Metal free sulfenylation of active methylene compounds and indole: TBATB mediated synthesis

Article abstract of DOI:10.1016/j.tetlet.2015.05.062

The present work addresses a development of metal free one pot direct method for sulfenylation of active methylene compounds and indole. The reaction might proceed through sulfenyl bromide as an intermediate, which initiates the C-S bond formation. The re

Full text of DOI:10.1016/j.tetlet.2015.05.062

Accepted Manuscript
Metal free sulfenylation of active methylene compounds and indole: TBATB
mediated synthesis
Rajjakfur Rahaman, Namita Devi, Pranjit Barman
PII:
S0040-4039(15)00871-0
DOI:
http://dx.doi.org/10.1016/j.tetlet.2015.05.062
TETL 46334
Reference:
Tetrahedron Letters
To appear in:
Received Date:
Revised Date:
Accepted Date:
31 March 2015
14 May 2015
18 May 2015
Please cite this article as: Rahaman, R., Devi, N., Barman, P., Metal free sulfenylation of active methylene
compounds and indole: TBATB mediated synthesis, Tetrahedron Letters (2015), doi: http://dx.doi.org/10.1016/
j.tetlet.2015.05.062
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers
we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and
review of the resulting proof before it is published in its final form. Please note that during the production process
errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Graphical Abstract
Leave this area blank for abstract info.
Metal free sulfenylation of active methylene
compounds and indole: TBATB mediated
synthesis
Rajjakfur Rahaman, Namita Devi, Pranjit Barman*

1
Tetrahedron Letters
journal homepage: www.els evier.com
Metal free sulfenylation of active methylene compounds and indole: TBATB
mediated synthesis
Rajjakfur Rahaman, Namita Devi, Pranjit Barman∗
Department of Chemistry, National Institute of Technology Silchar, Silchar 788010, India
ARTICLE INFO
ABSTRACT
Article history:
Received
The present work addresses a development of metal free one pot direct method for sulfenylation
of active methylene compounds and indole. The reaction might proceed through sulfenyl
bromide as an intermediate, which initiates the C-S bond formation. The reaction was performed
using tetrabutylammonium tribromide (TBATB) as a brominating agent, CH2Cl2 as a solvent at
room temperature.
Received in revised form
Accepted
Available online
2009 Elsevier Ltd. All rights reserved.
Keywords:
Metal free
Sulfenylation
Active methylene
Indole
TBATB mediated
1. Introduction
In 2004, Shimizu et al. reported reactions of organosulfur
compounds with active methylene compounds, but they used
Over the past few decade, there has been much attention for
C-S bond formation because of their presence in many
pharmaceutically and biologically important molecules.1 Because
of their greater therapeutic value in the treatment of HIV, cancer,
cardiovascular and bacterial diseases sulfenylated indole moieties
have increased importance in organosulfur chemistry.2 Many
organosulfur compounds are used as an intermediate for the
synthesis of various types of sulfur containing compounds.3 The
C-S cross coupling between electrophilic carbon and nucleophilic
sulfur species has been broadly accepted.4 However, the C-S
cross coupling between a nucleophilic carbon centre and a
nucleophilic sulfur species is generally not feasible. But when the
sulfur atom is attached to a halogen or heterocyclic compounds,
it acts as an electrophilic centre and reacts with various types of
nucleophilic compounds such as ketones,5 amines,6 active
methylenes,7 indoles,8 oxindoles9 etc. Because the halogen or
heterocyclic atom acts as a good leaving group, the yield of the
product increases dramatically.10 In most of the sulfenylation
reactions, the sulfur sources are either difficult to prepare, or they
are expensive, hazardous or moisture and air sensitive. In 2008
Liang and Liu et al. reported that reaction between disulfide and
active methylene was not possible after a long period of reaction
time though it was possible between active methylene and carbon
disulfide as well as thiol under harsh reaction conditions.11
only one type of organosulfur moiety in strongly basic
conditions.12 Next, M. Arisawa et al. described a rhodium-
catalyzed sulfenylation of diethyl malonate, but the product
formation is very much low and long time needed for completion
of the reactions.13
In this communication we have reported an efficient protocol
in mild reaction conditions without using any transition metal for
sulfenylation of active methylene compounds and indole with
diaryl disulfide through sulfenyl bromide as an intermediate. We
used TBATB as a brominating agent, which was synthesized
using a simple method.14 TBATB is a solid source of bromine.15
The sulfenyl bromide is formed in situ in the reaction mixture,
this step is the key step as it makes the sulfur atom a good
electrophilic centre. The sulfenyl bromide is attacked by an
active methylene or indole via SN2 type of reaction to give the
product.
2. Result and discussion
At first we examined a model reaction between o-nitrosulfenyl
bromide and acetyl acetone for optimizing the reaction condition.
The reaction was carried out in various solvents such as DMSO,
EtOH, DMF, CH2Cl2, THF, toluene and CH3OH. Among them
CH2Cl2 was the best solvent for the sulfenylation reaction. The
effect of the base was then examined. We examined number of
———
∗ Corresponding author. Tel.: +91 9435374128; fax: +91 3842 224797;
e-mail: barmanpranjit@yahoo.co.in

2
Tetrahedron Letters
EWG1
EWG2
2
S
bases such as Et3N, NaOH, KOH, Na2CO3 and K2CO3; it was
Et3N,
TBATB
S
R
EWG1
EWG2
3a-q
R
+
R
S
observed that Et3N provided the desired product in high yield
when used in stoichiometric amount. There was no reaction
product obtained without using triethylamine.
rt
,
CH2Cl2
1
After optimization in open air at room temperature, the
mixture comprising 1a (0.5 equiv), 2a (1.2 equiv), TBATB (1
equiv), and triethylamine (1.2 equiv) gave the sulfenylated
product 3a in 90 % yield. Other bromine sources like NBS, Br2
were evaluated but not effective like TBATB (Table 1, entries
17, 18,). The product was characterized on the basis of FT-IR,
1H-NMR and 13C-NMR spectral and analytical data.
NO2
NO2
S
COCH3
COCH3
S
S
COCH3
COCH3
COCH3
COCH3
O2N
Cl
3a, 90 %
3b, 85 %
NO2
3c, 87 %
NO2
S
S
S
COCH3
CO2Et
COCH3
COCH3
COCH3
CO2Et
O2N
O2N
3e, 83 %
3d, 75 %
NO2
3f, 78 %
Table 1. Optimization of the reaction conditionsa
NO2
S
S
S
COCH3
COCH3
CO2Et
NO2
CO2Et
NO2
S
COCH3
COCH
3 base, TBATB
COCH3
COCH3
CO2Et
S
H3C
Cl
+
H2C
S
3h, 92 %
COCH3
solvent, rt
3g, 80 %
3i, 78 %
NO2
NO2
2a
3a
1a
S
S
S
CO2Et
CO2Et
COCH3
CO2Et
CO2Et
COCH3
Cl
O2N
Entry
1a/2a
(equiv)
0.5/1.0
Bromine
Base
(equiv)
-
Solvent
Yield
(%)b
NR
3k, 77 %
3l, 85 %
3j, 75 %
source (equiv)
TBATB (1.0)
TBATB (1.0)
TBATB (1.0)
1
2
3
-
-
S
CN
CN
S
CO2CH3
S
COCH3
COCH3
0.5/1.0
0.5/1.0
Et3N (1.0)
Et3N (1.0)
trace
40
CO2CH3
3o, 80 %
Br
MeO
DMSO
3m, 80 %
3n, 94 %
COCH3
COCH3
3p 82 %
4
5
6
7
8
0.5/1.0
0.5/1.0
0.5/1.0
0.5/1.0
0.5/1.0
TBATB (1.0)
TBATB (1.0)
TBATB (1.0)
TBATB (1.0)
TBATB (1.0)
Et3N (1.0)
Et3N (1.0)
Et3N (1.0)
Et3N (1.0)
Et3N (1.0)
EtOH
DMF
35
50
20
40
45
CO2Et
S
CO2Et
S
CH3OH
THF
3q 80 %
Toluene
The reactions were carried out on a 1 mmol scale using 0.5 mmol
of diaryl disulfide, 1.2 mmol of active methylene compounds, 1.2
mmol of Et3N, and 1 mmol of TBATB in 10 mL of CH2Cl2 stirred
for 1.5 h (monitored by TLC) at room temperature. Yield of
isolated product 75-94 %.
9
0.5/1.0
0.5/1.0
0.5/1.2
0.5/1.2
0.5/1.2
0.5/1.2
0.5/1.2
0.5/1.2
0.5/1.2
0.5/1.2
TBATB (1.0)
TBATB (1.0)
TBATB (1.0)
TBATB (0.5)
TBATB (1.0)
TBATB (1.0)
TBATB (1.0)
TBATB (1.0)
NBS (1.0)
Et3N (1.0)
Et3N (1.2)
Et3N (1.2)
Et3N (1.2)
NaOH (1.2)
KOH (1.2)
Na2CO3 (1.2)
K2CO3 (1.2)
Et3N (1.2)
Et3N (1.2)
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
65
75
90
45
70
72
65
74
25
65
10
11
12
13
14
15
16
17
18
Scheme 1. Scope of substrates
The NMR spectra of compounds 3a, 3b, 3e, 3f, 3g and 3p in
1
CDCl3 showed that they exist as the enol isomers. The H-NMR
spectrum the assigned peak of O-H peak of the enol displayed a
singlet at downfield δ = 13-15. In some compounds the O-H peak
was not assigned but the absence of the methylene proton
strongly suggested that the compounds were in the enol form. In
the 13C-NMR spectra, a low field peak at δc = 90-100 indicated
that the Sp3 carbon atom of the active methylenes transformed to
a Sp2 carbon.
Br2 (1.0)
aReaction conditions: 1a (0.5 mmol), 2a (1.2 mmol), base (1.2 mmol),
TBATB (1 mmol), solvent (10 mL) stirred for 1.5 h (monitored by TLC) at
room temperature.
bYield of isolated product after column chromatography 90 %.
NR= no reaction.
We have also investigated the reaction between diaryl
disulfide and indole under the same reaction condition. However,
in this case some sort of heat was necessary for completion of the
reactions. So many processes have been developed for
sulfenylation of indole, but in our case we used TBATB as a
brominating agent and disulfides as a sulfenylating agent. The
protocol for sulfenylation of indole is environmental friendly;
excellent yield with short reaction time. We have done
sulfenylation of unsubstituted indole only; sulfenylation of
substituted indoles are ongoing in our laboratory.
With the optimized reaction condition (Table 1 entry 11), a
series of sulfenylated compounds were synthesized between
diaryl disulfides and active methylenes. All the substrate reacted
smoothly and gave the respective products with excellent yields.
In general, the disulfides with electron donating groups provided
products in better yields than those with electron withdrawing
groups. Halogens (-Cl, -Br) containing disulfides afforded the
corresponding desired products with high yields without any
difficulties. The disulfides with electron donating groups like –
Me produced the desired products with high yields. The results in
scheme 1 show that the reaction has a high degree of functional
group tolerance with a broad substrate scope.
O2N
S
NO2
Et3N, TBATB
S
+
S
CH2Cl2, 70 o
3-4 h
C
N
H
N
H
NO2
5a, 90 %
4
1a

3
200-300 mesh, packed as slurry in hexane and ethyl acetate
S
Cl
S
NO2
(9:1) solvent system. Proton nuclear magnetic resonance and
carbon nuclear magnetic resonance spectra were recorded on
Bruker 500 MHz and 125 MHz FT NMR spectrometer
respectively. All chemical shift resonance are referenced by the
solvent resonance peak δ 7.26 (CDCl3) for 1H NMR and δ 77.00
(CDCl3) for 13C NMR Spectra. The following abbreviations are
used to classify the multiplicity of the protons s = singlet, d =
doublet, t = triplet, q = quartet, m = multiplet, dd = doublet of
doublet. 1H NMR data are represented as follows: chemical shift,
multiplicity, coupling constant in Hz and number of protons.
N
N
H
H
5c, 83 %
5b, 85 %
The reactions were carried out on a mmol scale using 1 mmol of indole, 0.5
mmol of diaryl disulfide, 1.2 mmol of Et3N, and 1 mmol of TBATB in 10
mL of CH2Cl2 stirred for 3-4 h (monitored by TLC) at room temperature.
Yield of isolated product 83-90 %.
Scheme 2. Extension of substrate scope to indole
Typical procedure for the preparation of 3 (3a as an example):
A mixture of diaryl disulfide 1a (0.5 mmol, 154 mg), TBATB (1
mmol, 482 mg) and Et3N (1.2 mmol, 0.17 mL) in anhydrous
CH2Cl2 (10 mL) were stirred for a 30 minutes in an ice water
bath. After 30 minute 2a (1.2 mmol, 0.12 mL) was added and the
reaction mixture was stirred for additional 1.5 hour at room
temperature. After completion of the reaction monitored by TLC
the reaction mixture was diluted by distilled water. The mixture
was extracted with CH2Cl2. The organic layer was separated,
dried over Na2SO4, and concentrated under vacuum. The reaction
mixture was purified by column chromatography on silica gel
using hexane/ethyl acetate (9:1) to give the desired 3a (228 mg,
On the basis of the above reactions, a plausible mechanism
for the formation of the compounds was proposed in Scheme 3.
Initially, formation of the arylsulfenyl bromide (B) occurs from
the diaryl disulfide (A). The brominating agent TBATB liberates
Br2, which brominates the disulfide to the corresponding sulfenyl
bromide. The formation of sulfenyl bromide is the key step,
where the nucleophilic sulfur atom is converted to an
electrophilic centre. In the next step, electrophilic sulfur atom is
attacked by the nucleophiles, which leads to the formation of the
desired product (C). The whole process can be understood by
umpolung strategy.16
1
90 %) as a yellow solid. m.p. 110-113 oC; H NMR (CDCl3, 500
MHz) δ = 11.87 (s, 1H), 8.36-8.35 (dd, J = 8.5 Hz and 1.5 Hz,
1H), 7.87-7.85 (dd, J = 8.5 Hz and 1 Hz, 1H), 7.62-7.58 (m, 1H),
7.44-7.40 (m, 1H), 2.31 (s, 3H), 1.71 (s, 3H). 13CNMR (CDCl3,
125 MHz) δ = 198.6, 146.0, 138.0, 134.5, 127.2, 127.0, 126.39,
125.5, 100.6, 24.2, 8.59; anal. calcd. for C11H11NO4S: C 52.16, H
4.38, N 5.53 %; found: C 52.18, H 4.39, N 5.54 %.
Bu4N Br3
+
Bu4N Br
2 R
Br2
Br
Br2
S
S
R
R
S
0-5 oC
B
A
CH2Cl2
2 Et3N
+
2 NuH
2 Nu
Br
rt
Acknowledgements
NuH = active methylenes
and indole
Et N H
3
2
2
S
Nu
2
R
The authors thank the Director of NIT, Silchar for financial
support, R.F.R. and N.D. thankful to MHRD for their fellowship.
Authors also thank SAIF IIT Madras for spectral and analytical
data.
C
2 Et3N
2HBr
+
+
2 Br
Et N
3
H
2
Scheme 3. Plausible mechanism for the C-S bond formation
Notes and References
Conclusions
1. (a) Kondo, T.; Mitsudo, T. Chem. Rev. 2000, 100, 3205;
(b) Norcross, R. D.; Paterson, I. Chem. Rev. 1995, 95,
2041; (c) Liu, G.; Link, J. T., Pei, Z.; Reilly, E.
B.; Leitza, S.; Nguyen, B.; Marsh, K. C.; Okasinski,
G. F.; Geldern, T. W.; Ormes, M. ; Fowler, M.;
Gallatin, M. J. Med. Chem. 2000, 43, 4025; (d) Kita,
Y.; Iio, K.; Kawaguchi, K.; Fukuda, N.; Takeda, Y.;
Ueno, H.; Okunaka, R.; Higuchi, K.; Tsujino, T.;
Fujioka, H.; Akai, S. Chem. Eur. J. 2000, 6, 3897; (e)
Faulkner, D. J. Nat. Prod. Rep. 1995, 12, 223.
We have developed a fast and efficient method for
sulfenylation of active methylene compounds and indole with a
metal free, one pot, simple and mild reaction conditions. This
new process afforded the desired products in good to excellent
yields. The reaction might proceeds through in situ formation of
a sulfenyl bromide intermediate.11,15a The process is carried out
using brominating agent TBATB and CH2Cl2 as solvent at the
room temperature. The developed process is not air or moisture
sensitive.
2. (a) Hutchinson, J. H.; Riendeau, D.; Brideau, C.; Chan,
C.; Falgueyret, J.-P.; Guay, J.; Jones, T. R.; Lepine, C.;
Macdonald, D.; McFarlane, C. S.; Piechuta, H.;
Scheigetz, J.; Tagari, P.; Therien, M.; Girard, Y. J.
Med. Chem. 1994, 37, 1153; (b) Avis, I.; Martinez, A.;
Tauler, J.; Zudaire, E.; Mayburd, A.; Abu-Ghazeleh, R.;
Ondrey, F.; Mulshine, J. L. Cancer Res. 2005, 65, 4181;
(c) Funk, C. D. Nat. Rev. Drug Discovery 2005, 4, 664;
(d) Khandekar, S. S.; Gentry, D. R.; Van Aller, G. S.;
Doyle, M. L.; Chambers, P. A.; Konstantinidis, A. K.;
Brandt, M.; Daines, R. A.; Lonsdale, J. T. J. Biol.
Chem. 2001, 276, 30024; (e) Regina, G. L.; Bai, R.;
Rensen, W. M.; Cesare, E. D.; Coluccia, A.; Piscitelli,
Experimental Section
General Information
All reagents were purchased from commercially available
sources and used without further purification unless otherwise
noted. When necessary, solvents and reagents were dried prior to
use. CH2Cl2 was distilled from CaH2. All experiments were
monitored by analytical thin layer chromatography (TLC) by a
pre-coated plate. Column chromatography was performed with a

4
Tetrahedron Letters
F.; Famiglini, V.; Reggio, A.; Nalli, M.; Pelliccia, S.;
Chem. Soc. Jpn., 1972, 45, 866; (g) Helmkamp, G. K.;
Pettitt, D. J. J. Org. Chem. 1964, 29, 3258; (h) Trost, B.
M.; Ziman, S. D. J. Org. Chem. 1973, 38, 932.
Pozzo, E. D.; Costa, B.; Granata, I.; Porta, A.; Maresca,
B.; Soriani, A.; Iannitto, M. L.; Santoni, A.; Li, J.;
Cona, M. M.; Chen, F.; Ni, Y.; Brancale, A.; Dondio,
G.; Vultaggio, S.; Varasi, M.; Mercurio, C.; Martini, C.;
Hamel, E.; Lavia, P.; Novellino, E.; Silvestri, R. J. Med.
Chem. 2013, 56, 123; (f) Regina, G. La.; Coluccia, A.;
Brancale, A.; Piscitelli, F.; Gatti, V.; Maga, G.;
Samuele, A.; Pannecouque, C.; Schols, D.; Balzarini, J.;
Novellino, E.; Silvertri, R. J. Med. Chem. 2011, 54,
1587; (g) Regina, G. L.; Bai, R.; Rensen, W. M.;
Coluccia, A.; Piscitelli, F.; Gatti, V.; Bolognesi, A.;
Lavecchia, A.; Granata, I.; Porta, A.; Maresca, B.;
Soriani, A.; Iannitto, M. L.; Mariani, M.; Santoni, A.;
Brancale, A.; Farlini, C.; Dondio, G.; Varasi, M.;
Mercurio, C.; Hamel, E.; Lavia, P.; Novellino, E.;
Silvestri, R. J. Med. Chem. 2011, 54, 8394; (h) Rango,
R.; Artico, M.; Martino, G. D.; Regina, G. L.; Coluccia,
A.; Pasquali, A. D.; Silvestri, R. J. Med. Chem. 2005,
48, 213; (i) Martino, G. D.; Edler, M. C.; Regina, G. L.;
Coluccia, A.; Barbera, M.C.; Barrow, D.; Nicholson, R.
I.; Chiosis, G.; Brancale, A.; Hamel, E.; Artico, M.;
Silvestri, R. J. Med. Chem. 2006, 49, 947.
8. (a) Wu, Q.; Zhao, D.; Qin, X.; Lan, J.; You, J. Chem.
Commun. 2011, 47, 9188; (b) Schlosser, K. M.;
Krasutsky, A. P.; Hamilton, H. W.; Reed, J. E.; Sexton,
K. Org. Lett. 2004, 6, 819; (c) Chen, M.; Huang, Z.-T.;
Zheng, Q.-Y. Chem. Commun. 2012, 48, 11686; (d) Li,
Z.; Hong, J.; Zhou, X. Tetrahedron 2011, 67, 3690; (e)
Browder, C. C.; Mitchell, M. O.; Smith, R. L.;
Sulayman, G. Tetrahedron Lett. 1993, 34, 6245; (f)
Tudge, M.; Tamiya, M.; Savarin, C.; Humphrey, G. R.
Org. Lett. 2006, 8, 565; (g) Yang, F.-L.; Tian, S.-K.
Angew. Chem. Int. Ed. 2013, 52, 4929; (h) Hamel, P.;
Girard, M. J. Heterocycl. Chem. 1996, 33, 1695; (i)
Prasad, Ch. D.; Kumar, S.; Sattar, M.; Adhikary, A.;
Kumar, S. Org. Biomol. Chem. 2013, 11, 8036.
9. Li, X.; Liu, C.; Xue, X.-S.; Cheng, J.-P. Org. Lett.
2012, 14, 4374.
10. (a) Raban, M.; Chern, L.-J. J. Org. Chem. 1980, 45,
1688; (b) Gilow, H. M.; Brown, C. S.; Copeland, J. N.;
Kelly, K. E. J. Heterocycl. Chem. 1991, 28, 1025; (c)
Wu, X.-S.; Tian, S.-K. Chem. Commun. 2012, 48, 898;
(d) Marcantoni, E.; Cipolletti, R.; Marsili, L.;
Menichetti, S.;Properzi, R.; Viglianisi, C. Eur. J. Org.
Chem. 2013, 1, 132; (e) Ge, W; Wei, Y. Green Chem.
2012, 14, 2066.
11. Tan, J.; Liang, F.; Wang, Y.; Cheng, X.; Liu, Q.; Yuan,
H. Org. Lett. 2008, 10, 2485.
12. Bao, M.; Shimizu, M.; Shimada, S.; Inoue, J.;
Konakahara, T. Tetrahedron 2004, 60, 11359.
13. Arisawa, M.; Nihei, Y.; Yamaguchi, M. Tetrahedron
3. (a) Parker, A. J.; Kharasch, N. Chem. Rev. 1959, 59,
583; (b) Craine, L.; Raban, M. Chem. Rev. 1989, 89,
689.
4. (a) Yin, J. M.; Pidgeon, C. A. Tetrahedron Lett. 1997,
38, 5953; (b) Georing, H. L.; Towns, D. L.; Dittmar, B.
J. Org. Chem. 1962, 27, 736; (c) Herriott, A. W.;
Pickerzb, D. J. Am. Chem. Soc. 1975, 97, 2345; (d)
Shah, S. T. A.; Khan, K. M.; Heinrich, A. M.; Voelter,
W. Tetrahedron Lett. 2002, 43, 8281; (e) Yonoki, S. I.;
Takimiya, K.; Aso, Y.; Otsubo, T. Tetrahedron Lett.
1997, 38, 3017; (f) Azizi, N.; Aryanasab, F.; Torkiyan,
L.; Ziyaei, A.; Saidi, M. R. J. Org. Chem. 2006, 71,
3634.
Lett. 2012, 53, 5729.
14. Chaudhuri, M. K.; Bora, U.; Dhar, S. S. et al., Process
of preparing quaternary ammonium tribromides, US
Patent 7005548 (2006).
5. (a) Yadav, J. S.; Reddy, B. V. S.; Jain, R.; Baishya, G.
Tetrahedron Lett. 2008, 49, 3015; (b) Poladura, B.;
Castaneda, A. M.; Rodríguez-Solla, H.; Concellon , C.;
Amo, V. Tetrahedron 2012, 68, 6438.
6. (a) Bao, M.; Shimizu, M. Tetrahedron 2003, 59, 303;
(b) Harpp, D. N.; Back, T. G. Tetrahedron Lett. 1971,
12, 4953.
7. (a) Grossert, J. S.; Dubey, P. K. J. Chem. Soc., Chem.
Commun. 1982, 1183; (b) Mukaiyama, T.; Kobayashi,
S.; Kumamoto, T. Tetrahedron Lett. 1970, 11, 5115; (c)
Fujisawa, T.; Hata, K.; Kojima, T. Chem. Lett., 1973,
287; (d) Gopinath, P.; Nilaya, S.; Devi, T. R.;
Ramkumar, V.; Muraleedharan, K. M. Chem. Commun.,
2009, 7131; (e) Guo, S.-r.; He, W.-m.; Xiang J.-n.;
Yuan, Y.-q. Chem. Commun., 2014, 50, 8578; (f)
Kumamoto, T.; Kobayashi, S.; Mukaiyama, T. Bull.
15. (a) Hazarika, S.; Gogoi, P.; Barman, P. RSC Adv. 2015,
5, 25765; (b) Gopinath, R.; Haque, S. J.; Patel, B. K. J.
Org. Chem. 2002, 67, 5842.
16. (a) Seebach, D. Angew. Chem., Int. Ed. 1979, 18, 239;
(b) Fischer, C.; Smith, S. W., Powell, D. A.; Fu, G. C.
J. Am. Chem., Soc. 2006, 128, 1472; (c) Trost, B. M.,
Li, C.-J. J. Am. Chem. Soc. 1994, 116, 3167; (d)
Kieltsch, I., Eisenberger, P.; Togni, A. Angew. Chem.,
Int. Ed. 2007, 46, 754; (e) Baryal, K. N.; Zhu, D.; Li,
X.; Zhu, J. Angew. Chem. Int. Ed. 2013, 52, 1.
Supplementary Material
Supplementary material is available with a separate file.