An efficient synthesis of dihydrofuranyl spirooxindoles from isatin-derived propargylic alcohols and 1,3-dicarbonyls

Article abstract of DOI:10.1016/j.tetlet.2016.11.077

Various dihydrofuranyl spirooxindoles have been synthesized via montmorillonite K-10-catalyzed propargylation of 1,3-dicarbonyl compounds with isatin-derived propargylic alcohols and subsequent base-mediated 5-exo-dig cyclization.

Full text of DOI:10.1016/j.tetlet.2016.11.077

Accepted Manuscript
An efficient synthesis of dihydrofuranyl spirooxindoles from isatin-derived
propargylic alcohols and 1,3-dicarbonyls
Hwa Jung Roh, Su Yeon Kim, Beom Kyu Min, Jae Nyoung Kim
PII:
S0040-4039(16)31558-1
DOI:
http://dx.doi.org/10.1016/j.tetlet.2016.11.077
TETL 48363
Reference:
Tetrahedron Letters
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16 November 2016
18 November 2016
Please cite this article as: Jung Roh, H., Yeon Kim, S., Kyu Min, B., Nyoung Kim, J., An efficient synthesis of
dihydrofuranyl spirooxindoles from isatin-derived propargylic alcohols and 1,3-dicarbonyls, Tetrahedron Letters
(2016), doi: http://dx.doi.org/10.1016/j.tetlet.2016.11.077
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An efficient synthesis of dihydrofuranyl spirooxindoles
from isatin-derived propargylic alcohols and 1,3-dicarbonyls
Hwa Jung Roh, Su Yeon Kim, Beom Kyu Min, Jae Nyoung Kim*
O
O
Ph
O
O
HO
acetylacetone
Montmorillonite K-10
K2CO3, CH3CN
reflux, 1 h
Ph
Ph

O
ClCH2CH2Cl
reflux, 1 h
O
5-exo-dig cyclization
N
O
N
Me
N
Me
Me
dihydrofuranyl spirooxindole

1
Tetrahedron Letters
An efficient synthesis of dihydrofuranyl spirooxindoles from isatin-derived
propargylic alcohols and 1,3-dicarbonyls
Hwa Jung Roh, Su Yeon Kim, Beom Kyu Min, Jae Nyoung Kim
Department of Chemistry and Institute of Basic Science, Chonnam National University, Gwangju 500-757, Republic of Korea
ARTICLE INFO
ABSTRACT
Article history:
Received
Received in revised form
Accepted
Various dihydrofuranyl spirooxindoles have been synthesized via montmorillonite K-10-
catalyzed propargylation of 1,3-dicarbonyl compounds with isatin-derived propargylic alcohols
and subsequent base-mediated 5-exo-dig cyclization.
2016 Elsevier Ltd. All rights reserved.
Available online
Keywords:
Spirooxindoles
Dihydrofuran
Propargylic alcohols
1,3-Dicarbonyls
Various types of spirooxindoles exist in a large number of
natural products and biologically interesting compounds.1 Thus,
developments of efficient synthetic protocols to access these
important motifs have received much attention over the past
years.1-4 Especially, spirooxindoles bearing five-membered
oxacycles have been found in many biologically important
synthetic and natural compounds.3,4 The five-membered
oxacyclic moieties found in reported spirooxindoles include 2,3-
dihydrofurans,3a-e,r 2,5-dihydrofurans,3f-q -butyrolactones,4a-c -
methylene--butyrolactones,4d-h
tetrahydrofurans,4i-k
butenolides,4l,m and 1,3-dioxolanes.3o,p
During our recent synthesis of 3-naphtho[2,1-b]furanyl-2-
oxindoles, we found that 2,3-dihydrofuranyl spirooxindole could
be synthesized readily from 3-(ortho-hydroxyaryl)-2-oxindole by
base-catalyzed cyclization reaction,5 as shown in Scheme 1. Bi
and co-workers also reported the synthesis of spirodihydrofurans
by base-catalyzed cyclization reaction of the propargylated
acetylacetone derivative.6 In these contexts, we envisioned that
dihydrofuranyl spirooxindole 4a could be synthesized by base-
mediated 5-exo-dig cyclization reaction of propargylated
acetylacetone derivative 3a, as also shown in Scheme 1.
The propargylation of acetylacetone (2a), as a typical 1,3-
dicarbonyl compound, with propargylic alcohols has been
extensively studied, as shown in Scheme 2.7 Secondary
propargylic alcohols afforded the corresponding -adducts in
good yields in most papers.7a-i However, the reaction with tertiary
propargylic alcohols afforded different products depending on
the substrates. Takai and co-workers reported the synthesis of -
Scheme 1. Synthetic rationale of dihydrofuranyl spirooxindole 4a.
adduct in low yield (10%) from 2-methyl-4-phenylbut-3-yn-2-ol
by rhenium-catalyzed reaction.7i Roy and co-workers obtained the
same -adduct in moderate yield (45%) by using Ir-Sn catalyst.7j
In contrast to the dimethyl derivative,7i,j the reaction with 1,1,3-
triphenylprop-2-yn-1-ol gave allene or its isomerized diene
derivative.7a-e Thus, at the outset of this study, we examined the
synthesis of starting material 3a from isatin-derived propargylic
alcohol 1a.
———
*Corresponding author. Tel.: +82 62 530 3381; fax: +82 62 530 3389; E-mail address: kimjn@chonnam.ac.kr (J. N. Kim)

2
Tetrahedron
Table 1. Optimization study for the synthesis of -adduct 3a.
aAppreciable amount of 1a remained.
b1a-Boc derivative was used.
equiv. of 2a (entry 8). From the results, we decided to use MK10
in DCE with 3.0 equiv. of 2a (entry 6).9
Scheme 2. Propargylation of 2a with various propargylic alcohols.
Thus, some representative -adducts 3b-3l were prepared in
moderate to good yields by the reactions of isatin-derived
propargylic alcohols 1a-1j and 1,3-dicarbonyl compounds 2a-2c
under the optimized condition, as shown in Table 2.10
Acetylacetone (2a), dibenzoylmethane (2b), and ethyl
acetoacetate (2c) were used as representative 1,3-dicarbonyl
compounds. The reactions of 1b and 1c with 2a afforded 3b
(67%) and 3c (63%) in moderate yields. However, the yield of 5-
methoxyisatin derivative 3d (47%) was somewhat lower than
other entries. Three arylacetylene and two aliphatic alkyne
derivatives 3e-3i were synthesized in moderate to good yields
(55-83%). The reactions of 1a with 2b and 2c afforded 3j (39%)
and 3k (48%) in low yields presumably due to steric reason. The
reaction of N-unprotected derivative 1j produced 3l in a similar
yield (65%) to that of N-methyl derivative 3a.
The reaction of isatin-derived propargylic alcohol 1a and
acetylacetone (2a) was examined in the presence of some
representative acid catalysts, as shown in Table 1. The reaction in
the presence of p-TsOH (CH3CN, reflux, entry 1) afforded 3a in
a low yield (14%) for 10 h. The reactions using FeCl3 (toluene,
80 C, entry 2) or Yb(OTf)3 (CH3NO2, 80 C, entry 3) provided
3a in low yields. Trifluoroacetic acid was not an efficient catalyst
for the reaction (entry 4). To our delight, the use of
montmorillonite K-10 (MK10, 300%, w/w) in 1,2-dichloroethane
(DCE, reflux, entry 5) afforded 3a in moderate yield (47%) in
short time (2 h).8 The yield could be increased by using 2a in an
excess amount (3.0 equiv.) up to 64% (entry 6) in short time (1
h). When we used Boc carbonate of 1a, the yield of 3a increased
slightly (entry 7). The same yield of 3a was obtained by using 5.0
o
o
Table 2. Synthesis of -adduct 3.
aConditions: Propargyl alcohol 1 (1.0 mmol), 1,3-dicarbonyls 2 (3.0 mmol), montmorillonite K-10 (300%, w/w), DCE, reflux, 1 h.
bReaction time was 8 h. cReaction time was 2 h. dInseparable 1:0.9 diastereomeric mixture.

3
Table 3. Synthesis of spirooxindoles 4.
aConditions: substrate 3 (0.5 mmol), K2CO3 (0.5 mmol), CH3CN, reflux, 1 h.
bReaction time was 3 h. cReaction time was 8 h.
A following base-mediated cyclization of 3a to 4a was
examined under the optimized reaction condition in our previous
cyclization reaction of 3-(ortho-hydroxyaryl)-2-oxindoles.5 To
our delight, the reaction of 3a in CH3CN in the presence of
K2CO3 (1.0 equiv.) afforded spirooxindole 4a in good yield
(91%) in short time (1 h), as shown in Table 3.10,11 The
spirooxindole 4a was obtained as a single isomer, and the
stereochemistry of the benzylidene moiety would be Z-form
presumably due to steric hindrance between the oxindole moiety
and the phenyl group of benzylidene moiety, as previously
reported by Bi6 and us5 in a similar system. Three 5-substituted
isatin derivatives 3b-3d afforded the corresponding
spirooxindoles 4b-4d in high yields (94-95%). Spirooxindoles
4e-4i were synthesized in good yields (79-92%) from the
corresponding -adducts 3e-3i bearing various arylacetylene and
aliphatic alkyne moieties. The cyclization of 3h and 3i required
somewhat longer reaction time (3-8 h) than other entries. In
addition, sterically congested compounds 4j (91%) and 4k (85%)
as shown in Scheme 3. The -adduct 3a might be present in its
intramolecular hydrogen-bonded six-membered structure and the
cyclization of 3a to 4a would be difficult, as shown in Scheme 3.
Actually, 3a was not converted to 4a under the influence of
MK10 (DCE, reflux) even after 20 h. As compared to 3a, an
intramolecular hydrogen-bond was not possible for the -adduct
3m. Thus, the cyclization of an -adduct intermediate 3m to the
spirooxindole 4m could proceed under the same acidic reaction
condition.12,13
In summary, various dihydrofuranyl spirooxindoles have been
synthesized via montmorillonite K-10-catalyzed propargylation
of 1,3-dicarbonyl compounds with isatin-derived propargylic
alcohols and subsequent base-mediated 5-exo-dig cyclization.
Acknowledgments
This work was supported by National Research Foundation of
Korea (NRF) grant funded by the Korea government (NRF-
were produced in good yields. The reaction of N-unprotected
derivative 3l afforded 4l in somewhat lower yield (62%) than
other entries.
2015R1A4A1041036
Spectroscopic data were obtained from the Korea Basic Science
Institute, Gwangju branch.
and
NRF-2014R1A1A2053606).
References and notes
1. For reviews on spirooxindoles, see: (a) Yu, B.; Yu, D.-Q.; Liu, H.-M.
Eur. J. Med. Chem. 2015, 97, 673; (b) Santos, M. M. M. Tetrahedron
2014, 70, 9735; (c) Cheng, D.; Ishihara, Y.; Tan, B.; Barbas, C. F., III
ACS Catal. 2014, 4, 743; (d) Hong, L.; Wang, R. Adv. Synth. Catal.
2013, 355, 1023; (e) Singh, G. S.; Desta, Z. Y. Chem. Rev. 2012, 112,
6104; (f) Ball-Jones, N. R.; Badillo, J. J.; Franz, A. K. Org. Biomol.
Chem. 2012, 10, 5165; (g) Trost, B. M.; Brennan, M. K. Synthesis
2009, 3003; (h) Marti, C.; Carreira, E. M. Eur. J. Org. Chem. 2003,
2209.
2. For our recent synthesis of spirooxindoles, see: (a) Kim, K. H.; Moon,
H. R.; Lee, J.; Kim, J.; Kim, J. N. Adv. Synth. Catal. 2015, 357, 1532;
(b) Kim, K. H.; Moon, H. R.; Lee, J.; Kim, J. N. Adv. Synth. Catal.
2015, 357, 701; (c) Lim, J. W.; Moon, H. R.; Kim, S. Y.; Kim, J. N.
Tetrahedron Lett. 2016, 57, 133.
3. For similar spirooxindoles bearing dihydrofuran moiety, see: (a) Liu,
Y.-L.; Wang, X.; Zhao, Y.-L.; Zhu, F.; Zeng, X.-P.; Chen, L.; Wang,
C.-H.; Zhao, X.-L.; Zhou, J. Angew. Chem. Int. Ed. 2013, 52, 13735;
(b) Liu, Z.; Fang, J.; Yan, C. Chin. J. Chem. 2013, 31, 1054; (c) Zhou,
R.; Zhang, K.; Chen, Y.; Meng, Q.; Liu, Y.; Li, R.; He, Z. Chem.
Commun. 2015, 51, 14663; (d) Basavaiah, D.; Badsara, S. S.; Sahu, B.
C.; Chem. Eur. J. 2013, 19, 2961; (e) Savitha, G.; Niveditha, S. K.;
Scheme 3. Synthesis of spirooxindole 4m.
It is interesting to note that the formation of -adduct 3m was
not observed in the reaction of 1a and dimedone (2d). The
spirooxindole 4m was obtained directly in moderate yield (55%),

4
Tetrahedron
Muralidharan, D.; Perumal, P. T. Tetrahedron Lett. 2007, 48, 2943;
chromatographic purification process (hexanes/EtOAc, 1:1) compound
4a was obtained as a white solid, 157 mg (91%). Other compounds
were synthesized similarly, and the selected spectroscopic data of 3a
and 4a are as follows.
(f) Alcaide, B.; Almendros, P.; Gonzalez, A. M.; Luna, A.; Martinez-
Ramirez, S. Adv. Synth. Catal. 2016, 358, 2000; (g) Alcaide, B.;
Almendros, P.; Luna, A.; Prieto, N. Org. Biomol. Chem. 2013, 11,
1216; (h) Alcaide, B.; Almendros, P.; Luna, A.; Gomez-Campillos, G.;
Torres, M. R. J. Org. Chem. 2012, 77, 3549; (i) Alcaide, B.;
Almendros, P.; Rodriguez-Acebes, R. J. Org. Chem. 2006, 71, 2346; (j)
Alcaide, B.; Almendros, P.; Rodriguez-Acebes, R. Chem. Eur. J. 2005,
11, 5708; (k) Liu, J.; Peng, H.; Yang, Y.; Jiang, H.; Yin, B. J. Org.
Chem. 2016, 81, 9695; (l) Liu, J.; Xu, X.; Li, J.; Liu, B.; Jiang, H.; Yin,
B. Chem. Commun. 2016, 52, 9550; (m) Huang, L.; Zhang, X.; Li, J.;
Ding, K.; Li, X.; Zheng, W.; Yin, B. Eur. J. Org. Chem. 2014, 338; (n)
Yin, B.-L.; Lai, J.-Q.; Zhang, Z.-R.; Jiang, H.-F. Adv. Synth. Catal.
2011, 353, 1961; (o) Muthusamy, S.; Karikalan, T. Tetrahedron 2012,
68, 1443; (p) Muthusamy, S.; Ramkumar, R.; Mishra, A. K.
Tetrahedron Lett. 2011, 52, 148; (q) Muthusamy, S.; Gunanathan, C.;
Nethaji, M. J. Org. Chem. 2004, 69, 5631. During preparation of this
manuscript, Kumarswamyreddy and Kesavan reported Cu(OTf)2-
mediated synthesis of spirooxindol[2,1-b]furan derivatives, see: (r)
Kumarswamyreddy, N.; Kesavan, V. Eur. J. Org. Chem. 2016, 5301.
Compound 3a: 64%; pale yellow solid, mp 125-127 oC; IR (KBr) 1722,
1611, 1493, 1471, 1354 cm-1; H NMR (CDCl3, 500 MHz)  2.19 (s,
1
3H), 2.57 (s, 3H), 3.31 (s, 3H), 4.68 (s, 1H), 6.89 (d, J = 8.0 Hz, 1H),
7.08 (t, J = 7.5 Hz, 1H), 7.25-7.35 (m, 4H), 7.36-7.43 (m, 3H); 13C
NMR (CDCl3, 125 MHz)  27.1, 30.2, 33.3, 46.4, 70.4, 84.9, 85.1,
108.7, 121.9, 123.1, 124.5, 128.1, 128.3, 128.8, 129.1, 131.8, 143.6,
173.5, 200.5, 203.2; ESIMS m/z 346 [M+H]+. Anal. Calcd for
C22H19NO3: C, 76.50; H, 5.54; N, 4.06. Found: C, 76.78; H, 5.81; N,
3.92.
Compound 4a: 91%; white solid, mp 230-232 oC; IR (KBr) 1720, 1690,
1631, 1610, 1493, 1385, 1370, 1345, 1230 cm-1; H NMR (CDCl3, 500
1
MHz)  2.03 (s, 3H), 2.59 (s, 3H), 3.30 (s, 3H), 5.08 (s, 1H), 6.91 (d, J
= 7.5 Hz, 1H), 7.02 (t, J = 7.5 Hz, 1H), 7.06 (d, J = 7.5 Hz, 1H), 7.14 (t,
J = 7.5 Hz, 1H), 7.25 (t, J = 7.5 Hz, 2H), 7.31 (t, J = 7.5 Hz, 1H), 7.43
(d, J = 7.5 Hz, 2H); 13C NMR (CDCl3, 125 MHz)  15.5, 27.1, 29.0,
62.8, 104.4, 108.6, 118.7, 123.5, 123.7, 127.0, 128.4, 128.6, 129.3,
131.9, 133.8, 144.1, 154.2, 167.8, 175.4, 191.4; ESIMS m/z 346
[M+H]+. Anal. Calcd for C22H19NO3: C, 76.50; H, 5.54; N, 4.06.
Found: C, 76.58; H, 5.73; N, 4.17.
4. For similar spirooxindoles bearing -butyrolactone, -methylene--
butyrolactone, tetrahydrofuran, and butenolide moieties, see: (a)
Cerisoli, L.; Lombardo, M.; Trombini, C.; Quintavalla, A. Chem. Eur.
J. 2016, 22, 3865; (b) Li, G.; Huang, L.; Xu, J.; Sun, W.; Xie, J.; Hong,
L.; Wang, R. Adv. Synth. Catal. 2016, 358, 2873; (c) Buttachon, S.;
Chandrapatya, A.; Manoch, L.; Silva, A.; Gales, L.; Bruyere, C.; Kiss,
R.; Kijjoa, A. Tetrahedron 2012, 68, 3253; (d) Rana, S.; Blowers, E. C.;
Tebbe, C.; Contreras, J. I.; Radhakrishnan, P.; Kizhake, S.; Zhou, T.;
Rajule, R. N.; Arnst, J. L.; Munkarah, A. R.; Rattan, R.; Natarajan, A.
J. Med. Chem. 2016, 59, 5121; (e) Jayakumar, S.; Muthusamy, S.;
Prakash, M.; Kesavan, V. Eur. J. Org. Chem. 2014, 1893; (f)
Takahashi, M.; Murata, Y.; Yagishita, F.; Sakamoto, M.; Sengoku, T.;
Yoda, H. Chem. Eur. J. 2014, 20, 11091; (g) Murata, Y.; Takahashi,
M.; Yagishita, F.; Sakamoto, M.; Sengoku, T.; Yoda, H. Org. Lett.
2013, 15, 6182; (h) Rana, S.; Natarajan, A. Org. Biomol. Chem. 2013,
11, 244; (i) Franz, A. K.; Dreyfuss, P. D.; Schreiber, S. L. J. Am. Chem.
Soc. 2007, 129, 1020; (j) Zhou, M.; Miao, M.-M.; Du, G.; Li, X.-N.;
Shang, S.-Z.; Zhao, W.; Liu, Z.-H.; Yang, G.-Y.; Che, C.-T.; Hu, Q.-F.;
Gao, X.-M. Org. Lett. 2014, 16, 5016; (k) Tang, Z.; Liu, Z.; An, Y.;
Jiang, R.; Zhang, X.; Li, C.; Jia, X.; Li, J. J. Org. Chem. 2016, 81,
9158; (l) Li, J.; Liu, Y.; Li, C.; Jia, X. Chem. Eur. J. 2011, 17, 7409;
(m) Li, J.; Liu, Y.; Li, C.; Jie, H.; Jia, X. Green Chem. 2012, 14, 1314.
5. Roh, H. J.; Lim, J. W.; Ryu, J. Y.; Lee, J.; Kim, J. N. Tetrahedron Lett.
2016, 57, 4280.
11. For metal-free 5-exo-dig cyclizations, see: (a) Taylor, C.; Bolshan, Y.
Tetrahedron Lett. 2015, 56, 4392; (b) Kraus, G. A.; Wie, J.; Thite, A.
Synthesis 2008, 2427; (c) Chenevert, R.; Page, J.; Plante, R.; Beaucage,
D. Synthesis 1982, 75.
12. For acid-catalyzed 5-exo-dig cyclization, see: (a) Imagawa, H.; Kotani,
S.; Nishizawa, M. Synlett 2006, 642; (b) Liu, C.-R.; Li, M.-B.; Yang,
C.-F.; Tian, S.-K. Chem. Eur. J. 2009, 15, 793; (c) Yuan, F.-Q.; Han,
F.-S. Adv. Synth. Catal. 2013, 355, 537; (d) Wang, Y.; Bi, X.; Li, D.;
Liao, P.; Wang, Y.; Yang, J.; Zhang, Q.; Liu, Q. Chem. Commun. 2011,
47, 809.
13. The reaction of 1a with other cyclic 1,3-dicarbonyl compounds such as
1,3-cyclohexanedione or N,N-dimethylbarbituric acid was very
sluggish, and isolation of the corresponding -adducts or
spirooxindoles failed. The reason is not clear at this stage, and further
studies are currently underway.
Supplementary Data
Supplementary data
(experimental
procedures
and
characterization data for compounds 1g-1i, 3a-3l, and 4a-4m)
associated with this article can be found, in the online version, at
xxxxxxxxxxxx.
6. Ma, Q.; Wang, Y.; Zhao, Y.; Liao, P.; Sun, B.; Bi, X. Eur. J. Org.
Chem. 2014, 4999.
7. For introduction of 1,3-dicarbonyl compounds at the -position of
propargylic alcohols, see: (a) Sanz, R.; Miguel, D.; Martinez, A.;
Alvarez-Gutierrez, J. M.; Rodriguez, F. Org. Lett. 2007, 9, 727; (b)
Huang, W.; Wang, J.; Shen, Q.; Zhou, X. Tetrahedron 2007, 63, 11636;
(c) Funabiki, K.; Komeda, T.; Kubota, Y.; Matsui, M. Tetrahedron
2009, 65, 7457; (d) Maiti, S.; Biswas, S.; Jana, U. Synth. Commun.
2011, 41, 243; (e) Chatterjee, P. N.; Roy, S. Tetrahedron 2011, 67,
4569; (f) Yadav, J. S.; Reddy, B. V. S.; Pandurangam, T.; Rao, K. V.
R.; Praneeth, K.; Kumar, G. G. K. S. N.; Madavi, C.; Kunwar, A. C.
Tetrahedron Lett. 2008, 49, 4296; (g) Aridoss, G.; Laali, K. K.
Tetrahedron Lett. 2011, 52, 6859; (h) Reddy, C. R.; Vijaykumar, J.;
Gree, R. Synthesis 2010, 3715; (i) Kuninobu, Y.; Ueda, H.; Takai, K.
Chem. Lett. 2008, 37, 878; (j) Maity, A. K.; Chatterjee, P. N.; Roy, S.
Tetrahedron 2013, 69, 942.
8. For use of montmorillonite catalyst in nucleophilic substitution reaction
of alcohols with 1,3-dicarbonyls, see: (a) Wang, J.; Masui, Y.; Onaka,
M. Synlett 2010, 2493; (b) Motokura, K.; Nakagiri, N.; Mizugaki, T.;
Ebitani, K.; Kaneda, K. J. Org. Chem. 2007, 72, 6006; (c) Motokura,
K.; Fujita, N.; Mori, K.; Mizugaki, T.; Ebitani, K.; Kaneda, K. Angew.
Chem. Int. Ed. 2006, 45, 2605.
9. The reaction of 1a and 2a under typical Mitsunobu reaction conditions
(PPh3, diethyl azodicarboxylate) in toluene at room temperature did not
produce 3a at all.
10. Typical procedure for the synthesis of 3a and 4a: A stirred mixture
of 1a (263 mg, 1.0 mmol), acetylacetone (2a, 300 mg, 3.0 mmol),
montmorillonite K-10 (790 mg, 300%, w/w) in ClCH2CH2Cl (3.0 mL)
was heated to reflux for 1 h. The reaction mixture was filtered through a
pad of Celite and washed thoroughly with ClCH2CH2Cl. After removal
of solvent and column chromatographic purification process
(CH2Cl2/EtOAc, 40:1) compound 3a was obtained as a pale yellow
solid, 221 mg (64%). A stirred mixture of 3a (173 mg, 0.5 mmol) and
K2CO3 (69 mg, 0.5 mmol) in CH3CN (2.0 mL) was heated to reflux for
1
h. After the usual aqueous extractive workup and column

Highlights
*Efficient synthesis of dihydrofuranyl spirooxindoles
*Montmorillonite-catalyzed propargylation of 1,3-dicarbonyls
*Synthetic usefulness of isatin-derived propargylic alcohols