Diastereoselective synthesis of strained spiro-cyclopropanooxindoles from cyclic diazoamides

Article abstract of DOI:10.1016/j.tetlet.2010.07.159

Reaction of cyclic diazoamides and cyclic olefins or heteroaromatic systems using copper(I) triflate as a catalyst furnished a variety of strained spiro-cyclopropanooxindoles in a diastereoselective manner under mild reaction conditions. The effect of copper(I) triflate and rhodium(II) acetate catalysts on the cyclopropanation was also studied.

Full text of DOI:10.1016/j.tetlet.2010.07.159

Tetrahedron Letters 51 (2010) 5662–5665
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Tetrahedron Letters
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Diastereoselective synthesis of strained spiro-cyclopropanooxindoles
from cyclic diazoamides
⇑
Sengodagounder Muthusamy , Datshanamoorthy Azhagan, Boopathy Gnanaprakasam, Eringathodi Suresh
School of Chemistry, Bharathidasan University, Tiruchirappalli 620 024, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Reaction of cyclic diazoamides and cyclic olefins or heteroaromatic systems using copper(I) triflate as a
catalyst furnished a variety of strained spiro-cyclopropanooxindoles in a diastereoselective manner
under mild reaction conditions. The effect of copper(I) triflate and rhodium(II) acetate catalysts on the
cyclopropanation was also studied.
Received 16 June 2010
Revised 26 July 2010
Accepted 27 July 2010
Available online 2 August 2010
Ó 2010 Elsevier Ltd. All rights reserved.
Keywords:
Copper(I) triflate
Cyclopropanation
Diazoamides
Oxindoles
Rhodium(II) acetate
Spiro[cyclopropan-1,30-oxindoles] are known to have inotropic1
and herbicidal2 properties and their novel ring-expansion reaction3
with a range of imines furnished spiro[pyrrolidin-3,30-oxindoles],4
on cyclic diazoamides for the stereoselective cyclopropanation
process with cyclic olefins. In this Letter, we describe a mild meth-
od for the construction of strained spiro-cyclopropanooxindole
systems utilizing cyclic diazoamides and cyclic olefins or heteroar-
omatic systems in the presence of copper(I) triflate or rhodium(II)
acetate catalyst in a diastereoselective manner.
Initially, the rhodium(II)-catalysed reaction of cyclic diazoa-
mides 1 with cyclic olefins such as indene, dihydronapthalene
and cyclooctadiene was planned. Towards this, reaction16 of cyclic
diazoamide 1a and indene with 2 mol % of rhodium(II) acetate dimer
catalyst for 4 h at room temperature afforded the spiro-cyclopro-
pane 2a in 90% yield (Scheme 1) as a single isomer based on the
crude NMR analysis. Further, the product was confirmed by the
characteristic C–H protons in proton NMR and two C–H carbons
in carbon NMR. Mass spectrum shows the required mass value of
284 (M+Na)+. Subsequently, the rhodium(II)-catalysed reaction of
cyclic diazoamides 1b–d with indene was carried out for 4 h at
which are well-known indole-based natural products. a-Diazocar-
bonyl compounds have found extensive applications in organic
synthesis due to their versatile reactivities.5 Research in this area
has been mostly concentrated on the transition metal complex-
catalysed diazo decomposition, which generates metallo-carbe-
noid intermediates. Transition metal complexes catalysed a large
number of organic reactions which led to a variety of C–C bond for-
mations that are important for creation of the basic skeleton of the
organic structure. Particularly, copper- or rhodium-catalysed reac-
tion of
a-diazocarbonyl compound with alkene is an efficient
method for the preparation of cyclopropane derivatives.6 The inter-
molecular7 cyclopropanation reactions are limited only to simple
precursors like acyclic diazo ketones or diazo esters. The cyclic
diazo ketones and amides always have a tendency to furnish
cycloadducts8 via 1,3-dipolar cycloaddition reactions in the pres-
ence of olefins. We have reported many stereo- and regioselective
reactions of diazocarbonyl compounds based on ylide formation,9
carbenoid insertion,10 N–H insertion,11 O–H insertion12 and nucle-
ophilic trapping of ylide.13 There is only scarcity of reports14
available on the cyclic diazocarbonyl compounds used for the
cyclopropanation process. Our earlier work15 on the rhodium(II)
acetate catalyzed cyclopropanation of diazomides led to a mixture
of products. To the best of our knowledge, there is no report dealt
H
R1
N2
O
Indene
N
O
Catalyst, rt
N
R1
H
1a: R1 = methyl
1b: R1 = benzyl
1c: R1 = allyl
2a-d
1d: R1 = propargyl
⇑
Corresponding author. Tel.: +91 431 2407053; fax: +91 431 2407045.
E-mail address: muthu@bdu.ac.in (S. Muthusamy).
Scheme 1.
0040-4039/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2010.07.159

S. Muthusamy et al. / Tetrahedron Letters 51 (2010) 5662–5665
5663
Table 1
H
R1
N2
O
Synthesis of spiro-cyclopropanooxindoles 2
Dihydro-
naphthalene
N
Entry
Cyclopropanooxindoles 2
Yield of 2a (%) and time (h)
O
Cat. CuOTf
Dry DCM, rt
H
N
R1
Rhodium catalyst
Copper catalyst
1
2
3
4
2a
2b
2c
2d
90 (4)
92 (4)
86 (4)
81 (4)
94 (0.5)
90 (0.5)
88 (0.5)
92 (0.5)
1a-d
3a-d
Scheme 2.
a
Yields are unoptimized and refer to isolated yields.
Table 3
Synthesis of spiro-cyclopropanooxindoles 3
room temperature and the chromatographic purification of the
reaction mixture gave the respective spiro-cyclopropanes 2b–d in
very good yields with diastereoselectivity (Table 1).
Entry Cyclopropanooxindoles 3 Catalyst
Yield of 3a (%) and time (h)
1
2
3
4
5
3a
3b
3c
3d
3a
CuOTf
CuOTf
CuOTf
CuOTf
94 (0.5)
94 (0.5)
89 (0.5)
86 (0.5)
—
Next, we studied the cyclopropanation reactions in the presence
of CuOTf. Thus, reaction of 1a–d with indene was performed with
20 mol % of CuOTf as catalyst. The reaction was completed within
30 min at room temperature to afford the corresponding strained
cyclopropanes 2a–d in very good yields (Table 1). All the products
were characterized based on the spectral data. The stereochemistry
of the representative product17 2d was unequivocally supported18
by single-crystal X-ray (Fig. 1) analysis.
Rh2(OAc)4
a
Yields are unoptimized and refer to isolated yields.
the cyclopropane product 3a was observed when the reaction
was carried out with rhodium(II) acetate catalyst.
The reaction was completed in less duration and improves the
yield up to 10% when compared to rhodium(II) catalyst. The facile
diastereoselective synthesis of substituted strained cyclopropanes
2 in good yield was demonstrated evidently from the above exam-
ples. Representatively, the formation of product 2a was studied
with other catalysts (Table 2) such as Cu(bis-oxazoline), Cu(II),
Co(I), Rh(I) and Rh(III). Only Cu(bis-oxazoline) catalyst afforded
the cyclopropane 2a in 86% yield after stirring at room temperature
for 24 h whereas other catalysts failed to provide cyclopropane.
Subsequently, we investigated the copper-catalysed reaction of
cyclic diazoamide 1a with dihydronapthalene. Thus, the reaction
was performed in the presence of 20 mol % of CuOTf catalyst at
room temperature to furnish the spiro-cyclopropane 3a in 94%
yield (Scheme 2) as a single isomer based on the crude NMR anal-
ysis. 3-Diazooxindoles 1b–d were subjected in the presence of
CuOTf to afford the corresponding cyclopropanes17 3b–d in very
good yield with diastereoselectivity (Table 3). No formation of
Encouraged by the above results with CuOTf, we then per-
formed the cyclopropanation reaction with cyclooctadiene. To this
end, diazoamide 1a was reacted with cyclooctadiene in the pres-
ence of 20 mol % of CuOTf for 30 min to yield the corresponding
cyclopropane 4a in 79% yield (Scheme 3). The above reaction in
the presence of rhodium(II) acetate did not furnish the product
4a and the starting material might be dimerized. Reaction of other
cyclic diazoamides 1b–d with cyclooctadiene in the presence of
CuOTf afforded the respective products16 4b–d in good yield.
In order to extend the study of cyclopropanation, the reaction
was then anticipated with heteroaromatic systems instead of cyclic
olefins. Thus, the reaction of cyclic diazoamide 1a with N-benzylin-
dole in the presence of CuOTf afforded the corresponding 3-alkyl-
ated product10a 7a in 98% yield (Scheme 4). Similarly, the product
7b was also obtained from 1b. This indicates that the formation of
product 7 may be produced via the corresponding spiro-cyclopropane
H
N2
R1
Cycloocta-
1,5-diene
O
N
O
Cat. CuOTf
Dry DCM, rt
N
R1
H
1a-d
4a: 79%; 4b: 80%
4c: 72%; 4d: 60%
Scheme 3.
R2
H
N2
R1
O
N
N-substituted
indoles
N
O
Figure 1. X-ray structure of compound 2d.
N
CuOTf
R1
H
1a,b
5
Table 2
Effect of catalyst for spiro-cyclopropanooxindole 2a
R2
Yield of 2aa (%) and time (h)
N
Entry
Catalyst
R2
N
1
2
3
4
5
6
7
Rh2(OAc)4
CuOTf
92 (4)
90 (0.5)
86 (24)
—
—
—
—
R1
O
N
CuOTf and bis-oxazoline ligand
Cu(OTf)2
Cyanocobalamine
Wilkinson catalyst [Rhodium(I)]
RhCl3 [Rhodium(III)]
O
H
N
R1
7a,b
6
a
Yields are unoptimized and refer to isolated yields.
Scheme 4.

5664
S. Muthusamy et al. / Tetrahedron Letters 51 (2010) 5662–5665
viding 400 MHz NMR facility under FIST program. B.G. thanks CSIR,
New Delhi, for a Senior Research Fellowship.
H
N2
R1
O
X
X
N
O
Cat. CuOTf
Dry DCM, rt
N
R1
References and notes
H
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8a-d and 9a-c
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Syntheis with Diazo Compounds. From Cyclopropanes to Ylides; Wiley-
Interscience: New York, 1998.
6. (a) Davies, H. M. L.. In Comprehensive Organic Chemistry; Trost, B. M., Fleming, I.,
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M. C.; Zhang, J.; McPhail, A. T. J. Org. Chem. 1991, 56, 6269; (e) Pirrung, M. C.;
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Dastidar, P. J. Org. Chem. 2002, 67, 8019; (b) Muthusamy, S.; Babu, S. A.;
Gunanathan, C.; Suresh, E.; Dastidar, P. Bull. Chem. Soc. Jpn. 2002, 75, 801; (c)
Muthusamy, S.; Krishnamurthi, J.; Babu, S. A.; Suresh, E. J. Org. Chem. 2007, 72,
1252; (d) Muthusamy, S.; Krishnamurthi, J.; Nethaji, M. Chem. Commun. 2005,
3862; (e) Muthusamy, S.; Gnanaprakasam, B. Tetrahedron 2007, 63, 3355.
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Soc., Chem. Commun. 2002, 824; (b) Muthusamy, S.; Gunanathan, C. Synlett
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16. General procedure for the synthesis of spiro-cyclopropanooxindoles 2–4, 8 and 9:
To an oven-dried flask, a solution containing cyclic diazoamide 1 (1 mmol) and
cyclic olefin (1.1 mmol) in dry dichloromethane (50 mL) under inert
atmosphere was added 20 mol % of CuOTf or 2.0 mol % of rhodium(II) acetate
dimer and stirred for appropriate duration at room temperature. The reaction
was monitored by TLC and IR. After the decomposition of all diazoamide, the
reaction mixture was evaporated and subjected to 100–200 mesh silica-gel
column chromatography (EtOAc/hexane) to afford the respective spiro-
cyclopropanooxindoles 2–4, 8 and 9.
Synthesis of spiro-cyclopropanooxindoles 8 and 9
Entry
Cyclopropanooxindoles 8
X
Time (min)
Yield of 8,9a (%)
1
2
3
4
5
6
7
8a
8b
8c
8d
9a
9b
9c
O
O
O
O
S
30
30
30
86
92
90
91
83
86
85
30
120
120
120
S
S
a
Yields are unoptimized and refer to isolated yields.
5 and followed by ring opening to zwitterion 6 as intermediates
in the presence of copper catalyst as observed in our previous
study10a using rhodium catalyst. Hence, the reactions of diazoa-
mides with indoles did not provide the corresponding spiro-
cyclopropanooxindoles.
Further, we explored the cyclopropanation with other heteroar-
omatic systems such as benzofuran and benzothiophene. Thus, the
reaction of diazoamide 1a and benzofuran was carried out in the
presence of 20 mol % of CuOTf to yield the respective spiro-cyclo-
propane17 8a in 86% yield with diastereoselectivity (Scheme 5, en-
try 1, Table 3). The above reaction was repeated in presence of
rhodium(II) acetate to afford the product 8a in 80% yield. The reac-
tion with benzofuran was generalized in the presence of CuOTf to
afford the products 8b–d in good yield (Table 4). It may be noted
that the reaction of cyclic diazoketone with benzofuran furnished8c
a mixture of cycloadducts.
Next, the cyclopropanation with benzothiophene was carried
out. Reaction of diazoamide 1a and benzothiophene was per-
formed in the presence of 20 mol % of CuOTf to furnish the respec-
tive spiro-cyclopropane17 9a in 83% yield (Scheme 5). The reaction
with benzothiophene was also generalized in the presence of
CuOTf to afford the products 9b,c in good yield (Table 4). The reac-
tion was repeated in the presence of rhodium(II) acetate to afford
the product 9b in 81% yield. It is noteworthy that benzofuran
and benzothiophene furnished the respective spiro-cyclopropano-
oxindole in a diastereoselective manner whereas indole facilitates
C-alkylation. No other isomers were detected by 1H NMR analysis
of the crude reaction mixture involved in the above study. Based
on the crystal structure of 2d, the stereochemistry of other prod-
ucts is tentatively assigned.
In conclusion, we have demonstrated that the diastereoselec-
tive synthesis of strained spiro-cyclopropanooxindoles from dia-
zoamides using copper(I) triflate as a catalyst. A variety of spiro-
cyclopropanooxindoles were achieved using symmetrical as well
as asymmetrical cyclic olefins and heteroaromatic systems such
as benzofuran and benzothiophene under mild reaction conditions.
The effect of catalysts on the cyclopropanation was also studied
and it was found that copper(I) triflate is better than rhodium(II)
acetate.
17. Selected spectral data. Product 2d: Brown colour solid; mp 141–143 °C; IR
(neat)
m ;
3047, 2918, 1696, 1466, 1382, 1280, 736 cmꢀ1 1H NMR (200 MHz,
CDCl3) d 2.24 (s,1H, „CH), 2.92–2.98 (t, 1H, CH), 3.20–3.59 (m, 2H, CH2), 4.58
(d, 2H, NCH2), 5.65–5.69 (d, 1H, CH), 6.63–7.32 (m, 8H, @CH); 13C NMR
(50 MHz, CDCl3) d 29.2 (NCH2), 32.3 (CH), 34.9 (CH2), 35.5 (quat-C), 42.6 (CH),
72.0 (CH), 76.9 (quat-C), 108.8 (@CH), 120.9 (@CH), 121.9 (@CH), 124.1 (@CH),
125.4 (quat-C), 125.9 (@CH), 126.5 (@CH), 126.9 (@CH), 127.4 (@CH), 139.1
(quat-C), 142.5 (quat-C), 144.3 (quat-C). 174.4 (C@O); HRMS (ESI) calcd for
C
20H15NONa (M+Na)+: 308.1051, found 308.1039. Product 3b: Brown colour
solid; mp 178–180 °C; IR (neat)
m
3046, 2918, 1698, 1470, 1382, 1280,
736 cmꢀ1
;
1H NMR (200 MHz, CDCl3) d 1.21–3.27 (m, 5H, CH and CH2), 4.87–
5.11 (q, 2H, NCH2), 5.72 (d, 1H, CH, J = 8 Hz), 6.58–7.32 (m, 13H, Arom-H); 13C
NMR (50 MHz, CDCl3), d 18.5 (CH2), 28.3 (CH2), 29.1 (CH), 30.7 (CH), 38.9 (quat-
C), 44.0 (NCH2), 108.7 (@CH), 121.1 (@CH), 122.0 (@CH), 125.8 (quat-C), 126.2
(@CH), 126.8 (@CH), 127.3 (@CH), 128.7 (@CH), 131.0 (@CH), 136.3 (@CH),
136.3 (quat-C), 138.9 (quat-C), 143.6 (quat-C), 144.5 (quat-C), 176.0 (C@O);
HRMS (ESI) calcd for C25H21NONa (M+Na)+: 374.1521, found 374.1534. Product
4b: Brown colour solid; mp 87–89 °C; IR (neat)
m 3046, 2918, 1696, 1466, 1382,
1280, 736 cmꢀ1 1H NMR (200 MHz, CDCl3) d 0.75–2.43 (m, 10H, CH and CH2),
;
4.82–4.92 (m, 2H, NCH2), 5.63–5.64 (m, 2H, @CH), 6.62 (d, 1H, Arom-H,
J = 8 Hz), 6.75 (d, 1H, Arom-H, J = 8 Hz), 6.90–7.21 (m, 7H, Arom-H); 13C NMR
(50 MHz, CDCl3), d 23.0 (CH2), 26.7 (CH2), 34.5 (CH), 43.6 (CH), 44.1 (NCH2),
108.9 (@CH), 121.3 (@CH), 122.4 (@CH), 126.1 (@CH), 127.3 (@CH), 128.7
(@CH), 129.5 (@CH), 133.1 (quat-C), 136.5 (quat-C), 143.1 (quat-C), 177.4
(C@O); HRMS (ESI) calcd for C23H23NONa (M+Na)+: 352.1677, found 352.1664.
Acknowledgements
This research was supported by the Department of Science and
Technology (DST), New Delhi. We thank DST, New Delhi, for pro-
Product 8a: Brown colour solid; m.p 127–129 °C; IR (neat)
m 3043, 2914, 1698,

S. Muthusamy et al. / Tetrahedron Letters 51 (2010) 5662–5665
1610, 1492, 1468, 1378, 1346, 1124, 751, 726, cmꢀ1 1H NMR (400 MHz, CDCl3)
5665
;
(100 MHz, CDCl3) d 30.45 (quat-C), 38.54 (NCH2), 42.12 (CH), 54.40 (@CH),
109.0 (@CH), 110.0 (@CH), 121.2 (@CH), 121.9 (@CH), 122.1 (@CH), 123.4
(quat-C), 124.3 (quat-C), 126.5 (@CH), 127.3 (@CH), 127.6 (@CH), 127.8 (@CH),
128.7 (@CH), 129.0 (@CH), 135.9 (quat-C), 143.7 (quat-C), 145.78 (quat-C),
175.2 (C@O); HRMS (ESI) calcd for C23H17NOS Na (M+Na)+: 378.0929, found
378.0921.
3.20, (s, 3H, NCH3), 3.75–3.76 (d, 1H, CH), 5.33 (d, 1H, CH, J = 8 Hz), 6.60–7.33
(m, 8H, Arom-H); 13C NMR (100 MHz, CDCl3) d 26.5 (NCH3), 28.51 (quat-C),
38.3 (CH), 74.21 (CH), 108.0 (@CH), 110.0 (@CH), 121.1 (@CH), 121.9 (@CH),
122.0 (@CH), 123.3 (quat-C), 124.4 (quat-C) 126.4 (@CH), 126.9 (@CH), 129.0
(@CH), 144.6 (quat-C), 161.7 (quat-C), 175.0 (C@O); HRMS (ESI) calcd for
C
17H13NO2Na (M+Na)+: 286.0844, found 286.0859. Product 9b: Brown colour
18. Crystallographic data for 2d have been deposited (CCDC 647633) with the
Cambridge Crystallographic Data Centre. Copy of the data can be obtained free
of charge on application to 12, Union Road, Cambridge CB21EZ, UK (fax: +44
1223 336 033; e-mail: deposit@ccdc.cam.ac.uk).
solid; m.p 161–163 °C; IR (neat)
m
3049, 3024, 2926, 1695, 1611, 1464, 1361,
;
1345, 1279, 1187, 731, 702, 679 cmꢀ1
1H NMR (400 MHz, CDCl3) d 3.83–3.84
(d, 1H, CH), 4.90 (s, 2H, NCH2), 5.53–5.60 (d, 1H, CH, J = 8 Hz), 6.53–6.57 (t, 1H,
Arom-H), 6.69–6.70 (d, 1H, Arom-H), 7.00–7.31 (m, 11H, Arom-H); 13C NMR