FeCl3 promoted highly regioselective [3 + 2] cycloaddition of dimethyl 2-vinyl and aryl cyclopropane-1,1-dicarboxylates with aryl isothiocyanates

Article abstract of DOI:10.1039/c2ob25682g

A FeCl₃ promoted [3 + 2] annulation of dimethyl 2-vinyl and arylcyclopropane-1,1-dicarboxylate with aryl isothiocyanates has been developed to give pyrrolidine-2-thiones in good yields with high regioselectivity.

Full text of DOI:10.1039/c2ob25682g

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COMMUNICATION
FeCl3 promoted highly regioselective [3 + 2] cycloaddition of dimethyl 2-vinyl
and aryl cyclopropane-1,1-dicarboxylates with aryl isothiocyanates†
Huina Wang,a Wei Yang,a Hong Liu,a Wei Wang*a,b and Hao Li*a,b
Received 6th April 2012, Accepted 21st May 2012
DOI: 10.1039/c2ob25682g
Table 1 Lewis acids screening for [3 + 2] cycloaddition reactions
A FeCl3 promoted [3 + 2] annulation of dimethyl 2-vinyl and
arylcyclopropane-1,1-dicarboxylate with aryl isothiocyanates
has been developed to give pyrrolidine-2-thiones in good
yields with high regioselectivity.
Entrya
Lewis acid
Additive
Time (h)
Yieldb (%)
Introduction
1
FeCl3
FeCl3
Pd(OAc)2
AgOTf
CuCl2
Zn(NTf2)2
Yb(OTf)3
Sc(OTf)3
AlCl3
In(OTf)3
Sn(OTf)2
—
24
24
48
48
48
48
48
24
24
24
24
45
65
0
0
0
0
0
Trace
17
54
49
Lewis acid promoted [3 + 2] annulation reactions of functiona-
lized cyclopropanes have received considerable attention in the
past decade.1 The processes serve as a powerful tool for the
facile construction of synthetically valuable 5-membered rings
such as cyclopentanes, tetrahydrofurans, pyrrolidines and pyrrolidin-
2-ones from respective olefins,2 carbonyls,3 imines4 and isocya-
nates5 as dipolarophiles. In these transformations, it is recog-
nized that transition metals such as palladium,6 rhodium,7
ruthenium,8 nickel,9 and non-toxic ytterbium10 are often
employed as effective promoters. Recently the use of less toxic
and inexpensive Lewis acids such as Mg(II),4d,11 Cu(II),12 and Fe
(III)13 for the related processes has gained significant interest.
Nevertheless, such cases are still very rare.
2c
3c
4c
5c
6c
7c
8c
9c
10c
11c
4 Å MS
4 Å MS
4 Å MS
4 Å MS
4 Å MS
4 Å MS
4 Å MS
4 Å MS
4 Å MS
4 Å MS
a On a 0.3 mmol scale, 1.0 eq. of Lewis acid. b Isolated yield. c 250 mg
of 4 Å MS was added in the reaction mixture.
isocyanates5 and the only one cycloaddition example of special
2,2-dimethoxy-cyclopropane-1-carboxylates with phenyl isothio-
cyanate17 have been reported, the study represents the prepa-
ration of pyrrolidine-2-thiones using the powerful [3 + 2]
cycloaddition approach from cyclopropanes and isothiocyanates
promoted by FeCl3.
Pyrrolidine-2-thiones can be used as intermediates to syn-
thesize biologically important compounds, displaying intriguing
anti-cancer properties.14 However, methods for the synthesis of
pyrrolidine-2-thiones from isothiocyanates are very rare. Kim
reported samarium diiodide promoted intramolecular cyclization
of β-ketoisothiocyanates.15 Wang reported the Michael/cycliza-
tion of α-isothiocyanato imides, esters, and lactones with methy-
leneindolinones.16 Herein, we describe our results on
investigating a new [3 + 2] cycloaddition of dimethyl 2-vinyl-
cyclopropane-1,1-dicarboxylate with commercially available and
inexpensive isocyanates to afford pyrrolidine-2-thiones in the
presence of FeCl3. To the best of our knowledge, although
reactions of 2-vinylcyclopropane-1,1-dicarboxylates with
Results and discussion
We began our initial [3 + 2] cycloaddition study using dimethyl
2-vinylcyclopropane-1,1-dicarboxylate (1a) (0.3 mmol) and iso-
thiocyanatobenzene (2a) (1.2 eq.) as reactants in the present of
FeCl3 (1.0 eq.) as the Lewis acid in CH2Cl2 at rt (Table 1). To
our delight, the reaction occurred to give the expected cyclo-
addition product pyrrolidine-2-thione (3a) in low yield (45%)
after stirring for 24 h (entry 1). Our continuing investigations
showed that the addition of 4 Å molecular sieves (MS) could
improve the reaction yield to 65% under the same reaction con-
ditions (entry 2). Then we examined various Lewis acids includ-
ing Pd(OAc)2, AgOTf, CuCl2, Zn(NTf2)2, Yb(OTf)3, Sc(OTf)3,
aShanghai Institute of Materia Medica, Shanghai, 201203, P. R. China.
E-mail: weiwangsimm@gmail.com; Fax: (+86) 21-6425-3739
bSchool of Pharmacy, East China University of Science and Technology,
130 Meilong Lu, Shanghai, 200237, P. R. China.
E-mail: hli77@ecust.edu.cn; Fax: (+86) 21-6425-3299
†Electronic supplementary information (ESI) available: Experimental
1
procedures, compound characterizations, and H and 13C NMR spectra.
See DOI: 10.1039/c2ob25682g
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Table 2 Solvent effect for [3 + 2] cycloaddition reactions
Entrya
Lewis acid
Solvent
Time (h)
Yieldb (%)
1
2
3
4
5
6
7
FeCl3 (1 eq.)
FeCl3 (1 eq.)
FeCl3 (1 eq.)
FeCl3 (1 eq.)
FeCl3 (1 eq.)
FeCl3 (1 eq.)
FeCl3 (0.3 eq.)
CH2Cl2
CHCl3
ClCH2CH2Cl
CH3CN
Toluene
Benzene
ClCH2CH2Cl
24
24
24
48
48
48
36
65
34
67
16
<10
<10
56
a On a 0.3 mmol scale. b Isolated yield.
In(OTf)3 and Sn(OTf)2 for this [3 + 2] cycloaddition process.
However, it was found that they were inferior to FeCl3 promoted
annulation reaction (entries 3–11).
The above results indicated that FeCl3 had the highest activity
for this cycloaddition reaction. The study of solvent effect was
next investigated under optimized conditions (Table 2). The reac-
tion in chloroform ran much slower than that in dichloro-
methane, and the isolated yield was only about half of that in
CH2Cl2 (entries 1–2). The reactions in ClCH2CH2Cl had a little
higher yield than that in dichloromethane (entry 3, 67%). Never-
theless, CH3CN, toluene and benzene gave rise to even poorer
yields and all the isolated yields were less than 20% after 48 h
(entries 4–6). Notably, reducing the amount of FeCl3 (0.3 eq.,
entry 7) could still catalyze the [3 + 2] cycloaddition reaction,
although the progress was much slower and reaction yield was
decreased (56%, entry 7).
Fig. 1 Scopes of pyrrolidine-2-thiones.
With the optimized reaction conditions in hand, structurally
diverse cyclopropanes and isothiocyanates were investigated to
prove the generality of the reaction. The results were summarized
in Fig. 1. Notably, in all cases, the processes proceeded highly
regioselectively. Exploration of the structural demand of dipolar-
ophiles revealed that significant structure variation could be tole-
rated. It appeared that the electronic and steric effects were
limited. The arylisothiocyanates bearing electron-withdrawing
groups of Br, Cl at para-, meta- and ortho-position with steric
hindrance (Fig. 1, 3b–3e, 3i, 3k, and 3m), and -donating groups
of methyl and methoxy group (3f–3g, 3j and 3l) and neutral Ph
groups (3h) gave 53–68% yields of cycloaddition products.
When benzyl isothiocyanate reacted with 1a, the reaction was
sluggish and the reaction yield was only 28% after 48 h (3n). A
structural variation of 1,3-dipole components was also examined.
Vinyl (3a–g) and aryl (3h–m) cyclopropanes could participate in
the reactions. However, the limitation of the process was also
recognized. When dimethyl 2-benzylcyclopropane-1,1-dicarboxy-
late was used, no cycloaddition product was found even after
48 h.
Scheme 1 Proposed mechanism for the [3
reactions.
+ 2] cycloaddition
stabilize the positive charge of 1,3-dipoles to help the subsequent
[3 + 2] annulation. Alkylcyclopropane won’t stabilize the posi-
tive charge to make the reaction happen due to the absence of
the conjugated π system. The germinal diester group dictates the
observed regioselectivity of the products formed.
Conclusion
In conclusion, we have developed an unprecedented FeCl3 pro-
moted [3 + 2] cycloaddition between functionalized cyclo-
propanes and isothiocyanates with a relatively broad substrate
scope. Notably, the process takes place in a highly regioselective
manner to give structurally diverse pyrrolidine-2-thiones, which
are difficult to obtain through classic methods. Further explora-
tion of the chemistry and the biologically interesting pyrrolidine-
2-thiones are being pursued in our laboratory.
A plausible reaction mechanism was proposed, as depicted in
Scheme 1. Lewis acid activates the oxygen of the ester to open
the cyclopropane to generate 1,3-dipoles A and B. It is hypoth-
esized that the conjugated π system of vinyl or phenyl ring can
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41.50. HRMS (ESI) cacld for [M + Na]+ C16H16BrNO4S:
419.9881, found: 419.9865.
Experimental
General information
Dimethyl 1-(2-bromophenyl)-2-thioxo-5-vinylpyrrolidine-3,3-
dicarboxylate (3d). 1H NMR (400 MHz, CDCl3) δ 7.56 (dd, J =
7.9, 1.0 Hz, 1H), 7.26 (ddd, J = 7.7, 6.8, 1.2 Hz, 1H), 7.05–6.92
(m, 2H), 5.76 (ddd, J = 16.9, 9.9, 8.5 Hz, 1H), 5.29 (d, J = 16.9
Hz, 1H), 5.15 (d, J = 10.0 Hz, 1H), 4.34–4.20 (m, 1H), 3.90
(s, 3H), 3.87 (s, 3H), 3.04 (dd, J = 13.1, 5.2 Hz, 1H), 2.73 (dd,
J = 13.1, 10.5 Hz, 1H). 13C NMR (100 MHz): δ 170.05, 167.68,
167.50, 149.11, 135.23, 132.97, 127.96, 126.15, 120.23, 118.80,
115.00, 70.49, 53.68, 53.55, 50.52, 41.72. HRMS (ESI) cacld
for [M + H]+ C16H17NO4SBr: 398.0062, found: 398.0074.
Unless stated otherwise, the reagents and solvents of the highest
purity available were used as purchased or purified/dried by stan-
1
dard procedures when necessary. H and 13C NMR spectra were
recorded on a Varian instrument (300 MHz and 75 MHz,
400 MHz and 100 MHz, respectively) and internally referenced
to tetramethylsilane signal or residual protio solvent signals.
Data for 1H NMR are recorded as follows: chemical shift
(δ, ppm), multiplicity (s = singlet, d = doublet, t = triplet, m =
multiplet or unresolved, br = broad singlet, coupling constant(s)
in Hz, integration). Data for 13C NMR are reported in terms of
chemical shift (δ, ppm).
Dimethyl 1-(4-chlorophenyl)-2-thioxo-5-vinylpyrrolidine-3,3-
dicarboxylate (3e). 1H NMR (400 MHz, CDCl3) δ 7.39–7.19
(m, 2H), 7.01–6.83 (m, 2H), 5.74 (ddd, J = 16.9, 9.9, 8.4 Hz,
1H), 5.28 (d, J = 16.8 Hz, 1H), 5.15 (d, J = 10.0 Hz, 1H), 4.21
(ddd, J = 10.4, 8.4, 5.2 Hz, 1H), 3.89 (s, 3H), 3.85 (s, 3H), 3.01
(dd, J = 13.1, 5.2 Hz, 1H), 2.68 (dd, J = 13.1, 10.5 Hz, 1H).
13C NMR (100 MHz): δ 168.85, 167.82, 167.61, 149.26,
135.24, 130.33, 129.03, 121.42, 118.79, 70.70, 53.77, 53.59,
General procedure for synthesis of pyrrolidine-2-thiones
All reactions were carried out under a nitrogen atmosphere.
FeCl3 (49 mg, 0.3 mmol), 4 Å MS (250 mg), cyclopropane
(0.3 mmol in 1.5 mL of CH2Cl2) and imine (0.36 mmol in
1.5 mL of CH2Cl2) was sequentially added to an oven-dried
reaction tube. The resulting solution was further stirred at room
temperature. After the reaction was complete (monitored by
TLC), the mixture was filtered rapidly through a glass funnel
with a thin layer of silica gel, washed with CH2Cl2. The filtrate
was concentrated and the residue was purified by flash column
chromatography (petroleum ether– EtOAc = 15 : 1) to afford the
desired product.
50.26, 41.45. HRMS (ESI) cacld for [M
C16H16NO4SClNa: 376.0386, found: 376.0407.
+
Na]+
Dimethyl 2-thioxo-1-(p-tolyl)-5-vinylpyrrolidine-3,3-dicarboxy-
late (3f). 1H NMR (400 MHz, CDCl3) δ 7.22–7.05 (m, 2H),
6.95–6.83 (m, 2H), 5.75 (ddd, J = 16.9, 10.0, 8.4 Hz, 1H), 5.27
(d, J = 16.8 Hz, 1H), 5.13 (d, J = 10.0 Hz, 1H), 4.20 (ddd, J =
10.5, 8.4, 5.3 Hz, 1H), 3.90 (s, 3H), 3.86 (s, 3H), 3.00 (dd, J =
13.1, 5.2 Hz, 1H), 2.66 (dd, J = 13.1, 10.6 Hz, 1H), 2.32 (s,
3H). 13C NMR (100 MHz): δ 168.10, 167.85, 167.12, 148.30,
135.58, 134.69, 129.45, 119.95, 118.48, 70.65, 53.72, 53.54,
50.02, 41.34, 20.98. HRMS (ESI) cacld for [M + H]+
C17H20NO4S: 334.1113, found 334.1110.
Dimethyl 1-phenyl-2-thioxo-5-vinylpyrrolidine-3,3-dicarboxy-
late (3a). 1H NMR (400 MHz, CDCl3) δ 7.37–7.28 (m, 2H),
7.17–7.09 (m, 1H), 6.97 (m, 2H), 5.75 (ddd, J = 16.9, 10.0, 8.4
Hz, 1H), 5.35–5.21 (d, J = 16.9 Hz, 1H), 5.14 (d, J = 10.0 Hz,
1H), 4.20 (ddd, J = 10.5, 8.4, 5.2 Hz, 1H), 3.90 (s, 3H), 3.86 (s,
3H), 3.01 (dd, J = 13.1, 5.2 Hz, 1H), 2.68 (dd, J = 13.1, 10.6
Hz, 1H). 13C NMR (100 MHz): δ 168.02, 167.81, 167.78,
150.87, 135.48, 128.90, 125.04, 119.91, 118.57, 70.63, 53.74,
53.56, 50.07, 41.46. HRMS (ESI) cacld for [M + Na]+
C16H17NO4SNa: 342.0776, found: 342.0777.
Dimethyl
1-(4-methoxyphenyl)-2-thioxo-5-vinylpyrrolidine-
3,3-dicarboxylate (3g). 1H NMR (400 MHz, CDCl3)
δ
7.04–6.94 (m, 2H), 6.92–6.83 (m, 2H), 5.75 (ddd, J = 16.9, 9.9,
8.4 Hz, 1H), 5.28 (d, J = 16.9 Hz, 1H), 5.14 (d, J = 10.0 Hz,
1H), 4.21 (ddd, J = 10.5, 8.5, 5.3 Hz, 1H), 3.89 (s, 3H), 3.85 (s,
3H), 3.79 (s, 3H), 2.99 (dd, J = 13.1, 5.3 Hz, 1H), 2.64 (dd, J =
13.1, 10.6 Hz, 1H). 13C NMR (100 MHz): δ 168.16, 167.89,
166.35, 157.12, 143.77, 135.62, 121.69, 118.49, 113.99, 70.80,
55.35, 53.72, 53.53, 50.10, 41.13. HRMS (ESI) cacld for
[M + H]+ C17H20NO5S: 350.1062, found: 350.1047.
Dimethyl 1-(4-bromophenyl)-2-thioxo-5-vinylpyrrolidine-3,3-
dicarboxylate (3b). 1H NMR (400 MHz, CDCl3) δ 7.49–7.39
(m, 2H), 6.89–6.81 (m, 2H), 5.74 (ddd, J = 16.9, 10.0, 8.4 Hz,
1H), 5.31–5.25 (m, 1H), 5.22–5.07 (m, 1H), 4.29–4.13 (m, 1H),
3.89 (s, 3H), 3.84 (s, 3H), 3.01 (dd, J = 13.1, 5.2 Hz, 1H), 2.68
(dd, J = 13.1, 10.5 Hz, 1H). 13C NMR (100 MHz): δ 168.85,
167.78, 167.57, 149.76, 135.22, 131.98, 121.77, 118.79, 118.14,
70.69, 53.77, 53.59, 50.26, 41.46. HRMS (ESI) cacld for
[M + H]+ C16H17NO4SBr: 398.0062, found: 398.0081.
Dimethyl 1,5-diphenyl-2-thioxopyrrolidine-3,3-dicarboxylate
(3h). 1H NMR (400 MHz, CDCl3) δ 7.41–7.37 (m, 2H),
7.37–7.27(m, 5H), 7.16–7.09 (m, 1H), 7.05–6.99 (m, 2H), 4.74
(dd, J = 11.7, 4.9 Hz, 1H), 3.95 (s, 3H), 3.86 (s, 3H), 3.17 (dd,
J = 13.1, 5.0 Hz, 1H), 2.98 (dd, J = 13.1, 11.7 Hz, 1H).
13C NMR (100 MHz): δ 168.13, 167.75, 167.68, 150.85,
137.68, 128.93, 128.79, 128.36, 127.64, 125.09, 120.03, 71.20,
53.84, 53.60, 51.03, 43.68. HRMS (ESI) cacld for [M + H]+
C20H20NO4S: 370.1113, found: 370.1103.
Dimethyl 1-(3-bromophenyl)-2-thioxo-5-vinylpyrrolidine-3,3-
dicarboxylate (3c). 1H NMR (400 MHz, CDCl3) δ 7.25 (d, J =
7.3 Hz, 1H), 7.19 (t, J = 7.9 Hz, 1H), 7.13 (s, 1H), 6.90 (d, J =
7.8 Hz, 1H), 5.75 (dt, J = 18.2, 9.1 Hz, 1H), 5.29 (d, J = 16.9
Hz, 1H), 5.16 (d, J = 10.0 Hz, 1H), 4.22 (td, J = 10.1, 5.4 Hz,
1H), 3.90 (s, 3H), 3.85 (s, 3H), 3.01 (dd, J = 13.1, 5.2 Hz, 1H),
2.69 (dd, J = 13.0, 10.6 Hz, 1H). 13C NMR (100 MHz):
δ 169.44, 167.71, 167.49, 152.01, 135.14, 130.26, 127.82,
122.93, 122.40, 118.79, 118.55, 70.65, 53.74, 53.55, 50.30,
Dimethyl
1-(4-chlorophenyl)-5-phenyl-2-thioxopyrrolidine-
3,3-dicarboxylate (3i). 1H NMR (400 MHz, CDCl3) δ 7.40–7.36
(m, 2H), 7.36–7.28 (m, 5H), 7.04–6.89 (m, 2H), 4.76 (dd, J =
11.6, 4.9 Hz, 1H), 3.95 (s, 3H), 3.86 (s, 3H), 3.18 (dd, J = 13.1,
5034 | Org. Biomol. Chem., 2012, 10, 5032–5035
This journal is © The Royal Society of Chemistry 2012

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5.0 Hz, 1H), 2.98 (dd, J = 13.1, 11.7 Hz, 1H). 13C NMR
(100 MHz): δ 168.70, 167.94, 167.58, 149.26, 137.44, 130.40,
129.07, 128.84, 128.46, 127.61, 121.54, 71.27, 53.88, 53.64,
51.24, 43.69. HRMS (ESI) cacld for [M + H]+ C20H18ClNO4S:
404.0723, found: 404.0719.
Acknowledgements
The financial support from the Shanghai Pujiang Program
(11PJ1411900), East China University of Science & Technology
and the China 111 Project (Grant B07023) is appreciated.
Dimethyl 5-phenyl-2-thioxo-1-(p-tolyl)pyrrolidine-3,3-dicar-
boxylate (3j). 1H NMR (400 MHz, CDCl3) δ 7.59 (d, J = 7.7
Hz, 2H), 7.50 (dt, J = 19.0, 7.1 Hz, 3H), 7.35 (d, J = 7.8 Hz,
2H), 7.15 (d, J = 7.7 Hz, 2H), 4.96 (dd, J = 11.6, 4.8 Hz, 1H),
4.15 (s, 3H), 4.07 (s, 3H), 3.38 (dd, J = 13.1, 4.9 Hz, 1H), 3.17
(t, J = 12.3 Hz, 1H), 2.52 (s, 3H). 13C NMR (100 MHz):
δ 168.10, 167.71, 166.86, 148.20, 137.72, 134.65, 129.40,
128.68, 128.23, 127.56, 120.00, 71.15, 53.71, 53.46, 50.89,
Notes and references
1 For reviews on annulation of cyclopropanes, see: (a) H.-U. Reissig and
R. Zimmer, Chem. Rev., 2003, 103, 1151; (b) M. Rubin, M. Rubina and
V. Gevorgyan, Chem. Rev., 2007, 107, 3117; (c) T. F. Schneider and D.
B. Werz, Org. Lett., 2011, 13, 1848.
2 Selected examples: (a) M. Komatsu, I. Suehiro, Y. Horiguchi and
I. Kuwajima, Synlett, 1991, 771; (b) W. F. Berkowitz and S. C. Grenetz,
J. Org. Chem., 1976, 41, 10; (c) B. Bajtos, M. Yu, H. Zhao and B.
L. Pagenkopf, J. Am. Chem. Soc., 2007, 129, 9631; (d) K. Sapeta and M.
A. Kerr, Org. Lett., 2009, 11, 2081.
3 Perspective article: (a) M. J. Campbell, J. S. Johnson, A. T. Parsons, P.
D. Pohlhaus and S. D. Sanders, J. Org. Chem., 2010, 75, 6317. Pioneer-
ing examples: (b) H.-U. Reissig, Tetrahedron Lett., 1981, 22, 2981;
(c) S. Shimada, Y. Hashimoto, A. Sudo, M. Hasegawa and K. Saigo, J.
Org. Chem., 1992, 57, 7126; (d) S. Shimada, Y. Hashimoto,
T. Nagashima, M. Hasegawa and K. Saigo, Tetrahedron, 1993, 49, 1589;
(e) S. Shimada, Y. Hashimoto and K. Saigo, J. Org. Chem., 1993, 58,
5226; (f) Y. Sugita, K. Kawai and I. Yokoe, Heterocycles, 2000, 53, 657;
(g) Y. Sugita, K. Kawai and I. Yokoe, Heterocycles, 2001, 55, 135;
(h) Z. Han, S. Uehira, T. Tsuritani, H. Shinokubo and K. Oshima, Tetra-
hedron, 2001, 57, 987.
4 Selected examples: (a) P. B. Alper, C. Meyers, A. Lerchner, D. R. Siegel
and E. M. Carreira, Angew. Chem., Int. Ed., 1999, 38, 3186; (b) C.
A. Carson and M. A. Kerr, J. Org. Chem., 2005, 70, 8242; (c) Y.-
B. Kang, Y. Tang and X.-L. Sun, Org. Biomol. Chem., 2006, 4, 299;
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Chem. Soc., 2010, 132, 9688.
43.49, 20.90. HRMS (ESI) cacld for [M
C21H21NO4NaS: 406.1089, found: 406.1082.
+
Na]+
Dimethyl
1-(4-bromophenyl)-5-phenyl-2-thioxopyrrolidine-
3,3-dicarboxylate (3k). 1H NMR (400 MHz, CDCl3)
δ 7.52–7.42 (m, 2H), 7.41–7.20 (m, 5H), 6.97–6.86 (m, 2H),
4.76 (dd, J = 11.6, 4.9 Hz, 1H), 3.94 (s, 3H), 3.85 (s, 3H), 3.18
(dd, J = 13.1, 5.0 Hz, 1H), 2.98 (dd, J = 13.1, 11.7 Hz, 1H). 13
C
NMR (100 MHz): δ 168.72, 167.88, 167.53, 149.73, 137.38,
132.00, 128.82, 128.44, 127.58, 121.88, 118.19, 71.24, 53.86,
53.62, 51.23, 43.68. HRMS (ESI) cacld for [M + H]+
C20H19NO4SBr: 448.0218, found: 448.0225.
Dimethyl 1-(4-methoxyphenyl)-5-phenyl-2-thioxopyrrolidine-
3,3-dicarboxylate (3l). 1H NMR (400 MHz, CDCl3) δ 7.39 (dd,
J = 8.1, 1.4 Hz, 2H), 7.42–7.36 (m, 3H), 7.05–6.99 (m, 2H),
6.90–6.83 (m, 2H), 4.75 (dd, J = 11.7, 4.9 Hz, 1H), 3.94 (s, 3H),
3.86 (s, 3H), 3.79 (s, 3H), 3.16 (dd, J = 13.1, 5.0 Hz, 1H), 2.94
(dd, J = 13.0, 11.8 Hz, 1H). 13C NMR (100 MHz): δ 168.27,
167.85, 166.15, 157.16, 143.73, 137.83, 128.78, 128.32, 127.67,
121.83, 114.02, 71.37, 55.37, 53.81, 53.56, 51.05, 43.39.
HRMS (ESI) cacld for [M + Na]+ C21H21NO5SNa: 422.1038,
found: 422.1028.
5 K. Yamamoto, T. Ishida and J. Tsuji, Chem. Lett., 1987, 1157.
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Dimethyl
5-(4-bromophenyl)-1-phenyl-2-thioxopyrrolidine-
3,3-dicarboxylate (3m). 1H NMR (400 MHz, CDCl3) δ 7.44 (d,
J = 8.2 Hz, 2H), 7.34 (t, J = 7.8 Hz, 2H), 7.29–7.21 (m, 2H),
7.13 (t, J = 7.4 Hz, 1H), 7.02 (dd, J = 8.3, 0.9 Hz, 2H), 4.70
(dd, J = 11.6, 4.9 Hz, 1H), 3.94 (s, 3H), 3.86 (s, 3H), 3.16 (dd,
J = 13.1, 5.0 Hz, 1H), 2.91 (dd, J = 13.0, 11.7 Hz, 1H).
13C NMR (100 MHz): δ 167.90, 167.53, 167.00, 150.68,
136.81, 131.88, 129.29, 128.93, 125.17, 122.18, 119.93, 71.04,
53.82, 53.59, 50.30, 43.55. HRMS (ESI) cacld for [M + Na]+
C20H18NO4NaSBr: 470.0038, found: 470.0046.
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13 During our study on this research, the following ion catalytic reactions
were reported recently: (a) F. Benfatti, F. Nanteuil and J. Waser, Org.
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Dimethyl 1-benzyl-2-thioxo-5-vinylpyrrolidine-3,3-dicarboxy-
late (3n). 1H NMR (400 MHz, CDCl3) δ 7.73–7.04 (m, 5H),
5.81 (ddd, J = 16.9, 9.9, 8.4 Hz, 1H), 5.32 (d, J = 16.9 Hz, 1H),
5.18 (d, J = 10.0 Hz, 1H), 4.53 (s, 2H), 4.23 (ddd, J = 10.6, 8.4,
5.2 Hz, 1H), 3.84 (s, 3H), 3.80 (s, 3H), 2.98 (dd, J = 13.0, 5.2
Hz, 1H), 2.64 (dd, J = 13.0, 10.6 Hz, 1H). 13C NMR (126 MHz,
CDCl3): δ 168.31, 168.11, 166.36, 138.69, 135.83, 128.23,
127.43, 126.71, 118.57, 70.53, 60.73, 53.60, 53.42, 50.06,
41.93. HRMS (ESI) cacld for [M + H]+ C17H20NO4S: 334.1113,
found: 334.1106.
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