Synthesis of indene derivatives via reactions of vinylidenecyclopropanes with the N-acyliminium cations generated from hydroxylactams

Article abstract of DOI:10.1016/j.tetlet.2014.02.039

A novel route for the synthesis of 1H-indene derivatives via the reactions of vinylidenecyclopropanes (VCPs) with the N-acyliminium cations generated from hydroxylactams is described.

Full text of DOI:10.1016/j.tetlet.2014.02.039

Tetrahedron Letters 55 (2014) 2022–2026
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Tetrahedron Letters
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Synthesis of indene derivatives via reactions
of vinylidenecyclopropanes with the N-acyliminium
cations generated from hydroxylactams
a
b
a
Alexander V. Stepakov a, , Anna G. Larina , Vitaly M. Boitsov , Vladislav V. Gurzhiy ,
⇑
Alexander P. Molchanov a, Rafael R. Kostikov a
a Chemistry Department, Saint-Petersburg State University, Universitetsky prosp. 26, St-Petersburg 198504, Russian Federation
b Saint-Petersburg Academic University—Nanotechnology Research and Education Centre RAS, Khlopin Str. 8/3, St-Petersburg 194021, Russian Federation
a r t i c l e i n f o
a b s t r a c t
Article history:
A novel route for the synthesis of 1H-indene derivatives via the reactions of vinylidenecyclopropanes
(VCPs) with the N-acyliminium cations generated from hydroxylactams is described.
Ó 2014 Elsevier Ltd. All rights reserved.
Received 23 November 2013
Revised 21 January 2014
Accepted 12 February 2014
Available online 20 February 2014
Keywords:
Hydroxylactams
Vinylidenecyclopropanes
N-Acyliminium cation
1H-Indenes
Lewis acid
The 1H-indene subunit appears in compounds displaying a con-
siderable range of biological activity: cyclooxygenase-2 (COX-2)
inhibitors,1 oxytocin antagonists,2 estrogen receptor modulators,3
an 5-HT6 serotonin receptor4 and in compounds with antiprolifer-
ative activity.5 Indene derivatives are also used as precursors of
metallocene complexes for catalytic polymerization processes
vinylidenecyclopropanes with N-acyliminium cations have not
been previously studied. N-Acyliminium ions are known as impor-
tant reactive species in organic synthesis for the construction of
carbon–carbon bonds.16 Numerous examples of N-acyliminium
ion based intramolecular cyclizations can be found in the synthesis
of alkaloid derivatives.17 Recently, Wang and Zhang reported the
first examples of the Lewis acid catalyzed [4+2] cycloaddition reac-
tions of N-acyliminium ions with alkenes.18 In continuation of our
earlier work,19 we have studied the reactions of non-activated
vinylidenecyclopropanes (VCPs) with N-acyliminium cations. In
the present work we show for the first time that 1-(2-methylprop-
enylidene)-2,2-diarylcyclopropanes react with the N-acyliminium
cations generated from hydroxylactams to give the corresponding
5-[2-methyl-1-(3-Ar1-1H-inden-2-yl)prop-1-enyl]-1-Ar2-1H-pyrro
l-2(5H)-ones and 3-[2-methyl-1-(3-Ar1-1H-inden-2-yl)prop-1-
enyl]-2-Ar2-isoindolin-1-ones in moderate yields. Of the Lewis
acids and solvents screened, the combination of BF3ÁOEt2 and
dichloromethane produced the best results in these reactions.
In our initial studies, the reaction of 1a with VCP 2a was
investigated. Under a nitrogen atmosphere, compound 1a was
reacted with an equimolar amount of 2a in the presence of
BF3ÁOEt2 (1.0 equiv) in CH2Cl2 at ambient temperature for one
hour, to give 3-{2-methyl-1-[6-methyl-3-(4-methylphenyl)-1H-in-
den-2-yl]prop-1-en-1-yl}-2-phenylisoindolin-1-one (3a) in 41%
and as functional materials.6 Consequently,
a number of
approaches to the synthesis of the indene ring system have been
developed, including new methods such as intramolecular
cyclization of tetraaryl substituted 1,3-butadienes,7 cycloaddition
of methylenecyclopropanes with acetals,8 cycloisomerizations of
alkynes,9 annulation of benzylic alcohols with alkynes,10 rear-
rangement of ortho-(alkynyl)styrenes,11 and cycloisomerization of
arylvinylcyclopropenes.12 Tsuji and co-workers have reported a
novel synthetic method for the preparation of indenes by the
reaction of aliphatic ketones with aryl-substituted alkynes in the
presence of NbCl3(DME)13
The chemistry of vinylidenecyclopropanes has been explored
extensively. Novel intramolecular rearrangements and cycloaddi-
tion reactions have been studied.14,15 However, reactions of
⇑
Corresponding author. Fax: +7 812 4286939.
E-mail address: alstepakov@yandex.ru (A.V. Stepakov).
http://dx.doi.org/10.1016/j.tetlet.2014.02.039
0040-4039/Ó 2014 Elsevier Ltd. All rights reserved.

A. V. Stepakov et al. / Tetrahedron Letters 55 (2014) 2022–2026
2023
isolated yield (Table 1, entry 1). Although several other products
could be seen in the TLC analysis of the reaction mixture, no other
potential products were successfully isolated. When the reaction of
1a with VCP 2a was carried out at low temperature (À20 °C), the
corresponding indene 3a was produced in 36% yield. Under
refluxing conditions, product 3a was isolated in only 14% yield.
The reactions of hydroxylactams 1 with VCPs 2 were carried out
in dichloromethane under similar conditions to those described
previously (Table 1). The reactions proceeded smoothly to give
the corresponding indene derivatives 3 in moderate yields at room
temperature. The presence of either electron-donating or electron-
withdrawing substituents on the benzene ring of the VCPs 2 had
only a slight effect upon the yields of the produced indenes 3.
For example, decreased yields of the indenes 3 were obtained by
using VCPs 2 with electron-donating groups (MeO) on the benzene
ring (Table 1, entries 2 and 4). The presence of electron-donating or
electron-withdrawing groups on the phenyl ring of the
hydroxylactams 1 also had a minor effect upon the yields of the
produced indenes 3. 2-[Bis(4-methoxyphenyl)methylene]-5,5-
dimethyldihydrofuran-3(2H)-one (4) was isolated in 7–9% yields
as the side product in all the cases of the reactions with bis(4-
methoxyphenyl)vinylidenecyclopropane (2d). In cases where R1
was a phenyl group, or R2 a methyl group (VCPs 2e–g), complicated
reaction mixtures were formed under the standard conditions
(Table 1, entries 10–12). Dihydrofuranone 4 is the oxidation prod-
uct of VCP 2d; its formation might occur either due to aerial oxy-
gen or during chromatographic separation. The exact reaction
mechanism for the formation of 4 is still not clear. Using degassed
solvent resulted in only a slight decrease of the amount of 4 in the
reaction mixture. The reaction of 2d with BF3ÁOEt2 in CH2Cl2 re-
sulted in the formation of dihydrofuranone 4 in 23% yield. Forma-
tion of analogous products 4 was not observed from VCPs 2a–c.
The compositions and structures of the products 3 and 4 were
established by elemental and spectral analyses. The structures of
compounds 3c and 4 were confirmed by X-ray diffraction analysis
(Figs. 1 and 2).20,21 The single crystal of 3c clearly showed that the
aryl group on the indene segment and the aryl ring of the phthal-
C33
C29
C22
C26
C21
C28
C18
C23
C24
C27
C30
C20A
C31
C20
C24A
C32
C16
C25
C19
C15
C17
C4
C5
C3A
C3
C13
C8
C12
C9
C7A
C11
C10
N2
C6
C14
C7
C1
O1
Figure 1. ORTEP representation of 3c.
C52
C5
C4
C51
O2
C3
O1
C2
C62
C63
C61
C71
C6
C72
C73
C67
C76
C64
C65
C75
C74
C66
O3
O4
C77
Figure 2. ORTEP representation of 4.
Table 1
Reactions of hydroxylactams 1a–c with vinylidenecyclopropanes 2a–d
R1
OH
R2
R3
O
R1
R1
R1
Me
R2
BF3.OEt2
R4
+
N
Ar
+
C
R2
H
CH2Cl2
1 h, r.t.
Me
O
Ar
N
R2 = R3 =4-MeOC6H4
R3
O
1a-c
2a-g
3a-i
R3
4
O
Entry
Ar
R1
R2
R4
Yield of 3a (%)
1
2
3
4
5
6
7
8
Ph (1a)
Ph (1a)
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Ph
4-MeC6H4
4-MeC6H4 (2b)
4-MeOC6H4 (2d)
4-MeC6H4 (2b)
4-MeOC6H4 (2d)
Ph (2a)
4-ClC6H4 (2c)
Ph (2a)
4-ClC6H4 (2c)
4-ClC6H4 (2c)
Ph (2e)
Me
MeO
Me
MeO
H
Cl
H
Cl
Cl
41 (3a)
32 (3b)b
39 (3c)
29 (3d)c
40 (3e)
66 (3f)
43 (3g)
58 (3h)
44 (3i)
4-MeOC6H4
4-MeC6H4
4-MeOC6H4
Ph
4-ClC6H4
Ph
4-ClC6H4
4-ClC6H4
Me
4-MeC6H4 (1b)
4-MeC6H4 (1b)
4-MeC6H4 (1b)
4-ClC6H4 (1c)
4-ClC6H4 (1c)
Ph (1a)
4-MeC6H4 (1b)
Ph (1a)
Ph (1a)
9
d
10
11
12
H
H
H
—
—
d
Me
Ph
Ph (2f)
Ph (2g)
d
Ph (1a)
Ph
—
a
b
c
Isolated yield.
7% of 4 was also formed.
9% of 4 was also formed.
d
A complicated reaction mixture was observed.

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A. V. Stepakov et al. / Tetrahedron Letters 55 (2014) 2022–2026
Table 2
Reactions of hydroxylactams 5a–d with vinylidenecyclopropanes 2a–d
Me
OH
R1
R1
O
Me
Me
R1
Me
Me
Me
BF3.OEt2
R2
N
Ar
+
C
+
R1
H
CH2Cl2
1 h, r.t.
O
Ar
O
N
R1 = 4-MeOC6H4
R1
O
2a-d
6a-j
4
5a-d
Entry
Ar
R1
R2
Yield of 6a (%)
1
2
3
4
5
6
7
8
Ph (5a)
4-MeC6H4 (2b)
4-MeC6H4 (2b)
4-MeC6H4 (2b)
Ph (2a)
Ph (2a)
Ph (2a)
Ph (2a)
4-ClC6H4 (2c)
4-ClC6H4 (2c)
4-MeOC6H4 (2d)
4-MeOC6H4 (2d)
Me
Me
Me
H
H
H
H
Cl
Cl
MeO
MeO
43 (6a)
45 (6b)
42 (6c)
40 (6d)
28 (6e)
37 (6f)
31 (6g)
55 (6h)
57 (6i)
(6j+4)b
4-MeC6H4 (5b)
4-MeOC6H4 (5d)
Ph (5a)
4-MeC6H4 (5b)
4-ClC6H4 (5c)
4-MeOC6H4 (5d)
4-MeC6H4 (5b)
4-ClC6H4 (5c)
4-MeC6H4 (5b)
4-ClC6H4 (5c)
9
10
11
c
—
a
b
c
Isolated yield.
A chromatographically inseparable mixture of 6j and 4 was obtained.
Only a trace amount of the indene was observed; dihydrofuranone 4 was isolated in 12% yield.
Cl1
C9
C637
C635
C53
C52
C51
C54
C636
C631
C634
C633
C8
C7
C10
C12
C4
C13
C14
C62
C61
C11
C5
N1
C632
C6
C63
C63A
C4
C64
Cl2
C12
C5
C65
C22
C67A
C15
C3
C13
C14
C3
C2
C17
C18
C11
C16
C1
C16
C21
C67
C2
C66
C141
O1
C23
C19
C20
C661
N1
C24
C15
O2
C25
Figure 3. ORTEP representation of 6b.
C26
C27
C29
C28
C30
imide fragment were face-to-face aligned. As could be seen from
the NMR spectra, it was apparent that compounds 3a–i existed
as a mixture of rotamers at ambient temperature on account of
slow C3–C1 and C1–C2 bond rotation. In all cases, the presence
of rotamers made the NMR spectra complex. At room temperature,
the 1H NMR spectra of products 3a–i revealed two sets of signals
for each CH3 group of the isopropylidene fragment. Similarly, the
1H NMR spectra of compounds 3 have two sets of signals belonging
to the methylene group of the indene ring. Rotational isomerism
was confirmed by temperature-dependent NMR experiments on
compounds 3a,f,g: coalescence was observed at 75–80 °C (see Sup-
plementary information, Figs. 43–45).
For the next step in our study, we treated VCPs 2a–d with
hydroxylactams 5a–d (Table 2). The reactions proceeded smoothly
at room temperature producing the corresponding indene deriva-
tives 6 in trace-to-moderate yields (Table 2). It should be noted
that the yield did not improve upon stirring the reaction for a long-
er period of time or at a higher temperature. The formation of a
trace amount of indene 6 was observed in the reaction of 5c with
Figure 4. ORTEP representation of 6h.
O
Ph
OH
N
2a
BF3.OEt2
N
Ph
CH2Cl2
1 h, r.t.
N
24%
O
7
O
8
Scheme 1. BF3ÁOEt2-mediated reaction of 7 with 2a at room temperature.

A. V. Stepakov et al. / Tetrahedron Letters 55 (2014) 2022–2026
2025
Ar2
Ar2
Ar2
Me
Me
OH
N
C
Ar2
Ar2
Me
Me
Me
Ar2
BF3*Et2O
2
Ar1
N
Ar1
C
H
Me
Ar1
O
N
O
N
O
Ar1
O
10
9
1, 5
Me
N
Ar2
Me
Ar2
Me
Me
R
R
H
H
Ar1
O
Ar1
N
11
3, 6
O
Scheme 2. A possible pathway for the reaction of hydroxylactams 1 and 5 with vinylidenecyclopropanes 2.
VCP 2d, which contains electron-donating groups (MeO) on the
phenyl rings, and only the dihydrofuranone 4 was isolated in this
case (Table 2, entry 11). The reaction of hydroxylactam 5b with
VCP 2d led to an inseparable mixture of 6j and 4 (Table 2, entry
10). The reaction products were purified by preparative thin-layer
chromatography on silica. The structures of 6b and 6h were estab-
lished unequivocally by X-ray diffraction analysis (Figs. 3 and
4).22,23 In the reaction of 5-hydroxy-1-phenylpyrrolidin-2-one (7)
with 2a, no indene product was observed, but dimer 8 derived
from 7 under the reaction conditions was produced as a mixture
of isomers (Scheme 1)18,24
Based on the above results, a plausible mechanism for the for-
mation of compounds 3 and 6 is proposed in Scheme 2. Activation
of the C–O by BF3ÁOEt2 leads to the formation of N-acyliminium
cations 9. Next, regioselective attack of the N-acyliminium cations
9 on the central carbon atom of the allene system results in the for-
mation of cyclopropyl cation 10, which undergoes a cyclopropyl–
allyl rearrangement to give cation 11. This undergoes cyclization
to give substituted indenes 3 and 6. Clearly, the steric factors are
favorable to the addition of the N-acyliminium cations to the viny-
lidenecyclopropanes from the less sterically hindered side.
In conclusion, we have developed novel Lewis acid (BF3ÁOEt2)
mediated reactions of vinylidenecyclopropanes (VCPs) with the
N-acyliminium cations generated from hydroxylactams, which
can be utilized for the synthesis of indene derivatives.
References and notes
1. Hong, H. C.; Chamberlain, T. S.; Seiber, K.; Koboldt, C. M.; Isakson, P. C.; Reitz, D.
B. Bioorg. Med. Chem. Lett. 1995, 5, 2377.
2. Evans, B. E.; Leighton, J. L.; Rittle, K. E.; Gilbert, K. F.; Lundell, G. F.; Gould, N. P.;
Hobbs, D. W.; Dipardo, R. M.; Veber, D. F.; Pettibone, D. J.; Clineschmidt, B. V.;
Anderson, P. S.; Freidinger, R. M. J. Med. Chem. 1992, 35, 3919.
3. (a) Watanabe, N.; Nakagawa, H.; Ikeno, A.; Minato, H.; Kohayakawa, C.; Tsuji, J.-
I. Bioorg. Med. Chem. Lett. 2003, 13, 4317; (b) Anstead, G. M.; Peterson, C. S.;
Pinney, K. G.; Wilson, S. R.; Katzenellenbogen, J. A. J. Med. Chem. 1990, 33, 2726.
4. Kolanos, R.; Siripurapu, U.; Pullagurla, M.; Riaz, M.; Setola, V.; Roth, B. L.; Dukat,
M.; Glennon, R. A. Bioorg. Med. Chem. Lett. 2005, 15, 1987.
5. (a) Serge, K.; Pantelis, G. K.; Daniel, P.; Francoise, B.; Patrick, V. D. V. Il Farmaco
1999, 54, 678; (b) Karaguni, I.-M.; Glusenkamp, K.-H.; Langerak, A.; Geisen, C.;
Ullrich, V.; Winde, G.; Moroy, T.; Muller, O. Bioorg. Med. Chem. Lett. 2002, 12,
709.
6. (a) Wang, B. Q. Coord. Chem. Rev. 2006, 250, 242; (b) Alt, H. G.; Koppl, A. Chem.
Rev. 2000, 100, 1205; (c) Zargarian, D. Coord. Chem. Rev. 2002, 233–234, 157; (d)
Barber, J.; Rakitin, O. A.; Ros, M. B.; Torroba, T. Angew. Chem., Int. Ed. 1998, 37,
296; (e) Yang, J.; Lakshmikantham, M. V.; Cava, M. P.; Lorcy, D.; Bethelot, J. R. J.
Org. Chem. 2000, 65, 6739; (f) Leino, R.; Lehmus, P.; Lehtonen, A. Eur. J. Inorg.
Chem. 2004, 3201; (g) Kim, D. H.; Lee, J. A.; Son, S. Uk.; Chung, Y. K.; Choi, C. H.
Tetrahedron Lett. 2005, 46, 4627.
7. Sun, X.; Izumi, K.-J.; Hu, Ch.-Q.; Lin, G.-Q. Chin. J. Chem. 2006, 24, 430.
8. Shao, L.-X.; Xu, B.; Huang, J.-W.; Shi, M. Chem. Eur. J. 2006, 12, 510.
9. (a) Liu, Y.; Zhou, S.; Li, G.; Yan, B.; Guo, S.; Zhou, Y.; Zhang, H.; Wang, P. G. Adv.
Synth. Catal. 2008, 350, 797; (b) Nun, P.; Gaillard, S.; Poater, A.; Cavallo, L.;
Nolan, S. P. Org. Biomol. Chem. 2011, 9, 101.
10. Bu, X.; Hong, J.; Zhou, X. Adv. Synth. Catal. 2011, 353, 2111.
11. (a) Martinez, A.; Garcia-Garcia, P.; Fernandez-Rodriguez, M. A.; Rodriguez, F.;
Sanz, R. Angew. Chem., Int. Ed. 2010, 49, 4633; (b) Sanz, R.; Martinez, A.; Garcia-
Garcia, P. Chem. Commun. 2010, 7427.
12. Zhu, Z.-B.; Shi, M. Chem. Eur. J. 2008, 14, 10219.
13. Obora, Y.; Kimura, M.; Tokunaga, M.; Tsuji, Y. Chem. Commun. 2005, 901.
14. (a) Shi, M.; Shao, L.-X.; Lu, J.-M.; Wei, Y.; Mizuno, K.; Maeda, H. Chem. Rev.
2010, 110, 5883; (b) Su, C.; Huang, X. Adv. Synth. Catal. 2009, 351, 135; (c) Yao,
L.-F.; Shi, M. Chem. Eur. J. 2009, 15, 3875; (d) Wu, L.; Shi, M. Eur. J. Org. Chem.
2011, 1099; (e) Lu, J.-M.; Shi, M. Chem. Eur. J. 2009, 15, 6065; (f) Yao, L.-F.; Shi,
M. Eur. J. Org. Chem. 2009, 4036; (g) Su, C.; Huang, X.; Liu, Q.; Huang, X. J. Org.
Chem. 2009, 74, 8272; (h) Li, W.; Shi, M. J. Org. Chem. 2009, 74, 856; (i) Li, W.;
Shi, M. Tetrahedron 2009, 65, 6815; (j) Lu, B.-L.; Lu, J.-M.; Shi, M. Tetrahedron
2009, 65, 9328; (k) Lu, B.-L.; Lu, J.-M.; Shi, M. Tetrahedron Lett. 2010, 51, 321; (l)
Lu, J.-M.; Shi, M. J. Org. Chem. 2008, 73, 2206; (m) Li, W.; Shi, M. J. Org. Chem.
2008, 73, 4151; (n) Li, W.; Shi, M. J. Org. Chem. 2008, 73, 6698; (o) Shi, M.; Wu,
L.; Lu, J.-M. J. Org. Chem. 2008, 73, 8344; (p) Lu, J.-M.; Shi, M. Org. Lett. 2008, 10,
1943; (q) Campbell, M. J.; Pohlhaus, P. D.; Min, G.; Ohmatsu, K.; Johnson, J. S. J.
Am. Chem. Soc. 2008, 130, 9180; (r) Maeda, H.; Hirai, T.; Sugimoto, A.; Mizuno,
K. J. Org. Chem. 2003, 68, 7700.
Acknowledgments
We gratefully acknowledge the financial support from the Rus-
sian Foundation for Basic Research (Project No. 12-03-01008-a).
This research made use of resources from the X-ray Diffraction
Centre, the Centre for Magnetic Resonance and the Centre for
Chemical Analysis and Materials of Saint-Petersburg State
University.
Supplementary data
15. (a) Li, Q.; Shi, M.; Timmons, C.; Li, G. Org. Lett. 2006, 8, 625; (b) Shao, L.-X.;
Zhang, Y.-P.; Qi, M.-X.; Shi, M. Org. Lett. 2007, 9, 117; (c) Lu, J.-M.; Shi, M. Org.
Lett. 2007, 9, 1805; (d) Xu, G.-C.; Ma, M.; Liu, L.-P.; Shi, M. Synlett 2005, 1869;
(e) Shi, M.; Lu, J.-M. Synlett 2005, 2352; (f) Lu, J.-M.; Shi, M. Tetrahedron 2007,
63, 7545; (g) Shi, M.; Wu, L.; Lu, J.-M. Tetrahedron 2008, 64, 3315; (h) Mizuno,
K.; Sugita, H.; Hirai, T.; Maeda, H.; Otsuji, Y.; Yasuda, M.; Hashiguchi, M.;
Shima, K. Tetrahedron Lett. 2001, 42, 3363; (i) Stepakov, A. V.; Larina, A. G.;
Supplementary data (experimental procedures, characteriza-
tion data, and copies of NMR spectra) associated with this article
can be found, in the online version, at http://dx.doi.org/10.1016/
j.tetlet.2014.02.039. These data include MOL files and InChiKeys
of the most important compounds described in this article.

2026
A. V. Stepakov et al. / Tetrahedron Letters 55 (2014) 2022–2026
Molchanov, A. P.; Stepakova, L. V.; Starova, G. L.; Kostikov, R. R. Russ. J. Org.
19. Stepakov, A. V.; Larina, A. G.; Boitsov, V. M.; Molchanov, A. P.; Gurzhiy, V. V.;
Starova, G. L. Tetrahedron Lett. 2012, 53, 3411.
20. Crystallographic data for the structure 3c have been deposited with the
Cambridge Crystallographic Data Centre as supplementary publication number
CCDC 936478. Copies of these data can be obtained on application to CCDC, 12
Union Road, Cambridge CB2 1EZ, UK (email: deposit@ccdc.cam.ac.uk).
Chem. 2007, 43, 41; (j) Stepakov, A. V.; Larina, A. G.; Radina, O. V.; Boitsov, V.
M.; Molchanov, A. P. Chem. Heterocycl. Compd. 2008, 44, 430; (k) Stepakov, A.
V.; Larina, A. G.; Radina, O. V.; Molchanov, A. P.; Kostikov, R. R. Vestnik SPbGU
2009, 1, 110; (l) Larina, A. G.; Stepakov, A. V.; Boitsov, V. M.; Molchanov, A. P.;
Gurzhiy, V. V.; Starova, G. L.; Lykholay, A. N. Tetrahedron Lett. 2011, 52, 5777.
16. (a) Othman, R. B.; Affani, R.; Tranchant, M.-J.; Antoniotti, S.; Dalla, V. Angew.
Chem., Int. Ed. 2010, 49, 776; (b) Maryanoff, B. E.; Zhang, H.-C.; Cohen, J. H.;
Turchi, I. J.; Maryanoff, C. A. Chem. Rev. 2004, 104, 1431; (c) Speckamp, W. N.;
Moolenaar, M. J. Tetrahedron 2000, 56, 3817.
17. (a) Bahajaj, A. A.; Vernon, J. M.; Wilson, G. D. J. Chem. Soc., Perkin Trans. 1 2001,
1446; (b) Katritzky, A. R.; Mehta, S.; He, H.-Y. J. Org. Chem. 2001, 66, 148; (c)
Raheem, I. T.; Thiara, P. S.; Peterson, E. A.; Jacobsen, E. N. J. Am. Chem. Soc. 2007,
129, 13404; (d) King, F. D.; Aliev, A. E.; Caddick, S.; Tocher, D. A. Org. Biomol.
Chem. 2011, 9, 1547; (e) Hilt, G.; Galbiati, F.; Harms, K. Synthesis 2006, 21,
3575; (f) Allin, S. M.; James, S. L.; Martin, W. P.; Smith, T. A. D. Tetrahedron Lett.
2001, 42, 3943; (g) Allous, I.; Comesse, S.; Berkeš, D.; Alkyat, A.; Daïch, A.
Tetrahedron Lett. 2009, 50, 4411; (h) Stepakov, A. V.; Ledovskaya, M. S.; Boitsov,
V. M.; Molchanov, A. P.; Kostikov, R. R.; Gurzhiy, V. V.; Starova, G. L. Tetrahedron
Lett. 2012, 53, 5414.
21. Crystallographic data for the structure
4 have been deposited with the
Cambridge Crystallographic Data Centre as supplementary publication number
CCDC 970376. Copies of these data can be obtained on application to CCDC, 12
Union Road, Cambridge CB2 1EZ, UK (email: deposit@ccdc.cam.ac.uk).
22. Crystallographic data for the structure 6b have been deposited with the
Cambridge Crystallographic Data Centre as supplementary publication number
CCDC 936477. Copies of these data can be obtained on application to CCDC, 12
Union Road, Cambridge CB2 1EZ, UK (email: deposit@ccdc.cam.ac.uk).
23. Crystallographic data for the structure 6h have been deposited with the
Cambridge Crystallographic Data Centre as supplementary publication number
CCDC 963391. Copies of these data can be obtained on application to CCDC, 12
Union Road, Cambridge CB2 1EZ, UK (email: deposit@ccdc.cam.ac.uk).
24. Spectroscopic and analytical characterizations for 8 have been previously
18a
reported in Ref.
.
18. (a) Qiao, L.; Zhou, Y.; Zhang, W. Chin. J. Chem. 2010, 28, 449; (b) Zhang, W.;
Zhen, A.; Liu, Z.; Yang, L.; Liu, Z. L. Tetrahedron Lett. 2005, 46, 5691; (c) Zhang,
W.; Huang, L.; Wang, J. Synthesis 2006, 2053.