Facile, efficient, and diastereoselective synthesis of heterohelicene-like molecules

Article abstract of DOI:10.1021/ol400154j

A concise and efficient route to new and interesting heterohelicene-like molecules has been developed through the one-pot, cascade reductive coupling reaction of o-hydroxydiimines or o-nitrodiimines and triphosgene in the presence of TiCl₄/Sm.

Full text of DOI:10.1021/ol400154j

ORGANIC
LETTERS
2013
Vol. 15, No. 6
1238–1241
Facile, Efficient, and Diastereoselective
Synthesis of Heterohelicene-like Molecules
WeiLin, Guo-Lan Dou, Ming-Hua Hu, Cheng-PaoCao, Zhi-Bin Huang,* andDa-QingShi*
Key Laboratory of Organic Synthesis of Jiangsu Province, College of Chemistry,
Chemical Engineering and Materials Science, Soochow University, Suzhou 215123,
P. R. China
zbhuang@suda.edu.cn; dqshi@suda.edu.cn
Received January 18, 2013
ABSTRACT
A concise and efficient route to new and interesting heterohelicene-like molecules has been developed through the one-pot, cascade reductive
coupling reaction of o-hydroxydiimines or o-nitrodiimines and triphosgene in the presence of TiCl4/Sm. Purification of the final products only
required a single recrystallization leading to high purity. High diastereoselectivity was also achieved, and two structures of the final products were
confirmed by X-ray diffraction analysis.
Helicenes and helicene-like molecules have been re-
garded as an academic curiosity because they show non-
planar ortho-fused characteristics and exhibit the feature
of helical chirality.1 With the recent advances in this
research area, helicenes and helicene-like molecules are
considered to be potential candidates serving as liquid
crystal molecules,2 sensors,3 and dyes.3 They can also find
applications in areas of asymmetric catalysis,4 chiral mo-
lecular recognition,5 and molecular machinery.6
Traditionally, helicenes have been synthesized via the
oxidative photocyclization of bis(stilbene)s.7,8 Several new
synthetic methodologies have been developed in the past
10 years that include DielsꢀAlder cycloaddition,9 [2 þ 2þ 2]
(1) (a) Schmuck, C. Angew. Chem. 2003, 115, 2552. Angew. Chem.,
€
Int. Ed. 2003, 42, 2448. (b) Meurer, K. P.; Vogtle, F. Top. Curr. Chem.
1985, 127, 1. (c) Laarhoven, W. H.; Prinsen, W. J. Top. Curr. Chem.
1984, 125, 63. (d) Martin, R. H. Angew. Chem. 1974, 86, 727. Angew.
Chem., Int. Ed. Engl. 1974, 13, 649. (e) Rajca, A.; Miyasaka, M.
Synthesis and Characterization of Novel Chiral Conjugated Materials,
In Functional Organic Materials: Syntheses and Strategies; Mueller,
T. J. J., Bunz, U. H. F., Eds.; Wiley-VCH: Weinheim, 2007; pp 543ꢀ577.
(f) Urbano, A. Angew. Chem., Int. Ed. 2003, 42, 3986. (g) Shen, Y.; Chen,
C.-F. Chem. Rev. 2012, 112, 1463.
(5) (a) Murguly, E.; McDonald, R.; Branda, N. R. Org. Lett. 2000, 2,
3169. (b) Weix, D. J.; Dreher, S. D.; Katz, T. J. J. Am. Chem. Soc. 2000,
122, 10027. (c) Owens, L.; Thilgen, C.; Diederich, F.; Knobler, C. B.
Helv. Chim. Acta 1993, 76, 2757. (d) Yamamoto, K.; Ikeda, T.; Kitsuki,
T.; Okamoto, Y.; Chikamatsu, H.; Nakazaki, M. J. Chem. Soc., Perkin
Trans. 1 1990, 271.
(6) (a) Llunell, M.; Alemany, P.; Bofill, J. M. Chem. Phys. Chem.
2008, 9, 1117. (b) Kelly, T. R.; Cai, X.; Damkaci, F.; Panicker, S. B.; Tu,
B.; Bushell, S. M.; Cornella, I.; Piggott, M. J.; Salives, R.; Cavero, M.;
Zhao, Y.; Jasmin, S. J. Am. Chem. Soc. 2007, 129, 376.
(2) Nuckolls, C.; Shao, R.; Jiang, W.-G.; Clark, N. A.; Walba, D. M.;
Katz, T. J. Chem. Mater. 2002, 14, 773.
(3) (a) Laleu, B.; Mobian, P.; Herse, C.; Laursen, B. W.; Hopfgartner,
G.; Bernardinelli, G.; Lacour, J. Angew. Chem. 2005, 117, 1913. Angew.
Chem., Int. Ed. 2005, 44, 1879. (b) Reetz, M. T.; Sostmann, S. Tetrahedron
2001, 57, 2515.
^
ꢀ
(7) (a) Abed, R. E.; Hassine, B. B.; Genet, e J.-P.; Gorsane, M.;
Marinetti, A. Eur. J. Org. Chem. 2004, 1517. (b) Meier, H.; Schwertel,
M.; Schollmeyer, D. Angew. Chem. 1998, 110, 2224. Angew. Chem., Int.
Ed. 1998, 37, 2110. (c) Gilbert, A. M.; Katz, T. J.; Geiger, W. E.; Robben,
M. P.; Rheingold, A. L. J. Am. Chem. Soc. 1993, 115, 3199. (d) Liberko,
C. A.; Miller, L. L.; Katz, T. J.; Liu, L. J. Am. Chem. Soc. 1993,
115, 2478. (e) Yang, B.; Liu, L.; Katz, T. J.; Liberko, C. A.; Miller, L. L.
J. Am. Chem. Soc. 1991, 113, 8993. (f) Liu, L.; Yang, B.; Katz, T. J.;
Poindexter, M. K. J. Org. Chem. 1991, 56, 3769. (g) Talele, H. R.;
Chaudlhary, A. R.; Patel, P. R.; Bedeker, A. V. ARKIVOC 2011, 9, 15.
(h) Hoffmann, N. Chem. Rev. 2008, 108, 1052.
(4) (a) Sato, I.; Yamashima, R.; Kadowaki, K.; Yamamoto, J.;
Shibata, T.; Soai, K. Angew. Chem., Int. Ed. 2001, 40, 1096. (b) Dreher,
S. D.; Katz, T. J.; Lam, K.-C.; Rheingold, A. L. J. Org. Chem. 2000, 65,
815. (c) Reetz, M. T.; Sostmann, S. J. Organomet. Chem. 2000, 603, 105.
(d) Okubo, H.; Yamaguchi, M.; Kabuto, C. J. Org. Chem. 1998, 63,
€
9500. (e) Reetz, M. T.; Beuttenmuller, E. W.; Goddard, R. Tetrahedron
Lett. 1997, 38, 3211.
r
10.1021/ol400154j
Published on Web 03/01/2013
2013 American Chemical Society

cycloisomerization,10 carbenoid coupling,11 radical tandem
cyclization,12 domino FriedelꢀCrafts type cyclization,13
Pd-mediated techniques,14 intramolecular McMurry reac-
tion,15 and olefin metathesis.16 Some of them have high
diastereo-17 or regioselectivity.18 Recently, Rajca et al.
reported the synthesis of a novel oligothiophene, in which
the thiophene rings are cross-conjugated and annelated
into a helix.19 However, among the numerous literatures,
only a few of them describe the synthesis of heterohelicenes,20
such as azahelicenes and oxa-helicenes, which suffer from
some disadvantages such as drastic reaction conditions,
unsatisfactory yields, long-reaction time, complex manipula-
tion, and inaccessible starting materials. Thus, the develop-
ment of new divergent and efficient synthetic strategies to
heterohelicenes remains highly demanding and challenging.
Herein, we report our preliminary results on the facile
and efficient synthesis of new and interesting heterohe-
licene-like molecules in very good yields with excellent
diastereoselectivities.
(8) (a) Yano, K.; Osatani, M.; Tani, K.; Adachi, T.; Yamamoto, K.;
Matsubara, H. Bull. Chem. Soc. Jpn. 2000, 73, 185. (b) Stammel, C.;
Froehlich, R.; Wolff, C.; Wenck, H.; de Meijere, A.; Mattay, J. Eur. J.
Starting material diimines, such as 6,60-((1,10)-(ethane-
1,2-diylbis(azanylylidene))bis(methanylylidene)) bis(phenol)
3a, are readily obtained from the reaction of salicylaldehyde
1a with ethane-1,2-diamine2a. The intramolecular cascade
reductive coupling reaction of 3atogether with triphosgene
was examined in the presence of 4 equiv of TiCl4/Sm as
the promoter in THF under reflux for 2 h, which gave the
desired dioxo-diaza[5]helicene-like 4a in 88% yield after
purification of the crude product through a single recrys-
tallization. Having established the optimal reaction con-
ditions, the substrate scope and limitations of the domino
reductive coupling reaction were subsequently investi-
gated. The representative results are summarized in
Scheme 1. The diimines were easily reduced by a low-valent
titanium reagent, so the main factor driving the reaction was
the nucleophilicity of the hydroxy group of diimines. We
found that the electronic properties of the substituents
attached to the phenyl rings had more influence than
the steric properties of the substituents on the reactivity.21
Some dioxo-diaza[5]helicene-like compounds containing a
hydroxy group, 4lꢀn, were obtained in 85ꢀ86% yields by
demethylation from their corresponding compounds con-
taining a methoxy group in the presence of BBr3.
€
Org. Chem. 1999, 1709. (c) Terfort, A.; Gorls, H.; Brunner, H. Synthesis
1997, 79. (d) Liu, L.; Katz, T. J. Tetrahedron Lett. 1991, 32, 6831.
(e) Laarhoven, W. H.; Prinsen, W. J. C. Top. Curr. Chem. 1984, 125, 63.
(f) Hernandez-Perez, A. C.; Vlassova, A.; Collins, S. K. Org. Lett. 2012,
14, 2988.
(9) (a) Carreno, M. C.; Gonzalez-Lopez, M.; Urbano, A. Chem.
Commun. 2005, 611. (b) Carreno, M. C.; Garcia-Cerrada, S.; Urbano, A.
Chem.;Eur. J. 2003, 9, 4118. (c) del Mar Real, M.; Sestelo, J. P.;
Sarandeses, L. A. Tetrahedron Lett. 2002, 43, 9111. (d) Carreno, M. C.;
Garcia-Cerrada, S.; Urbano, A. J. Am. Chem. Soc. 2001, 123, 7929. (e)
Paruch, K.; Katz, T. J.; Incarvito, C.; Lam, K.-C.; Rhatigan, B.;
Rheingold, A. L. J. Org. Chem. 2000, 65, 7602. (f) Katz, T. J. Angew.
Chem. 2000, 112, 1997. Angew. Chem., Int. Ed. 2000, 39, 1921. (g)
Latorre, A.; Urbano, A.; Carreno, M. C. Chem. Commun. 2011, 8103. (h)
Latorre, A.; Urbano, A.; Carreno, M. C. Chem. Commun. 2009, 6652. (i)
Carreno, M. C.; Enrıquez, A.; Garcıa-Lerrada, S.; Sanz-Cuesta, M. J.;
Urbano, A.; Maseras, F.; Nonell-Canala, A. Chem.;Eur. J. 2008, 14,
603–620.
~
~
~
(10) (a) Misek, J.; Teply, F.; Stara, I. G.; Tichy, M.; Saman, D.;
Cisarova, I.; Vojtisek, P.; Stary, I. Angew. Chem., Int. Ed. 2008, 47, 3188.
(b) Adriaenssens, L.; Severa, L.; Salova, T.; Cisarova, I.; Pohl, R.;
Saman, D.; Rocha, S. V.; Finney, N. S.; Pospisil, L.; Slavicek, P.; Teply,
ꢁ
ꢁ
F. Chem.;Eur. J. 2009, 15, 1072. (c) Stara, I. G.; Alexandrova, Z.;
ꢀꢀ
ꢁ
ꢁ
^
ꢁ
ꢀ
Teply, F.; Sehnal, P.; Stary, I.; Saman, D.; Budesınsky, M.; Cvacka
ꢁ
ꢁ
ꢁ
ꢀ
J. Org. Lett. 2005, 7, 2547. (d) Stara, I. G.; Stary, I.; Kollarovic, A.;
ꢁ
^
Teply, F.; Saman, D.; Fiedler, P. Collect. Czech. Chem. Commun. 2003,
ꢀ
68, 917. (e) Teply, F.; Stara, I. G.; Stary, I.; Kollarovic, A.; Saman, D.;
ꢁ
ꢁ
ꢁ
ꢁ
ꢀ
ꢀ
ꢀ
ꢁ
ꢁ
Vyskocil, S.; Fiedler, P. J. Org. Chem. 2003, 68, 5193. (f) Teply, F.; Stara,
ꢀ
I. G.; Stary, I.; Kollarovic, A.; Saman, D.; Rulisek, L.; Fiedler, P. J. Am.
ꢁ
ꢁ
ꢀ
ꢀ
ꢁ
ꢁ
ꢁ
ꢀ
Chem. Soc. 2002, 124, 9175. (g) Stara, I. G.; Stary, I.; Kollarovic, A.;
ꢀ
ꢀ
ꢁ
ꢀ
Teply, F.; Vyskocil, S.; Saman, D. Tetrahedron Lett. 1999, 40, 1993.
(h) Tanaka, K.; Fukawa, N.; Suda, T.; Noguchi, K. Angew. Chem., Int.
Ed. 2009, 48, 5470. (i) Heller, B.; Hapke, M.; Fischer, C.; Andronova, A.;
Single crystals of compound 4c were obtained and
analyzed by X-ray structural analysis, as shown in Figure 1.
The crystal belongs to the triclinic space group P1(2). In
the structure, the central piperazine ring shows a typical
chair conformation, combining with the two ortho-fused
lactonic rings and benzene rings to form the helicene-like
conformation. The H2 and H10 are in a trans stereoche-
mical configuration, while the interplanar angle between
the terminal benzene rings is 34.5°.
ꢁ
ꢁ
Stary, I.; Stara, I. G. J. Organomet. Chem. 2013, 723, 98.
(11) Gingras, M.; Dubois, F. Tetrahedron Lett. 1999, 40, 1309.
(12) (a) Harrowven, D. C.; Guy, I. L.; Nanson, L. Angew. Chem., Int.
Ed. 2006, 45, 2242. (b) Harrowven, D. C.; Nunn, M. I. T.; Fenwick,
D. R. Tetrahedron Lett. 2002, 43, 7345. (c) Harrowven, D. C.; Nunn,
M. I. T.; Fenwick, D. R. Tetrahedron Lett. 2002, 43, 3189.
(13) (a) Ichikawa, J.; Yokota, M.; Kudo, T.; Umezaki, S. Angew.
Chem., Int. Ed. 2008, 47, 4870. (b) Fuchibe, K.; Jyono, H.; Fujiwara, M.;
Kudo, T.; Yokot, M.; Ichikawa, J. Chem.;Eur. J. 2011, 17, 12175.
(14) (a) Takenaka, N.; Sarangthem, R. S.; Captain, B. Angew Chem.,
Int. Ed. 2008, 47, 9708. (b) Kamikawa, K.; Takemoto, I.; Takemoto, S.;
Matsuzaka, H. J. Org. Chem. 2007, 72, 7406. (c) Caeiro, J.; Pena, D.;
Cobas, A.; Perez, D.; Guitian, E. Adv. Synth. Catal. 2006, 348, 2466. (d)
Pena, D.; Dohas, A.; Perez, D.; Guitian, E.; Castedo, L. Org. Lett. 2003,
5, 1863. (e) Pena, D.; Perez, D.; Guitian, E.; Castedo, L. Org. Lett. 1999,
1, 1555.
~
In the present work, the use of TiCl4/Sm as a potent
reductive coupling combination has been successfully
ꢁ
ꢁ
~
ꢁ
ꢁ
~
ꢁ
ꢁ
(20) (a) Dumitrascu, F.; Dumitrescu, D. G.; Aron, I. ARKIVOC
2010, 1, 1. (b) Hatakeyama, T.; Hashimoto, S.; Oba, T.; Nakamura, M.
(15) Wang, Z.-H.; Shi, J.-W.; Wang, J.-G.; Li, C.-L.; Tian, X.-Y.;
Cheng, Y.-X.; Wang, H. Org. Lett. 2010, 12, 456.
(16) (a) Grandbois, A.; Collins, S. K. Chem.;Eur. J. 2008, 14, 9323.
^ ꢁ
(b) Collins, S. K.; Grandbois, A.; Vachon, M. P.; Cote, J. Angew. Chem.,
Int. Ed. 2006, 45, 2923. (c) Cote, J.; Collins, S. K. Synthesis 2009, 1499.
ꢀ
ꢁ
ꢁ
ꢀ ꢀ
J. Am. Chem. Soc. 2012, 134, 19600. (c) Zadny, J.; Jancarık, A.;
ꢀ
ꢁ
ꢀ ꢁ
Andronova, A.; Samal, M.; Chocholousova, J. V.; Vacek, J.; Pohl, R.;
ꢀ
ꢀ
ꢁ
ꢁ
ꢁ
Saman, D.; Cısarova, I.; Stara, I. G.; Stary, I. Angew. Chem., Int. Ed.
2012, 51, 5857. (d) Yavari, K.; Moussa, S.; Hassine, B. B.; Retailleau, P.;
Voituriez, A.; Marinetti, A. Angew. Chem., Int. Ed. 2012, 51, 6748. (e)
Goto, K.; Yamaguchi, R.; Hiroto, S.; Ueno, H.; Kawai, T.; Shinokubo,
^ ꢁ
(17) Talele, H. R.; Sahoo, S.; Bedekar, A. V. Org. Lett. 2012, 14,
3166.
ꢁ
(18) Kelgtermans, H.; Dobrzanska, L.; Meervelt, V. V.; Dehaen, W.
Org. Lett. 2012, 14, 5200.
ꢀꢁ
H. Angew. Chem., Int. Ed. 2012, 51, 10333. (f) Severa, L.; Oncak, M.;
ꢀ
ꢀ ꢁ ꢁ
Koval, D.; Pohl, R.; Saman, D.; Cısarova, I.; Reyes-Gutierrez, P. E.;
ꢁ
ꢁ
ꢀ ꢀ
ꢁ
ꢀ
Sazelova, P.; Kasicka, V.; Teply, F.; Slavıcek, P. Angew. Chem., Int. Ed.
(19) (a) Rajca, A.; Wang, H.; Pink, M.; Rajca, S. Angew. Chem., Int.
Ed. 2000, 39, 4481. (b) Rajca, A.; Miyasaka, M.; Pink, M.; Wang, H.;
Rajca, S. J. Am. Chem. Soc. 2004, 126, 15211. (c) Miyasaka, M.; Rajca,
A.; Pink, M.; Rajca, S. J. Am. Chem. Soc. 2005, 127, 13806. (d)
Miyasaka, M.; Rajca, A.; Pink, M.; Rajca, S. Chem.;Eur. J. 2004,
10, 6531. (e) Zak, J. K.; Miyasaka, M.; Rajca, S.; Lapkowski, M.; Rajca,
A. J. Am. Chem. Soc. 2010, 132, 3246. (f) Miyasaka, M.; Pink, M.;
Olankitwanit, A.; Rajca, S.; Rajca, A. Org. Lett. 2012, 14, 3076.
2012, 51, 11972. (g) Waghray, D.; Zhang, J.; Jacobs, J.; Nulens, W.;
ꢁ
Basaric, N.; Meervelt, L. V.; Dehaen, W. J. Org. Chem. 2012, 77, 10176. (h)
Shibata, T.; Uchiyama, T.; Yoshinami, Y.; Takayasu, S.; Tsuchikama, K.;
Endo, K. Chem. Commun. 2012, 48, 1311.
ꢁ
(21) (a) Poriel, C.; Barrie, F.; Thirion, D.; Rault-Berthelot, R.
Chem.;Eur. J. 2009, 15, 13304. (b) Yao, L.-F.; Tan, D.; Miao, X.;
Huang, K.-W. RSC Adv. 2012, 2, 7594.
Org. Lett., Vol. 15, No. 6, 2013
1239

Scheme 1. Synthesis of Dioxo-diaza[5]helicene-like Compounds
4aꢀn
Figure 1. X-ray structure of compound 4c.
Scheme 2. Synthesis of Tetraaza[5]helicene-like Compounds
7aꢀe
a Determined by 1H NMR.
extended to assemble the structures of tetraaza[5]helicene-
like compounds 7aꢀe in which salicylaldehyde derivatives
were replaced by ortho-nitrobenzaldehyde derivatives
5aꢀc. Due to an additional reduction of the nitro group
to the amino group, 8 equiv of TiCl4/Sm relative to
substrate 5 had to be used in this transformation. The
tandem reductive coupling of 6aꢀd and double cyclization
with triphosgene were performed in THF under the above
optimized reaction conditions.
a Determined by 1H NMR.
The reaction can be completed within 3 h with the results
summarized in Scheme 2. After purification of the final
products through a single recrystallization, the desired
tetraaza[5]helicene-like compounds 7aꢀd were obtained
in 73ꢀ89% yields with good to excellent diastereoselec-
tivities, regardless of the variations in electronic and steric
properties of the substituents attached to the phenyl rings
of the ortho-nitrobenzaldehyde derivatives. The desired
compound 7e was also obtained in 83% yield by the
demethylation from compound 7b.
molecules through the tandem reductive coupling reaction
of triphosgene and diimines 9aꢀdresulted from 2-hydroxy-1-
naphthaldehyde 8aꢀb with substituted ethane-1,2-diamines
2aꢀb in the presence of 4 equiv of TiCl4/Sm in THF under
reflux for 2 h. As shown in Scheme 3, the desired dioxo-
diaza[7]helicene-like compounds 10aꢀd were obtained in
very good chemical yields (75ꢀ89%) with excellent dia-
stereoselectivities. Similarly, compound 10e was obtained
in 87% yield by demethylation from corresponding com-
pound 10b.
Because the steric hindrance did not show any obvious
detrimental effect on the reactivity, this effective process
was further applied to the synthesis of [7]-helicene-like
To demonstrate the value of our developed synthetic
method in the scaleable synthesis of heterohelicene-
like compounds, a gram-scale synthesis of 10a was
1240
Org. Lett., Vol. 15, No. 6, 2013

Scheme 3. Synthesis of Dioxo-diaza[7]helicene-like Molecules
10aꢀe
Figure 2. X-ray structure of compound 10a.
4gꢀk, 7cꢀd, and 10cꢀd) led to the formation of a mixture
of diastereoisomers22 (see Supporting Information). Their
1H NMR spectra also show two doublets for the two
methenyl protons because of the lack of C2 symmetry.
From the dr values of the above-mentioned compounds,
we can presume that the diastereoselectivities are related to
the numberof helicenesand the positionof the substituents
attached to the phenyl rings.
In conclusion, a facile and efficient route has been devel-
oped for the synthesis of complex [5]- and [7]heterohelicene-
like compounds by using o-hydroxydiimines or o-nitrodii-
mines and triphosgene in the presence of TiCl4/Sm as the
reductive coupling reagent. Purification of the final products
only required a single recrystallization leading to high purity.
Good chemical yields and a high diastereoselectivity have
been achieved. Structures of the final products were con-
firmed by X-ray diffraction analysis. This novel synthetic
method provides an easy access to heterohelicene-like
molecules withremarkablestructural complexityby taking
advantage of readily available starting materials, opera-
tional simplicity, a short reaction time, high yields, and
convenient purification. Further exploitation of this meth-
od and application of these products are underway.
a Determined by 1H NMR.
performed, resulting in 2.85 g with 68% yield and 96%
purity.
The structure of 10a was also confirmed by X-ray dif-
fraction analysis. The molecular structure of product 10a is
shown in Figure 2. Similar to the case of 4c, 10a belongs to
the triclinic space group P1(2). Due to the repulsion
between the two terminal naphthalene rings, the two fused
benzene rings in the naphthalene moiety in 10a show a
slight deviation from coplanarity. The average interplanar
angles between the two benzene rings in the naphthalene
moiety are 3.0° for (P)-10a and 2.9° for (M)-10a. The inter-
planar angles between the two terminal benzene rings are
31.9° for (P)-10a and 30.5° for (M)-10a.
During the synthesis, when ethane-1,2-diamine 2a was
chosen as the starting material, the resulting helicenes
(such as 4aꢀf, 7aꢀb, and 10aꢀb) clearly show a C2 sym-
metricarrangement. 1H NMR spectra ofthosecompounds
exhibit a singlet for the two methenyl protons. When the
ethane-1,2-diamine was replaced by propane-1,2-diamine
2b, the helicenes bearing a methyl group at C-7 (such as
Acknowledgment. This research was supported by the
Natural Science Foundation of China (21072144), the
Major Basic Research Project of the Natural Science
Foundation of the Jiangsu Higher Education Institu-
tions (10KJA150049), A Project Funded by the Priority
Academic Project Development of Jiangsu Higher Educa-
tion Institutions, and the Jiangsu College Graduate Re-
search and Innovation Project of the Jiangsu Province
Department of Education (CXZZ12_0809).
Supporting Information Available. Experimental pro-
cedures; characterization, crystallographic data, and CIF
files for the products. This materials is available free of
charge via the Internet at http://pubs.acs.org.
(22) (a) Rosa, M. D.; Alonso, J. L. T. J. Org. Chem. 1978, 43, 2639.
(b) Lachia, M.; Poriel, C.; Slawin, A. M. Z.; Moody, C. J. Chem.
Commun. 2007, 286.
The authors declare no competing financial interest.
Org. Lett., Vol. 15, No. 6, 2013
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