Iodine-Mediated Copper-Catalyzed Efficient α-C(sp2)-Thiomethylation of α-Oxoketene Dithioacetals with Dimethyl Sulfoxide in One Pot

Article abstract of DOI:10.1002/adsc.201500634

The direct α-Csp²￡H functionalization and thiomethylation of α-oxoketene dithioacetals (DTAs) has been accomplished with dimethyl sulfoxide (DMSO) in the presence of iodine and a copper(I) salt for the first time. A prerequisite is the in situ iodination of the α-Csp² atom of dithioacetals that could offer other reaction channels. The operationally simple one-pot protocol includes region-defined consecutive iodination and sulfenylation of the challenging α-Csp²￡H bond of dithioacetals employing cheap and readily available reagents. DMSO here plays a dual role as thiomethyl source and solvent.

Full text of DOI:10.1002/adsc.201500634

FULL PAPERS
DOI: 10.1002/adsc.201500634
Iodine-Mediated Copper-Catalyzed Efficient a-C(sp2)-Thiomethy-
lation of a-Oxoketene Dithioacetals with Dimethyl Sulfoxide in
One Pot
Gaurav Shukla,a Abhijeet Srivastava,a Anugula Nagaraju,a Keshav Raghuvanshi,b
and Maya Shankar Singha,*
a
Department of Chemistry, Faculty of Science, Banaras Hindu University, Varanasi – 221005, India
Fax: (+91)-542-268-127; e-mail: mayashankarbhu@gmail.com (homepage: http://www.drmssinghchembhu.com)
Institute für Organische und Biomolekulare Chemie, Georg-August-Universität, Tammannstrass 2, 37077 Gçttingen,
b
Germany
Received: July 1, 2015; Revised: September 17, 2015; Published online: December 9, 2015
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/adsc.201500634.
2
2
À
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Abstract: The direct a-Csp H functionalization and challenging a-Csp H bond of dithioacetals employ-
thiomethylation of a-oxoketene dithioacetals ing cheap and readily available reagents. DMSO
(DTAs) has been accomplished with dimethyl sulfox- here plays a dual role as thiomethyl source and sol-
ide (DMSO) in the presence of iodine and a cop- vent.
per(I) salt for the first time. A prerequisite is the in
situ iodination of the a-Csp2 atom of dithioacetals
that could offer other reaction channels. The opera- Keywords:
cascade
reaction;
1,4-diazabicy-
tionally simple one-pot protocol includes region-de- clo[2.2.2]octane (DABCO); dimethyl sulfoxide
fined consecutive iodination and sulfenylation of the (DMSO); iodination; thiomethylation
Introduction
and Kornblum reaction.[9] Furthermore, DMSO serves
as a multipurpose precursor for the O, CH2SMe, Me,
The introduction of the thioalkyl group into a chemi- CN, and CHO units.[10] However, DMSO as a thio-
cal species is a fundamentally important process in or- methyl source was rarely exploited.[11] Recently, Li
ganic synthesis.[1] The direct and selective thioalkyla- et al. and Gao and co-workers[12] employed DMSO as
2
À
tion of Csp H bond of internal olefins is one of the a source of thiomethyl groups for the synthesis of a-
most versatile approaches for the construction of thio- alkoxy methyl sulfides and thiomethylated heterocy-
alkylated compounds. During past decades, thioalky- cles, respectively.
lation of various organic species has been achieved
During the past few years, we have explored polar-
employing sulfonyl hydrazides,[2] disulfides,[3] sulfen- ized olefins in the form of a-oxoketene dithioacetals
amides[4] and thiols.[5] Although the above reagents (DTAs) as key precursor for the synthesis of numer-
successfully insert the thioalkyl group, they suffer ous heterocycles.[13] This time, we envisioned to func-
from incomparable difficulties such as typical han- tionalize the sterically hindered and electron rich a-
2
À
dling of the reagents, harsh conditions, poor yield, Csp H bond of DTAs by the thiomethyl group,
and tedious work-up procedure. From a practical per- which has seldom been explored. It is worth mention-
spective, the synthesis of important motifs by thioal- ing that the only disclosure of the thiomethylation of
kylation with cheaper reagents and easy operation is dithioacetals was reported by Junjappa et al.[14] via
highly desirable. In this context, the new candidate is a two-step process employing thiols as alkyl sulfide
dimethyl sulfoxide (DMSO), an inexpensive and low- agent (Scheme 1a). However, the reported strategy
toxic polar aprotic solvent, which has been widely suffers from low selectivity, expensive reagents, harsh
used in organic synthesis. Moreover, being an effec- conditions, and a multistep reaction procedure. Func-
À
tive polar reaction medium, DMSO also been utilized tionalization of an internal olefinic C H bond has
as a oxidant in the well-known reactions such as been a challenging task in organic synthesis due to
Swern oxidation,[6] Pfitzner–Moffatt oxidation,[7] the intrinsic steric hindrance and electronic environ-
Corey–Chaykovsky epoxidation, cyclopropanation[8] ment around the carbon-carbon double bond. It has
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Maya Shankar Singh et al.
Results and Discussion
To test the above hypothesis, the present study was
initiated with 1-(4-chlorophenyl)-3,3-bis(thiomethyl)-
prop-2-en-1-one 1d (1.0 mmol) as model substrate in
DMSO (5 mL) under varying conditions and the re-
sults are listed in Table 1. The above model reaction
was performed with iodine (1 equiv.) and K2CO3
(2 equiv.) at room temperature, no trace of the de-
sired product was obtained even after 48 h (Table 1,
entry 1). Literature reports indicate that the genera-
tion of the thiomethyl unit from DMSO requires high
temperatures. Therefore, next we carried out the
above reaction at 1208C. Only traces of the desired
product were obtained after 48 h of heating (Table 1,
entry 2). Next, increasing the amount of I2 also could
not provide a satisfactory result (Table 1, entries 3
and 4). In an effort to improve the efficiency of the
reaction, we performed the reaction in the presence
of CuI and the ligand 1,4-diazabicyclo[2.2.2]octane
(DABCO) (10 mol% each). To our pleasure, the de-
sired product was obtained in 50% yield (Table 1,
entry 5). Increasing the amount of CuI and DABCO
improved the yield to 75% (Table 1, entry 6). Further
increments in the loading of CuI and DABCO did not
improve the result (Table 1, entry 7).
The success of this protocol prompted us to investi-
gate some other copper salts such as CuCl and CuBr,
which could not provide any better results (Table 1,
entries 8 and 9).The use of Cs2CO3 in place of K2CO3
afforded a similar result (Table 1, entry 10). From our
experiences, we assumed that the ligand DABCO
may also act as base. Consequently, the use of 2 equiv.
of DABCO without an inorganic base in the above
Scheme 1. Thiomethylation of a-oxoketene dithioacetals
(DTAs).
2
À
been reported that replacement of the H of Csp
H
by a thioalkyl group, first requires activation followed reaction provided the desired product in 80% yield
by coupling with a suitable thioalkyl source.[15] One of (Table 1, entry 11). Finally, we optimized the loading
the significant ways to activate the internal olfenic of DABCO, and it was found that 2.5 equiv. of
2
À
Csp H bond is in situ iodination followed by oxida- DABCO furnished the best result (Table 1, entries 12
tive coupling.[16]
and 13). Utilization of Cu(OAc)2 instead of CuI could
It is envisioned that if the selective iodination of not provide a better result (Table 1, entries 14 and
2
À
Csp H bond of DTAs is feasible by molecular 15). To observe the efficiency of iodine as a reagent
iodine, then in situ oxidation of the carbon-iodine as well as oxidizing agent, we used some other oxidiz-
bond could generate a transition metal complex inter- ing agents like NBS and Cu(OAc)2 with iodine. All
mediate primed for selective thiomethylation by these studies indicated that 3 equiv. of iodine was suit-
DMSO. As a proof of our concept, we successfully able for this conversion (Table 1, entries 16 and 17).
achieved this goal and report here a highly efficient Increasing the temperature did not improve the result
and effective one-pot direct thiomethylation of a-oxo- (Table 1, entry 18) and at low temperature i.e., 100
ketene dithioacetal with DMSO via iodine-mediated and 808C the iodized product could not be fully con-
Cu(I) catalysis in a tandem fashion (Scheme 1b). This verted to the thiomethylated product even after 24 h
strategy provides a powerful and general route to ac- (Table 1, entries 19 and 20).
2
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tivate the sterically hindered Csp H bond of DTAs,
During our optimization of the loading of iodine, it
which could be further functionalized to privileged was found that the reaction was completed within
and prevalent motifs for various purposes.
24 h when we used 3 equiv. of iodine. Increasing the
amount of iodine further did not provide any signifi-
cant change in the result and with less iodine a signifi-
cant decrease in yield was observed (Table 1, en-
tries 21 and 22). Control reactions in the absence of I2
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Iodine-Mediated Copper-Catalyzed Efficient a-C(sp2)-Thiomethylation
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Table 1. Optimization of the reaction conditions.[a]
Entry I2
(equiv.)
Oxidizing agent
(equiv.)
Base
(equiv.)
DABCO
(equiv.)
Catalyst
(equiv.)
Temp. [oC]/Time
[h]
Yield
[%][c]
1
2
3
4
5
6
7
8
(1)
(1)
(2)
(3)
(3)
(3)
(3)
(3)
(3)
(3)
(3)
(3)
(3)
(3)
(3)
(2)[d]
(1)
(3)
(3)
(3)
(4)
(2)
none
none
none
none
none
none
none
none
none
none
none
none
none
none
none
none
NBS (1)
Cu(OAc)2 (2)
none
none
none
none
none
none
K2CO3 (2)
K2CO3 (2)
K2CO3 (2)
K2CO3 (2)
K2CO3 (2)
K2CO3 (2)
K2CO3 (2)
K2CO3 (2)
K2CO3 (2)
none
none
none
none
(0.1)
(0.2)
(0.3)
(0.2)
(0.2)
none
none
none
none
CuI (0.1)
CuI (0.2)
CuI (0.3)
CuCl (0.2)
CuBr (0.2)
CuI (0.2)
CuI (0.2)
CuI (0.2)
CuI (0.2)
r.t./48
none
trace
trace
10
50
75
75
60
65
75
80
85
85
75
75
50
60
80
120/48
120/48
120/48
120/24
120/24
120/24
120/24
120/24
120/24
120/24
120/24
120/24
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
Cs2CO3 (2) (0.2)
none
none
none
none
none
none
none
none
none
none
none
none
none
(2.0)[b]
(2.5)[b]
(3.0)[b]
(2.5)[b]
(2.5)[b]
(2.5)[b]
(2.5)[b]
(2.5)[b]
(2.5)[b]
(2.5)[b]
(2.5)[b]
(2.5)[b]
(2.5)[b]
Cu(OAc)2 (0.1) 120/30
Cu(OAc)2 (0.2) 120/24
CuI (0.2)
CuI (0.2)
CuI (0.2)
CuI (0.2)
CuI (0.2)
CuI (0.2)
CuI (0.2)
CuI (0.2)
120/24
120/24
140/24
100/24
80/24
120/24
120/24
120/24
60
40
85
70
none
[a]
Reaction conditions: All reactions were performed with 1d (1.0 mmol), I2 (3.0 equiv.), CuI (20 mol%), DABCO
(2.5 equiv.), DMSO (5 mL) in the open atmosphere.
DABCO acts both as a base and ligand.
Isolated yield.
a-Brominated product was obtained in 20% yield.
[b]
[c]
[d]
did not proceed at all indicating that molecular iodine omatic ring of a-oxoketene dithioacetals had no obvi-
is essential for this cascade reaction (Table 1, ous influence on the reaction efficiency (3a–j).
entry 23). Thus, 1d (1.0 mmol), I2 (3.0 equiv.), Cul
Sterically hindered extended aromatics (1g, 1h) and
(20 mol%), DABCO (2.5 equiv.), DMSO (5 mL) at heteroaromatics (1i, 1j) as R1 substituents of dithio-
1208C was found to represent the optimal reaction acetals did not disturb the outcome of the reaction,
conditions, which provided 3d in 85% yield (Table 1, and afforded the desired products in good to excellent
entry 12).
yields (Table 2, 3g–j). However, when the chain
With the optimized reaction conditions in hand, the length at the sulfur atom was augmented from methyl
generality and scope of the molecular iodine-mediat- to ethyl, propyl, and n-butyl a significant lowering in
ed copper-catalyzed direct thiomethylation of the a- the reaction time was observed. In the case of ethyl,
2
À
Csp H bond of a-oxoketene dithioacetals was next the reaction was completed within 20 h (3m–r). In the
explored. To our satisfaction, the results indicated case of propyl and n-butyl groups, the reactions were
that dithioacetals bearing diverse functional groups completed within 15 h (3s–u) and 12 h (3v, w), respec-
and substitution patterns afforded the desired prod- tively. This lowering in time upon increasing the
ucts in good to excellent yields (Table 2, up to 95%). length of the thioalkyl group may be due to enhanced
In general, electron-neutral (1a, 1b), electron-donat- electron density at the a-carbon of long chain thioalk-
ing (1c, 1f, 1k, 1l) and electron-withdrawing (1d, 1e) yl substituents, which further boosts the rate of the in
a-oxoketene dithioacetals were successfully converted situ iodination reaction (first step of the reaction).
to their corresponding thiomethylated products in 80– Our all efforts for the thiomethylation of a-oxoketene
85% yields. The electronic and steric nature of the ar-
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Maya Shankar Singh et al.
Table 2. Scope of a-oxoketene dithioacetals 1.
dithioacetals containing R1 as methyl and R2 as the reaction afforded the a-iodo derivative 2a sug-
benzyl were futile.[17]
gesting that the first step of the reaction is iodination
To illustrate the broad synthetic utility and general- of the dithioacetal. The formation of 2a is supported
1
ity of our developed one-pot cascade reaction, we fur- by disappearance of the a-H peak in the H NMR at
ther investigated various unsymmetrical dithioacetals 6.61 ppm, while methyl peaks of SMe of the parent
(both sulfur atoms being differently substituted) dithioacetal 1f shifted up field from 2.45 and
under the optimized conditions (Scheme 2, 1x–1aa). 2.48 ppm to 2.16 and 2.47 ppm (i) and (ii). An HR-MS
Remarkably, all these unsymmetrical dithioacetals study also supported the formation of 2a. Next, we
1
were tolerated well, and the reactions proceeded analyzed the reaction after 16 h. The H NMR study
smoothly providing the desired products (3x–3aa) as showed a mixture of 2a and our desired product 3f
inseparable mixtures of E/Z isomers in 80–90% yields with clear appearance of SMe peaks at 2.12, 2.13 and
(Scheme 2).
2.42 ppm together with the parent SMe peaks at 2.17
Our all efforts to separate these E/Z isomers were and 2.48 ppm (iii). The above results suggest that 2a
futile. The structures of all the newly synthesized slowly converts into the desired product 3f. Finally,
compounds 3x–3aa were elucidated by their satisfac- we stopped the reaction after complete conversion of
1
tory spectral (IR, H, 13C NMR and HR-MS) studies. 2a into 3f (monitored through TLC), and work-up of
To have a deeper understanding into the reaction the reaction mixture furnished the desired product 3f
process, we performed the thiomethylation of 1f in 80% yield (iv).
under the optimized reaction conditions followed by
To gain some more insights into the mechanism of
the segregation of products at different intervals, that the reaction, a series of control experiments was per-
1
were monitored by H NMR (Scheme 3). After 10 h, formed. The isolated iodo derivative 2a was treated
under the optimized conditions. Notably, 2a was con-
verted quantitatively to the desired product 3f within
14 h. These results clearly confirmed the intermediacy
of 2a in the tandem thiomethylation of dithioacetal 1f
[Eq. (1)]. To prove the formation of methanethiol
from DMSO, we performed the thioalkylation of 1j
with a mixture of DMSO, EtSSEt and EtSH. This re-
action leads the formation of 3j in 45% yield with se-
lective formation of the a-thioethylated product 4 in
30% yield [Eq. (2)]. To further improve the efficiency
of the above reaction, we performed the thioethyla-
Scheme 2. Region-defined thiomethylation of unsymmetrical
dithioacetals.
tion of 1j with EtSSEt and EtSH independently.
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1
Scheme 3. Determination of the reaction pathway by H NMR.
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Maya Shankar Singh et al.
Scheme 3. (Continued)
These reactions provided approximately 70% of thio- during the course of the reaction. Furthermore, to
ethylated product 4 [Eq. (3)]. confirm the source of the thiomethyl group in this
The structure of 4 was fully established by its satis- transformation, we treated dithioacetal 1l with
factory spectral analysis. Thus, the above two sets of DMSO-d6 under the optimized conditions. To our
reactions clearly suggested the intermediacy of MeSH great pleasure, dithioacetal 1l was converted to the
corresponding deuterated derivative 5 in 85%. This
deuterium labelling experiment confirmed that the
source of thiomethyl is DMSO [Eq. (4)].
Based on literature reports and our experimental
observations, a plausible reaction scenario is proposed
in Scheme 4. First, the a-oxoketene dithioacetal 1 un-
dergoes iodination at the a-position to give a-aroyl-a-
iodoketene dithioacetal 2, which has been isolated
and fully characterized. DMSO in the presence of
iodine generates precursor MeSH or MeSSMe, which
undergoes nucleophilic co-ordination with the Cu(I)
species in the presence of DABCO to form complex
L-Cu(I)-SMe A. Subsequently, complex A undergoes
oxidative addition with in situ formed intermediate 2
Scheme 4. Possible mechanism for the thiomethylation of
DTAs 1 with DMSO.
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Iodine-Mediated Copper-Catalyzed Efficient a-C(sp2)-Thiomethylation
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residue thus obtained was purified by column chromatogra-
phy over silica gel using increasing percentage of ethyl ace-
tate in hexane as eluent to afford the pure thiomethylated
products 3.
to form a Cu(III) complex B as key intermediate,
which upon reductive elimination gave our desired
product 3 with elimination of the Cu(I) species to
complete the catalytic cycle. Fascinatingly, in the
whole reaction sequence, DABCO plays a dual role
of ligand as well as base and DMSO acts both as
a source of thiomethyl group and as a solvent.
Acknowledgements
We gratefully acknowledge the generous financial support
from the Science and Engineering Research Board (SB/S1/
OC-30/2013) and the Council of Scientific and Industrial Re-
search, New Delhi, India (02(0072)/12/EMR-II). G.S., A.S.
and A.N. are thankful to CSIR, India and K.R. is thankful to
DAAD, Germany for research fellowships.
Conclusions
In summary, we have developed a new synthetic strat-
egy for the selective thiomethylation of the a-Csp2
atom of a-oxoketene dithioacetals by a dimethyl sulf-
oxide-iodine-Cu(I) system in excellent yield for the
first time. The protocol proceeds smoothly employing
independent multiple reactions in a one-pot cascade.
Owing to the readily available and inexpensive re-
agents, operationally simple process, broad substrate
scope, high functional group tolerance and high
yields, this method should expand the scope of activa-
References
[1] a) V. Gomez-Benitez, O. Baldovino-Pentaleon, C. Her-
rera-Alvarez, R. A. Toscano, D. Morales-Morales, Tet-
rahedron Lett. 2006, 47, 5059; b) N. Taniguchi, J. Org.
Chem. 2004, 69, 6904; c) S. M. Soria-Castro, A. B. Pene-
nory, Beilstein J. Org. Chem. 2013, 9, 467; d) L. C.
Schmidt, V. Rey, A. B. Penenory, Eur. J. Org. Chem.
2006, 2210; e) L. Wang, Z.-C. Chen, Synth. Commun.
2001, 31, 1227.
2
À
tion and thiomethylation of challenging Csp
H
bonds. Furthermore, the construction of useful motifs
utilizing these synthesized molecules as new precur-
sors for other transformations is underway in our lab-
oratory.
[2] F.-L. Yang, F.-X. Wang, T.-T. Wang, Y.-J. Wang, S.-K.
Tian, Chem. Commun. 2014, 50, 2111.
[3] a) B. M. Trost, M. Ochiai, P. G. McDougal, J. Am.
Chem. Soc. 1978, 100, 7103; b) B. Movassagh, M.
Navidi, Tetrahedron Lett. 2008, 49, 6712.
[4] a) H. Wang, D. Huang, D. Cheng, L. Li, Y. Shi, Org.
Lett. 2011, 13, 1650; b) H. Guan, H. Wang, D. Huang,
Y. Shi, Tetrahedron 2012, 68, 2728.
Experimental Section
General Remarks
All the commercially available reagents were purchased
from Merck, Aldrich, and Fluka, and were used as received.
a-Oxoketene dithioacetals were synthesized by reported
[5] C. C. Eichman, J. P. Stambuli, J. Org. Chem. 2009, 74,
4005.
1
procedure.[13e] All H and 13C NMR spectra were recorded
on a JEOL AL 300 FT-NMR spectrometer. Chemical shifts
are given as d values (in parts per million, ppm) with refer-
ence to tetramethylsilane (TMS) as the internal standard.
The IR spectra were recorded on Perkin–Elmer Spectrum
Version 10.03.05 FT-IR spectrophotometer. Mass spectra
were recorded on Agilent Q-TOF and Waters-Q-Tof Pre-
mier-HAB213 instruments. All the reactions were moni-
tored by TLC using precoated sheets of silica gel G/UV-254
of 0.25 mm thickness (Merck 60F254) using UV light for vis-
ualization.
[6] K. Omura, A. K. Sharma, D. Swern, J. Org. Chem.
1976, 41, 957.
[7] K. E. Pfitzner, J. G. Moffatt, J. Am. Chem. Soc. 1963,
85, 3027.
[8] E. J. Corey, M. Chaykovsky, J. Am. Chem. Soc. 1962,
84, 867.
[9] a) M. B. Floyd, M. T. Du, P. F. Fabio, L. A. Jacob, B. D.
Johnson, J. Org. Chem. 1985, 50, 5022; b) E. Schipper,
M. Cinnamon, L. Rascher, Y. H. Chiang, W. Oroshnik,
Tetrahedron Lett. 1968, 9, 6201; c) J. M. McKenna, F.
Halley, J. E. Souness, I. M. McLay, S. D. Pickett, A. J.
Collis, K. Page, I. Ahmed, J. Med. Chem. 2002, 45,
2173; d) N. Mupparapu, S. Khan, S. Battula, M. Kush-
waha, A. P. Gupta, Q. N. Ahmed, R. A. Vishwakarma,
Org. Lett. 2014, 16, 1152.
[10] a) W. W. Epstein, F. W. Sweat, Chem. Rev. 1967, 67,
247; b) L. Chu, X. Yue, F.-L. Qing, Org. Lett. 2010, 12,
1644; c) F.-L. Liu, J.-R. Chen, Y.-Q. Zou, Q. Wei, W.-J.
Xiao, Org. Lett. 2014, 16, 3768; d) S. M. Patil, S. Kul-
karni, M. Mascarenhas, R. Sharma, S. M. Roopan, A.
Roychowdhury, Tetrahedron 2013, 69, 8255; e) D. J.
Keddie, T. E. Johnson, D. P. Arnold, S. E. Bottle, Org.
Biomol. Chem. 2005, 3, 2593; f) X. Ren, J. Chen, F.
Chen, J. Cheng, Chem. Commun. 2011, 47, 6725; g) Z.
Typical Procedure for the Thiomethylation of a-Oxo-
ketene Dithioacetals (1)
A mixture of a-oxoketene dithioacetal 1 (1.0 mmol), CuI
(20 mol%) and DABCO (2.5 equiv.) in 5 mL of DMSO was
stirred in presence of 3 equiv. of iodine at 1208C for the
stipulated period of time (see Table 2). After completion of
the reaction (monitored by TLC), the mixture was diluted
with 10 mL of DCM followed by washing with aqueous
Na2S2O3 (2”10 mL) and aqueous NH4Cl (2”10 mL) to
remove unutilized iodine and excess of base, respectively.
The organic layer was dried over anhydrous Na2SO4, and
solvent was evaporated under reduced pressure. The crude
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FULL PAPERS
Maya Shankar Singh et al.
Zhang, Q. Tian, J. Qian, Q. Liu, T. Liu, L. Shi, G.
Zhang, J. Org. Chem. 2014, 79, 8182.
Adv. 2013, 3, 245; e) G. K. Verma, R. K. Verma, G.
Shukla, N. Anugula, A. Srivastava, M. S. Singh, Tetra-
hedron 2013, 69, 6612.
[11] a) X. Gao, X. Pan, J. Gao, H. Huang, G. Yuan, Y. Li,
Chem. Commun. 2015, 51, 210; b) G. Yuan, J. Zheng,
X. Gao, X. Li, L. Huang, H. Chen, H. Jiang, Chem.
Commun. 2012, 48, 7513; c) F. Luo, C. Pan, L. Li, F.
Chen, J. Cheng, Chem. Commun. 2011, 47, 5304; d) P.
Sharma, S. Rohilla, N. Jain, J. Org. Chem. 2015, 80,
4116.
[12] a) X. Gao, X. Pan, J. Gao, H. Jiang, G. Yuan, Y. Li,
Org. Lett. 2015, 17, 1038; b) C. Dai, Z. Xu, F. Huang,
Z. Yu, Y.-F. Gao, J. Org. Chem. 2012, 77, 4414.
[13] Recent papers: a) R. K. Verma, H. Ila, M. S. Singh, Tet-
rahedron 2010, 66, 7389; b) M. S. Singh, G. C. Nandi, S.
Samai, Green Chem. 2012, 14, 447; c) R. K. Verma,
G. K. Verma, G. Shukla, M. S. Singh, RSC Adv. 2012, 2,
2413; d) G. K. Verma, R. K. Verma, M. S. Singh, RSC
[14] G. Singh, H. Ila, H. Junjappa, Synthesis 1985, 165.
[15] a) L. Zhu, X. Cao, R. Qiu, T. Iwasaki, V. P. Reddy, X.
Xu, S.-F. Yin, N. Kambe, RSC Adv. 2015, 5, 39358;
b) P. J. Amal Joseph, S. Priyadarshini, M. Lakshmi Kan-
tam, B. Sreedhar, Tetrahedron 2013, 69, 8276.
[16] a) Q. Gao, X. Wu, S. Liu, A. Wu, Org. Lett. 2014, 16,
1732; b) G. Yin, B. Zhou, X. Meng, A. Wu, Y. Pan,
Org. Lett. 2006, 8, 2245; c) X. Wu, Q. Gao, S. Liu, A.
Wu, Org. Lett. 2014, 16, 2888; d) X. Wu, Q. Gao, M.
Lian, S. Liu, A. Wu, RSC Adv. 2014, 4, 51180.
[17] Note: a-oxoketene dithioacetals with R1 =Me and R2 =
Bn furnished highly complex TLC patterns with several
overlapping spots, which could not be isolated.
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Adv. Synth. Catal. 2015, 357, 3969 – 3976