Organocatalytic asymmetric C-S bond formation: Synthesis of α-methylene-β-mercapto esters with simple alkyl thiols

Article abstract of DOI:10.1002/adsc.201100522

A highly efficient organocatalytic enantioselective C-S bond formation reaction between simple alkyl thiols and Morita-Baylis-Hillman (MBH) carbonates is described. The optically active α-methylene β-mercapto esters could be obtained under mild reaction conditions with excellent enantioselectivities (up to 97% ee). The broad scope and simple operation make this methodology very practical. Copyright

Full text of DOI:10.1002/adsc.201100522

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DOI: 10.1002/adsc.201100522
À
Organocatalytic Asymmetric C S Bond Formation: Synthesis of
a-Methylene-b-mercapto Esters with Simple Alkyl Thiols
Aijun Lin,a Haibin Mao,a Xi Zhu,a Huiming Ge,b Renxiang Tan,b Chengjian Zhu,a,*
and Yixiang Chenga,*
a
School of Chemistry and Chemical Engineering, State Key Laboratory of Coordination Chemistry, Nanjing University,
Nanjing 210093, Peopleꢀs Republic of China
Fax : (+86)-25-8359-4886; e-mail: cjzhu@nju.edu.cn or yxcheng@nju.edu.cn
State Key Laboratory of Pharmaceutical Biotechnology, School of Medicine, Nanjing University, Nanjing 210093, Peopleꢀs
b
Republic of China
Received: July 3, 2011; Published online: December 8, 2011
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/adcs.201100522.
Abstract: A highly efficient organocatalytic enan-
tioselective C S bond formation reaction between
active but synthetically more useful simple alkyl
thiols seems to be of great importance.
À
simple alkyl thiols and Morita–Baylis–Hillman
(MBH) carbonates is described. The optically
active a-methylene b-mercapto esters could be ob-
tained under mild reaction conditions with excellent
enantioselectivities (up to 97% ee). The broad
scope and simple operation make this methodology
very practical.
b-Heterosubstituted carbonyl compounds contain-
ing a-alkylidene group are highly valuable building
blocks which are widely applied in the synthesis of
medicinally relevant compounds as well as complex
natural products.[9] Unlike the b-oxy- and the b-ami-
nocarbonyl compounds which could be prepared
through the classic Morita–Baylis–Hillman (MBH)
and aza-MBH reactions,[10] a-methylene-b-mercapto
esters could not be reached by this synthetic route
due to the poor electrophilicity and instability of the
thiocarbonyl compounds.[11] Recently, upon conver-
sion of the alcohol to a leaving group, MBH adducts
have emerged as powerful substrates for the enantio-
selective construction of multifunctional carbonyl
compounds through successive SN2’–SN2’ reactions
Keywords: alkyl thiols; enantioselectivity; Morita–
Baylis–Hillman (MBH) carbonates; organocatalysis
Recently, chiral sulfur-containing compounds have re- under the catalysis of chiral Lewis base catalysts.[12]
ceived wide attention as a result of their increasing (Scheme 1) Inspired by this impressive progress and
[13]
applications as chiral auxiliaries,[1] ligands for metal- our interest in the formation of chiral C S bonds,
À
based catalysts,[2] organic catalysts,[3] and also synthet- we anticipated that this tactic might be applied to the
ic intermediates in medical chemistry and biology.[4] construction of optically active a-methylene-b-mer-
The construction of such compounds in an asymmet- capto esters with simple alkyl thiols.[14]
ric catalytic manner has attracted considerable inter-
est and witnessed significant progress. The enantiose-
lective conjugate addition of thiol nucleophiles to
electron-deficient olefins constitutes one of the most
direct and versatile methods.[5] However, the substrate
scope was usually restricted to a,b-unsaturated alde-
hydes,[6] ketones[7] and imides.[8] Additionally, the
dearylation process of aryl sulfides to yield the even-
tually desired free thiol was not always straightfor-
ward when aromatic thiols were used as nucleophiles.
Thus, the development of easy and readily available
catalytic methods for the construction of optically
active sulfur-containing compounds involving the less MBH carbonates.
Scheme 1. The catalytic successive SN2’–SN2’ reactions of
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Figure 1. Structures of the organocatalysts.
An initial examination was carried out by using the
Having established the optimal reaction conditions,
MBH carbonate 2a (2.0 equiv.) and the alkyl thiol 3a we then examined a spectrum of MBH carbonates 2
(1.0 equiv.) as the substrates in the presence of the and alkyl thiols 3 to explore the generality of this new
chiral catalysts 1a–1g (Figure 1) in DCE at room tem- asymmetric transformation. The reactions were con-
perature. The results are summarized in Table 1. ducted in 0.5 mL of 1,4-dioxane with 20 mol% of cat-
When catalyst 1a was tested, no corresponding prod- alyst 1e and 24 mg MgSO4 at 108C. The results are
uct was isolated. To our gratification, the modified summarized in Table 2. All the alkyl thiols containing
Cinchona alkaloid 1b shown high catalytic activity, either an aromatic or an aliphatic group accomplished
the desired product 4a was obtained in 90% yield the reaction smoothly and the corresponding products
with moderate enantioselectivity (entry 2). A similar were obtained in good yields with excellent enantiose-
enantioselectivity was obtained, but with a sharply de- lectivities (entries 1–10). The use of a hindered mer-
creased yield under the catalysis of 1d (entry 4). The captan greatly improved the enantioselectivity of the
best enantioselectivity (85% ee) was observed when reaction. For example, the bulky trityl thiol afforded
catalyst 1e was used (entry 5). Decreasing the catalyst the product 4j with 97% ee.
loading to 10 mol% had a negative impact on both
The addition of aryl thiol to the reaction led to a
the yield and the enantioselectivity (entry 8). Howev- simple SN2’ product 5 as the main product.[15] This was
er, increasing catalyst loading did not improve the probably because the nucleophilicity of the aryl thiols
enantioselectivity (entry 9). The examination of sol- is too strong, and a direct SN2’ reaction occurred with-
vent effects with catalyst 1e revealed that 1,4-dioxane out the assistance of the nucleophilic catalyst.[16] The
was the best reaction medium for this reaction, which electronic properties of the phenyl ring of the MBH
can significantly facilitate the reaction to produce the carbonates appeared to slightly influence the level of
corresponding product in 64% yield with 90% ee (en- the enantioselectivity and all these MBH carbonates
tries 5 and 10–15). A lower temperature (108C) can participated in this process in high efficiency (en-
lead to the increase in the ee value from 90% to 93% tries 13–19). Moreover, when 2-thienyl-substituted
(entries 15 and 16). After screening of additives, the MBH carbonate was used as the substrate, the asym-
reaction was found to be accelerated in the presence metric sulfenylation reaction could also be completed
of MgSO4, and the anticipated product was obtained in 90% yield with 80% ee (entry 20). A b-alkyl-substi-
in 84% yield with 94% ee (entry 20).
tuted MBH carbonate was also tested under the opti-
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Organocatalytic Asymmetric C S Bond Formation: Synthesis of a-Methylene-b-mercapto Esters
Table 1. Optimization of the reaction conditions.[a]
Entry
Catalyst
Solvent
Additive
Yield [%][b]
ee [%][c]
1
2
3
4
5
6
7
8
1a
1b
1c
1d
1e
1f
1g
1e
1e
1e
1e
1e
1e
1e
1e
1e
1e
1e
1e
1e
1e
DCE
DCE
DCE
DCE
DCE
DCE
DCE
DCE
DCE
EtOH
MeCN
PhOMe
PhCF3
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
trace
90
35
18
59
62
44
52
62
31
trace
61
57
51
64
56
trace
27
35
n.d[d]
À57[i]
À25[i]
À66[i]
85
60
72
81[e]
84[f]
64
9
10
11
12
13
14
15
16
17
18
19
20
21
n.d[d]
85
78
88
90
DME
1,4-dioxane
1,4-dioxane
1,4-dioxane
1,4-dioxane
1,4-dioxane
1,4-dioxane
1,4-dioxane
93[g]
n.d[d,g]
93[g]
76[g,h]
94[g]
92[g]
K2CO3
CH3COOH
4 ꢂ MS
MgSO4
Na2SO4
84
65
[a]
Reaction conditions: 0.10 mmol of alkyl thiol 3a was added to a mixture of 0.20 mmol of MBH carbonate 2a and
0.02 mmol of catalyst 1 with 0.02 mmol of additive in 0.5 mL of solvent, the mixture was stirred for 36 h.
Yield of isolated product.
The ee values were determined by chiral HPLC analysis.
Not determined.
10 mol% of catalyst 1e was used.
30 mol% of catalyst 1e was used.
The reaction was performed at 108C for 72 h.
30 mg of 4ꢂ MS were used.
The opposite configuration.
[b]
[c]
[d]
[e]
[f]
[g]
[h]
[i]
mal protocol, unfortunately, the result was not as pos- Experimental Section
itive as those presented above.[17] Optically pure 4l
was obtained upon recrystallization (entry 12), and General Procedure for the Organocatalytic
the absolute configuration was determined to be S by Sulfenylation of Morita–Baylis–Hillman Carbonates
X-ray crystallographic analysis (Figure 2).[18]
In summary, we have provided a useful catalytic
method for the synthesis of optically active a-methyl-
ene-b-mercapto esters. The reaction proceeded in
good yields with excellent enantioselectivities (up to
97% ee) for a wide range of alkyl thiols while tolerat-
A mixture of catalyst 1e (15.5 mg, 0.02 mmol), MBH car-
bonate 2a (58.4 mg, 0.2 mmol) and 24 mg MgSO4 in 1,4-di-
oxane (0.5 mL) was stirred for 30 min at 108C before the
thiol 3a (12.4 mg, 0.10 mmol) was added, and then the re-
sulting mixture was stirred for another 72 h. The crude reac-
tion mixture was diluted with ethyl acetate and then directly
ing a considerable degree of MBH carbonates under purified by flash chromatography on silica gel (PE/EA) to
afford the corresponding product 4a, the ee value was deter-
the catalysis of a commercially available Cinchona al-
kaloid. Further exploration of other b-functionaliza-
tions of MBH carbonates is now in progress in our
laboratory.
1
mined by chiral HPLC analysis, H and 13C NMR, respec-
tively see Supporting Information for details.
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Table 2. Catalytic enantioselective b-sulfenylation of MBH carbonates 2.[a]
Entry
2 (Ar, R1)
3 (R2)
Yield [%][b] (Product)
ee [%][c]
1
2
3
4
5
6
7
8
Ph, Me
Ph, Et
Ph, Me
Ph, Me
Ph, Me
Ph, Me
Ph, Me
Ph, Me
C6H5CH2
C6H5CH2
Et
cyclopentyl
t-Bu
4-MeO-C6H4CH2
4-Cl-C6H4CH2
2-Cl-C6H4CH2
4-F-C6H4CH2
CPh3
84 (4a)
78 (4b)
90 (4c)
85 (4d)
92 (4e)
89 (4f)
87 (4g)
94 (4h)
91 (4i)
70 (4j)
67 (4k)
63 (4l)
93 (4m)
95 (4n)
88 (4o)
94 (4p)
87 (4q)
90 (4r)
84 (4s)
90 (4t)
94
92
92
90
95
93
93
93
93
97
95
92
94
90
93
90
92
91
85
80
9
Ph, Me
Ph, Me
10
11
12
13
14
15
16
17
18
19
20
4-Cl-C6H4, Me
4-Br-C6H4, Me
4-F-C6H4, Me
4-Cl-C6H4, Me
3-Cl-C6H4, Me
4-Br-C6H4, Me
4-NO2-C6H4, Me
4-Me-C6H4, Me
4-MeO-C6H4, Me
2-thienyl, Me
CPh3
CPh3
4-MeO-C6H4CH2
4-MeO-C6H4CH2
4-MeO-C6H4CH2
4-MeO-C6H4CH2
4-MeO-C6H4CH2
4-MeO-C6H4CH2
4-MeO-C6H4CH2
4-MeO-C6H4CH2
[a]
Reaction conditions: 0.10 mmol of alkyl thiol 3 was added to the mixture of 0.20 mmol of MBH carbonate 2 and
0.02 mmol of catalyst 1e with 24 mg MgSO4 in 0.5 mL of 1,4-dioxane, the resulting mixture was stirred for 48–144 h at
108C.
[b]
[c]
Yield of isolated product.
The ee values were determined by chiral HPLC analysis.
Figure 2. ORTEP representation of the X-ray structure of enantiopure 4l (thermal ellipsoids at 30% probability).
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Organocatalytic Asymmetric C S Bond Formation: Synthesis of a-Methylene-b-mercapto Esters
2141; h) N. K. Rana, S. Selvakumar, V. K. Singh, J. Org.
Acknowledgements
Chem. 2010, 75, 2089–2091; i) Y. H. Hui, J. Jiang, W. T.
Wang, W. L. Chen, Y. F. Cai, L. L. Lin, X. H. Liu,
X. M. Feng, Angew. Chem. 2010, 122, 4386–4389;
Angew. Chem. Int. Ed. 2010, 49, 4290–4293; j) M.
Ueno, T. Kitanosono, M. Sakai, S. Kobayashi, Org.
Biomol. Chem. 2011, 9, 3619–3621.
We gratefully acknowledge the National Natural Science
Foundation of China (20832001, 20972065, 21074054) and
the National Basic Research Program of China
(2007CB925103, 2010CB923303) for their financial support.
[8] a) S. Kanemasa, Y. Oderaotoshi, E. Wada, J. Am.
Chem. Soc. 1999, 121, 8675–8676; b) L. Zu, J. Wang, H.
Li, H. Xie, W. Jiang, W. Wang, J. Am. Chem. Soc. 2007,
129, 1036–1037; c) A. M. M. Abe, S. J. K. Sauerland,
A. M. P. Koskinen, J. Org. Chem. 2007, 72, 5411–5413;
d) Y. Liu, B. F. Sun, B. M. Wang, M. Wakem, L. Deng,
J. Am. Chem. Soc. 2009, 131, 418–419.
[9] For some selective applications in total synthesis, see:
a) L. R. Reddy, P. Saravanan, E. J. Corey, J. Am. Chem.
Soc. 2004, 126, 6230–6231; b) B. M. Trost, M. R. Macha-
cek, H. C. Tsui, J. Am. Chem. Soc. 2005, 127, 7014–
7024; c) T. Motozaki, K. Sawamura, A. Suzuki, K.
Yoshida, T. Ueki, A. Ohara, R. Munakata, K.-i. Takao,
K.-i. Tadano, Org. Lett. 2005, 7, 2265–2267; d) L. J.
Reddy, L. F. Fournier, B. V. S. Reddy, E. J. Corey, Org.
Lett. 2005, 7, 2699–2701; e) X. Lei, J. A. Porco, J. Am.
Chem. Soc. 2006, 128, 14790–14791.
References
[1] a) M. T. Crimmins, B. W. King, E. A. Tabet, K. Chaudh-
ary, J. Org. Chem. 2001, 66, 894–902; b) S. Fanjul, A. N.
Hulme, J. W. White, Org. Lett. 2006, 8, 4219–4222.
[2] a) J. C. Anderson, M. Harding, Chem. Commun. 1998,
393–394; b) D. A. Evans, K. R. Campos, J. S. Tedrow,
F. E. Michael, M. R. Gagnꢃ, J. Am. Chem. Soc. 2000,
122, 7905–7920; c) P. Y. Wu, H. L. Wu, B. J. Uang, J.
Org. Chem. 2006, 71, 833–835; d) H. L. Wu, P. Y. Wu,
B. J. Uang, J. Org. Chem. 2007, 72, 5935–5937; e) M. J.
Jin, S. M. Sarkar, D. H. Lee, H. L. Qiu, Org. Lett. 2008,
10, 1235–1237.
[3] C. E. Aroyan, S. J. Miller, J. Am. Chem. Soc. 2007, 129,
256–257.
[4] For some selective references, see: a) Sulfur-Centered
Reactive Intermediates in Chemistry and Biology, (Eds.:
C. Chatgilialoglu, K. D. Asmus), Springer, New York,
1991; b) Sulfur Reagents in Organic Synthesis, (Eds.: P.
Metzner, A. Thuillier), Academic Press, New York,
1994; c) A. M. MasdeuBultꢄ, M. Diꢃguez, E. Martin,
M. Gꢄmez, Coord. Chem. Rev. 2003, 242, 159–201.
[5] a) K. Nishimura, M. Ono, Y. Nagaoka, K. Tomioka, J.
Am. Chem. Soc. 1997, 119, 12974–12975; b) T. Kondo,
T. Mitsudo, Chem. Rev. 2000, 100, 3205–3220; c) D.
Enders, K. Lꢅttgen, A. A. Narine, Synthesis 2007, 959–
980; d) D. Enders, K. Hoffman, Eur. J. Org. Chem.
2009, 1665–1668; e) K. L. Kimmel, M. T. Robak, J. A.
Ellman, J. Am. Chem. Soc. 2009, 131, 8754–8755;
f) H. H. Lu, F. G. Zhang, X. G. Meng, S. W. Duan, W. J.
Xiao, Org. Lett. 2009, 11, 3946–4949; g) J. W. Sun, G. C.
Fu, J. Am. Chem. Soc. 2010, 132, 4568–4569.
[6] a) M. Saito, M. Nakajima, S. Hashimoto, Chem.
Commun. 2000, 1851–1852; b) M. Marigo, T. Schulte, J.
Franzꢃn, K. A. Jørgensen, J. Am. Chem. Soc. 2005, 127,
15710–15711; c) W. Wang, H. Li, J. Wang, L. Zu, J. Am.
Chem. Soc. 2006, 128, 10354–10355; d) S. Brandau, E.
Maerten, K. A. Jørgensen, J. Am. Chem. Soc. 2006,
128, 14986–14991; e) P. Galzerano, F. Pesciaioli, A.
Mazzanti, G. Bartoli, P. Melchiorre, Angew. Chem.
2009, 121, 8032–8034; Angew. Chem. Int. Ed. 2009, 48,
7892–7894.
[10] For reviews see: a) D. Basavaiah, P. D. Rao, R. S.
Hyma, Tetrahedron 1996, 52, 8001–8062; b) D. Basa-
vaiah, A. J. Rao, T. Satyanarayana, Chem. Rev. 2003,
103, 811–892; c) Y. L. Shi, M. Shi, Eur. J. Org. Chem.
2007, 2905–2916; d) G. Masson, C. Housseman, J. P.
Zhu, Angew. Chem. 2007, 119, 4698–4712; Angew.
Chem. Int. Ed. 2007, 46, 4614–4628; e) D. Basavaiah,
K. V. Rao, R. J. Reddy, Chem. Soc. Rev. 2007, 36, 1581–
1588.
[11] R. Okazaki, in: Organosulfur Chemistry, Vol. 1, (Ed.: P.
Page), Academic Press, London, 1995, 225.
[12] a) C. W. Cho, M. J. Krische, Angew. Chem. 2004, 116,
6857–6859; Angew. Chem. Int. Ed. 2004, 43, 6689–6691;
b) Y. Du, X. Han, X. Lu, Tetrahedron Lett. 2004, 45,
4967–4971; c) C. W. Cho, J. R. Kong, M. J. Krische,
Org. Lett. 2004, 6, 1337–1339; d) D. J. V. C. van Steenis,
T. Marcelli, M. Lutz, A. L. Spek, J. H. van Maarseveen,
H. Hiemstra, Adv. Synth. Catal. 2007, 349, 281–286;
e) T. Z. Zhang, L. X. Dai, X. L. Hou, Tetrahedron:
Asymmetry 2007, 18, 1990–1994; f) Y. Q. Jiang, Y. L.
Shi, M. Shi, J. Am. Chem. Soc. 2008, 130, 7202–7203;
g) H. L. Cui, X. Feng, J. Peng, J. Lei, K. Jiang, Y. C.
Chen, Angew. Chem. 2009, 121, 5847–5850; Angew.
Chem. Int. Ed. 2009, 48, 5737–5740; h) H. L. Cui, J.
Peng, X. Feng, W. Du, K. Jiang, Y. C. Chen, Chem.
Eur. J. 2009, 15, 1574–1577; i) K. Jiang, J. Peng, H. L.
Cui, Y. C. Chen, Chem. Commun. 2009, 3955–3957;
j) S. J. Zhang, H. L. Cui, K. Jiang, R. Li, Z. Y. Ding,
Y. C. Chen, Eur. J. Org. Chem. 2009, 5804–5809; k) X.
Feng, Y. Q. Yuan, H. L. Cui, K. Jiang, Y. C. Chen, Org.
Biomol. Chem. 2009, 7, 3660–3662; l) G. N. Ma, S. H.
Cao, M. Shi, Tetrahedron: Asymmetry 2009, 20, 1086–
1092; m) H. L. Cui, J. R. Huang, J. Lei, Z. F. Wang, S.
Chen, L. Wu, Y. C. Chen, Org. Lett. 2010, 12, 720–723;
n) L. Hong, W. S. Sun, C. X. Liu, D. P. Zhao, R. Wang,
Chem. Commun. 2010, 2856–2858; o) W. S. Sun, L.
Hong, C. X. Liu, R. Wang, Org. Lett. 2010, 12, 3914–
3917; p) J. Peng, X. Huang, H. L. Cui, Y. C. Chen, Org.
[7] a) H. Hiemstra, H. Wynberg, J. Am. Chem. Soc. 1981,
103, 417–430; b) E. Emori, T. Arai, H. Sasai, M. Shiba-
saki, J. Am. Chem. Soc. 1998, 120, 4043–4044; c) P.
McDaid, Y. G. Chen, L. Deng, Angew. Chem. 2002,
114, 348–350; Angew. Chem. Int. Ed. 2002, 41, 338–340;
d) R. Rios, H. Sundꢃn, I. Ibrahem, G. L. Zhao, A. Cꢄr-
dova, Tetrahedron Lett. 2006, 47, 8679–8682; e) P. Ricci,
A. Carlone, G. Bartoli, M. Bosco, L. Sambri, P. Mel-
chiorre, Adv. Synth. Catal. 2008, 350, 49–53; f) A.
ˇ
Badoiu, G. Bernardinelli, C. Besnard, E. P. Kꢅndig,
Org. Biomol. Chem. 2010, 8, 193–200; g) L. Dai, S. X.
Wang, F. E. Chen, Adv. Synth. Catal. 2010, 352, 2137–
Adv. Synth. Catal. 2011, 353, 3301 – 3306
ꢁ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
asc.wiley-vch.de
3305

Aijun Lin et al.
COMMUNICATIONS
Lett. 2010, 12, 4260–4263; q) J. R. Huang, H. L. Cui, J.
Lei, X. H. Sun, Y. C. Chen, Chem. Commun. 2011, 47,
4784–4786; r) H. P. Deng, Y. Wei, M. Shi, Eur. J. Org.
Chem. 2011, 1956–1960; s) Y. L. Yang, C. K. Pei, M.
Shi, Org. Biomol. Chem. 2011, 9, 3349–3358; t) Z. K.
Hu, H. L. Cui, K. Jiang, Y. C. Chen. Sci China Ser B-
Chem. 2009, 52, 1309–1313; u) J. Peng, H. L. Cui, Y. C.
Chen. Sci China Ser B – Chem. 2011, 54, 81–86.
[15] The addition of aryl thiol to the reaction led to a
simple SN2’ product as the main product..
[13] a) J. T. Sun, F. Yuan, M. H. Yang, Y. Pan, C. J. Zhu, Tet-
rahedron Lett. 2009, 50, 548–551; b) J. T. Sun, M. H.
Yang, F. Yuan, X. F. Jia, X. Yang, Y. Pan, C. J. Zhu,
Adv. Synth. Catal. 2009, 351, 920–930; c) L. Fang, A. J.
Lin, H. W. Hu, C. J. Zhu, Chem. Eur. J. 2009, 15, 7039–
7043; d) A. J. Lin, L. Fang, X. Zhu, C. J. Zhu, Y. X.
Cheng, Adv. Synth. Catal. 2011, 353, 545–549.
[14] One achiral example of thiol addition to MBH carbo-
nates: H. S. Lee, S. H. Kim, J. N. Kim, Tetrahedron
Lett. 2009, 50, 6480–6483.
[16] a) B. Das, N. Chowdury, K. Damodar, J. Banerjee,
Chem. Pharm. Bull. 2007, 55, 1274–1276; b) P. S. Selig,
S. J. Miller, Tetrahedron Lett. 2011, 52, 2148–2151.
[17] A similar phenomenon was observed in other allylic
nucleophilic substitution of MBH carbonates, please
see refs.[12g,12h,12i,12j,12m,12o]
[18] CCDC 816420 contains the supplementary crystallo-
graphic data for 4l. These data can be obtained free of
charge from The Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_request/cif.
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ꢁ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Synth. Catal. 2011, 353, 3301 – 3306