Synthesis of isoindolinones via a ruthenium-catalyzed cyclization of N-substituted benzamides with allylic alcohols

Article abstract of DOI:10.1039/c4cc09877c

N-Substituted aromatic and heteroaromatic amides reacted with substituted allylic alcohols in the presence of a ruthenium catalyst, AgSbF₆ and a Cu(OAc)₂·H₂O oxidant, affording 3-substituted isoindolinone derivatives with diverse substituents in good to excellent yields. A possible reaction mechanism involving a five-membered ruthenacycle intermediate was proposed and strongly supported by experimental evidence.

Full text of DOI:10.1039/c4cc09877c

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COMMUNICATION
Synthesis of isoindolinones via a ruthenium-catalyzed cyclization of
N-substituted benzamides with allylic alcohols
Ramaswamy Manoharan and Masilamani Jeganmohan*
Received (in XXX, XXX) Xth XXXXXXXXX 20XX, Accepted Xth XXXXXXXXX 20XX
5
DOI: 10.1039/b000000x
8
b-g
N-Substituted aromatic and heteroaromatic amides reacted
isoindolinones in good to excellent yields.
In the reaction,
with substituted allylic alcohols in the presence of ruthenium
mostly activated alkenes such as acrylates, ethyl vinyl ketone,
catalyst, AgSbF6 and Cu(OAc) H O oxidant, affording 3- 40 acrylamide and conjugated 1,2-diketones were used.
.
8
2
2
Due to the vast availability, easy accessibility and simple
preparation of allylic alcohols, these have been widely used as
alkene partners in the coupling reaction with aromatic
electrophiles or organometallic reagents in the presence of metal
substituted isoindolinone derivatives with diverse substituents
in good to excellent yields. A possible reaction mechanism
involving a five-membered ruthenacycle intermediate was
proposed and strongly supported by experimental evidence.
1
0
9
4
5
5
5
0
5
catalysts. It is important to note that in most of the catalytic
reactions, allylic alcohols are chemically equivalent to α,β-
unsaturated enones and aldehydes. Recently, allylic alcohols are
also efficiently used as a coupling partner in the reaction with
heteroatom substituted aromatics, and this transformation leads to
ortho alkylated aromatics in the presence of metal catalysts via
The isoindolinone core unit is present in various natural products,
1
biologically active molecules and pharmaceuticals (Figure 1). It
1
2
2
5
0
5
has been serving as a key synthetic intermediate for synthesizing
2
various highly useful organic molecules and natural products.
Particularly, the 3-substituted isoindolinone skeleton is found in
1
0
3
C-H bond activation. Herein, we report a ruthenium-catalyzed
cyclization of N-substituted benzamides with allylic alcohols to
give 3-substituted isoindolinone derivatives in good yields. A
various biologically active molecules. As a result, various
synthetic methods are available in the literature to synthesize 3-
4-7
substituted isoindolinone derivatives. Generally, 3-substituted
isoindolinones are prepared by nucleophilic addition of metal
possible reaction mechanism involving
a
five-membered
4
a
ruthenacycle intermediate was proposed and strongly supported
by experimental evidence.
reagents into isoindoline-1,3-diones, the cyclization of ortho-
4
b-c
substituted aryllithiums with imines,
or strong base-induced
metalation followed by functionalization at the 3-position of
4
d
isoindolinones. Additionally, 3-substituted isoindolinones can
be prepared by metal-catalyzed cyclization of ortho-halo
5
a
substituted aromatics with imines and tandem cyclization of
5
b
ortho halo substituted aromatics with CO and amines.
Scheme 1 Cyclization of N-substituted Benzamides with 2a
Treatment of n-benzyl 4-methoxy benzamide (1a) with 3-
6
0
2
buten-2-ol (2a) (2.2 equiv) in the presence of [{RuCl (p-
cymene)} ] (5.0 mol %), AgSbF (20 mol %) and Cu(OAc) H O
2 6 2 2
.
3
0
Figure 1. Isoindolinone core biologically active molecules.
(
2.2 equiv) in 1,2-dichloroethane at 110 C for 16 h gave 3-
substituted isoindolinone derivative 3aa in 72% isolated yield
Scheme 1). Initially, the cyclization reaction was examined with
Generally, Recently, 3-substituted isoindolinones were
efficiently prepared by using metal catalysts via C-H bond
activation in a highly atom economical and environmentally
(
6
5
various solvents such as MeOH, iso-PrOH, THF, DMF, 1,2-
dimethoxyethane and toluene under similar reaction conditions.
Among them, ClCH CH Cl was very effective, giving 3aa in
7
6-8
friendly manner. Aromatic imines underwent cyclization with
isocyanates in the presence of a rhenium catalyst, providing 3-
3
5
8
a
2
2
substituted isoindolinones. N-Substituted benzamides reacted
9% GC yield. THF, 1,4-dioxane and 1,2-dimethoxyethane were
with alkenes in the presence of metal catalysts, giving
partially effective, affording product 3aa in 34%, 45% and 48%
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[journal], [year], [vol], 00–00 | 1

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Page 2 of 4
GC yields, where as remaining solvents were totally ineffective.
amount is sufficient for the reaction. The amount of reactant 2a
(1.2 equiv and 3.0 equiv apart from 2.2 equiv) was also tested. In
a
Table 1 Scope of the N-benzyl substituted benzamides
View Article Online
1
.2 equiv of 2a, product 3aa was observed in 55% GC yield and
DOI: 10.1039/C4CC09877C
b
Entry
1
Product 3
Yield (%)
in 3.0 equiv of 2a, product 3aa was observed in 79% GC yield.
The cyclization reaction was also tested at 60 C and 80 C apart
from 110 C. In 60 C, no product 3aa was observed and at 80 C
product 3aa was observed in 35% GC yield. Control experiments
3
3
4
4
5
5
6
6
0
5
0
5
0
5
0
5
6 2 2
showed that in the absence of AgSbF or [{RuCl (p-cymene)} ]
2
2
.
1
2
3
4
5
6
7
8
1j: R = Me
3ja: R = Me
69
60
61
59
58
47
54
46
or Cu(OAc) H O, no 3aa was obtained.
2 2
2
2
1k: R = H
3ka: R = H
Under the optimized reaction conditions, the cyclization of
other N-substituted benzamides 1b-i with 2a was tested (Scheme
2
2
1l: R = I
3la: R = I
2
2
1m: R = Br
3ma: R = Br
2
2
1
). N-Phenyl 1b and cyclohexyl 1c substituted benzamides
reacted with 2a, providing cyclization products 3ba and 3ca in
9% and 46% yields, respectively. N-Methyl substituted
1n: R = Cl
3na: R = Cl
2
2
1o: R = F
3oa: R = F
2
2
1p: R = CF
3
3pa: R = CF
3
5
2
2
1q: R = NO
2
3qa: R = NO
2
benzamide 1d gave isoindolinone derivative 3da in 67% yield.
But, N-tert butyl benzamide 1e provided a mixture of cyclic
product 3ea and ortho alkenylated product 3ea’ in 45% combined
yield in a 1:0.4 ratio. In other N-substituted benzamides 1f-i, the
expected cyclization product was not observed.
3
3
9
1r: R = OMe
3ra: R = OMe
80
65
62
The scope of the cyclization reaction was examined with N-
benzyl substituted benzamides 1j-v (Table 1). Benzamides 1j and
3
3
1
1
0
1
1s: R = Me
3sa: R = Me
3
3
1t: R = Br
3ta: R = Br
1
3
2
k reacted efficiently with 2a, providing the cyclization products
ja and 3ka in 69% and 60% yields, respectively (entries 1 and
). Halogen groups such as I, Br, Cl and F substituted benzamides
1
2
53
58
1l-o reacted efficiently with 2a, affording products 3la-3oa in
good to moderate yields, respectively (entries 3-6). Interestingly,
electron-withdrawing groups such as CF and NO substituted
c
O
3
2
Ph
benzamides 1p and 1q reacted with 2a, giving cyclization
products 3pa and 3qa in 54% and 46% yields, respectively
(entries 7 and 8). Apart from the para substituted benzamides,
ortho OMe, Me and Br substituted benzamides 1r-t also
efficiently participated in the reaction, yielding products 3ra-ta in
N
1
3c
O
3
va
c
80%, 65% and 62% yields, respectively (entries 9-11).
1
4
60
Unsymmetrical 3,4-dimethoxy (1u) and 2-naphthyl (1v)
substituted benzamides regioselectively reacted with 2a yielding
products 3ua and 3va in 53% and 58% yields, respectively
(entries 12 and 13). In the substrates 1u and 1v, the C-H bond
activation takes place at the C-6 position of benzene ring and the
C-3 position of naphthalene ring selectively. Interestingly,
heteroaromatic amide 1w also efficiently participated in the
reaction, affording product 3wa in 60% yield (entry 14).
a
All reactions were carried out using 1j-w (100 mg), ethyl-2- buten-2-ol
2a) (2.2 equiv), [{RuCl (p-cymene)} ] (5 mol %), AgSbF (20 mol %)
O (2.2 equiv) in ClCH CH Cl (3.0 mL) at 110 C for 16
(
2
2
6
.
5
and Cu(OAc)
2
H
2
2
2
b
c
h. Isolated yield. The reaction was carried at 110 C for 28 h.
6
The reaction was also tested with additives such as AgSbF ,
AgBF , AgOTf and KPF . Among them, AgSbF was very
4
6
6
effective, giving product 3aa in 79% GC yield. AgBF
AgOTf were partially effective, yielding 3aa in 47% and 27%
GC yields, respectively. KPF was not suitable for the reaction.
4
and
1
1
2
2
0
5
0
5
6
The cyclization reaction was also tested with various acetate and
oxidant sources such as AgOAc, CsOAc, KOAc, NaOAc, Ag O
2
.
.
2 2 2 2
and Cu(OAc) H O. Among them, Cu(OAc) H O was very
effective, providing 3aa in 79% GC yield. Remaining acetate
sources were not effective. The reaction was also tested with less
.
than 50 mol % of Cu(OAc)
2
H
2
O under an air atmosphere.
However, in the reaction, product 3aa was observed only in 38%
GC yield. The reaction was tested with other catalysts (5 mol %)
.
such as Ru(COD)Cl , Ru(PPh ) Cl and RuCl H O apart from
2
3 3
2
3
2
Scheme 2 Scope of the substituted allylic alcohols
[{RuCl
2 2
(p-cymene)} ]. However, no cyclization product 3aa was
The scope of the cyclization reaction was also further
examined with substituted allylic alcohols (Scheme 2). Treatment
of pent-1-en-3-ol (2b), hex-1-en-3-ol (2c) and hept-1-en-3-ol (2d)
with benzamide 1a under similar reaction conditions gave
cyclization products 3ab-ad in 67%, 65% and 62% yields,
observed in these complexes. The amount of catalyst [{RuCl (p-
2
7
0
2
cymene)} ] (2 mol %) and (10 mol %) was also examined. In 2
mol % and 10 mol % of catalyst, product 3aa was observed in
32% and 80% GC yields, respectively. Thus, 5 mol % of catalyst
2
|
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.
respectively. 1-Phenylbut-3-en-2-ol (2e) also nicely participated
6 2 2
complex (1.0 equiv), AgSbF (4.0 equiv) and Cu(OAc) H O (1.2
in the reaction, affording the corresponding cyclization product 45 equiv) in DCE solvent at 60 C for 8 h. In the reaction,
View Article Online
DOI: 10.1039/C4CC09877C
3
ae in 68% yield. Interestingly, prop-2-en-1-ol (2f) reacted
metalacycle intermediate 5 was isolated. However, we were not
efficiently with 1a, giving a formyl substituted cyclic compound
3af in 60% yield.
able to crystallize the intermediate 5. But, the complex 5 was
tentatively assigned by H, C NMR, HRMS and MALDI-TOF
spectroscopic techniques (see Supporting Information). To
1
13
5
0
5
0
5
0
6-10
Based on the previous reports
and our observation, a
possible reaction mechanism is proposed in Scheme 3. Basically, 50 confirm the formation of activated alkene 6, 1-phenylbut-3-en-2-
a multi-step reaction is involved in the cyclization reaction. First,
ol (2e) was treated with ruthenium catalyst, AgSbF
6
and
-
.
AgSbF likely removes the Cl ligand from [{RuCl (p-cymene)} ]
Cu(OAc) H O at 110 C for 3 h. In the reaction, approx. 1:1
6
2
2
2
2
1
1
2
2
3
complex in the presence of Cu(OAc)
2
providing a cationic
mixture of 1-phenylbut-3-en-2-one (6e) and the reduced 1-
phenylbutan-2-one (6e’) were observed in a combined 76% yield.
ruthenium acetate species 4. Coordination of the nitrogen atom of
1
to the ruthenium species 4 followed by ortho-metalation 55 It seems in the cyclization reaction, initially product 6e is formed
provides ruthenacycle intermediate 5. Coordinative insertion of
α,β-unsaturated enone 6 into the Ru–carbon bond of intermediate
5 gives intermediate 7. We strongly believe that the allylic
alcohols 2 convert into α,β-unsaturated enones 6 in the presence
which further reacted with benzamide 1 providing the cyclization
product 3. If benzamide is not present in the reaction mixture,
alkene moiety of 6e subsequently reduced. Further, we have tried
to isolate ortho alkenylated benzamide 8 in the reaction of 2-
1
1
of ruthenium catalyst and Cu(OAc)
2
.
β-Deprotonation of 60 thienyl amide (1w) with 2a under the optimized reaction
intermediate 7 by acetate source followed by protonation of
nitrogen affords ortho-alkenylated benzamide 8 and regenerates
conditions at the shorter reaction time 8 h. In the reaction, the
expected alkenylated product 8a was observed in 47% yield.
11c
the ruthenium species 4 (proceeds via path A).
Later,
Later, ortho alkylated benzamide 8a was treated with ruthenium
.
coordination of the nitrogen atom of ortho-alkenylated
benzamide 8 into ruthenium species 4 followed by intramolecular 65 expected cyclic compound 3wa in 85% yield. Further, benzamide
catalyst, AgSbF
6
and Cu(OAc)
2
H
2
O at 110 C for 16 h giving the
coordination of double bond into ruthenium affords intermediate
and AcOH. Intramolecular coordinative insertion of N-Ru bond
1a reacted with methyl vinyl ketone (6a) under the optimized
reaction conditions providing the expected cyclic product 3aa in
63% yield. This experimental evidence clearly supports the
proposed mechanism in Scheme 3.
9
of intermediate 9 into the alkene moiety followed by enolization
provides ruthenium enolate intermediate 10. Protonation of
intermediate 10 in the presence of AcOH provides product 3 and
regenerates the active ruthenium species 4. The control of the
product formation 11 which proceeds via enolization of
intermediate 7 followed by protonation is highly important to
1
0
success the present cyclization reaction (via path B).
O
N
R2
[{RuCl2(L)}2]
O
R1
O
R2
AgSbF6
AgCl
N
3
H
R3
Cu(OAc)2
R1
1
[
Ru(OAc)n(L)]+[SbF6]-n
4
L = p-cymene
-
2 AcOH
R2
n = 1 or 2
O
O
AcOH
O
N
Ru
R2
N
R2
ORuL
R3
N
H
R1
L
R1
5
10
R1
O
11
R3
AcOH
O
R2
O
Path B
R2
O
N
N
Ru
L
Ru
L
R1
R3
R1
7
O
R3
9
O
R2
6
O
R3
N
H
Ru cat.
Cu(OAc)2
-
H2
R1
O
Path A
8
OH
R3
R3
2
Scheme 3 Proposed mechanism
The formation of
a
key five-membered ruthenacycle
70
3
5
intermediate 5 is a rate determining reversible step in the
reaction. To support the reversible step, N-benzyl 4-methoxy
Scheme 4 Mechanistic evidence
To success the present cyclization reaction, to suppress the
enolization of intermediate 7 into 11 is highly important. It is
known that N-N-disubstituted benzamides reacted with allylic
benzamide (1a) was treated with ruthenium catalyst, AgSbF
6
and
.
Cu(OAc) H O, D O in DCE solvent at 110 C for 16 h. As
2
2
2
expected, 54% deuterium incorporations were observed at both 75 alcohols leading to ortho alkylated benzamides in the presence of
1
0
4
0
ortho carbons of benzamide d-1a in a combined 74 % yield
Scheme 4). In the meantime, we have tried to isolate the key
ruthenacycle intermediate 5 in the reaction of 4-methoxy
benzamide 1a with a stoichiometric amount of ruthenium
rhodium or ruthenium complexes. But, in the present reaction,
N-substituted benzamides reacted with allylic alcohols yielding
isoindolinone derivatives 3. To know the clear mechanism, we
have tried the reaction of N-N-diethyl benzamide 14 with 2a
(
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Page 4 of 4
5
0
J. B. Campbell, R. F. Dedinas and S. Trumbower-Walsh, Synlett.
010, 3008.
(a) J. B. Campbell, R. F. Dedinas and S. Trumbower-WVaileswh,ASrtyicnleleOttn.line
under the optimized reaction conditions (Scheme 5). In the
reaction, ortho alkenylated benzamide 15 and ortho alkylated
benzamide 16 were observed in combined 57% yields in a 1:1
ratio. But, in the presence of AcOH (3.0 equiv) under similar
reaction conditions, the same reaction provided a major amount
of ortho alkylated benzamide 16 along with a minor amount of 15
in 69% yield in a 10:1 ratio. Similarly, the reaction of N-
substituted benzamide 1a with 2a was tried in the presence of 3.0
equiv of AcOH under the optimized reaction conditions. In the
reaction, cyclization product 3aa and ortho alkylated benzamide
2
5
6
2
010, 2010, 3008. (b) X. Gai, R. Gri Dg gO ,I: T1 0. .1 K0 3h 9a /mC n4 aCe Cn ,0 9 S8 .7 7C
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5
0
5
55
60
Selected cyclization reviews: (a) P. Thansandote and M. Lautens,
Chem. Eur. J. 2009, 15, 5874. (b) T. Satoh and M. Miura, Chem. Eur
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2
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1
2
014, 47, 281.
1
8 were observed in 21% and 69% yields, respectively. In this
7
Selected recent ruthenium papers: (a) P. B. Arockiam, C.
Fischmeister, C. Bruneau and P. H. Dixneuf, Green Chem. 2011, 13,
3075; (b) Y. Hashimoto, K. Hirano, T. Satoh, F. Kakiuchi and M.
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stage, we conclude that an excess amount of AcOH might
increases the electrophilicity of carbonyl group in intermediate 7
via protonation. It is likely that intermediate 19 could be formed.
Thus, instead of β-hydride elimination, enoloization takes place
6
7
7
8
8
9
9
5
0
5
0
5
0
5
1
1
0c, 12
effectively.
3
478; (e) Y. Kommagalla, K. Srinivas and C. V. Ramana, Chem. Eur.
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Chem. Int. Ed. 2013, 52, 11879. Rhodium: (b) F. Wang, G. Song and
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8
2
011, 13, 1214. (e) F. W. Patureau, T. Besset and F. Glorius, Angew.
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9
Scheme 5 Reaction of N-N-Diethyl Benzamide with 2a
In conclusion, we have demonstrated a ruthenium-catalyzed
cyclization of N-substituted benzamides with allylic alcohols in
10 (a) L. Huang, Q. Wang, J. Qi, X. Wu, K. Huang and H. Jiang,
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2
0
the presence of ruthenium catalyst.
A possible reaction
mechanism involving a five-membered ruthenacycle intermediate
was proposed and strongly supported by experimental evidence.
We thank the DST (SR/S1/OC-26/2011), India for the support
of this research. R. M. thanks the CSIR for a fellowship.
6
489.
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Notes and references
a
Department of Chemistry, Indian Institute of Science Education and
Research, Pune 411021, India; E-mail: mjeganmohan@iiserpune.ac.in
†
Electronic Supplementary Information (ESI) available: Detailed
experimental procedures and spectroscopic data. See
DOI: 10.1039/b000000x/
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