Synthesis of functionalized azet-2(1 H)-imines through [2+2] cycloaddition of imines and ketenimines

Article abstract of DOI:10.1055/s-0033-1338747

The reaction between ketenimine intermediates, generated from terminal alkynes and sulfonyl azides, trichloroacetonitrile, and sodium arylsulfinates in N,N-dimethylformamide at room temperature affords N-[3-aryl(alkyl)-4-arylazet- 2(1H)-ylidene]-arene(alk

Full text of DOI:10.1055/s-0033-1338747

1420▌
LETTER
lSetyternthesis of Functionalized Azet-2(1H)-imines through [2+2] Cycloaddition of
Imines and Ketenimines
Functionalized Azet-2(1H)-imines
Issa Yavari,* Manijeh Nematpour
Department of Chemistry, Tarbiat Modares University, P.O. Box 14115-175, Tehran, Iran
Fax +98(21)82883455; E-mail: yavarisa@modares.ac.ir
Received: 26.02.2013; Accepted after revision: 18.04.2013
CuCl, and copper powder were tested with CuI giving the
Abstract: The reaction between ketenimine intermediates, generat-
best results. Among several solvents screened, N,N-di-
ed from terminal alkynes and sulfonyl azides, trichloroacetonitrile,
methylformamide (DMF) was the best. When the reaction
and sodium arylsulfinates in N,N-dimethylformamide at room
was performed in DMF in the presence of one equivalent
of Et3N at room temperature for six hours, it was found
that the desired product 7a was indeed obtained in 84%
yield (Table 1). Thus, the optimized reaction conditions
used were 10 mol% of CuI, 1 mmol of alkyne, 1.2 mmol
of sulfonyl azide, 1 mmol of sodium arylsulfinate, and
1 mmol of 5 in DMF at room temperature.
temperature affords N-[3-aryl(alkyl)-4-arylazet-2(1H)-ylidene]-
arene(alkane)sulfonamides in moderate to good yields.
Key words: 2-azetines, copper iodide, trichloroacetonitrile,
sodium arylsulfinates, ketenimines, sulfonyl azides, terminal al-
kynes
The replacement of carbon atoms of cyclobutane by het-
eroatoms introduces functionalities which exhibit in-
creased reactivity resulting from the ring strain. This often
leads to unusual properties which make four-membered
heterocycles useful as synthetic intermediates.1–3 Howev-
er, it also adds a new dimension of difficulty concerning
the synthesis of these heterocycles. Azetines comprise a
rare class of constrained azaheterocycles with high syn-
thetic potential due to their usually unstable nature. This
class can be divided into 1-azetines and 2-azetines, de-
pending on the position of the double bond. The chemistry
of azetines is still not much developed, despite the fact
that since the early 1980s fundamental information was
available for the further unraveling of this class of com-
pounds.4 Herein, we report a simple and efficient proce-
dure for the synthesis of N-[3-aryl(alkyl)-4-arylazet-
2(1H)-ylidene]arene(alkane)sulfonamides 7 via the cop-
per-catalyzed four-component coupling reaction of termi-
nal alkynes 1, sulfonyl azides 2, sodium arylsulfinates 4,
and trichloroacetonitrile 5 (Table 1).5 This protocol builds
on works published by Fokin6 and Xu,7 using a different
imine for the [2+2] reaction. This allows subsequent elim-
ination of chloroform to give the azetine products 7.
Phenylacetylene readily participates in these coupling re-
actions to furnish the compounds 7a–f in good yields (Ta-
ble 1). Butylacetylene served as low-yielding substrate
compared to phenylacetylene. Aromatic and aliphatic sul-
fonyl azides reacted efficiently, and the corresponding
products were obtained in good yields.
Table 1 Synthesis of N-[3-aryl(alkyl)-4-arylazet-2(1H)-
ylidene]arene(alkane)sulfonamides 7
O
Ar –S
Cl3C CN
Na+
+
O
5
4
DMF, r.t.
NH
O
O
Cl3C
S
R2
O
O
R1
R1
N
S
H
CuI (10 mol%),
Et3N
N
R2
O
1
Ar
S
6
O
+
C
NH
DMF, r.t., 6 h
Ar
O
S
O
R1
O
S
R2
N3
O
2
3
7
Among several methods leading to the generation of ke-
tenimines, the copper-catalyzed azide–alkyne cycloaddi-
tion reaction attracted much attention because of its mild
formation conditions.8 The ketenimine intermediates gen-
erated in this reaction could be trapped by various nucleo-
philes.9,10 In this way, skeletons of various heterocycles
were successfully synthesized.11–14
1–4, 6, 7 R1
R2
Ar
Yield (%) of 7
a
b
c
d
e
f
Ph
4-Tol
Ph
4-Tol
4-Tol
4-Tol
Ph
84
80
74
78
73
70
67
60
58
Ph
Ph
Me
Ph
4-Tol
Ph
Initially, phenylacetylene (1a), p-toluenesulfonyl azide
(2a), sodium p-tolylsulfinate (4a), and 5 were selected as
the model substrates. Several catalysts such as CuI, CuBr,
Ph
Ph
Ph
Me
Ph
g
h
i
n-Bu
n-Bu
n-Bu
4-Tol
Ph
4-Tol
4-Tol
4-Tol
SYNLETT 2013, 24, 1420–1422
Advanced online publication: 17.05.2013
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9
3
6
-
5
2
1
4
1
4
3
7
-
2
0
9
6
DOI: 10.1055/s-0033-1338747; Art ID: ST-2013-D0177-L
© Georg Thieme Verlag Stuttgart · New York
Me

LETTER
Functionalized Azet-2(1H)-imines
1421
1
(4) Davies, D. E.; Storr, R. C. In Comprehensive Heterocyclic
Chemistry I; Vol. 7; Katritzky, A. R.; Rees, C. W., Eds.;
Elsevier: Oxford, 1984, 237.
Structures of compounds 7a–i were assigned by IR, H
1
NMR, 13C NMR, and mass spectral data. The H NMR
spectrum of 7a exhibited three singlets for methyl (δ =
2.47, 2.48 ppm), and NH (δ = 5.07 ppm) protons, along
with characteristic multiplets for the phenyl protons. The
13C NMR spectrum of 7a showed 17 signals in agreement
with the proposed structure. The mass spectrum of 7a dis-
played the molecular ion peak at m/z = 452. The NMR
spectra of compounds 7b–i are similar to those of 7a, ex-
cept for the substituents, which showed characteristic
signals in the appropriate regions of the spectra.
(5) General Procedure for the Synthesis of Compounds 7
To a mixture of sulfonyl azide 2 (1.2 mmol), alkyne 1 (1
mmol), and CuI (0.1 mmol), Et3N (1 mmol) in DMF (2 mL)
was slowly added 5 (1 mmol) and sodium arylsulfinate 4 (1
mmol) stirred at r.t. under N2 atmosphere. After completion
of the reaction [about 6 h; TLC (EtOAc–hexane, 1:5)
monitoring], the mixture was diluted with CH2Cl2 (2 mL)
and aq NH4Cl solution (3 mL), stirred for 30 min, and the
layers were separated. The aqueous layer was extracted with
CH2Cl2 (3 × 3 mL), and the combined organic fractions were
dried (Na2SO4) and concentrated under reduced pressure.
The residue was purified by flash column chromatography
[silica gel (230–400 mesh; Merck), hexane–EtOAc, 5:1] to
give the product.
A plausible mechanism for the formation of compounds 7
is given in Scheme 1. The yellow copper acetylide 8,
formed from 1 and CuI, is converted into ketenimine 3 by
well-documented transformations.15–17 Susequently, a
[2+2] cycloaddition reaction6,7,18 takes place between 3
and 6 (generated in situ from 4 and 5) to produce 11.
Intermediate 11 affords product 7 by loss of chloroform.
4-Methyl-N-[3-Phenyl-4-tosylazet-2(1H)-ylidene]-
benzenesulfonamide (7a)
Pale yellow powder, mp 120–123 °C; yield 0.38 g (84%). IR
(KBr): νmax = 3430, 2921, 1516, 1392, 1275, 1132, 1080 cm–
1. 1H NMR (500 MHz, CDCl3): δ = 2.47 (3 H, s, Me), 2.48
(3 H, s, Me), 5.07 (1 H, s, NH), 7.26–7.30 (3 H, m, Ph), 7.34–
7.40 (4 H, m, Ph), 7.47 (2 H, d, 3J = 7.9 Hz, Ar), 7.83 (2 H,
d, 3J = 7.7 Hz, Ar), 7.91 (2 H, d, 3J = 7.9 Hz, Ar). 13C NMR
(125.7 MHz, CDCl3): δ = 27.2 (Me), 27.3 (Me), 122.5 (C),
127.5 (2 CH), 128.0 (2 CH), 128.7 (2 CH), 129.2 (CH),
130.6 (2 CH), 130.7 (2 CH), 132.5 (2 CH), 135.0 (C), 136.0
(CH), 142.1 (C), 146.7 (C), 147.3 (C), 166.7 (C), 167.3 (C).
MS (EI): m/z (%) = 452 (2) [M+], 375 (8), 361 (12), 297 (14),
196 (23), 155 (100), 91 (70), 77 (51). Anal. Calcd (%) for
C23H20N2O4S2 (452.09): C, 61.04; H, 4.45; N, 6.19. Found:
C, 61.49; H, 4.52; N, 6.28.
SO2R2
H+
R1
Cu
N2
R1
N
2
R1
Cu
CuI
1 +
N
N
SO2R2
– N2
Cu
N
8
9
10
O
Ar –S
Cl3C CN
+
Na+
O
4
5
NH
O
S
N-[3-Phenyl-4-tosylazet-2(1H)-ylidene]benzene-
sulfonamide (7b)
O
Cl3C
R1
Cl3C
N
SO2R2
H
Pale yellow powder, mp 111–113 °C; yield 0.35 g (80%). IR
(KBr): νmax = 3437, 2939, 1528, 1400, 1271, 1140, 1084 cm–
1. 1H NMR (500 MHz, CDCl3): δ = 2.48 (3 H, s, Me), 5.08
(1 H, s, NH), 7.29–7.36 (3 H, m, Ph), 7.40 (2 H, d, 3J = 7.7
Hz, Ar), 7.48 (2 H, d, 3J = 7.7 Hz, Ar), 7.62 (2 H, t, 3J = 7.9
Hz, Ar), 7.75 (1 H, t, 3J = 7.9 Hz, Ar), 7.91 (2 H, d, 3J = 7.6
Hz, Ar), 8.03 (2 H, d, 3J = 7.9 Hz, Ar). 13C NMR (125.7
MHz, CDCl3): δ = 28.2 (Me), 122.6 (C), 127.4 (2 CH), 127.5
(2 CH), 128.7 (2 CH), 129.2 (CH), 130.2 (2 CH), 130.7 (2
CH), 132.5 (2 CH), 135.7 (CH), 136.2 (C), 142.1 (C), 144.8
(C), 147.3 (C), 165.1 (C), 168.8 (C). MS (EI): m/z (%) = 438
(3) [M+], 361 (11), 283 (13), 256 (15), 155 (76), 141 (100),
91 (34), 77 (44). Anal. Calcd (%) for C22H18N2O4S2
(438.07): C, 60.26; H, 4.14; N, 6.39. Found: C, 60.06; H,
4.18; N, 6.45.
Ar
6
C
C
NSO2R2
7
NH
– HCCl3
O
R1
S
O
Ar
11
3
Scheme 1
In summary, we have developed a multicomponent reac-
tion involving ketenimine intermediates, trichloroacetoni-
trile, and sodium arylsulfinates, which affords a new route
to the synthesis of N-[3-aryl(alkyl)-4-arylazet-2(1H)-
ylidene]arene(alkane)sulfonamides in moderate to good
yields. The present method may be considered as a practi-
cal route for the synthesis of functionalized azet-2(1H)-
imines. The potential diversity of this reaction and avail-
able starting materials are the main advantages of this
methodology.
N-[3-Phenyl-4-tosylazet-2(1H)-ylidene]methane-
sulfonamide (7c)
Pale yellow powder, mp 98–100 °C; yield 0.28 g (74%). IR
(KBr): νmax = 3425, 2945, 1541, 1401, 1279, 1126 cm–1. 1H
NMR (500 MHz, CDCl3): δ = 2.47 (3 H, s, Me), 3.65 (3 H,
s, Me), 5.08 (1 H, s, NH), 7.29–7.34 (3 H, m, Ph), 7.40 (2 H,
d, 3J = 7.7 Hz, Ar), 7.49 (2 H, d, 3J = 7.8 Hz, Ar), 7.91 (2 H,
d, 3J = 7.8 Hz, Ar). 13C NMR (125.7 MHz, CDCl3): δ = 26.2
(Me), 33.0 (Me), 122.5 (C), 127.5 (2 CH), 128.8 (2 CH),
129.3 (CH), 130.7 (2 CH), 132.5 (2 CH), 135.0 (C), 142.1
(C), 147.4 (C), 162.8 (C), 167.1 (C). MS (EI): m/z (%) = 376
(M+, 2), 299 (10), 256 (14), 221 (12), 155 (40), 78 (100), 77
(44). Anal. Calcd (%) for C17H16N2O4S2 (376.06): C, 54.24;
H, 4.28; N, 7.44. Found: C, 54.66; H, 4.34; N, 7.56.
4-Methyl-N-[3-phenyl-4-(phenylsulfonyl)azet-2(1H)-
ylidene]benzenesulfonamide (7d)
References and Notes
(1) Durckheimer, W.; Blumbach, J.; Lattrell, R.; Scheunemann,
K. H. Angew. Chem., Int. Ed. Engl. 1985, 24, 180.
(2) Barrett, A. G. M.; Sturgess, M. A. Tetrahedron 1988, 44,
5615.
(3) (a) Small Ring Heterocycles, In The Chemistry of
Heterocyclic Compounds; Hassner, A., Ed.; Wiley: New
York, 1983, Part 2, Vol. 42. (b) Small Ring Heterocycles, In
The Chemistry of Heterocyclic Compounds; Hassner, A.,
Ed.; Wiley: New York, 1985, Part 3, Vol. 42.
Pale yellow powder, mp 129–132 °C; yield 0.34 g (78%). IR
© Georg Thieme Verlag Stuttgart · New York
Synlett 2013, 24, 1420–1422

1422
I. Yavari, M. Nematpour
LETTER
N-[3-Butyl-4-tosylazet-2(1H)-ylidene]benzene-
(KBr): νmax = 3436, 2925, 1512, 1397, 1278, 1131, 1082 cm–
1. 1H NMR (500 MHz, CDCl3): δ = 2.48 (3 H, s, Me), 5.08
(1 H, s, NH), 7.29-7.36 (3 H, m, Ph), 7.40 (2 H, d, 3J = 7.7
Hz, Ar), 7.49 (2 H, d, 3J = 7.6 Hz, Ar), 7.62 (2 H, t, 3J = 7.7
Hz, Ar), 7.75 (1 H, t, 3J = 7.7 Hz, Ar), 7.91 (2 H, d, 3J = 7.9
Hz, Ar), 8.05 (2 H, d, 3J = 7.9 Hz, Ar). 13C NMR (125.7
MHz, CDCl3): δ = 32.2 (Me), 122.6 (C), 127.4 (2 CH), 127.5
(2 CH), 128.7 (2 CH), 129.2 (CH), 130.1 (2 CH), 130.7 (2
CH), 132.6 (2 CH), 135.7 (C), 136.0 (CH), 142.1 (C), 144.8
(C), 147.3 (C), 164.8 (C), 167.7 (C). MS (EI): m/z (%) = 438
(2) [M+], 361 (14), 347 (13), 283 (16), 196 (14), 155 (100),
141 (68), 91 (55), 77 (44). Anal. Calcd (%) for
sulfonamide (7h)
Yellow oil; yield 0.25 g (60%). IR (KBr): νmax = 3411, 2924,
1518, 1471, 1298, 1145, 1086 cm–1. 1H NMR (500 MHz,
CDCl3): δ = 0.90 (3 H, t, 3J = 6.9 Hz, Me), 1.39–1.45 (2 H,
m, CH2), 1.48–1.53 (2 H, m, CH2), 2.17 (2 H, t, 3J = 7.0 Hz,
CH2), 2.48 (3 H, s, Me), 5.09 (1 H, s, NH), 7.39 (2 H, d, 3J =
7.8 Hz, Ar), 7.62 (2 H, t, 3J = 7.8 Hz, Ar), 7.76 (1 H, t, 3J =
7.8 Hz, Ar), 7.91 (2 H, d, 3J = 8.0 Hz, Ar), 8.05 (2 H, d, 3J =
8.0 Hz, Ar). 13C NMR (125.7 MHz, CDCl3): δ = 14.0 (Me),
18.5 (CH2), 22.1 (CH2), 22.5 (CH2), 31.0 (Me), 122.4 (C),
127.4 (2 CH), 127.5 (2 CH), 130.1 (2 CH), 130.7 (2 CH),
135.7 (CH), 142.1 (C), 144.8 (C), 147.2 (C), 164.9 (C),
167.6 (C). MS (EI): m/z (%) = 418 (2) [M+], 361 (10), 341
(16), 277 (32), 155 (34), 141 (100), 91 (49), 77 (35), 57 (50).
Anal. Calcd (%) for C20H22N2O4S2 (418.10): C, 57.39; H,
5.30; N, 6.69. Found: C, 57.76; H, 5.44; N, 6.75.
N-[3-Butyl-4-tosylazet-2(1H)-ylidene]methane-
sulfonamide (7i)
Yellow oil; yield 0.21 g (58%). IR (KBr): νmax = 3513, 2934,
1524, 1408, 1279, 1118, 1044 cm–1. 1H NMR (500 MHz,
CDCl3): δ = 0.91 (3 H, t, 3J = 6.9 Hz, Me), 1.38–1.43 (2 H,
m, CH2), 1.47–1.51 (2 H, m, CH2), 2.17 (2 H, t, 3J = 7.0 Hz,
CH2), 2.48 (3 H, s, Me), 3.66 (3 H, s, Me), 5.07 (1 H, s, NH),
7.39 (2 H, d, 3J = 7.9 Hz, Ar), 7.91 (2 H, d, 3J = 7.9 Hz, Ar).
13C NMR (125.7 MHz, CDCl3): δ = 13.9 (Me), 18.5 (CH2),
22.1 (CH2), 22.3 (CH2), 31.0 (Me), 33.0 (Me), 122.6 (C),
127.5 (2 CH), 130.7 (2 CH), 142.1 (C), 147.3 (C), 162.2 (C),
167.5 (C). MS (EI): m/z (%) = 356 (2) [M+], 277 (12), 236
(10), 155 (39), 91 (45), 78 (100), 57 (46). Anal. Calcd (%)
for C15H20N2O4S2 (356.46): C, 50.54; H, 5.66; N, 17.86.
Found: C, 50.76; H, 5.74; N, 18.01.
C22H18N2O4S2 (438.07): C, 60.26; H, 4.14; N, 6.39. Found:
C, 60.69; H, 4.21; N, 6.44.
N-[3-Phenyl-4-(phenylsulfonyl)azet-2(1H)-ylidene]-
benzenesulfonamide (7e)
Pale yellow powder, mp 114–117 °C; yield 0.31 g (73%). IR
(KBr): νmax = 3450, 2922, 1511, 1264, 1140, 1082 cm–1. 1H
NMR (500 MHz, CDCl3): δ = 5.06 (1 H, s, NH), 7.31–7.36
(5 H, m, Ph), 7.51–7.53 (3 H, m, Ph), 7.59 (2 H, t, 3J = 7.7
Hz, Ar), 7.72 (1 H, t, 3J = 7.7 Hz, Ar), 7.98 (2 H, d, 3J = 7.9
Hz, Ar), 8.05 (2 H, d, 3J = 7.9 Hz, Ar). 13C NMR (125.7
MHz, CDCl3): δ = 122.6 (C), 127.4 (2 CH), 127.9 (2 CH),
128.8 (2 CH), 129.3 (CH), 130.2 (2 CH), 130.7 (CH), 132.6
(2 CH), 135.3 (CH), 135.7 (2 CH), 139.0 (C), 142.2 (C),
144.8 (C), 166.4 (C), 168.3 (C). MS (EI): m/z (%) = 424 (3)
[M+], 347 (13), 283 (8), 242 (10), 182 (21), 141 (100), 77
(34). Anal. Calcd (%) for C21H16N2O4S2 (424.06): C, 59.42;
H, 3.80; N, 6.60. Found: C, 59.69; H, 3.84; N, 6.57.
N-[3-Phenyl-4-(phenylsulfonyl)azet-2(1H)-ylidene]-
methanesulfonamide (7f)
Pale yellow powder, mp 90–93 °C; yield 0.25 g (70%). IR
(KBr): νmax = 3439, 1513, 1269, 1145, 1086 cm–1. 1H NMR
(500 MHz, CDCl3): δ = 3.60 (3 H, s, Me), 5.08 (1 H, s, NH),
7.29–7.36 (3 H, m, Ph), 7.47 (2 H, d, 3J = 7.7 Hz, Ar), 7.63
(2 H, t, 3J = 7.8 Hz, Ar), 7.74 (1 H, t, 3J = 7.8 Hz, Ar), 8.04
(2 H, d, 3J = 7.8 Hz, Ar). 13C NMR (125.7 MHz, CDCl3): δ
= 33.0 (Me), 122.5 (C), 127.4 (2 CH), 128.8 (2 CH), 129.3
(CH), 130.2 (2 CH), 132.6 (2 CH), 135.7 (CH), 142.3 (C),
147.8 (C), 164.6 (C), 167.4 (C). MS (EI): m/z (%) = 362 (2)
[M+], 285 (11), 242 (18), 221 (21), 141 (54), 78 (100), 77
(25). Anal. Calcd (%) for C16H14N2O4S2 (362.04): C, 53.02;
H, 3.89; N, 7.73. Found: C, 53.41.; H, 3.94; N, 7.80.
N-[3-Butyl-4-tosylazet-2(1H)-ylidene]-4-methylbenzene-
sulfonamide (7g)
(6) Whiting, M.; Fokin, V. V. Angew. Chem. Int. Ed. 2006, 45,
3157.
(7) Xu, X.; Cheng, D.; Li, J.; Guo, H.; Yan, J. Org. Lett. 2007,
9, 1585.
(8) Rostovtsev, V. V.; Green, L. G.; Fokin, V. V.; Sharpless, K.
B. Angew. Chem. Int. Ed. 2002, 41, 2596.
(9) Wang, J.; Wang, J.; Zhu, Y.; Lu, P.; Wang, Y. Chem.
Commun. 2011, 47, 3275.
(10) Cui, S. L.; Wang, J.; Wang, Y. G. Tetrahedron 2008, 64,
487.
(11) Yavari, I.; Nematpour, M. Synlett 2012, 23, 2215.
(12) Yavari, I.; Nematpour, M.; Yavari, S.; Sadeghizadeh, F.
Tetrahedron Lett. 2012, 53, 1889.
Yellow oil; yield 0.29 g (67%). IR (KBr): νmax = 3452, 2932,
1525, 1461, 1278, 1118 cm–1. 1H NMR (500 MHz, CDCl3):
δ = 0.91 (3 H, t, 3J = 6.9 Hz, Me), 1.28–1.45 (2 H, m, CH2),
1.47–1.53 (2 H, m, CH2), 2.18 (2 H, t, 3J = 7.0 Hz, CH2), 2.43
(3 H, s, Me), 2.48 (3 H, s, Me), 5.10 (1 H, s, NH), 7.39–7.41
(4 H, m, Ph), 7.83 (2 H, d, 3J = 8.0 Hz, Ar), 7.91 (2 H, d, 3J
= 8.0 Hz, Ar). 13C NMR (125.7 MHz, CDCl3): δ = 13.9 (Me),
18.5 (CH2), 22.1 (CH2), 22.2 (CH2), 31.0 (Me), 32.3 (Me),
122.2 (C), 127.5 (2 CH), 128.0 (2 CH), 130.6 (2 CH), 130.7
(2 CH), 132.3 (C), 136.0 (C), 144.3 (C), 146.6 (C), 162.6
(C), 166.2 (C). MS (EI): m/z (%) = 432 (2) [M+], 375 (16),
341 (13), 277 (21), 196 (31), 155 (100), 91 (51), 77 (41), 57
(52). Anal. Calcd (%) for C21H24N2O4S2 (432.12): C, 58.31;
H, 5.59; N, 6.48. Found: C, 58.71; H, 5.65; N, 6.55.
(13) Yavari, I.; Nematpour, M.; Ghazanfarpour-Darjani, M.
Tetrahedron Lett. 2012, 53, 942.
(14) Yavari, I.; Nematpour, M. Mol. Diversity 2012, 16, 651.
(15) Recently, Sharpless and co-workers established anhydrous
conditions with CuI in CHCl3/2,6-lutidine at 0 °C to prevent
intermediate 9 from decomposing and provide selective
formation of the desired 1-sulfonyltriazoles. See: Yoo, E. J.;
Ahlquist, M.; Kim, S. H.; Bae, I.; Fokin, V. V.; Sharpless, K.
B.; Chang, S. Angew. Chem. Int. Ed. 2007, 46, 1730.
(16) Cassidy, M. P.; Raushel, J.; Fokin, V. V. Angew. Chem. Int.
Ed. 2006, 45, 3154.
(17) Lu, P.; Wang, Y. Synlett 2010, 165.
(18) Yao, W.; Pan, L.; Zhang, Y.; Wang, G.; Wang, X.; Ma, C.
Angew. Chem. Int. Ed. 2010, 49, 9210.
Synlett 2013, 24, 1420–1422
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