Rh2(OAc)4 catalyzed substrate selective [4+2]/[2+2] cycloaddition of acylketenes: A highly chemo- and regioselective synthesis of spiro(oxindolyl)oxazinones and β-lactams

Article abstract of DOI:10.1016/j.tetlet.2012.02.106

A rhodium(II) catalyzed [4+2]/[2+2] cycloaddition reaction of N-protected isatin-3-arylimine with acylketene derived from α-diazocarbonyl compounds has been achieved for the first time for the preparation of a novel class of spiro(oxindolyl)oxazinone and

Full text of DOI:10.1016/j.tetlet.2012.02.106

Tetrahedron Letters 53 (2012) 2396–2401
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Tetrahedron Letters
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Rh2(OAc)4 catalyzed substrate selective [4+2]/[2+2] cycloaddition
of acylketenes: a highly chemo- and regioselective synthesis
of spiro(oxindolyl)oxazinones and b-lactams
B.V. Subba Reddy a, , Govindaraju Karthik a, Tamilselvan Rajasekaran a, Aneesh Antony a, B. Sridhar b
⇑
a Natural Product Chemistry, Indian Institute of Chemical Technology, Hyderabad 500 007, India
b Center for X-ray Crystallography, Indian Institute of Chemical Technology, Hyderabad 500 007, India
a r t i c l e i n f o
a b s t r a c t
Article history:
A rhodium(II) catalyzed [4+2]/[2+2] cycloaddition reaction of N-protected isatin-3-arylimine with acylke-
Received 24 November 2011
Revised 21 February 2012
Accepted 24 February 2012
Available online 3 March 2012
tene derived from
a-diazocarbonyl compounds has been achieved for the first time for the preparation of
a novel class of spiro(oxindolyl)oxazinone and spiro(oxindolyl)-b-lactam derivatives.
Ó 2012 Elsevier Ltd. All rights reserved.
Keywords:
Rhodium(II) acetate
Cyclicketimines
Acylketenes
Diazocarbonyl compounds
Spiroxazinones
Spiro-b-lactams
The transition metal catalyzed cycloaddition reactions have
received significant interest in organic synthesis especially for
the construction of carbocycles and heterocycles.1 In particular,
the ketene cycloaddition is one of the most popular methods for
the synthesis of four-membered ring systems.2,3 Ketenes are
known to undergo preferentially [2+2] cycloaddition with unsatu-
rated systems to give the four-membered ring compounds. How-
ever, the reactivity of acylketene is quite different from a simple
ketene as it behaves exclusively as 1,3-oxadiene in inverse demand
hetero-Diels–Alder reaction with a ketone or an aldehyde to give
the 1,3-dioxinone derivatives.4 Recently, microwave-assisted
cycloaddition of aldimines with acylketenes, generated in situ from
cyclic 2-diazo-1,3-diketone via the Wolff rearrangement has been
reported. However, the scope of this method is limited to cyclic
diazodiketones.5 Though, aldehydes and aldimines have been suc-
cessfully utilized in trapping acylketenes, the ketimines are notori-
ously absent.
The spirooxindoles,6 oxazinones7 and b-lactams8 and related
heterocycles are important components of many natural products
and medicinally relevant compounds (Fig. 1).
The oxindole appended spirooxazinone or b-lactam may be
attractive class of compounds in medicinal chemistry, since the
concept of hybrid drugs is gaining popularity in medicine. In view
of the relevance of such spirocyclic moiety and the difficulty of its
synthesis necessitates the development of a novel and convenient
strategy.
O
Cl
H3C
NOH
Br
N
O
O
N
N
3
Br
Br
Br
MeO
N
N
H
O
N
N
H
Brevioxime
(Juvenilehormone inhibitor)
Chartelline A
(-)-Horsfiline
Figure 1. Representative examples of spirooxindole, oxazinones and spiro-b-lactam containing natural products.
⇑
Corresponding author. Fax: +91 40 27160512.
E-mail address: basireddy@iict.res.in (B.V. Subba Reddy).
0040-4039/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2012.02.106

B. V. Subba Reddy et al. / Tetrahedron Letters 53 (2012) 2396–2401
2397
Herein, we wish to report
a
rhodium(II) catalyzed [4+2]
O
Ph
cycloaddition of N-protected isatin-3-arylimine with 2-diazo-
acetylacetone. This protocol is extended to explore the acylke-
tene for a rare [2+2] cycloaddition. Initially, we attempted the
cycloaddition of N-methylisatin-3-phenylimine and 2-diazoacet-
ylacetone as model reaction using rhodium(II) acetate (5 mol
N
O
N
O
O
5 mol % Rh2(OAc)4
DCM, reflux
O
O
+
N
N
N2
2
1
3a
%) as
a catalyst. The reaction proceeded through a [4+2]
cycloaddition to give the spiro(oxindolyl)oxazinone in 79% yield
Scheme 1. Formation of spiro(oxindolyl)oxazinone 3a.
(Scheme 1).9
The structure of 3a, was established by various spectroscopic
methods such as NMR, IR and mass spectrometry. The characteris-
tic absorption bands at 1728 and 1674 cmꢀ1 correspond to amide
carbonyls in IR spectroscopy and the chemical shifts at d 164.1
and 170.0 (amide carbonyls) in 13C NMR spectroscopy provided
the required evidences for the proposed structure. Further evi-
dence for the proposed structure comes from HRMS. To confirm
the structure of spiro(oxindolyl)oxazinone, derivative 3e was
selected as a representative example and was characterized by
X-ray crystallography (CCDC 837878, Fig. 2).
Upon screening of various solvents to find out the best choice, it
was found that the reaction proceeds effectively in aprotic solvents
like dichloromethane and benzene. There seems to be no difference
between these solvents as they are equally effective in terms of
conversion. A catalytic loading of 5 mol % was found to be optimal
as reaction progressed well when compared to either higher
(10 mol %) or lower (2 mol %) catalyst loading. Next, we extended
our study to investigate the substrate scope and limitations. Thus
various isatin-3-arylimines treated with 2-diazoacetylacetone for
its efficiency under optimized conditions. Interestingly, a high level
of chemoselectivity was achieved with N-allylisatinimine. No evi-
dence for a possible cyclobutanone formation was observed from
N-allylisatinimine.3
Figure 2. Crystal structure of compound 3e.
O
N
O
Ph
We next attempted the cycloaddition of isatin-3-arylimine with
other diazo compounds such as diazoketoesters. To our surprise, a
four-membered b-lactam was formed when isatin-3-arylimine re-
acts with diazoketoester.
N
MeO
O
O
5 mol % Rh2(OAc)4
DCM, reflux
O
+
O
OMe
N
N
N2
We assume that acylketene generated from 2-diazoalkylace-
toacetate undergoes a rare [2+2] cycloaddition to produce the
spiro(oxindolyl)-b-lactam 5a (Scheme 2, Table 2).
1
4
5a
Scheme 2. Formation of spiro(oxindolyl)-b-lactam 5a.
Table 1
[4+2] Cycloaddition between isatin-3-arylimines and 2-diazo-1,3-diketonesa
Entry Imine (1) Diazo (2)
Product (3)b
Time (min)
Yieldc (%)
O
O
O
O
O
N
N
N2
a
30
79
O
O
O
O
N
N
O
O
O
O
O
N
N
N2
b
30
83
N
N
Bn
Bn
O
O
N
N2
N
c
30
83
O
N
O
Bn
N
Bn
(continued on next page)

2398
B. V. Subba Reddy et al. / Tetrahedron Letters 53 (2012) 2396–2401
Table 1 (continued)
Entry
Imine (1)
Diazo (2)
Product (3)b
Time (min)
Yieldc (%)
O
O
O
O
O
N
N2
O
O
d
N
30
84
N
Bn
O
O
N
Bn
O
O
O
O
O
O
O
O
N
N
N
N2
e
30
81
O
O
N
N
N
N2
N
f
30
83
O
N
O
O
O
O
O
O
O
O
O
N
N
N2
N
O
g
O
O
30
82
N
N
O
N
Cl
N2
N
Cl
h
30
84
O
N
O
O
O
O
Cl
Br
O
O
Cl
O
O
N
N
N
N2
i
j
30
30
30
78
84
70
O
O
O
N
N
N
N2
N
Br
O
N
N
O
O
Br
Br
O
O
N
N2
k
O
O
N
N
a
The reactions were carried out under reflux conditions for 30 min.
All products were characterized by 1H & 13C NMR, IR spectroscopy.
Yield refers to pure products after chromatography.
b
c

B. V. Subba Reddy et al. / Tetrahedron Letters 53 (2012) 2396–2401
2399
The structure of 5a was established by spectroscopic methods
such as 13C NMR, IR and mass spectrometry. The structure of
b-lactam was characterized by infrared spectral data in which
the characteristic amide absorption peaks were identified at
1767 and 1722 cmꢀ1. Further support for the formation of b-lactam
comes from the 13C NMR spectrum in which the characteristic car-
bonyl peaks were appeared at d 163.2, 170.1, and 172.0.
The product selectivity in both 2-diazo-1,3-diketones and
2-diazo alkylacetoacetate are found to be excellent. No formation
of possible side products such as spiro(oxindolyl)aziridine or
Table 2
[2+2] Cycloaddition between isatin-3-arylimines and alkyl diazoacetoacetatesa
Entry
Imine (1)
Diazoketoester (4)
Product (5)b
Time (min)
Yieldc (%)
O
O
O
O
O
N
O
O
N
N2
a
30
78
O
O
N
N
O
O
O
O
N
O
O
N
N2
N
b
30
80
O
O
O
N
O
O
O
O
O
O
O
O
O
O
N
N2
N
c
30
82
O
N
O
O
N
Br
O
N
N2
N
d
e
f
30
30
30
84
68
80
Br
O
N
O
O
N
N
O
O
O
O
Br
O
O
O
N
Br
O
O
N2
O
O
N
O
N
Cl
O
N
N2
N
O
Cl
N
O
O
N
Cl
O
O
O
O
O
O
O
N
Cl
O
O
N2
g
30
72
N
O
O
N
O
O
N
O
N
N
N2
h
30
78
O
N
Bn
N
Bn
(continued on next page)

2400
B. V. Subba Reddy et al. / Tetrahedron Letters 53 (2012) 2396–2401
Table 2 (continued)
Entry
Imine (1)
Diazoketoester (4)
Product (5)b
Time (min)
Yieldc (%)
O
O
O
O
O
N
O
N
N2
i
30
78
O
O
N
N
a
The reactions were carried out under reflux conditions for 30 min.
All products were characterized by 1H & 13C NMR, IR spectroscopy.
Yield refers to pure products after chromatography.
b
c
the [2+2] cycloaddition of isatin-3-arylimine with acylketene de-
rived from 2-diazoalkylacetoacetate.
O
O
O
O
O
O
R2
R3
R2
R3
O
R2
R3
C
O
R2
R3
Rh Rh
N2
Rh Rh
Acknowledgments
G.K. and A.A. thank CSIR and T.R. thanks UGC, New Delhi for the
award of fellowship.
Scheme 3. A plausible mechanism of ketene generation through rhodium
carbenoid.
References and notes
spiro(oxindolyl)oxazoline was observed in both reaction pathways.
The formation of ketene intermediate from 2-diazo-1,3-diketone
and its monoester counterpart is shown in Scheme 3.
Mechanistically, the acylketene is generated from the rhodium
carbenoid through a Wolf rearrangement.
1. (a) Padwa, A.; Pearson, W. H. In Synthetic Applications of 1,3-Dipolar Cycloaddition
Chemistry Toward Heterocycles and Natural Products; Wiley-Interscience: New
York, 2002; Vols. 1&2,; (b) Lebuf, D; Gandon, V.; Malacria, M. In Handbook of
Cyclization Reactions; Ma, S., Ed.; Wiley-VCH: Weinheim, Germany, 2009; Vol. 1,
p 367; (c) Lautens, M.; Klute, W.; Tam, W. Chem. Rev. 1996, 96, 49; (d) Chopade,
P.; Louie, J. Adv. Synth. Catal. 2006, 348, 2307; (e) Louie, J. Curr. Org. Chem. 2005,
9, 605; (f) Domínguez, G.; Perez-Castells, J. Chem. Soc. Rev. 2011, 40, 3430; (g)
Kumar, P.; Troast, D. M.; Cella, R.; Louie, J. J. Am. Chem. Soc. 2011, 133, 7719.
2. (a) Tidwell, T. T. Ketenes; Wiley: New York, 1991; (b) Georg, G. I.; Ravikumar, V.
T. Stereocontrolled ketene-imine cycloaddition reactions. In The Organic
Chemistry of b-Lactams; Georg, G. I., Ed.; VCH Publishers: New York, 1992; p
295; (c) Palomo, C.; Aizpurua, J. M.; Ganboa, I.; Oiarbide, M. Eur. J. Org. Chem.
1999, 12, 3223; (d) Taggi, A. E.; Hafez, A. M.; Wack, H.; Young, B.; Ferraris, D.;
Lectka, T. J. Am. Chem. Soc. 2002, 124, 6626; (e) Hodous, B. L.; Fu, G. C. J. Am.
Chem. Soc. 2002, 124, 1578; (f) France, S.; Weatherwax, A.; Taggi, A. E.; Lectka, T.
Acc. Chem. Res. 2004, 37, 592; (g) Cossio, P. F.; Arrieta, A.; Sierra, M. A. Acc. Chem.
Res. 2008, 41, 925.
3. Ovalles, S. R.; Hansen, J. H.; Davies, H. M. L. Org. Lett. 2011, 13, 4284.
4. (a) Reber, K. P.; Tilley, S. D.; Sorensen, E. J. Chem. Soc. Rev. 2009, 38, 3022; (b)
Rybalova, T. V.; Gatilov, Y. V.; Nekrasov, D. D.; Rubtsov, A. E.; Tolstikov, A. G. J.
Struct. Chem. 2005, 46, 1126.
5. Presset, M.; Coquerel, Y.; Rodriguez, J. Org. Lett. 2009, 11, 5706.
6. (a) Marti, C.; Carreira, E. M. Eur. J. Org. Chem. 2003, 2209; (b) Galliford, C. V.;
Scheidt, K. A. Angew. Chem., Int. Ed. 2007, 46, 8748; (c) Vintonyak, V.; Warburg,
K.; Kruse, H.; Grimme, S.; Hubel, K.; Rauh, D.; Waldmann, H. Angew. Chem., Int.
Ed. 2010, 49, 5902.
Thus formed acylketene may undergo either [4+2] or [2+2]
cycloaddition depending on the diazodicarbonyl compound used.
The reaction between 2-diazo-1,3-diketone and isatin-3-arylimine
afforded the spiro(oxindolyl)oxazinone via [4+2] cycloaddition
whereas 2-diazoalkylacetoacetate (alkyl = methyl and ethyl) gave
the spiro(oxindolyl)-b-lactam through [2+2] cycloaddition
(Scheme 4). The regioselectivity of the reaction depends on the
nature of acylketene intermediate. The exclusive formation of
two different products from different diazo compounds may be ex-
plained on the basis of reactivity as depicted in Scheme 4. The dif-
ference in reactivity may be explained by the presence of
tautomerism in acylketene derived from 2-diazo-1,3-diketone,
which is lacking in acylketene generated from 2-diazoketoester.
In conclusion, we have demonstrated the rhodium(II) acetate
catalyzed cycloaddition of cyclic ketimines with acylketenes gen-
erated in situ from diazo compounds for the synthesis of a novel
class of spiro(oxindolyl)oxazinone and spiro(oxindolyl)-b-lactam
derivatives. The acylketene derived from 2-diazo-1,3-diketone
was successfully trapped with N-protected isatin-3-arylimine to
7. (a) Moya, P.; Castillo, M.; Primo-Yufera, E.; Couillaud, F.; Martinez-Manez, R.;
Garcera, M. D.; Miranda, M. A.; Primo, J.; Martinez-Pardo, R. J. Org. Chem. 1997,
62, 8544; (b) Cantın, A.; Moya, P.; Castillo, M. A.; Primo, J.; Miranda, M. A.;
Primo-Yufera, E. Eur. J. Org. Chem. 1999, 221; (c) Nicoletti, R.; Buommino, E.; De
Filippis, A.; Lopez-Gresa, M. P.; Manzo, E.; Carella, A.; Petrazzuolo, M.; Tufano, M.
A. World J. Microbiol. Biotechnol. 2008, 24, 189; (d) Doms, P.; Santel, H. J.;
Dollinger, M. Eur. Pat. Appl. EP0638563, 1995.
produce
a six-membered spiro(oxindolyl)oxazinone through
[4+2] cycloaddition. The spiro(oxindolyl)-b-lactam was formed by
R2
R3
O
O
N
R3= Me
R4
R2
O
O
O
N
R4
N
O
R4
C
R3
R1
O
R3
R2
N
O
O
R3
R2
O
O
N
N
R4
N
R3= OMe
R1
R1
O
N
R1
Scheme 4. A plausible mechanism for [4+2] and [2+2] cycloaddition.

B. V. Subba Reddy et al. / Tetrahedron Letters 53 (2012) 2396–2401
2401
8. (a) Palomo, C.; Aizpurua, J. M.; Ganboa, I.; Oiarbide, M. Eur. J. Org. Chem. 1999,
3223; (b) Dürkheimer, W.; Blumbach, J.; Lattrell, R.; Scheunemann, K. H. Angew.
Chem., Int. Ed. 1985, 24, 180; (c) Morin, R. B.; Gorman, M. In Chemistry and
Biology of b-Lactam Antibiotics; Academic Press: New York, 1982; Vol. 123,; (d)
Southgate, R; Branch, C.; Coulton, S.; Hunt, E. In Recent Progress in the Chemical
Synthesis of Antibiotics and Related Microbial Products; Lukacs, G., Ed.; Springer-
Verlag: Berlin, 1993; Vol. 2, p 621.
9. General procedure: A mixture of isatin-3-arylimine (1 mmol) and rhodium(II)
acetate (5 mol %) was stirred in dry dichloromethane (10 mL). A solution of diazo
compound (1.2 mmol) in dry dichloromethane (2 mL) was added drop wise over
15 min. The resulting mixture was stirred under reflux for a specified time (Table
1). After completion, as indicated by TLC, the solvent was removed under reduced
pressure and the resulting residue was purified by column chromatography on
silica gel using n-hexanes/EtOAc (8/2) as eluent to afford the product 3. In case of
b-lactam synthesis, the product was eluted with n-hexanes/EtOAc (3/1). All the
products were characterized by IR, NMR and mass spectral data.
2.02 (s, 3H), 2.23 (s, 3H), 3.97 (dd, J = 5.1, 11.3 Hz, 1H), 4.31 (dd, J = 4.7, 11.8 Hz,
1H), 4.78 (d, J = 17.1 Hz, 1H), 5.04 (d, J = 10.3 Hz, 1H), 5.52 (m, 1H), 6.52 (d,
J = 7.7 Hz, 1H), 6.78 (m, 2H), 6.98 (m, 3H), 7.24 (m, 1H), 7.55 (d, J = 7.3 Hz, 1H); 13
C
NMR (75 MHz, CDCl3): d 10.3, 17.5, 21.0, 42.1, 89.6, 105.0, 109.9, 117.4, 123.4,
124.9, 126.1, 129.2, 129.6, 130.0, 131.6, 133.8, 138.0, 142.1, 158.7, 164.01, 169.7;
IR (KBr): mmax 2919, 1742, 1659, 1607, 1469, 1394, 1355, 1270, 1186, 1120,
762 cmꢀ1; HRMS (ESI) calcd for C23H23N2O3 [M+H]: 375.1708, found: 375.1723.
Methyl-10,3-dimethyl-20,4-dioxo-1-(p-tolyl)spiro[azetidine-2,30-indoline]-3-
carboxylate (5c): Colourless solid, mp 183–184 °C; 1H NMR (400 MHz, CDCl3): d
1.77 (s, 3H), 2.24 (s, 3H), 3.35 (s, 3H), 3.60 (s, 3H), 7.01 (m, 6H), 7.26 (m, 1H), 7.44
(m, 1H); 13C NMR (100 MHz, CDCl3): d 13.7, 20.8, 26.9, 52.3, 66.8, 68.9, 109.1,
117.1, 122.2, 123.0, 124.1, 129.7, 131.1, 133.2, 134.5, 143.7, 162.9, 168.8, 171.6; IR
(KBr): mmax 2978, 2936, 1767, 1722, 1613, 1513, 1465, 1390, 1249, 1135, 1087,
1023, 826, 759 cmꢀ1; HRMS (ESI) calcd for C21H20N2O4Na: 387.1320, found:
387.1317.
Methyl-10-allyl-3-methyl-20,4-dioxo-1-phenylspiro[azetidine-2,30-indoline]-3-
carboxylate (5e): Colourless solid, mp 153–155 °C; 1H NMR (400 MHz, CDCl3): d
1.83 (s, 3H), 3.59 (s, 3H), 4.35 (dd, J = 4.0, 12.0 Hz, 1H), 4.57 (dd, J = 4.0, 12.0 Hz,
1H), 5.27 (m, 2H), 5.89 (m, 1H), 6.96 (d, J = 8.0 Hz, 1H), 7.09 (m, 4H), 7.26 (m, 3H),
7.41 (m, 1H); 13C NMR (100 MHz, CDCl3): d 13.8, 45.6, 52.4, 66.8, 69.0, 110.0,
117.1, 117.9, 122.1, 122.9, 124.1, 124.7, 129.2, 130.6, 131.0, 136.2, 142.8, 163.1,
The spectral data of the selected products: 1,50,60-trimethyl-30-phenylspiro
[indoline-3,20-[1,3]oxazine]-2,40(30H)-dione (3a): Colourless solid, mp 189–
192 °C; 1H NMR (400 MHz, CDCl3): d 1.95 (s, 3H), 2.03 (s, 3H), 3.04 (s, 3H), 6.73
(d, J = 8.0 Hz, 1H), 6.94 (m, 2H), 7.17 (m, 3H), 7.35 (t, J = 8.0 Hz, 1H), 7.57 (d,
J = 8.0 Hz, 1H); 13C NMR (100 MHz, CDCl3): d 10.3, 17.5, 26.2, 89.5, 105.1, 109.0,
123.5, 125.0, 125.8, 128.0, 128.9, 128.9, 131.7, 136.8, 142.9, 158.7, 164.1, 170.0; IR
(KBr): mmax 2932, 1728, 1674, 1610, 1471, 1392, 1347, 1245, 1178, 1086, 762,
692 cmꢀ1; HRMS (ESI) calcd for C20H19N2O3 [M+H]: 335.1395, found: 336.1388.
1-Benzyl-50,60-dimethyl-30-phenylspiro[indoline-3,20-[1,3]oxazine]-2,40(30H)-dione
(3b): Colourless solid, mp 179–182 °C; 1H NMR (400 MHz, CDCl3): d 1.99 (s, 3H),
2.07 (s, 3H), 4.45 (d, J = 16.0 Hz, 1H), 5.05 (d, J = 16.0 Hz, 1H), 6.59 (m, 1H), 6.80
(m, 2H), 7.00 (m, 1H), 7.28 (m, 7H), 7.65 (d, J = 7.6 Hz, 1H); 13C NMR (100 MHz,
CDCl3): d 10.3, 17.6, 43.8, 89.7, 105.1, 110.2, 123.6, 124.8, 126.2, 126.9, 127.6,
128.2, 128.77, 129.17, 129.7, 131.7, 134.4, 136.5, 142.0, 158.9, 164.0, 169.8; IR
168.6, 171.2; IR (KBr):
m
max 2930, 1768, 1731, 1605, 1499, 1380, 1277, 1188, 1137,
946, 751, 687 cmꢀ1
399.1338.
; HRMS(ESI) calcd for C22H20N2O4Na: 399.1320, found:
Methyl-10-allyl-3-methyl-20,4-dioxo-1-(p-tolyl)spiro[azetidine-2,30-indoline]-3-
carboxylate (5f): Colourless solid, mp 130–133 °C; 1H NMR (300 MHz, CDCl3): d
1.71 (s, 3H), 2.23 (s, 3H), 3.56 (s, 3H), 4.32 (dd, J = 4.9, 11.5 Hz, 1H), 4.53 (dd,
J = 5.1, 11.3 Hz, 1H), 5.27 (m, 2H), 5.88 (m, 1H), 6.88 (m, 3H), 6.99 (m, 3H), 7.23 (m,
1H), 7.34 (m, 1H); 13C NMR (75 MHz, CDCl3): d 13.8, 20.8, 42.7, 52.4, 66.8, 68.9,
110.0, 117.1, 117.9, 122.2, 122.9, 124.0, 129.6, 130.6, 131.0, 133.7, 134.5, 142.8,
162.9, 168.7, 171.3; IR (KBr): mmax 2929, 1769, 1728, 1611, 1515, 1377, 1275,
1175, 1133, 754, 701 cmꢀ1; HRMS(ESI) calcd for C23H22N2O4Na: 413.1477, found:
413.1497.
(KBr): m ;
max 2926, 1724, 1666, 1608, 1462, 1396, 1356, 1288, 1182, 744, 692 cmꢀ1
HRMS (ESI) calcd for C26H23N2O3 [M+H]: 411.1708, found: 411.1727.
1-Allyl-50,60-dimethyl-30-(p-tolyl)spiro[indoline-3,20-[1,3]oxazine]-2,40(30H)-dione
(3f): Colourless solid, mp 131–133 °C; 1H NMR (300 MHz, CDCl3): d 1.92 (s, 3H),