1 equiv. LiCl, 3 equiv. potassium base, and 2 equiv. allylic substrate in
DMF at 120°C. Next, we examined the synthesis of various aromatic ring fused pyrrole derivatives with
several o-iodoarylamines with allyl acetate under the optimized reaction conditions. The results are
summarized in Table 2. The reaction using unprotected 2-iodoaniline provided a slightly lower yield of
2-methylindole than the reaction with N-acetyl 2-iodoaniline. We also examined the synthesis of 5-, 6-, and

Table 2. Synthesis of aromatic ring fused pyrrole analogues by palladium-catalyzed annulation with
o-iodoarylamines with allyl acetate.
I
5 mol % Pd(OAc)2, 1 eq. LiCl
3 eq. K2CO3, DMF, 120 oC
OAc
2 eq.
CH3
+
N
R
NHR
Entry
1
Aryl iodide
Reaction time (h)
24
Product
Isolated yields (%)
I
CH3
47
N
NH2
H
(1)
I
12
48
20
20
20
CH3
CH3
CH3
2
3
65
47
N
N
N
NHBn
N
N
Bn
(2)
(3)
I
N
CH3
NHCH3
I
N
N
N
N
4
5
56
53
45
N
NHCH3
I
(4)
(5)
CH3
CH3
N
Bn
NHBn
I
6
CH3
CH3
N
N
N
Bn
NHBn
(6)
CH3
CH3NH
N
I
I
36
16
7
45
N
N
OCH3
OCH3
(7)
8
9
CH3
CH3
67
52
N
N
N
NHCH3
N
(8)
I
40
CH3
N
N
(9)
NHBn
Bn

7-azaindoles from different o-iodoaminopyridines (Entries 2-6). The annulation reactions gave moderate
yields of the desired azaindole. Finally, the reactions of o-iodoaminoquinolines afforded
pyrrolo[3,2-c]quinoline and pyrrolo[2,3-b]quinolines in reasonable yields (Entries 7-9).
Considering our identification of the Heck product intermediate, the annulation might proceed via the route
illustrated in Scheme 1. The formation of Pd(0) from Pd(OAc)2 could proceed in the reaction medium. The
palladium(0) complex reacts with aryl halide via oxidative addition. The arylpalladium complex next
coordinates and adds the double bond of allyl acetate. The resulting palladium intermediate sequentially
undergoes hydride elimination to generate the Heck product and palladium species. Subsequent
π-allylpalladium formation, followed by intramolecular nucleophilic attack on the π-allylpalladium species
generates the indole and regenerates Pd(0), which can be recycled.
Pd(OAc)2
I
NHR
Pd(0)
R
RHN
N
IPd
OAc
R
Base.HI
Base
RHN
IPd
N
HPdI
Pd
H
AcO
RHN
H
RHN
Pd
IPd
AcO
HPdI
RHN
Base.HI
AcO
Base
Scheme 1
In summary, the palladium-catalyzed annulation of o-iodoarylamines with allyl acetate gave indole,
azaindoles, and pyrroloquinolines in moderate yields. The annulation methodology might be applied to the
synthesis of a variety of heterocycles by varying the o-functionalized aryl halide.

EXPERIMENTAL
Infrared spectra were obtained using a JASCO FT-IR 410 spectrometer. All the 1H- and 13C-NMR spectra
were recorded on a Varian 400-MHz spectrometer. The chemical shifts are given as values relative to
tetramethylsilane (TMS) as an internal standard. The GC/MS spectra were obtained on a Shimadzu QP
1000. The melting points were determined on a Mut-TEM apparatus and are uncorrected. Microanalyses
were performed at Chungnam National University with a CE Instrument EA 1110. The products were
purified by flash chromatography on 230- to 400-mesh ASTM 60 silica gel. All the bases and palladium
species were purchased from Aldrich Chemical Co. The other chemicals were used as obtained from
commercial sources, unless otherwise noted.
General procedure for preparing o-amino aryl halide 15
2-Methylamino-3-iodoquinoline. n-BuLi (2.5 M in hexane, 20 mL, 50 mmol) was slowly added to a
magnetically stirred solution of diisopropylamine (5.05 g, 50 mmol) in dry THF (125 mL) under N2 at
-78°C. The solution of LDA was stirred at -78°C for 1 h. 2-Chloroquinoline (8.2 g, 50 mmol) in THF (25
mL) was added slowly to the reaction mixture at -78°C. The mixture was stirred for 4 h at the same
temperature. The iodine solution (15.2 g, 50 mL THF) was slowly added to a solution of lithiated
2-chloroquinoline. The resulting solution was stirred for 2 h at -78°C and allowed to warm to rt over 5 h.
After removing the solvent under reduced pressure, the residue was extracted using Et2O and decolorized
with saturated NaHSO3 aqueous solution. The organic layer was dried over MgSO4, filtered, and
concentrated. 2-Chloro-3-iodoquinoline (10.8 g, 75%) was obtained by column chromatography with
hexane/ethyl acetate (10:1): mp 145-146°C; IR (KBr) 3050, 3030, 1610, 1575, 1560, 1545, 1485 cm-1;
1H-NMR (CDCl3) δ 8.40 (s, 1H, ArH), 7.90-7.30 (m, 4 H, ArH); 13C-NMR (CDCl3) δ 162.7, 148.7, 146.3,
132.1, 128.7, 128.2, 127.9, 126.8, 84.7; MS m/z (relative intensity): 289 (M+, 38), 254 (26), 128 (30), 106
(48), 91 (100), 65 (28).
2-Chloro-3-iodoquinoline (1.4 g, 4.84 mmol), methylamine (40% aqueous solution, 10 mL), and ethanol
(10 mL) were added to a sealed tube. The reaction mixture was heated at 140°C for 10 h. The resulting
mixture was poured into water and the product was extracted with ethyl acetate. The organic layer was
dried over MgSO4, filtered, and concentrated. 2-Methylamino-3-iodoquinoline (1.0 g, 73%) was obtained
by column chromatography using hexane/ethyl acetate (10:1): mp 84-85ºC; IR (KBr) 3420, 3040, 2990,
2950, 2900, 1615, 1595, 1555, 1525 cm-1; 1H-NMR (CDCl3) δ 8.30 (s, 1H, ArH), 7.85-7.00 (m, 4H, ArH),
13
5.25 (br s, 1H, NH), 3.15 (d, 3H, J = 5.6 Hz, N-CH3); C-NMR (CDCl3) δ 154.2, 146.4, 139.8, 130.0,

127.1, 126.4, 126.3, 124.9, 122.4, 29.4; MS m/z (relative intensity): 284 (M+, 38), 155 (28), 125 (42), 106
(52), 91 (100), 65 (21); Anal. Calcd for C10H9N2I: C, 42.28; H, 3.19; N, 9.86. Found: C, 42.35; H, 3.17; N,
9.84.
2-Benzylamino-3-iodoquinoline. This compound was prepared in 75% yield by the substitution of
2-chloro-3-iodoquinoline with benzylamine: mp 179-180ºC (ethyl ether) ; IR (KBr) 3397, 3025, 1582,
1510, 694 cm-1; 1H-NMR (CDCl3) δ 8.35 (s, 1H, ArH), 7.73-7.17 (m, 9H, ArH), 5.55 (br s, 1H, NH), 4.81 (d,
2H, J = 5.6 Hz, ArCH2); 13C-NMR (CDCl3) δ 153.2, 147.3, 146.5, 129.3, 130.1, 128.6, 127.9, 127.3, 126.4,
126.3, 125.0, 122.6, 83.2, 46.4; MS m/z (relative intensity): 360 (M+, 36), 231 (29), 128 (28), 116 (33), 106
(100), 91 (48), 65 (28); Anal. Calcd for C16H13N2I: C, 53.35; H, 3.64; N, 7.78. Found: C, 53.40; H, 3.60; N,
7.75.
The starting o-aminoaryl halides were prepared using the above general procedures.
General synthetic procedure of aromatic ring fused pyrrole derivatives by palladium-catalyzed
heteroannulation with allyl acetate
2-Methyl-1H-indole (1)16
Palladium acetate (6 mg, 0.025 mmol), LiCl (21 mg, 0.5 mmol), K2CO3 (207 mg, 1.5 mmol), allyl acetate
(100 mg, 1.0 mmol), N-(2-iodophenyl)acetamide (130 mg, 0.5 mmol), and DMF (10 mL) were added to a
pressure tube equipped with a stirring bar. After heating the reaction mixture for 13 h at 120ºC, the resulting
solution was diluted with ethyl acetate and washed with saturated aqueous ammonium chloride. The
organic layer was dried over MgSO4, filtered, and concentrated. The residue was purified by column
chromatography using hexane-ethyl acetate (20:1). 2-Methyl-1H-indole (1) (44 mg, 67%) was obtained as
1
a white solid. mp 58-60ºC (hexane); H-NMR (CDCl3) δ 7.73 (br s, 1H, N-H), 7.42 (d, J = 8.4 Hz, 1H,
Ar-H), 7.18 (t, J = 7.6 Hz, 1H, Ar-H), 6.96-7.04 (m, 2H, Ar-H), 6.13 (s, 1H, Ar-H), 2.26 (s, 3H, Ar-CH3);
13C-NMR (CDCl3) δ 135.92, 134.94, 128.94, 120.80, 119.50, 110.12, 100.28, 13.74; MS m/z (relative
intensity): 131 (M+, 100), 103 (20), 77 (20), 63 (10); Anal. Calcd for C9H9N: C, 82.41; H, 6.92; N, 10.68.
Found: C, 82.40; H, 6.91; N, 10.68.
1-Benzyl-2-methyl- 1H-pyrrolo[2,3-b]pyridine (2)
The compound (2) was obtained as a white solid in 65% yield from benzyl(3-iodopyridin-2-yl)amine and
1
allyl acetate with a 12 h reaction. mp 103-104ºC (hexane); H-NMR (CDCl3) δ 8.23 (d, J = 4.4Hz, 1H,
Ar-H), 7.80 (d, J = 8.0 Hz, 1H, Ar-H), 7.02-7.37 (m, 6H, Ar-H), 6.24 (s, 1H, Ar-H), 5.52 (s, 2H, N-CH2),
2.33 (s, 3H, Ar-CH3); 13C-NMR (CDCl3) δ141.55, 137.93, 134.58, 128.50, 127.58, 127.09, 126.98, 126.34,

117.24, 115.78, 98.26, 44.76, 13.18; MS m/z (relative intensity): 222 (M+, 10), 206 (21), 144 (16), 130 (21),
91 (100), 65 (24); Anal. Calcd for C15H14N2: C, 81.05; H, 6.35; N, 12.60. Found: C, 81.07; H, 6.34; N,
12.58.
1,2-Dimethyl-1H-pyrrolo[2,3-b]pyridine (3)17
The compound (3) was obtained as a yellow oil in 47% yield from methyl(3-iodopyridin-2-yl)amine and
allyl acetate with a 48 h reaction. 1H-NMR (CDCl3) δ 8.22 (d, J = 4.0 Hz, 1H, Ar-H), 7.75 (d, J = 8.0 Hz,
1H, Ar-H), 6.98 (dd, J = 8.0 Hz, 4.0 Hz, Ar-H), 6.18 (s, 1H, Ar-H), 3.77 (s, 3H, N-CH3), 2.44 (s, 3H,
Ar-CH3); MS m/z (relative intensity): 146 (M+, 100), 131 (10), 118 (10), 104 (8), 73 (8), 63 (8); Anal. Calcd
for C9H10N2: C, 73.94; H, 6.89; N, 19.16. Found: C, 73.91; H, 6.91; N, 19.19.
1,2-Dimethyl-1H-pyrrolo[3,2-c]pyridine (4)
The compound (4) was obtained as a white solid in 56% yield from (3-iodopyridin-4-yl)methylamine and
allyl acetate with a 20 h reaction. mp 123-124ºC (hexane); 1H-NMR (CDCl3) δ 8.75 (s, 1H, Ar-H), 8.20 (d,
J = 5.8 Hz, 1H, Ar-H), 7.10 (d, J = 5.8 Hz, 1H, Ar-H), 6.30 (s, 1H, Ar-H) 3.62 (s, 3H, N-CH3), 2.40 (s, 3H,
Ar-CH3); 13C-NMR (CDCl3) δ142.18, 139.77, 138.00, 128.72, 104.13, 98.97, 29.45, 14.13, 13.69; MS m/z
(relative intensity): 146 (M+, 100), 131 (50), 97 (25), 71 (48), 57 (85); Anal. Calcd for C9H10N2: C, 73.94;
H, 6.89; N, 19.16. Found: C, 73.95; H, 6.90; N, 19.14.
1-Benzyl-2-methyl- 1H-pyrrolo[2,3-b]pyridine (5)
The compound (5) was obtained as a white solid in 53% yield from (3-iodopyridin-4-yl)benzylamine and
allyl acetate with a 20 h reaction. mp 102-104ºC; 1H-NMR (CDCl3) δ 8.82 (s, 1H, Ar-H ), 8.21 (d, J = 5.6
Hz, 1H, Ar-H), 7.44 (d, J = 5.6 Hz, 1H, Ar-H), 7.16-7.32 (m, 5H, Ar-H), 6.40 (s, 1H, Ar-H), 5.29 (s, 3H,
N-CH3), 2.37 (s, 3H, Ar-CH3); 13C-NMR (CDCl3) δ142.03, 140.93, 139.75, 138.21, 136.61, 128.82, 128.79,
127.57, 126.25, 125.82, 104.62, 99.93, 40.60, 12.76; MS m/z (relative intensity): 222 (M+, 10), 91 (14), 84
(90), 48(100); Anal. Calcd for C15H14N2: C, 81.05; H, 6.35; N, 12.60. Found: C, 81.03; H, 6.35; N, 12.62.
1-Benzyl-2-methyl- 1H-pyrrolo[2,3-c]pyridine (6)
The compound (6) was obtained as a yellow oil in 45% yield from benzyl(4-iodopyridin-3-yl)amine and
allyl acetate with a 20 h reaction. ; 1H-NMR (CDCl3) δ 8.60 (s, 1H, Ar-H), 8.18 (d, J = 5.6 Hz, 1H, Ar-H),
7.44 (d, J = 5.6 Hz, 1H, Ar-H), 7.25-7.35 (m, 5H, Ar-H), 6.35 (s, 1H, Ar-H), 5.37 (s, 2H, N-CH2), 2.41 (s,
3H, Ar-CH3); 13C-NMR (CDCl3) δ144.30, 141.49, 138.10, 136.60, 133.19, 131.46, 128.86, 127.62, 125.87,
114.23, 100.42, 46.86, 12.87; MS m/z (relative intensity): 222 (M+, 35), 149 (10), 91 (100), 65(15); Anal.
Calcd for C15H14N2: C, 81.05; H, 6.35; N, 12.60. Found: C, 81.04; H, 6.36; N, 12.61.

6-Methoxy-1,2-dimethyl-1H-pyrrolo[3,2-c]quinoline (7)
The compound (7) was obtained as a yellow oil in 45% yield from (3-iodo-8-methoxyquinolin-4-yl)
1
methylamine and allyl acetate in a 36 h reaction. H-NMR (CDCl3) δ 9.07 (s, 1H, Ar-H), 7.97(d, J = 8.8
Hz, 1H, Ar-H), 7.46 (t, J = 8.2 Hz, 1H, Ar-H), 6.99 (d, J = 7.6 Hz, 1H, Ar-H), 6.49 (s, 1H, Ar-H), 4.10 (s,
13
3H, O-CH3), 4.09 (s, 3H, N-CH3), 2.28 (s, 3H, Ar-CH3); C-NMR (CDCl3) δ 155.97, 147.59, 143.92,
136.91, 125.93, 125.30, 121.25, 112.34, 104.81, 100.94, 56.21, 55.89, 33.78, 13.29; MS m/z (relative
intensity): 225 (M+, 100), 197 (45), 181 (10) ; Anal. Calcd for C14H14N2O: C, 74.31; H, 6.24; N, 12.38.
Found: C, 74.29; H, 6.22; N, 12.40.
1,2-Dimethy-1H-pyrrolo[2,3-b]quinoline (8)
The compound (8) was obtained as a yellow solid in 67% yield from methyl(3-iodoquinolin-2-yl)amine and
allyl acetate in a 16 h reaction. mp 111-112ºC; 1H-NMR (CDCl3) δ 8.19 (s, 1H, Ar-H), 8.06(d, J = 8.0 Hz,
1H, Ar-H), 7.87 (d, J = 8.0 Hz , 1H, Ar-H), 7.59 (t, J = 7.6 Hz, 1H, Ar-H), 7.36 (t, J = 7.6 Hz, 1H, Ar-H),
6.30 (s, 1H, Ar-H), 3.86 (s, 3H, N-CH3), 2.51 (s, 3H, Ar-CH3); 13C-NMR (CDCl3) δ 150.37, 144.19, 142.22,
127.94, 127.57, 127.01, 125.31, 124.77, 122.44, 122.30, 96.88, 20.09, 13.64; MS m/z (relative intensity)
196 (M+, 100), 181 (59), 167 (17), 98 (30); Anal. Calcd for C13H12N2: C, 79.56; H, 6.16; N, 14.27. Found: C,
79.55; H, 6.19; N, 14.26.
1-Benzyl-2-methyl-1H-pyrrolo[2,3-b]quinoline (9)
The compound (9) was obtained as a yellow solid in 52% yield from benzyl(3-iodoquinolin-2-yl)amine and
allyl acetate in a 40 h reaction. mp 111-112ºC; 1H-NMR (CDCl3) δ 8.24 (s, 1H, Ar-H), 8.04 (d, J = 8.0 Hz,
1H, Ar-H), 7.88 (d, J = 8.0 Hz , 1H, Ar-H), 7.57 (t, J = 7.6 Hz, 1H, Ar-H), 7.36 (t, J = 7.6 Hz, 1H, Ar-H),
7.08-7.24 (m, 5H, Ar-H), 6.32 (s, 1H, Ar-H), 5.60 (s, 2H, N-CH2), 2.36 (s, 3H, Ar-CH3); 13C-NMR (CDCl3)
δ 144.35, 142.12, 138.19, 128.53, 128.49, 127.89, 127.81, 127.07, 126.97, 126.61, 125.33, 125.01, 122.55,
122.10, 97.73, 44.86, 13.78; MS m/z (relative intensity): 272 (M+, 55), 257 (25), 195 (17), 181 (25), 91
(100), 65 (34); Anal. Calcd for C19H16N2: C, 83.79; H, 5.92; N, 10.29. Found: C, 83.76; H, 5.93; N, 10.30.
ACKNOWLEDGMENTS
This work was supported by a grant (No. R11-2002-100-03002-2) from the ERC program of the Korea
Science & Engineering Foundation.
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