A Tandem Ring Opening/Closure Reaction in A BF3-Mediated Rearrangement of Spirooxindoles

Article abstract of DOI:10.1002/adsc.201700728

Treatment of the readily accessible spiro-cyclohexadienones from the PhI(OCOCF₃)₂-mediated spiro-cyclization of N-substituted benzanilides, with BF₃?Et₂O initiates a tandem ring opening/closure reaction leading to the formation of the biologically interesting 8-hydroxy-phenanthridin-6(5H)-one compounds. This unique rearrangement pattern involves the ‘migration’ of the electron-deficient N-methyl carbamoyl moiety rather than the electron-rich aryl group as observed and reported previously in all other similar transformations. (Figure presented.).

Full text of DOI:10.1002/adsc.201700728

Title: Migration of the Electron-Deficient N-Methyl Carbomoyl Moiety:
An Unusual BF3-Mediated Dienone-Phenol Rearrangement of
Spirooxindoles
Authors: Yunfei Du, Xuliang Guo, Qingyu Xing, Daisy Zhang-Negrerie,
and Kang Zhao
This manuscript has been accepted after peer review and appears as an
Accepted Article online prior to editing, proofing, and formal publication
of the final Version of Record (VoR). This work is currently citable by
using the Digital Object Identifier (DOI) given below. The VoR will be
published online in Early View as soon as possible and may be different
to this Accepted Article as a result of editing. Readers should obtain
the VoR from the journal website shown below when it is published
to ensure accuracy of information. The authors are responsible for the
content of this Accepted Article.
To be cited as: Adv. Synth. Catal. 10.1002/adsc.201700728
Link to VoR: http://dx.doi.org/10.1002/adsc.201700728

10.1002/adsc.201700728
Advanced Synthesis & Catalysis
UPDATE
DOI: 10.1002/adsc.201((will be filled in by the editorial staff))
A Tandem Ring Opening/Closure Reaction in A BF3-Mediated
Rearrangement of Spirooxindoles
Xuliang Guo,a Qingyu Xing,a Kunhua Lei,a Daisy Zhang-Negrerie,a Yunfei Du,a,b,* and
Kang Zhaoa,*
a
Tianjin Key Laboratory for Modern Drug Delivery & High-Efficiency, School of Pharmaceutical Science and
Technology, Tianjin University, Tianjin 300072, China.
Fax: +86-22-27404031; Tel: +86-22-27404031; duyunfeier@tju.edu.cn; kangzhao@tju.edu.cn
Collaborative Innovation Center of Chemical Science and Engineering (Tianjin), Tianjin 300072, China.
b
Received: ((will be filled in by the editorial staff))
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/adsc.201######.((Please
delete if not appropriate))
and alkyl group[10]) [Scheme 1, a]. Similarly, when
Abstract. Treatment of the readily accessible spiro-
cyclohexadienones from the PhI(OCOCF3)2-mediated
spiro-cyclization of N-substituted benzanilides, with
treated with catalytic amount of PTSA in refluxing
toluene, spirocyclohexadienones underwent a facile
rearrangement to give dibenzoazepinone derivatives
[Scheme 1, b].[11] Based on the pattern of these
reactions, it was reported that the spirooxindole with
one methylene less should undergo the aryl-migrated
BF3·Et2O initiates
reaction leading to the formation of the biologically
interesting 8-hydroxy-phenanthridin-6(5H)-one
a tandem ring opening/closure
compounds. This unique rearrangement pattern involves
the ‘migration’ of the electron-deficient N-methyl
carbamoyl moiety rather than the electron-rich aryl
group as observed and reported previously in all other
similar transformations.
Keywords: spirocyclohexadienones; BF3; 8-hydroxy-
phenanthridin-6(5H)-one; ring opening; ring closure
Spirocyclohexadienones are a class of potentially
useful building blocks that have found broad
applications in the synthesis of natural products[1] and
many other complex polycyclic compounds.[2] The
dienone-phenol
rearrangement
of
spirocyclohexadienones, particularly those bearing an
aryl group at the para-position of the carbonyl moiety,
is a powerful approach for constructing polycyclic
aromatic skeletons,[3] as well as the synthesis of the
biologically active natural products.[4] For examples:
in 1963, Ullah and coworkers reported that
spiro[cyclohexa[2,5]diene-1,9'-fluoren]-4-one, upon
treatment with acetic anhydride followed by the
subsequent hydrolysis, underwent a dienone-phenol
rearrangement reaction to give triphenylen-2-ol.[5] In
1996, Ward and Pelter realized the conversion of
Scheme 1. Aryl migration in dienone-phenol
rearrangement reactions
dienone-phenol rearrangement reaction to give 9-
hydroxy-phenanthridin-6(5H)-one [Scheme 1, c].[8e]
In 2014, we reported that spirolactam A, fairly easily
prepared from the PIFA-mediated spirocyclization of 2-
hydroxy-N-methyl-phenylbenzamide, could be converted
to dibenzo[d,f][1,3]oxazepine-6(7H)-one compound via a
BF3-mediated rearrangement reaction.[12] We proposed that
the presence of BF3 facilitated the ring opening of
spirooxindole resulting in generating the iminium salt
spirodienone
to
tetrahydrodibenzocyclooctene
mediated by trifluoroacetic acid in trifluoroethanol.[6]
In 1997, Kutchan described an intramolecular
dienone-phenol rearrangement which transformed
spirocyclohexadienone to aporphine alkaloid.[7] In all
these rearrangement reactions, it was always the
electron-rich aryl groups[8] that migrated (there are
also a few examples for migration of alkenyl group[9]
intermediate B, which underwent
a
subsequent
lactonization to form the cyclized product C [Scheme 2a].
1
This article is protected by copyright. All rights reserved.

10.1002/adsc.201700728
Advanced Synthesis & Catalysis
This BF3-mediated ring opening/closure mechanism could
finely account for this exclusive rearrangement reaction,
although all the attempts to isolate intermediate B for
further characterization failed.
To further study the mechanism of the rearrangement
reaction, we decided to check the reaction of compound 1a,
a structural isomer of A with the carbonyl moiety at the
different position. As described in Scheme 2b, if 1a
underwent an identical reaction of the BF3-mediated
rearrangement via the same mechanism, it would furnish 8-
hydroxy-phenanthridin-6(5H)-one compound 2a. However,
Entry Additive Solvent
Conc. (M)
0.05
0.05
0.05
0.05
0.05
0.1
0.2
0.5
1.0
Yieldb)
32%
29%
NDd)
ND
25%
38%
45%
51%
56%
92%
ND
1
BF3·Et2O MeCN
BF3·Et2O MeCN
BF3·Et2O TFA
BF3·Et2O HFIP
BF3·Et2O TFE
2c)
3
4
5
6
7
8
9
BF3·Et2O MeCN
BF3·Et2O MeCN
BF3·Et2O MeCN
BF3·Et2O MeCN
if the compound underwent
rearrangement,
would be obtained as shown in Scheme 1c.
a
dienone-phenol
9-hydroxy-phenanthridin-6(5H)-one
10e)
11
12f)
13
14
15
16
―
BF3·Et2O 0.25
TMSOTf MeCN
―
AlCl3
FeCl3
ZnCl2
TsOH
0.05
In this update, we report the results of the detailed
TMSOTf 0.25
ND
ND
ND
ND
study
on
BF3-mediated
rearrangement
of
MeCN
MeCN
MeCN
MeCN
0.05
0.05
0.05
0.05
spirooxindoles via a ring opening/closure reaction.
ND
a)
Reaction conditions: all reactions were carried out with
1a (0.4 mmol), additive (0.1 mmol) at rt for an hour unless
b)
c)
otherwise stated.
Isolated yields.
The reaction
temperature was -20 ˚C. d) No desired product. e) BF3·Et2O
was used as solvent. f) TMSOTf was used as solvent.
solvent among the other solvents including TFA,
HFIP, TFE [Table 1, entries 3-5] as well as THF,
toluene and MeOH (not shown). Increasing the
concentration of 1a from 0.05 M to 0.10 M improved
the yield of the desired product 2a to 38% [Table 1,
entry 6]. A positive correlation between the
concentration of the substrate and the yield of product
2a was observed with MeCN as the solvent [Table 1,
entries 5-9]. However, when no additional reagent
was added and excessive amount of BF3·Et2O used,
the reaction went to near-completion within 2 h.
When the substrate concentration was adjusted to
0.25 M, the reaction achieved the highest yield (92%)
[Table 1, entry 10]. Additive-screening showed that
no reaction occurred with any of the following as
additive in MeCN, containing both Lewis acids and
Brönsted acid: TMSOTf, AlCl3, FeCl3, ZnCl2 or
TsOH [Table 1, entries 11-16].
Scheme 2. Proposed BF3-mediated formation of 8-
hydroxy-phenanthridin-6(5H)-one based on the
previously reported BF3-mediated ring opening of
spirolactam.
The simplest, unsubstituted spirooxindole 1a was
used as the model substrate to investigate the
outcome of the proposed ring opening/closure
reaction. Building upon our previous work.[12] we
initiated our investigation by using BF3·Et2O as
additive to promote the reaction. It was found that the
reaction in acetonitrile provided the product 2a in
32% yield. The formation of the expected 8-hydroxy-
phenanthridin-6(5H)-one (2a) rather than 2a′, a
regioisomeric analogue, clearly indicated that it was
the electron-deficient N-methyl carbomyl group that
had ‘migrated’ during the rearrangement process.
Optimization of reaction conditions studies started
out with solvent screening.
To explore the generality and scope of this new
reaction, various spirooxindoles were synthesized[13]
and further used as substrates for reactions under the
optimized conditions. The established parameters of
reaction conditions were proven to be effective for
substrates bearing a wide range of substituents on
either of the two phenyl rings, especially the B ring.
Table 1. Optimization of Reaction Conditions.a)
Yield values suggested that acetonitrile was the best
Table 2. BF3-Mediated a Ring Opening/Closure Reaction of Spirolactam 1.a)
2
This article is protected by copyright. All rights reserved.

10.1002/adsc.201700728
Advanced Synthesis & Catalysis
a) Reaction conditions: all reactions were carried out with 1a (0.4 mmol) in BF3·Et2O (1.6 mL) at rt for 1 h. Reaction time
(for entries 12-16) was 2 h. b) Isolated yields. c) The structure of 2i’s methylation derivative (H) was confirmed by X-ray
f)
crystallography (see SI). d) The two regioisomeric products were inseparable: 2l/2l′ = 1:7. e) 2m/2m′ (inseparable) = 1:4.
2n/2n′ (inseparable) = 1:3. g) 2o/2o′ (inseparable) = 1:1. h) 2p/2p′ (inseparable) = 1:3.
。
Those bearing either electron-donating or electron-
withdrawing substituents on the B ring were all
converted to the corresponding products in excellent
yields of over 94% except for that with a bromo
group at 4-position of B ring [Table 2, entries 1-11,
17]. All five substrates, 1l-p, which carried a chloro
group on the A ring, furnished the desired products
(in two inseparable regioisomeric products) in
remarkably high yields [Table 2, entries 12-16]. The
difference in the yield values between 2p (93%) vs 2j
(74%) suggested that the electron-withdrawing
substituent on the A ring favored the reaction. It also
3
This article is protected by copyright. All rights reserved.

10.1002/adsc.201700728
Advanced Synthesis & Catalysis
seemed the presence of the chloro group could
overwrite the negative substituent effect of the bromo
group on the B ring.
No suitable crystal could be obtained from any of
the products 2, even though many trials were carried
out. Finally, we resorted to H, a methylated
derivative of compound 2i [Figure 1]. Its structure
was ambiguously corroborated by its X-ray
crystallography.
observed migration of electron-rich aryl group. The
outcome of the work undoubtedly supports the
tandem
fragmentation/Friedel-Crafts
reaction
pathway involving an iminium salt intermediate,
consistent with what we have proposed previously for
the PIFA-mediated spirocyclization of 2-hydroxy-N-
methyl-phenylbenzamide
in
forming
dibenzo[d,f][1,3]oxazepine-6(7H)-one.[12] Further-
more, this newly discovered reaction not only
rectifies the presumed ‘migration’ pattern reported in
previous literature,8e but also an alternative approach
for the synthesis of the biologically interesting 8-
hydroxy-phenanthridin-6(5H)-one compounds.[15-20]
Figure 1. The methylation of 2i leading to the formation of
H and its X-ray crystallography[14]
.
Scheme 3. Comparison of two mechanisms.
Based on all the experimental results from this
work in addition to our previous reports,[12] we
propose the reaction mechanism as depicted in path a,
Scheme 3 as: (i) ring opening of the spirooxindole
intermediate D via a concerted process to give the
key iminium ion intermediate 3a; (ii) electrophilic
attack of the iminium ion at the phenol ring resulting
in intermediate E; (iii) rearomatization by loss of a
proton which led to the formation of title product 2a.
Although the overall transformation appears as a
dienone-phenol rearrangement reaction, from the
mechanism point of view, it can also be regarded as a
Experimental Section
General Procedure for BF3-Mediated a Ring
Opening/Closure Reaction of Spirooxindoles 1
To a flask containing boron trifluoride ethyl ether (1.6 mL),
subsrate 1 (0.4 mmol) was added slowly under stirring at
room temperature. The reaction mixture was incubated at
the same temperature until total consumption of substrates
1 indicated by TLC. The reaction mixture was quenched
with chilled water (20 mL) and extracted with EtOAc (3 ×
20 mL). The organic phase was washed with brine (1 × 20
mL), dried over anhydrous Na2SO4, and then evaperated in
vacuo to afford product 2, which was further purified by
washing with 30% EtOAc/PE (3 × 2 mL).
tandem
fragmentation/Friedel-Crafts
reaction.
Between the two mechanisms, path a is favored over
path b probably for the reason that the iminium ion
intermediate in the former received extra stability
from the renewed aromaticity of ring A while the
carbon cation intermediate F in the latter would not.
Also, the observed substituent effect – positive effect
of the electron-withdrawing group on the B ring but
negative on the A ring – is consistent with the
formation of the iminium intermediate. Other
spirolactams such as spirocyclohexadienone in
Scheme 1c prefers path b type of rearrangement
because a carbocation, if formed through the path a
route, would be at the α-carbon which is expected to
be disfavored. In conclusion, without the possibility
of forming an iminium ion, path b would have been
preferred due to the allylic nature of the carbocation,
intermediate F.
Acknowledgements
We acknowledges the National Natural Science Foundation of
China (#21472136), the National Basic Research Project
(#2014CB932201) and the Tianjin Research Program of
Application
Foundation
and
Advanced
Technology
(#15JCZDJC32900) for financial support.
References
[1] a) E. M. Beccalli, F. Clerici, M. L. Gelmi, Tetrahedron
2003, 59, 4615; b) P. Magnus, N. Sane, B. P. Fauber, V.
Lynch, J. Am. Chem. Soc. 2009, 131, 16045; c) M.
Paladino, J. Zaifman, M. A. Ciufolini, Org. Lett. 2015, 17,
3422; d) J. Pereira, M. Barlier, C. Guillou, Org. Lett. 2007,
16, 3101.
In summary, we have reported
a
ring
opening/closure reaction of spirocyclo-hexadienones
involving the migration of the electron- deficient N-
methyl carbamoyl moiety instead of the commonly
4
This article is protected by copyright. All rights reserved.

10.1002/adsc.201700728
Advanced Synthesis & Catalysis
[2] a) F. Doi, T. Ohara, T. Ogamino, T. Sugai, K.
Higashinakasu, K. Yamada, H. Shigemori, K. Hasegawa, S.
Lehtio, A.-S. Jemth, R. Collins, O. Loseva, A. Johansson,
N. Markova, M. Hammarstrom, A. Flores, L. Holmberg-
Nishiyama, Phytochemistry 2004, 65, 1405; b) M. Varin, A. Schiavone, J. Weigelt, T. Helleday, H. Schuler, T.
Chiaroni, J. Lallemand, B. Iorga, C. Guillou, J. Org. Chem.
2007, 72, 6421; c) H. Nemoto, K. Takubo, K. Shimizu, S.
Akai, Synlett 2012, 23, 1978; d) A. E. Williamson, T.
Ngouansavanh, R. D. M. Pace, A. E. Allen, J. D.
Cuthbertson, M. J. Gaunt, Synlett 2016, 27, 116.
[3] a) N. Boden, R. J. Bushby, A. N. Cammidge, G.
Headdock, Synthesis 1995, 1, 31; b) D. J. Gregg, C. M. A.
Ollagnier, C. M. Fitchett, S. M. Draper, Chem. - Eur. J.
2006, 12, 3043.
Karlberg, J. Med. Chem. 2009, 52, 3108; e) F. Pierre, E.
Stefan, A.-S. Nédellec, M.-C. Chevrel, C. F. Regan, A.
Siddiqui-Jain, D. Macalino, N. Streiner, D. Drygin, M.
Haddach, S. E. O’Brien, K. Anderes, D. M. Ryckman,
Bioorg. Med. Chem. Lett. 2011, 21, 6687; f) A. L.
Ruchelman, J. E. Kerrigan, T.-K. Li, N. Zhou, A. Liu, L. F.
Liu, E. J. LaVoie, Bioorg. Med. Chem. 2004, 12, 3731; g)
F. Hussain, M. Shamma, Tetrahedron Lett. 1980, 21, 3315;
h) D. J. Hart, A. Kim, R. Krishnamurthy, G. H. Merriman,
A. M. Waltos, Tetrahedron 1992, 38, 8179. .
[4] a) J. Li, L. Serdyuk, V. Dana, D. V. Ferraris, G. Xiao,
K. L. Tays, P. W. Kletzly, W. Li, S. Lautar, J. Zhang, V. J.
Kalish, Bioorg. Med. Chem. Lett. 2001, 11, 1687; b) S.
[16] For the construction of phenanthridinone compounds
through carbonylation, see: a) Z. Liang, J. Zhang, Z. Liu, K.
Patil, S. Kamath, T. Sanchez, N. Neamati, R. F. Schinazi, J. Wang, Y. Zhang, Tetrahedron 2013, 69, 6519; b) D. N.
K. Buolamwini, Bioorg. Med. Chem. 2007, 15, 1212; c) D.
C. Hegan, Y. Lu, G. C. Stachelek, M. E. Crosby, R. S.
Bindra, P. M. Glazer, Proc. Natl. Acad. Sci. U. S. A. 2010,
107, 2201.
Rao, Sk. Rasheed, P. Das, Org. Lett. 2016, 18, 3142; c) D.
Liang, Z. Hu, J. Peng, J. Huang, Q. Zhu, Chem. Commun.
2013, 49, 173; d) R. Shi, H. Niu, A. Lei, Chem. Commun.
2017, 53, 1908; e) M. Feng, B. Tang, N. Wang, H. Xu, X.
[5] H. Plieninger, G. Ege, M. I. Ullah, Chem. Ber. 1963, 96, Jiang, Angew. Chem., Int. Ed. 2015, 54, 14960.
1610.
[17] For the construction of phenanthridinone compounds
through C-N coupling, see: a) P. Nealmongkol, J. Calmes,
S. Ruchirawat, N. Thasana, Tetrahedron 2017, 73, 735; b)
T. Hirata, I. Takahashi, Y. Suzuki, H. Yoshida, H.
Hasegawa, O. Kitagawa, J. Org. Chem. 2016, 81, 318; c)
H. Liu, W. Han, C. Li, Z. Ma, R. Li, X. Zheng, H. Fu, H.
[6] R. S. Ward, A. Pelter, A. Abd-El-Ghani, Tetrahedron
1996, 52, 1303.
[7] T. M. Kutchan, In The Alkaloids: Chemistry and
Biology; Cordell, G. A., Ed.; San Diego, 1998; Vol. 50, p
257.
[8] a) L. Crombie, P. Tuchinda, M. J. Powell, J. Chem. Soc. Chen, Eur. J. Org. Chem. 2016, 2, 389; d) R. Ferraccioli,
Perkin. Trans. 1 1982, 0, 1477; b) V. Fajardo, H. D. Carenzi, O. Rombola, M. Catellani, Org. Lett. 2004, 25,
Guinaudeau, V. Elango, M. Shamma, J. Chem. Soc., Chem. 4759; e) L. Donati, S. Michel, F. Tillequin, F. Poree, Org.
Commun. 1982, 23, 1350; c) H. Guinaudeau, V. Elango, M. Lett. 2010, 1, 156.
Shamma, V. Fajardo, J. Chem. Soc., Chem. Commun. 1982, [18] For the construction of phenanthridinone compounds
19, 1122; d) A. Karimov, M. G. Levkovich, N. D.
Abdullaev, R. Shakirov, Chem. Nat. Comp. 1993, 29, 361;
e) K．Hayashi，J. Takayama, Y. Shimano, M. Xuan, M.
Suda, H. Teramae, T. Sakamoto, Heterocycles 2016, 92,
1785.
[9] I. Herloff, K. Dieter, C. Claus, M. Klaus-Dieter, M.
Wolfgang, Eur. J. Org. Chem. 2006, 2006, 36.
[10] M. Yoshida, T. Nozaki, T. Nemoto, Y. Hamada,
Tetrahedron 2013, 69, 9609.
[11] L. Moisan, M. Wagner, S. Comesse, E. Doris,
Tetrahedron Lett. 2006, 47, 9093.
[12] S. Shang, D. Zhang-Negrerie, Y. Du, K. Zhao, Angew.
Chem., Int. Ed. 2014, 53, 6216.
[13] Z. Yu, X. Ju, J. Wang, W. Yu, Synthesis 2011, 9, 860.
[14] CCDC 1572353 ( H) contains the supplementary
crystallographic data for this paper.
[15] For previous reports describing the biological
activities of phenanthridinone compounds, see: a) E.
Vangrevelinghe, K. Zimmermann, J. Schoepfer, R.
Portmann, D. Fabbro, P. Furet, J. Med. Chem. 2003, 46,
2656; b) F. Pierre, P. C. Chua, S. E. O’Brien, A. Siddiqui-
Jain, P. Bourbon, M. Haddach, M. Haddach, J. Michaux, J.
Nagasawa, M. K. Schwaebe, E. Stefan, A. Vialettes, J. P.
Whitten, T. K. Chen, L. Darjania, R. Stansfield, K.
Anderes, J. Bliesath, D. Drygin, C. Ho, M. Omori, C.
Proffitt, N. Streiner, K. Trent, W. J. Rice, D. M. Ryckman,
J. Med. Chem. 2011, 54, 635; c) S. Antony, K. K. Agama,
Z.-H. Miao, K. Takagi, H. Mollie, M. H. Wright, A. I.
Robles, L. Varticovski, M. Nagarajan, K. Morrell, M.
Cushman, Y. Pommier, Cancer Res. 2007, 67, 10397; d) L.
through a two consecutive C-C bond-formation pathway,
see: a) Y. Yang, H. Huang, L. Wu, Y. Liang, Org. Biomol.
Chem. 2014, 12, 5351; b) X. Li, J. Pan, S. Song, N. Jiao,
Chem. Sci. 2016, 7, 5384; c) T. Furuta, Y. Kitamura, A.
Hashimoto, S. Fujii, K. Tanaka, T. Kan, Org. Lett. 2007, 2,
183.
[19] For the construction of phenanthridinone compounds
through a Heck-type coupling, see: a) K. C. Majumdar, B.
Chattopadhyay, S. Nath, Tetrahedron Lett. 2008, 49, 1609;
b) R. Bernini, S. Cacchi, G. Fabrizi, A. Sferrazza,
Synthesis 2008, 5, 729; c) P, H. Bernardo, W. Fitriyanto, C.
L. L. Chai, Synlett 2007, 12, 1935; d) N. Conde, F.
Churruca, R. SanMartin, M. T. Herrero, E. Dominguez,
Adv. Synth. Catal. 2015, 357, 1525; e) T. Harayama, T.
Akiyama, Y. Nakano, K. Shibaike, H. Akamatsu, A. Hori,
H. Abe, Y. Takeuchi, Synthesis 2002, 2, 237; f) H.
Nishioka, C. Nagura, H. Abe, Y. Takeuchi, T. Harayama,
Heterocycles 2006, 70, 549; g) G. Zhang, X. Zhao, Y. Yan,
C. Ding, Eur. J. Org. Chem. 2012, 4, 669.
[20] For the construction of phenanthridinone compounds
through oxidative coupling, see: a) H. Ohno, H. Iwasaki, T.
Eguchi, T. Tanaka, Chem. Commun. 2004, 19, 2228; b) Q.
Yu, N. Zhang, Y. Tang, H. Lu, J. Huang, S. Wang, Y. Du,
K. Zhao, Synthesis 2012, 44, 2374.
5
This article is protected by copyright. All rights reserved.

10.1002/adsc.201700728
Advanced Synthesis & Catalysis
COMMUNICATION
A Tandem Ring Opening/Closure Reaction in A
BF3-Mediated Rearrangement of Spirooxindoles
Adv. Synth. Catal. Year, Volume, Page – Page
Xuliang Guo,† Qingyu Xing,† Kunhua Lei,† Daisy
Zhang-Negrerie,† Yunfei Du, *,†,‡ and Kang Zhao*,†
6
This article is protected by copyright. All rights reserved.