Synthesis of highly functionalized allene-appended oxindoles and 2-oxo-1,2-dihydroindol-3-ylidene-2,5-dihydrofurans via claisen rearrangement and cyclization

Article abstract of DOI:10.1055/s-0029-1217194

Synthesis of highly functionalized allene appended oxindole derivatives from vinyl propargyl ether derivatives of Morita-Baylis-Hillman adducts of isatin via Claisen rearrangement has been achieved. Synthetic utility of the allene derivatives obtained has

Full text of DOI:10.1055/s-0029-1217194

LETTER
1591
Synthesis of Highly Functionalized Allene-Appended Oxindoles and
2-Oxo-1,2-dihydroindol-3-ylidene-2,5-dihydrofurans
via Claisen Rearrangement and Cyclization
Synthesis of
Highl
a
y Functiona
d
lized
A
llene
i
-Appen
v
ded Oxindol
e
e
s
l Vaithiyanathan, Kodirajan Selvakumar, Ponnusamy Shanmugam*1
Chemical Sciences and Technology Division, National Institute for Interdisciplinary Science and Technology (NIIST),
Thiruvananthapuram 695019, Kerala, India
Fax +91(44)24911589; E-mail: shanmu196@rediffmail.com
Received 10 October 2008
in the area of novel synthetic applications of MBH ad-
ducts,10 in particular with isatin derivatives,10a–c,e we have
developed a novel method for the synthesis of highly
functionalized allene-appended oxindoles and 2-oxo-1,2-
Abstract: Synthesis of highly functionalized allene appended oxin-
dole derivatives from vinyl propargyl ether derivatives of Morita–
Baylis–Hillman adducts of isatin via Claisen rearrangement has
been achieved. Synthetic utility of the allene derivatives obtained
has been demonstrated with the synthesis of methyl 2,5-dihydro- dihydro-indol-3-ylidene-2,5-dihydrofuran derivatives via
5-methyl-2-(1-methyl-2-oxoindolin-3-ylidene)furan-3-carboxylates in
Claisen rearrangement and cyclization reactions. The de-
a one-pot cyclization reaction under basic conditions. A plausible
tails of this preliminary study are the subject matter of this
mechanism of the reaction is presented.
communication.
Key words: Morita–Baylis–Hillman adduct, Claisen rearrange-
As shown in the retrosynthetic analysis in Scheme 1
ment, isatin, allenes, vinyl propargyl ethers, dihydrofuran
2-oxo-indol-3-ylidene-furan derivatives A could be ob-
tained from the allene derivative B which in turn could be
synthesized from propargyl vinyl ether derivative C via
The Claisen rearrangement2 permits new C–C bond for-
Claisen rearrangement. The propargyl ether derivative C
mation, intramolecular cyclization, and introduction of
could readily be obtained from propargyl ether D via a
1,3-allylic proton shift. Compound D can be prepared
from the MBH adduct of isatin E by an isomerization.
carbonyl functionality. Allenes3,4 are attractive substrates
with a unique electronic structure and high reactivity to-
wards a number of synthetic transformations.5 Allenes can
be prepared by a variety of methods,6 but they are partic-
ularly associated with the Claisen rearrangement of vinyl
propargyl ethers.7 The synthetic versatility of isatin and its
derivatives has led to the extensive use of this template in
heterocycle construction.8 Amongst various carbon–car-
bon bond-forming reactions, the Morita–Baylis–Hillman
(MBH) reaction has emerged as an important reaction giv-
ing rise to densely functionalized molecules and is consid-
ered to be atom economic.9 In continuation of our research
Preliminary work addressed the isomerization reaction of
MBH adducts 1–10 with propargyl alcohol and montmo-
rillonite K10 clay under thermal (low yield) and micro-
wave irradiation (better yield) conditions to afford
propargyl ether derivatives 11–20 as outlined in
Scheme 2. In order to obtain suitable substrates for
Claisen rearrangement, the propargyl ether derivatives
10–20 were further subjected to 1,3-allylic proton shift in
acetone using 1.2 equivalents of DABCO for 30 minutes
MeO2C
Z
Z
O
R2
R2
C
O
DABCO
acetone
chlorobenzene
O
135 °C, 4 h
O
O
N
R1
C
N
R1
O
N
A
B
DABCO
acetone
O
Z
R2
R2
HO
N
propargyl alcohol
Z
O
K10 clay, reflux, 1–4 h
(or)
O
N
R1
R1
MW, 15–30 min
E
D
Scheme 1
SYNLETT 2009, No. 10, pp 1591–1596
x
x
.x
x
.2
0
0
9
Advanced online publication: 02.06.2009
DOI: 10.1055/s-0029-1217194; Art ID: D35808ST
© Georg Thieme Verlag Stuttgart · New York

1592
V. Vaithiyanathan et al.
LETTER
O
O
H
C
Z
Z
R2
R2
R2
R2
HO
N
R2
Z
Z
Z
b
chlorobenzene
a
O
O
O
O
O
N
R1
O
135 °C, 4 h
[3,3]
O
N
R1
21–30
N
R1
N
R1
R1
1–10
11–20
21–30
R1 = Me, Et, Bn; R2 = H, Me, Br; Z = CO2Me, CN
31–40
R1 = Me, Et, Bn; R2 = H, Me, Br; Z = CO2Me, CN
Scheme 2 Reagents and conditions: (a) propargyl alcohol, K10
clay, reflux, 1–4 h (or) MW, 30 min; (b) DABCO, acetone, r.t., 30
min.
Scheme 3
O
O
O
O
O
O
3
[3,3]
at room temperature to afford the vinyl propargyl ethers
21–30 in excellent yields (Scheme 2). The results are
summarized in Table 1.
C
3
chlorobenzene
135 °C, 4 h
O
N
O
N
1
1
80%
Claisen rearrangement of vinyl propargyl ethers 21–30 in
refluxing chlorobenzene (Scheme 3) afforded the rear-
ranged allene products 31–40 as inseparable 1:1 mixtures
of diastereomers (based on two aldehyde peaks in the 1H
NMR spectra) in moderate to very good yields (Table 2).
41
43
Scheme 4
rangement and starting material was present even after ex-
tending the reaction time (12 h).
We further extended the strategy to propargyl derivatives
of spiro-g-butyrolactones 41 and 42.11 Thus, the propargyl
ether derivative of E-spiro-g-butyrolactone 41 in chlo-
robenzene was heated at 135 °C for four hours. As expect-
ed, the rearranged allene product 43 was obtained in
excellent yield (Scheme 4). The successful rearrangement
was confirmed unambiguously by 1H NMR analysis of 43
with the aldehyde proton at d = 9.48 ppm and allene pro-
tons at d = 4.80, 4.96 (dd, J = 7.0, 12.0 Hz), 5.62 (t, J = 7.0
Hz) ppm being diagnostic. It is interesting to note that the
rearranged product has a newly created quaternary center
to which allene and aldehyde groups are attached. Howev-
er, the Z-isomer 42 under the same Claisen rearrangement
conditions described for 41 did not undergo any rear-
To check the reactivity and synthetic utility of the allene
products obtained, we examined a one-pot, base-catalysed
reaction as shown in the Scheme 5. Thus, allene 31 with
DABCO (1.5 equiv) in acetone under reflux afforded a 1:1
mixture of E- and Z-isomers of methyl 2,5-dihydro-5-
methyl-2-(1-methyl-2-oxoindolin-3-ylidene) furan-3-car-
boxylate 44a,b in moderate combined yield (45%). The
1
structure of the product 44a was confirmed by H NMR
spectroscopic analysis. Three methyl signals, one as a
doublet at d = 2.00 (J = 6.9 Hz) ppm and two singlets at
d = 3.23 and 3.98 ppm corresponded to the N-methyl and
ester methyl groups, a multiplet at d = 6.11 ppm accounted
for methine proton in the furan ring, the aromatic protons
appeared as a multiplet at d = 6.77–7.21 ppm and the
Table 1 Isomerization Reactions of MBH Adducts
Entry
MBH adduct
Propargyl ether (A) Propargyl vinyl ethers (B)Yield (%)
A
B
Da
40
45
47
43
46
41
47
50
49
45
MWb
50
1
1
2
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
98
97
99
89
95
99
97
95
96
87
2
54
3
3
52
4
4
55
5
5
56
6
6
50
7
7
50
8
8
50
9
9
55
10
10
56
a Reflux for 1–4 h.
b Irradiated at 60% power level for 30 min, SAMSUNG, Model: CE 118KF.
Synlett 2009, No. 10, 1591–1596 © Thieme Stuttgart · New York

LETTER
Synthesis of Highly Functionalized Allene-Appended Oxindoles
1593
Table 2 Synthesis of Compounds 31–43 (continued)
alkene proton appeared as a doublet at d = 8.14 ppm with
a coupling constant J = 16.0 Hz.
Entry Substrate
Producta
Yield
(%)
The cyclization reactions were found to be general for de-
rivatives 45a,b–49a,b from the allene products 32–36
(Table 3).
O
C
O
Br
Br
CO2Me
7
CO2Me 70
Table 2 Synthesis of Compounds 31–43
O
O
N
Producta
Yield
(%)
N
Entry Substrate
27
37
O
C
O
C
O
O
CO2Me
CO2Me
1
80
84
79
65
CO2Me
CO2Me
8
64
77
59
O
O
O
N
N
N
O
N
Ph
Ph
31
21
28
38
O
C
O
O
C
O
CO2Me
2
3
4
CO2Me
CO2Me
CO2Me
9
O
O
N
N
O
O
N
N
22
32
Ph
Ph
29
39
O
C
O
Br
Br
O
C
CO2Me
O
CO2Me
CN
O
O
CO2Me
N
10
N
O
O
Ph
N
N
23
24
33
34
Ph
O
30
41
42
40
43
C
O
CN
CN
O
O
C
O
O
O
N
N
11
12
80
CN
O
O
N
O
N
Ph
O
C
O
O
O
CO2Me
5
CO2Me
82
O
O
O
N
–
N
O
N
25
26
35
36
O
C
O
A plausible mechanism for the formation of the dihydro-
furan derivatives from the allenes is shown in Scheme 6.
A base-promoted reaction affords cyclopropane interme-
diate F. Subsequently, the hydroxyl group in the interme-
diate F attacks the central allene carbon to form
intermediate G which, upon cyclopropane-ring-opening
results in the formation of the dihydrofuran derivatives.
CO2Me
6
CO2Me
77
O
O
N
N
In conclusion, we have demonstrated a novel and efficient
Claisen rearrangement of allene derivatives of oxindoles
Synlett 2009, No. 10, 1591–1596 © Thieme Stuttgart · New York

1594
V. Vaithiyanathan et al.
LETTER
MeO2C
O
C
MeO2C
O
CHO
CO2Me
DABCO
+
O
O
O
acetone, reflux
30 min
N
N
N
31
44a
44b
Scheme 5
Table 3 Synthesis of Compounds 45a,b–49a,b
MeO2C
C
O
MeO2C
R2
R2
R2
O
CHO
DABCO
CO2Me
+
acetone, reflux
30 min
O
O
O
N
N
N
R1
R1
R1
45a–49a
32–36
45b–49b
R1 = Me, Et; R2 = H, Me, Br; Z = CO2Me, CN
Entry
Substratea
Products
Combined yield (%)
E
Z
1
2
3
4
5
32
33
34
35
36
45a
46a
47a
48a
49a
45b
46b
47b
48b
49b
44
49
42
48
53
a Reactions were performed in 10 mg scale.
Me
C
C
HO
O
MeO2C
O
H
H
CO2Me
base
CO2Me
H
O
N
O
N
O
N
G
F
Me
O
CO2Me
O
N
Scheme 6
rified by silica gel column chromatography using gradient elution
with hexane and hexane–EtOAc to afford pure compounds.
derived from MBH chemistry of isatin to furnish highly
functionalized materials. Further work is in progress in
this laboratory.
Microwave Irradiation
A mixture of MBH adduct 50 mg (0.20 mmol), 50% w/w montmo-
rillonite K-10 clay, and propargyl alcohol as a paste and was irradi-
ated (60% power level) in a microwave oven (30 min, SAMSUNG,
Model: CE 118KF). The crude reaction mixture was purified by
silica gel column chromatography.
General Procedure: Isomerization
Conventional Heating
A mixture of MBH adduct 50 mg (0.20 mmol), 50% w/w montmo-
rillonite K-10 clay, and propargyl alcohol (1.5 mL) was refluxed for
1–4 h. After completion of the reaction, the crude mixture was pu-
Synlett 2009, No. 10, 1591–1596 © Thieme Stuttgart · New York

LETTER
Synthesis of Highly Functionalized Allene-Appended Oxindoles
1595
Allylic Isomerization
(2E)-Methyl 2,5-Dihydro-5-methyl-2-(1,5-dimethyl-2-oxoindo-
A mixture of MBH adducts of isomerized propargyl ether 50 mg
(0.17 mmol) and DABCO 23 mg (1.2 equiv) in acetone (3 mL) was
allowed to stir at r.t. for 30 min. After completion of the reaction,
the crude mixture was purified by silica gel column chromatogra-
phy using gradient elution with hexane–EtOAc to afford pure com-
pounds.
lin-3-ylidene)furan-3-carboxylate (45a)
1
IR (CH2Cl2): 1726, 1609 cm–1. H NMR (300.1 MHz, CDCl3,
TMS): d = 2.00 (d, J = 6.9 Hz, 3 H), 2.29 (s, 3 H), 3.20 (s, 3 H), 3.98
(s, 3 H), 6.09 (m, 1 H), 6.65 (d, J = 7.8 Hz, 1 H), 6.82 (s, 1 H), 7.03
(d, J = 7.8 Hz, 1 H), 8.14 (d, J = 16.0 Hz, 1 H). 13C NMR (75.3
MHz, CDCl3, TMS): d = 19.46, 21.40, 25.84, 29.78, 52.38, 107.73,
120.12, 121.06, 122.67, 125.32, 129.93, 131.16, 139.14, 139.63,
141.10, 167.26, 167.82. MS–FAB: m/z calcd for C17H17NO4:
299.11; found: 300.11 [M+ + 1].
Claisen Rearrangement
A mixture of MBH adduct of propargyl vinyl ether 10 mg (0.03
mmol) in chlorobenzene (1 mL) was heated to 135 °C for 4 h. After
completion of reaction, the solvent was removed under reduced
pressure to afford allene–aldehyde functionalized product which
was purified by silica gel column chromatography.
Acknowledgment
The authors thank Prof. Dr. T. K. Chandrashekar, Director-NIIST
for providing infrastructure facilities. Financial support (SR/S1/
OC-38/2005) from the DST (New Delhi) is gratefully acknowled-
ged. V.V. and K.S. thank CSIR and UGC (New Delhi) for the award
of a SRF and a JRF, respectively. Thanks are due to Mrs. Viji and
Mrs. Soumini Mathew for providing mass and NMR data, respec-
tively.
Spectroscopic Data for Selected Compounds
(E)-Methyl-2-(1,5-dimethyl-2-oxoindolin-3-yl)-3-(prop-2-yny-
loxy) Acrylate (22)
IR (CH2Cl2): 1716, 1607 cm–1. H NMR (300.1 MHz, CDCl3,
1
TMS): d = 2.29 (s, 3 H), 2.64 (t, J = 2.4 Hz, 1 H), 3.22 (s, 3 H), 3.57
(s, 3 H), 3.87 (s, 1 H), 4.67 (m, 2 H), 6.69 (d, J = 7.8 Hz, 1 H), 6.90
(s, 1 H), 6.92 (s, 1 H), 7.04 (d, J = 7.8 Hz, 1 H). 13C NMR (75.3
MHz, CDCl3, TMS): d = 21.09, 26.49, 47.89, 51.44, 61.26, 76.99,
77.41, 106.97, 107.55, 124.23, 128.40, 128.44, 131.64, 142.02,
156.33, 164.65, 175.99. MS–FAB: m/z calcd for C17H17NO4:
299.11; found: 300.13 [M+ + 1].
References and Notes
(1) Present address: Organic Chemistry Division, Central
Leather Research Institute (CLRI), Adyar, Chennai 600020,
India
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Methyl 2-Formyl-2-(1-methyl-2-oxoindolin-3-yl)penta-3,4-di-
enoate (31, 1:1 Inseparable Diastereomers)
1H NMR (300.1 MHz, CDCl3, TMS): d = 3.22 (s, 6 H), 3.50 (s, 1
H), 3.55 (s, 1 H), 3.59 (s, 3 H), 3.75 (s, 3 H), 4.86–4.90 (m, 4 H),
5.56 (t, J = 7.0 Hz, 1 H), 5.66 (t, J = 7.0 Hz, 1 H), 6.72–7.23 (m, 8
H), 9.59 (s, 1 H), 9.73 (s, 1 H). MS–FAB: m/z calcd for C16H15NO4:
285.10; found: 286.10 [M+ + 1].
Compound 41
IR (CH2Cl2): 1753, 1724, 1611 cm–1. 1H NMR (300.1 MHz, CDCl3,
TMS): d = 3.22 (s, 3 H), 4.44 (d, J = 9.0 Hz, 1 H), 4.51(d, J = 9.0
Hz, 1 H), 4.80 (dd, J = 7.0, 12.0 Hz, 1 H), 4.96 (dd, J = 7.0, 12.0 Hz,
1 H), 5.62 (t, J = 7.0 Hz, 1 H), 6.87 (d, J = 8.0 Hz, 1 H), 7.05 (t,
J = 7.5 Hz, 1 H), 7.15 (d, J = 8.0 Hz, 1 H), 7.36 (t, J = 7.5 Hz, 1 H),
9.48 (s, 1 H). MS–FAB: m/z calcd for C16H13NO4: 283.08; found:
284.08 [M+ + 1].
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(2E)-Methyl 2,5-Dihydro-5-methyl-2-(1-methyl-2-oxoindolin-3-
ylidene)furan-3-carboxylate (44a)
1
IR (CH2Cl2): 1726, 1609 cm–1. H NMR (300.1 MHz, CDCl3,
TMS): d = 2.00 (d, J = 6.9 Hz, 3 H), 3.23 (s, 3 H), 3.98 (s, 3 H), 6.11
(m, 1 H), 6.77 (d, J = 7.8 Hz, 1 H), 6.94 (t, J = 7.7 Hz, 1 H), 7.04 (d,
J = 7.7 Hz, 1 H), 7.21 (t, J = 7.7 Hz, 1 H), 8.14 (d, J = 16.0 Hz, 1
H). 13C NMR (75.3 MHz, CDCl3, TMS): d = 19.51, 25.84, 29.79,
52.48, 107.99, 119.86, 121.04, 121.83, 122.07, 125.27, 129.49,
139.52, 139.98, 143.19, 167.22, 167.76. MS–FAB: m/z calcd for
C16H15NO4: 285.10; found: 286.21 [M+ + 1].
(2Z)-Methyl 2,5-Dihydro-5-methyl-2-(1-methyl-2-oxoindolin-3-
ylidene)furan-3-carboxylate (44b)
1
IR (CH2Cl2): 1726, 1609 cm–1. H NMR (300.1 MHz, CDCl3,
TMS): d = 1.98 (d, J = 6.9 Hz, 3 H), 3.23 (s, 3 H), 3. 89 (s, 3 H),
6.21 (m, 1 H), 6.73 (d, J = 7.8 Hz, 1 H), 6.94 (t, J = 7.5 Hz, 1 H),
7.21 (t, J = 7.7 Hz, 1 H), 7.54 (d, J = 6.9 Hz, 1 H), 7.87 (d, J = 6.3
Hz, 1 H). MS–FAB: m/z calcd for C16H15NO4: 285.10; found:
286.07 [M+ + 1].
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V. Vaithiyanathan et al.
LETTER
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Synlett 2009, No. 10, 1591–1596 © Thieme Stuttgart · New York

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