Synthesis of isoindole derivatives by palladium-catalyzed domino reaction of (2-alkynyl)phenylketone o-pentafluorobenzoyloximes

Article abstract of DOI:10.1055/s-0030-1259556

Isoindole derivatives were synthesized by the palladium-catalyzed cyclization of (2-alkynyl)phenylketone O-pentafluoro-benzoyloximes in the presence of organometallic compounds such as sodium formate and aryl boronic acid. Georg Thieme Verlag Stuttgart - New York.

Full text of DOI:10.1055/s-0030-1259556

LETTER
643
Synthesis of Isoindole Derivatives by Palladium-Catalyzed Domino Reaction
of (2-Alkynyl)phenylketone O-Pentafluorobenzoyloximes
Synthesis of Isoindole
i
D
eriva
t
tives suru Kitamura,* Yohei Moriyasu, Tatsuo Okauchi
Department of Applied Chemistry, Kyushu Institute of Technology, 1-1 Sensuicho, Tobata, Kitakyushu 804-8550, Japan
E-mail: +81(93)8843304; E-mail: kita@che.kyutech.ac.jp
Received 12 January 2011
OCOC6F5
Abstract: Isoindole derivatives were synthesized by the palladium-
catalyzed cyclization of (2-alkynyl)phenylketone O-pentafluoro-
benzoyloximes in the presence of organometallic compounds such
as sodium formate and aryl boronic acid.
OCOC6F5
Pd
N
Pd(PPh3)4 (10 mol%)
Et3N
N
DMF, 80 °C
Ph
Ph
Key words: domino reaction, isoindoles, Mizoroki–Heck reaction,
oximes, palladium
1
PdX
Et3N
Me3SiCl
CH2Cl2
H
HN
N
N
The palladium-catalyzed coupling reaction of aryl and vi-
nyl halides or triflates with alkenes is known as the Mizo-
roki–Heck reaction1 which is one of the most efficient
carbon–carbon bond-formation reactions, given the ad-
Et3N•HX
Pd(0)
Ph
Ph
Ph
from E-isomer 86%
from Z-isomer 82%
vantages of its wide functional-group tolerance and its use Scheme 1 Amino-Heck reaction
of easily accessible alkenes.2 Various carbocycles and
heterocycles have been synthesized via the intramolecular
In Scheme 2, the outline of our strategy towards isoindole
derivatives based on the palladium(0)-catalyzed domino
amino-Heck-type reaction is depicted, which is carried
out using (2-alkynylphenyl)ketone O-pentafluorobenzoy-
loximes 2 in the presence of an organometallic compound
(RM). The oxidative addition of O-pentafluorobenzoyl-
oximes 2 to a Pd(0) complex would generate the alkylide-
neaminopalladium(II) species 3, which cyclize smoothly
to alkenyl palladium intermediate 4, because phenylene
tether in 3 hold on the reaction points, the alkylideneami-
nopalladium species, and the alkynyl group at nearby
sites. Subsequently, transmetalation between 4 and RM
and the successive reductive elimination would give
isoindole derivatives 6.
Mizoroki–Heck reaction.3
Previously, we reported the oxidative addition of oxime
derivatives to palladium(0) complexes to generate alkyli-
deneaminopalladium(II) species.4–6 This process was ap-
plied to the transformation of olefinic ketone O-
pentafluorobenzoyloximes to various azaheterocycles via
the intramolecular Mizoroki–Heck-type reaction (amino–
Heck reaction).4,5,7 This amino-Heck reaction is not af-
fected by the geometry of oximes probably due to the lin-
ear-like structures of the alkylideneaminometal species
such as 1.6,8 Both E- and Z-g,d-unsaturated ketoximes cy-
clize to give pyrroles in good yields (Scheme 1).5a,b The
trial run of the Pd-catalyzed cyclization of the alkynyl ke-
tone oxime and the successive capture by carbon monox-
ide has been examined while the yield of the cyclized
product obtained was low.9
X
Pd
X
R2
R2
Pd
N
R2
Isoindole derivatives have potential as functional materi-
als such as organic light-emitting devices (OLED), solar
cells,10 and photodynamic therapy (PDT).11 Therefore, the
development of an efficient synthetic method to synthe-
size isoindole derivatives has recently drawn much atten-
tion.12
OCOC6F5
N
N
Pd(0)
R2
R2
R2
3
4
2
R1
Pd
R1
We envisaged that the amino-Heck-type cyclization of (2-
alkynyl)phenylketone oximes could be applied to the syn-
thesis of isoindole derivatives and thus examined. In this
letter, we describe the outcome of this investigation.
R2
R2
R1M
– MX
N
N
R2
– Pd(0)
R2
6
5
SYNLETT 2011, No. 5, pp 0643–0646
Advanced online publication: 11.02.2011
DOI: 10.1055/s-0030-1259556; Art ID: U03011ST
x
x.
x
x.
2
0
1
1
Scheme 2 Synthetic plan of isoindole derivatives via a domino ami-
no-Heck type reaction
© Georg Thieme Verlag Stuttgart · New York

644
M. Kitamura et al.
LETTER
First we examined the reaction of 2-alkynylketone O-pen- formed by the hydrolysis of the ketimine 14 formed by the
tafluorobenzoyloxime (E)-7a13 under various reaction transmetalation between alkylideneaminopalladium spe-
conditions in the presence of sodium formate (Table 1). cies 12 and sodium formate.
When the reaction was carried out by the treatment of 10
mol% Pd(PPh3)4 in acetonitrile at 70 °C, the oxime 7a was
Then, to explore the scope of the domino cyclization of O-
pentafluorobenzoyloximes of the (2-alkynyl)phenylcar-
consumed after three hours to give isoindole 8a in 59%
bonyl compound, we subjected various oximes 7 to the
yield (entry 1). Addition of Et3N or N,N-diisopropylethyl-
optimized reaction conditions [10 mol% Pd(PPh3)4, N,N-
amine increased the yield of the cyclization product 8a to
diisopropylethylamine, sodium formate in MeCN], and
66% and 71%, respectively (entries 2 and 3). In the pres-
Table 2 lists the results. Entries 1–7 show the results of the
ence of tetrabutylammonium bromide, the reaction be-
reaction of the oximes with the phenyl group R2. In the re-
came slower and the yield of 8a decreased (entry 4). In the
action of 7b (R1 = 2-naphthyl) at 60 °C, it took 4.0 hours
previous report on amino-Heck reaction, DMF was the
to consume the starting material 7b, and the desired isoin-
dole derivative 8b was obtained in 84% yield (entry 1).
best solvent in general4,5 but was found to be unsuitable in
this reaction (entry 5). Although we examined several
combinations of Pd(OAc)2 and phosphine ligands, the
yield of isoindole 8a did not increase (entries 6–8).
Ph
Pd(PPh3)4 (0.1 equiv)
HCO2Na (1.5 equiv)
i-Pr2NEt (5.0 equiv)
C6F5OCO
Ph
N
H
N
O
Ph
+
Table 1 Cyclization of 2-Alkynyl Ketone Oxime under Various
Ph
MeCN
reflux, 0.5 h
Reaction Conditionsa
Ph
Ph
(E)-9
10 7%
11 19%
Ph
HCO2Na
Ph
cyclization
Pd(0)
Ph
N
OCOC6F5
Ph
Pd cat.
HCO2Na
additive
N
hydrolysis
Ph
Pd(0), CO2, NaX
X
Pd
N
Ph
H
Pd
N
Ph
HCO2Na
NH
(E)-7a
8a
CO2
NaX
Pd(0)
Entry Pd cat (mol%) Additive Solvent Conditions Yield (%)b
Ph
Ph
Ph
14
12
13
1
2
3
4
5
6
7
8
Pd(PPh3)4 (10)
–
MeCN 70 °C
3.0 h
59
66
71
29
34
47
40
37
Scheme 3 Reaction of ethylene-tethered alkynyl ketone oxime 9
Pd(PPh3)4 (10) Et3N
MeCN 70 °C
3.0 h
The trans-styryl ketone oxime 7c gave cyclized product in
53% yield (entry 2). The oximes (R1 = Me and Bn) were
also transformed to the corresponding isoindoles in good
yields, which were unstable on silica gel relative to the
isoindoles (R1 = Ar or alkenyl; entries 3 and 4). In con-
trast, the isoindole derivative 8f (R1 = t-Bu) was stable and
isolated in good yield (entry 5). As shown in entry 6, the
a-keto ester oxime was not suitable for this cyclization. In
the amino-Heck reaction, aldoxime could not be used gen-
erally because nitrile was formed under the cyclization
conditions probably via the Beckmann fragmentation-
type reaction.5f
Pd(PPh3)4 (10) i-Pr2NEt MeCN 60 °C
1.5 h
Pd(PPh3)4 (10) TBAB
Pd(PPh3)4 (10) Et3N
MeCN reflux
19 h
DMF
60 °C
2.5 h
Pd(OAc)2 (13) Et3N
PPh3 (72)
MeCN 60 °C
3.5 h
Pd(OAc)2 (13) i-Pr2NEt MeCN 70 °C
P(o-tol)3 (53) 8.5 h
In the cyclization reaction, aldoxime 7h did not cyclize
but gave nitrile 15 in 65% yield (entry 7; Figure 1). Next,
we examined the effects of the substituent R2 (entries 8–
12). When R2 was a n-alkyl group, the corresponding cy-
clized product 8i was obtained in 21% yield (entry 8). The
oximes with R2 = t-Bu or TMS gave isoindole derivatives
while the products 8j and 8k were unstable and low yields
were obtained (entries 9 and 10). Reaction of the terminal
alkynyloxime 7l gave no cyclized product (entry 11). In
the reaction of the terminal alkynyloxime 7l, we did not
obtain any cyclized product (entry 11).
Pd(OAc)2 (16) i-Pr2NEt MeCN 70 °C
DPPF (28) 3.5 h
a Molar ratio: 7a/HCO2Na/additive = 1.0:1.5:5.0.
b Isolated yield.
o-Phenylene tether is important for the Pd(0)-catalyzed
cyclization of b-alkynyl ketone oxime. When we treated
ethylene-tethered alkynyl ketone oxime (E)-9 with 10
mol% Pd(PPh3)4, 5 equivalents of N,N-diisopropylethyl-
amine, and 1.5 equivalents of sodium formate in acetoni-
trile, the reaction was slow and the desired pyrrole 10 was
obtained in 7% yield after stirring for 30 minutes at the re-
flux temperature (Scheme 3). In this reaction, ketone 11
was formed as a byproduct, which is supposed to be
Table 3 shows the results of the Pd(0)-catalyzed cycliza-
tion of (E)-7a in the presence of organoboronic acid.
When phenylboronic acid was used, the reaction proceed-
ed as expected to afford the isoindole derivative 16a with
Synlett 2011, No. 5, 643–646 © Thieme Stuttgart · New York

LETTER
Synthesis of Isoindole Derivatives
645
Table 2 Cyclization of Various (2-Alkynylphenyl)ketone O-Penta-
fluorobenzoyloximes 7a
Table 3 Pd-Catalyzed Cyclization of Oximes 7 in the Presence of
Boronic Acidsa
R2
Ph
Ar
R2
OCOC6F5
OCOC6F5
Ph
Ph
Pd(PPh3)4 (cat.)
HCO2Na
Pd(PPh3)4 (cat.)
Ar-B(OH)2
N
N
N
N
i-Pr2NEt
i-Pr2NEt
Ph
R1
R1
MeCN, reflux
MeCN
(E)-7a
16
7
8
Entry
Ar
Time (h) 16
Yield (%)b
Entry R1
R2
7
Conditions
8
Yield (%)b
8b 84
8c 53
8d 77e
1
2
2-naphthyl Ph
7bc 60 °C, 4.0 h
7cd reflux, 3.0 h
7dc 60 °C, 1.5 h
7ef 60 °C, 1.5 h
7fc 80 °C, 8.0 h
7gc 80 °C, 2.5 h
7hc 60 °C, 1.0 h
1
2
3
4
5
Ph
7.5
8.5
6.0
6.0
7.0
16a
60
42
78
33
18
4-Tol
16bc
16cd
16d
trans-styryl Ph
4-MeOC6H4
4-F3CC6H4
2-Tol
3
Me
Bn
Ph
Ph
Ph
Ph
Ph
4
8e
8f
60e
57
16ed
5
t-Bu
CO2Et
H
a Molar ratio: 7a/Pd(PPh3)4/Ar-B(OH)2/i-Pr2NEt = 1.0:0.1:1.5:5.0.
6
8g c.m.g
b Isolated yield.
c E/Z = 1:1
7
8h
8i
0h
21
d E/Z mixture (3:2). Stereochemistry is undetermined.
8
Ph
pentyl 7ic
t-Bu
7jf
75 °C, 9.0 h
80 °C, 5.0 h
proceeded rapidly to give the isoindole derivative 8a in
79% yield. Although we expected to obtain isoindole 18
in the reaction with HCO2Na, isoindole 8a was obtained
in 84% as the sole product under these reaction condi-
tions.
9
Ph
8j
8k
8l
4
8
0
10
11
Ph
TMS 7kd 70 °C, 4.0 h
7lc
H 60 °C, 8.0 h
Ph
a Molar ratio: 7/Pd(PPh3)4/HCO2Na/i-Pr2NEt = 1.0:0.1:1.5.5.0.
b Isolated yield.
Ph
c E-isomer.
OCOC6F5
Pd(PPh3)4 (0.1 equiv)
N
Ph
d E/Z = 1:1
N
e 1H NMR yield (1,1,2,2,-tetrachloroetane was used as an internal
i-Pr2NEt (5.0 equiv)
Ph
8a
79%
(84%)a
+
Ph
standard.).
MeCN
60 °C, 0.5 h
f E/Z = ca. 2:1.
g Complex mixture.
18 (0%)a
– Pd(0)
Pd-H
17
base
base⋅HX, Pd(0)
h Nitrile 15 (Figure 1) was obtained in 65% yield.
E/Z = 1:1
Pd(0)
CN
X
Ph
Ph
PdX
H
Ph
Pd
N
H
Ph
N
N
H
H
HCO2Na
15
Ph
Ph
Ph
Figure 1
19
20
21
a diphenylmethylene group in 60% yield (entry 1). The re- Scheme 4 Amino-Heck reaction of (2-alkenylphenyl) ketone oxime
17. a HCO2Na (1.5 equiv) was added in the reaction.
action with p-tolyl boronic acid gave the isoindole deriv-
ative 16b in 42% yield, which was a mixture of E- and Z-
isomers (entry 2). When p-methoxyphenylboronic was
used, isoindole derivative 16c was obtained in high yield
(entry 3). However, the use of electron-deficient-group-
substituted boronic acid caused a decrease of the yield of
the desired cyclized product (entry 4). By using o-tolyl
boronic acid, isoindole derivative 16e was formed in 18%
(entry 5).
In summary, we developed Pd-catalyzed synthesis of
isoindole derivatives from (2-alkynyl)phenylketone O-
pentafluorobenzoyl oximes in the presence of organome-
tallic compounds In this reaction, o-phenylene tether in
oxime is important for the efficient cyclization.
Similar isoindole derivative was synthesized by the ami-
no-Heck reaction of O-pentafluorobenzoyloxime of (2-
alkenyl)phenyl ketone 17 (Scheme 4). By treating
Pd(PPh3)4 and i-Pr2NEt in MeCN at 60 °C, the cyclization
Typical Procedure for the Synthesis of Isoindole Derivatives 8
by Pd-Catalyzed Cyclization of (2-Alkynyl)phenylketone
O-Pentafluorobenzoyloximes 7 (Table 2, Entry 1)
To a mixture of O-pentafluorobenzoyl oxime 7b (183 mg, 0.338
mmol), N,N-diisopropylethylamine (0.30 mL, 1.8 mmol), and sodi-
Synlett 2011, No. 5, 643–646 © Thieme Stuttgart · New York

646
M. Kitamura et al.
LETTER
um formate (38.3 mg, 0.56 mmol) in dry MeCN (6.7 mL),
Pd(PPh3)4 (41.5 mg, 0.036 mmol) was added under an argon atmo-
sphere at r.t. This mixture was stirred at 60 °C for 4 h. The mixture
was diluted with EtOAc, and filtered through a Celite pad. The fil-
trate was evaporated under vacuum. The residue was purified by
column chromatography (SiO2, hexane–EtOAc = 9:1) to afford 8b
(94.7 mg, 84%) as a yellow solid.
Saku, O.; Narasaka, K. Chem. Lett. 2002, 606. (h) Chiba,
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Spectral Data for Isoindole Derivative 8b
IR (KBr): 2723, 2667, 2360, 2325, 1639, 1197, 1143, 1066, 917,
1
757, 740, 725, 713, 680, 493, 466 cm–1. H NMR (400 MHz,
CDCl3): d = 7.34 (1 H, s), 7.38 (1 H, t, J = 7.3 Hz), 7.46–7.52 (4 H,
m), 7.55–7.59 (2 H, m), 7.93 (2 H, t, J = 6.4 Hz), 8.02 (2 H, d,
J = 8.8 Hz), 8.07 (1 H, d, J = 6.8 Hz), 8.38 (1 H, dd, J = 8.6, 1.5 Hz),
8.44 (2 H, d, J = 7.6 Hz), 8.69 (1 H, s). 13C NMR (100 MHz,
CDCl3): d = 120.0, 122.5, 126.1, 126.4, 126.5, 127.3, 127.6, 127.9,
128.3, 128.5, 128.7, 129.0, 129.4, 132.4, 132.5, 133.2, 134.5, 135.9,
136.4, 143.4, 149.7, 169.3. Anal. Calcd (%) for C25H17N: C, 90.60;
H, 5.17; N, 4.23. Found: C, 90.72; H, 5.33; N, 4.25.
Acknowledgment
This work was supported by a Grant-in-Aid from the Ministry of
Education, Culture, Sports, Science, and Technology of Japan.
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Y.; Yasuta, K.; Goto, R.; Kimura, M.; Taya, M. J. Am.
Chem. Soc. 2010, 132, 4054.
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4 steps: i) (CF3SO2)2O, N,N-dimethyl-4-aminopyridine
(cat.), pyridine, CH2Cl2, –78 °C to 0 °C, 1.5 h (99% yield);
ii) PhC≡CH, Pd(PPh3)4 (cat.), CuI (cat.), Et3N, n-Bu4NBr,
DMF, 70 °C, 2.5 h (97% yield);14 iii) NH2OH·HCl, pyridine,
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0 °C, 0.5 h (92% yield). Other (2-alkynyl)phenylketone
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