Sulfonylimino group transfer reaction using imino-λ3-iodanes with I2 as catalyst under metal-free conditions

Article abstract of DOI:10.3390/molecules24050979

A new practical procedure of imination for sulfide has been developed. The treatment of (N-tosylimino)-phenyl-λ³-iodane, PhINTs, with various sulfides in the presence of a catalytic amount of I₂ under metal-free conditions affords the corresponding N-tosylsulfilimine compounds with moderate to good yields. This facile transfer procedure of the sulfonylimino group can also be applied to triphenylphosphine to produce the respective iminotriphenylphosphoranes in high yields. According to the reaction mechanism studies, the process of imination from (N-tosylimino)-phenyl-λ³-iodane to sulfide under the conditions may involve radical steps within the reaction mechanism.

Full text of DOI:10.3390/molecules24050979

molecules
Article
Sulfonylimino Group Transfer Reaction Using
Imino-λ3-iodanes with I2 as Catalyst Under
Metal-free Conditions
Akira Yoshimura 1,2,
*
, Cody L. Makitalo 2, Melissa E. Jarvi 2, Michael T. Shea 2,
Pavel S. Postnikov 1 , Gregory T. Rohde 3 , Viktor V. Zhdankin 2, Akio Saito 4
and Mekhman S. Yusubov 1
1
Research School of Chemistry and Applied Biomedical Sciences, The Tomsk Polytechnic University,
634050 Tomsk, Russia; postnikov@tpu.ru (P.S.P.); yusubov@mail.ru (M.S.Y.)
Department of Chemistry and Biochemistry, University of Minnesota Duluth, Duluth, MN 55812, USA;
2
makit003@d.umn.edu (C.L.M.); jarvi201@d.umn.edu (M.E.J.); sheax152@d.umn.edu (M.T.S.);
vzhdanki@d.umn.edu (V.V.Z.)
Marshall School, Duluth, MN 55811, USA; greg.rohde@marshallschool.org
3
4
Division of Applied Chemistry, Institute of Engineering, Tokyo University of Agriculture and Technology,
2-24-16 Naka-cho, Koganei, Tokyo 184-8588, Japan; akio-sai@cc.tuat.ac.jp
*
Correspondence: ayoshimu@d.umn.edu; Tel.: +7-382-260-6119
ꢀꢁꢂꢀꢃꢄꢅꢆꢇ
Academic Editor: Kazunori Miyamoto
Received: 13 February 2019; Accepted: 7 March 2019; Published: 11 March 2019
ꢀꢁꢂꢃꢄꢅꢆ
Abstract: A new practical procedure of imination for sulfide has been developed. The treatment
of (N-tosylimino)-phenyl-
3-iodane, PhINTs, with various sulfides in the presence of a catalytic
λ
amount of I2 under metal-free conditions affords the corresponding N-tosylsulfilimine compounds
with moderate to good yields. This facile transfer procedure of the sulfonylimino group can
also be applied to triphenylphosphine to produce the respective iminotriphenylphosphoranes
in high yields. According to the reaction mechanism studies, the process of imination from
(N-tosylimino)-phenyl-λ
3-iodane to sulfide under the conditions may involve radical steps within the
reaction mechanism.
Keywords: iminoiodanes; imination; sulfide; sulfilimine; phosphine; iminophosphorane; amidyl
radical; catalytic cycle; iodine
1. Introduction
Sulfur–carbon ylides and sulfur–heteroatom ylide compounds are widely used in many chemical
reactions as important transformational reagents [
have been demonstrated in organic synthesis. In particular, sulfur–nitrogen ylides [
sulfilimines, such as mono-aza analogues of sulfoxides, are common aziridination reagents [
1
–
5
]. Numerous reactions employing sulfide ylides
], N-sulfonyl
],
6–8
9
epoxidation reagents [10], or palladium metal ligands [11]. Sulfilimine compounds are also used
as efficient synthons for sulfoximines, which can be easily prepared by the appropriate oxidants,
and these compounds are used in medicinal or synthetic chemistry [12–15]. Synthetic methodologies
for directly introducing N-sulfonylimino groups to sulfide atom using oxidants with nitrogen source
have been developed [16–19].
Organohypervalent iodine compounds are known as efficient oxidative reagents for organic
synthesis because of the exceptionally high leaving ability of the iodobenzene group [20–24].
The versatile reactivity of hypervalent iodine(III) compounds allows for various bond formations,
some of which are otherwise difficult reactions in the absence of iodine(III) reagents. Particularly,
N-sulfonylimino-λ
3-iodanes represent an important class of hypervalent iodine(III) compounds,
Molecules 2019, 24, 979; doi:10.3390/molecules24050979
www.mdpi.com/journal/molecules

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which are commonly used as N-sulfonylimino group sources or selective oxidative reagents for various
organic substrates [25 27]. For example, the reaction of sulfides with (N-tosylimino)-phenyl-
3-iodane
in the presence of Cu, Mn, or Fe metal catalyst gave the corresponding sulfoximine compounds
(Scheme 1a) [28 33]. However, a metal-free condition for reactions is a significant goal in the
development of eco-friendly reaction methodology. Recently, Lamar and Nicholas reported the
C-H amidation reaction of saturated or unsaturated hydrocarbons using imino-
3-iodanes in the
–
λ
–
λ
presence of a catalytic amount of elemental iodine under transition metal-free conditions [34]. Lamar’s
group also reported the imidation reaction of aldehydes under similar reaction conditions [35].
Metal-free aziridination reactions of styrenes using (N-tosylimino)-phenyl-λ
3-iodane in the presence of
I2-tetrabutylammonium iodide combination have been developed by Minakata and co-worker [36].
To the best of our knowledge, however, I2 mediated metal-free imination reactions of sulfides using
imino-
reaction from imino-
λ
3-iodanes have not been developed. In this paper, we report the sulfonylimino group transfer
λ
3-iodane to sulfide atom under metal-free conditions (Scheme 1b). Reaction
mechanisms of this sulfonylimino group transfer reaction may involve the radical process under
reaction conditions.
Scheme 1. Transfer reaction of sulfonylimino groups from imino-
(a) Metal-catalyzed imidation reaction of sulfides, (b) Metal-free imidation reaction of sulfides.
λ
3-iodane to sulfide atom.
2. Results
2.1. Optimization of Reaction Conditions
Our approach to metal-free sulfonylimino group transfer reaction is based on previously
reported reaction conditions such as (N-tosylimino)-phenyl-
a catalyst [34 36]. In the initial experiment, we investigated the reaction of thioanisole 1a (1 equiv.) with
(N-tosylimino)-phenyl-
3-iodane 2a (1.2 equiv.) in the presence of a catalytic amount of both I2 and
λ
3-iodane in the presence of I2 as
,
λ
tetrabutylammonium iodide (TBAI) as an additive under various solvents at room temperature (Table 1,
entries 1–9). We have found that dichloromethane is an efficient solvent for the metal-free imination
reaction of thioanisole 1a using (N-tosylimino)-phenyl-λ
3-iodane 2a. The presence of TBAI as an
additive did not affect this reaction (entry 10). However, in the absence of I2 as a catalyst, the reaction
dramatically changed, resulting in a low yield of the formation of the desired N-tosyl sulfilimine
3a (entries 11 and 12). Extension of the reaction time was effective for the desired product 3a yield
(entry 14). Decreasing the amount of I2 catalyst from 10 mol% to 2 mol% increased the yield of N-tosyl
sulfilimine 3a (entries 14–16). These results implied that the slow generation of the activated species was
very important for this reaction because the species generated from (N-tosylimino)-phenyl-λ
3-iodane
2a and I2 were probably unstable in the reaction mixtures. Meanwhile, further reduction of the amount
of I2 catalyst and a longer reaction time led to a decreased amount of the desired product 3a (entries 17
and 18). Finally, performing the reaction under the dark conditions slightly suppressed the product
yield, which supports a radical pathway in the reaction mixtures (entry 19) [36].

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Table 1. Optimization of imination reaction of thioanisole 1a using (N-tosylimino)-phenyl-λ .
3-iodane 2a 1
Entry
Time (h)
Solvent
I2 (mol%)
TBAI (mol%)
3a Yield (%) 2
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19 3
3
3
3
3
3
3
3
3
3
3
3
3
3
24
24
24
24
48
24
MeCN
Hexane
AcOEt
MeOH
THF
Et2O
PhH
CCl4
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
20
20
20
20
20
20
20
20
20
20
none
none
10
10
5
10
10
10
10
10
10
10
10
10
81 (80)
15
49
77
4
Trace
47
7
83 (83)
84
7
5
72
87
91
92 (88)
68
66
77
none
10
none
none
none
none
none
none
none
none
2
1
1
2
1 Reaction conditions: thioanisole 1a (0.20 mmol, 1 equiv.), iminoiodane 2a (0.24 mmol, 1.2 equiv.), and I2 (0–20 mol%)
2
with TBAI (0–10 mol%) stirred in a solvent (2 mL) at room temperature for 3–48 h. Yields of product 3a determined
3
from 1H NMR spectra of reaction mixtures are shown (numbers in parentheses show isolated yield of 3a). The
reaction was performed under dark conditions.
2.2. Scope of Reactions
According to the optimized conditions with 2 mol% I2, we have investigated the conversion
of various substituted sulfides
of thioanisoles 1a–i with either electron-donating or electron-withdrawing substituents using
(N-tosylimino)-phenyl-
3-iodane 2a in the presence of I2 as the catalyst gave the corresponding
1 to the corresponding sulfilimines 3. In general, the reactions
λ
N-tosyl sulfilimine compounds 3a-i in moderate to good yields (Table 2, entries 1–9). In the reaction
of the sterically hindered o-chlorothioanisole 1f or the strong electron-withdrawing substituted
p-nitrothioanisole 1i, products
diphenylsulfide 1j, benzyl phenyl sulfide 1k, and dibenzyl sulfide 1l gave the respective products 3j–k
in moderate yields (entries 10–12). This reaction also worked for the acyclic or cyclic aliphatic sulfides
3 were obtained in 59–69% yields (entries 6 and 9). The reaction of
1
1m-p to give the desired sulfilimines 3m-p in good yields (entries 13–16). However, the reaction
with the most steric bulky sulfide, di-tert-butyl sulfide 1q, afforded the desired product 3q in
only 8% (entry 17). As expected, the reaction of 1a using imino-λ
3-iodanes 2b–d with different
substituents afforded the corresponding sulfilimines 3r–s in moderate to good yields (entries 18–20).
This metal-free procedure gave comparable or higher yields of sulfilimines compared to the previously
reported metal catalyst mediated N-tosyl sulfonylimino group transfer reaction to sulfide from
(N-tosylimino)-phenyl-
optimized conditions gave the desired product 3a in 76%.
λ –33]. Particularly, the scaled up reaction of 1a (1 mmol) under
3-iodane [28

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1
Table 2. Metal-free imination reaction of thioanisoles 1 with imino-λ3-iodane 2 in the presence of I2
.
Entry
1 R1, R2
2 R3
3 Yield(%) 2
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
1a Ph, Me
1bp-tol, Me
2ap-Tol
2ap-Tol
2ap-Tol
2ap-Tol
2ap-Tol
2ap-Tol
2ap-Tol
2ap-Tol
2ap-Tol
2ap-Tol
2ap-Tol
2ap-Tol
2ap-Tol
2ap-Tol
2ap-Tol
2ap-Tol
2ap-Tol
3a 88% (76%) 3
3b 72%
3c 78%
3d 79%
3e 80%
3f 68%
3g 70%
3h 86%
3i 59%
1cp-MeOC6H4, Me
1dp-ClC6H4, Me
1em-ClC6H4, Me
1fo-ClC6H4, Me
1gp-BrC6H4, Me
1hp-NCC6H4, Me
1ip-NO2C6H4, Me
1j Ph, Ph
1k Ph, Bn
1l Bn, Bn
1mnBu, nBu
1nnOctyl, nOctyl
1o –(CH2)3–
1p –(CH2)4–
1qtBu, tBu
3j 56%
3k 65%
3l 66%
3m 79%
3n 90%
3o 97%
3p 76%
3q 8%
3r 92%
3s 51%
3t 67%
1a Ph, Me
1a Ph, Me
1a Ph, Me
2bp-NO2C6H4
2co-NO2C6H4
2d Ph
1
All reactions were performed using sulfide
1
(0.20 mmol, 1 equiv.) and imino-
λ
3-iodane
2
(0.24 mmol, 1.2 equiv.)
2
3
using I2 (2 mol%) in dichloromethane (2.0 mL) at room temperature for 24 h. Yields of isolated products. Large
scale experiment: thioanisole 1a (1.0 mmol, 1 equiv.) and imino-
in the dichloromethane (10 mL) were stirred for 24 h at room temperature.
λ 2 (1.2 mmol, 1.2 equiv.) using I2 (2 mol%)
3-iodane
Moreover, the reaction of triphenylphosphine
optimized conditions also allowed the transfer reaction of N-tosyl sulfonylimino group to give the
(N-tosylimino)-triphenylphosphorane in excellent yield (Scheme 2). The structure of was confirmed
by a single crystal X-ray crystallography (see Supplementary Materials) [37]. Compared to the
previously reported preparation of using imino-
3-iodanes, our reaction proceeds under very mild
4 with (N-tosylimino)-phenyl-λ
3-iodane 2a under
5
5
5
λ
conditions and affords the product in higher yields [38,39].
Scheme 2. Transfer reaction of N-tosyl sulfonylimino groups to triphenylphosphine 4.
3. Discussion
3.1. Mechanistic Study
To clarify the mechanism of metal-free sulfonylimino group transfer reaction, we have
performed several blank experiments (Scheme 3). Based on the previously reported experiment,
a amidyl radical precursor like N,N-diiodotosylamide or a related species might be generated from
3-iodane 2a with I2 [34
(N-tosylimino)-phenyl-λ –36,40]. A radical mechanism is plausible because

Molecules 2019, 24, 979
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performing the reaction under dark conditions results in relatively low yields of product 3a (Table 1,
entry 20). Therefore, the presence of a radical scavenger such as TEMPO or BHT in the reaction would
be effective for identification of the reaction mechanism. In the case of both reactions, the desired
sulfilimine 3a was detected in the reaction mixtures in low yields around 11% as compared to 88%
without the radical scavenger, which implies that the amidyl radical species were involved under
the reaction mixture. When benzene was added to the reaction instead of thioanisole 1a, azepine or
N-phenyl-p-toluenesulfonamide was not detected and only p-toluenesulonamide was recovered from
the reaction mixtures. This result suggested that highly active nitrene species were not present under
the reaction conditions.
Scheme 3. Blank experiments of imination reaction.
3.2. Proposed Reaction Mechanism
From blank experiments and previously related results involving the amidyl radical species from
imino-
Initially, (N-tosylimino)-phenyl-
(or related species) followed by generation of the amidyl radical
reaction conditions. The generated amidyl radical
intermediate compound , followed by loss of iodine radical to give the desired sulfilimine product 3a
λ –36,40], we proposed the reaction mechanism of imination (Scheme 4).
3-iodane 2a with I2 [34
λ
3-iodane 2a reacted with I2 to produce N,N-diiodotosylamide
6
7
and iodine radical under the
7
was trapped by thioanisole 1a to afford the
8
and reproduced I2. The regenerated I2 would continue the next catalytic cycle.
Scheme 4. Proposed reaction mechanism.

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4. Materials and Methods
4.1. General Experimental Remarks
All reactions were performed under dry argon atmosphere with flame-dried glassware.
All commercial reagents were ACS reagent grade and used without further purification.
Dichloromethane was distilled from CaH2 immediately prior to use. Melting points were determined in
an open capillary tube with a Mel-temp II melting point apparatus. Infrared spectra were recorded on
a Perkin-Elmer 1600 series FT-IR spectrophotometer, and peaks were reported in reciprocal centimeters
(cm–1). 1H NMR spectra were recorded on a Varian Inova 500 and 300 MHz NMR spectrometer;
13C NMR spectra were recorded on Varian Inova 500 and Varian 300 MHz NMR spectrometers at
1
125 and 75 MHz, respectively. Chemical shifts are reported in parts per million (ppm). H and 13
C
chemical shifts are referenced relative to tetramethylsilane. X-ray crystal analysis was performed
by Rigaku RAPID II XRD Image Plate using graphite-monochromated MoK radiation ( = 0.71073
41], (N-p-nosylimino)phenyl- 42],
3-iodane 2b
43], and N-(phenylsulfonylimino)-phenyl- 44
3-iodane 2d
α
λ
Å) at 173 K. (N-p-Tosylimino)phenyl-
λ
3-iodane 2a
[
λ
[
(N-o-nosylimino)phenyl-
λ
3-iodane 2c
[
λ
[ ]
were prepared according to the reported procedures.
4.2. General Procedure for Imination of Sulfides 1 with Imino-phenyl-λ3-iodane 2 in the Presence of I2
Imino- (0.12–0.24 mmol) was added at room temperature to a stirred mixture of sulfide
3-iodane
λ
2
1
(0.10–0.20 mmol) and I2 (0.002–0.004 mmol) in dichloromethane (1.0–2.0 mL). The reaction was
stirred at room temperature for 24 h. After the reaction, 5% aqueous Na2S2O3 (2.5–5.0 mL) was added
to the mixture and the solution was extracted with ethyl acetate. The organic layer was dried over
anhydrous Na2SO4 and concentrated under reduced pressure. The residue was separated by column
chromatography using the Hexane-EtOAc (1:1 to 0:100) to afford the pure product 3.
S-Methyl-S-phenyl-N-p-tosyl-sulfilimine (3a) [45]. Reaction of thioanisole 1a (25 mg, 0.20 mmol)
according to the general procedure afforded 52 mg (88%) of product 5a, isolated as a white solid: mp
129–130 ◦C (lit. [45]; mp 131.5–132 ◦C); 1H NMR (500 MHz, CDCl3): δ 7.73 (d, J = 8.5 Hz, 2H), 7.69 (d,
J = 8.0 Hz, 2H), 7.56–7.46 (m, 3H), 7.16 (d, J = 8.5 Hz, 2H), 2.84 (s, 3H), 2.37 (s, 3H).
S-Methyl-S-(4-tolyl)-N-p-tosyl-sulfilimine (3b) [29]. Reaction of methyl(4-tolyl)sulfide 1b (28 mg,
0.20 mmol) according to the general procedure afforded 44 mg (72%) of product 3b, isolated as a light
brown oil; 1H NMR (500 MHz, CDCl3):
δ
7.72 (d, J = 8.3 Hz, 2H), 7.57 (d, J = 8.5 Hz, 2H), 7.28 (d, J = 8.3
Hz, 2H), 7.16 (d, J = 8.5 Hz, 2H), 2.82 (s, 3H), 2.39 (s, 3H), 2.35 (s, 3H).
S-Methyl-S-(4-methoxyphenyl)-N-p-tosyl-sulfilimine 3c 46]. of
(
)
[
Reaction
4-methoxyphenyl(methyl)sulfide 1c (31 mg, 0.20 mmol) according to the general procedure
afforded 51 mg (78%) of product 3c, isolated as a white solid: mp 147 ◦C (lit. [46]; mp 146–147 ◦C);
1H NMR (500 MHz, CDCl3):
δ
7.68 (d, J = 7.3 Hz, 2H), 7.59 (d, J = 8.3 Hz, 2H), 7.13 (d, J = 7.3 Hz, 2H),
6.94 (d, J = 8.3 Hz, 2H), 3.81 (s, 3H), 2.80 (s, 3H), 2.33 (s, 3H).
S-Methyl-S-(4-chlorophenyl)-N-p-tosyl-sulfilimine 3d
(
)
[
46].
Reaction
of
4-chlorophenyl(methyl)sulfide 1d (32 mg, 0.20 mmol) according to the general procedure afforded 52
mg (79%) of product 3d, isolated as a light yellow solid: mp 111–112 ◦C (lit. [46]; mp 112–113 ◦C);
1H NMR (500 MHz, CDCl3):
δ 7.71 (d, J = 8.0 Hz, 2H), 7.64 (d, J = 8.5 Hz, 2H), 7.45 (d, J = 8.5 Hz, 2H),
7.17 (d, J = 8.0 Hz, 2H), 2.84 (s, 3H), 2.36 (s, 3H).
S-Methyl-S-(3-chlorophenyl)-N-p-tosyl-sulfilimine
(
3e
)
[
47].
Reaction
of
3-chlorophenyl(methyl)sulfide 1e (32 mg, 0.20 mmol) according to the general procedure afforded 53
mg (80%) of product 3e, isolated as a white solid: mp 137–138 ◦C; 1H NMR (500 MHz, CDCl3):
δ
7.68
(d, J = 8.0 Hz, 2H), 7.61 (s, 1H), 7.53 (d, J = 7.8 Hz, 1H), 7.44 (d, J = 7.8 Hz, 1H), 7.39 (t, J = 7.8 Hz, 1H),
7.15 (d, J = 8.0 Hz, 2H), 2.83 (s, 3H), 2.33 (s, 3H).
S-Methyl-S-(2-chlorophenyl)-N-p-tosyl-sulfilimine
2-chlorophenyl(methyl)sulfide 1f (32 mg, 0.20 mmol) according to the general procedure afforded
45 mg (68%) of product 3f, isolated as a white solid: mp 149–150 ◦C; 1H NMR (500 MHz, CDCl3):
(3f
)
[
48].
Reaction
of
δ

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8.12 (d, J = 7.5 Hz, 1H), 7.71 (d, J = 8.3 Hz, 2H), 7.52–7.41 (m, 3H), 7.20 (d, J = 8.3 Hz, 2H), 2.87 (s, 3H),
2.36 (s, 3H).
S-Methyl-S-(4-bromophenyl)-N-p-tosyl-sulfilimine
(
3g
)
[49].
Reaction
of
4-bromophenyl(methyl)sulfide 1g (41 mg, 0.20 mmol) according to the general procedure
afforded 52 mg (70%) of product 3g, isolated as a white solid: mp 110–111 ◦C; 1H NMR (500 MHz,
CDCl3):
δ 7.70 (d, J = 8.0 Hz, 2H), 7.60 (d, J = 9.0 Hz, 2H), 7.55 (d, J = 9.0 Hz, 2H), 7.16 (d, J = 8.0 Hz,
2H), 2.83 (s, 3H), 2.35 (s, 3H).
S-Methyl- S-(4-cyanophenyl)-N-p-tosyl-sulfilimine (3h). Reaction of 4-cyanophenyl(methyl)sulfide
1h (30 mg, 0.20 mmol) according to the general procedure afforded 55 mg (86%) of product 3h, isolated
as a light brown solid: mp 159–160 ◦C; IR (neat) cm−1: 3096, 3035, 2929, 2856, 2234, 1400, 1144, 758;
1H NMR (500 MHz, CDCl3):
δ
7.83 (d, J = 8.5 Hz, 2H), 7.74 (d, J = 8.5 Hz, 2H), 7.69 (d, J = 8.3 Hz, 2H),
142.3, 141.6, 140.7, 133.5,
7.17 (d, J = 8.3 Hz, 2H), 2.87 (s, 3H), 2.35 (s, 3H); 13C NMR (75 MHz, CDCl3):
δ
129.4, 126.6, 126.2, 117.1, 116.1, 38.8, 21.4; HRMS (ESI-TOF-positive mode): calcd for C15H14N2NaO2S2
([M + Na])+: 341.0394, found: 341.0382.
S-Methyl-S-(4-nitrophenyl)-N-p-tosyl-sulfilimine (3i) [50]. Reaction of 4-nitrophenyl(methyl)sulfide
1i (34 mg, 0.20 mmol) according to the general procedure afforded 40 mg (59%) of product 3i, isolated
◦
◦
as a yellow solid: mp 161–163 C (lit. [50]; mp 150 C); 1H NMR (500 MHz, CDCl3):
δ 8.33 (d, J = 9.0 Hz,
2H), 7.93 (d, J = 9.0 Hz, 2H), 7.74 (d, J = 8.0 Hz, 2H), 7.21 (d, J = 8.0 Hz, 2H), 2.92 (s, 3H), 2.37 (s, 3H).
S,S-Diphenyl-N-p-tosyl-sulfilimine (3j) [29]. Reaction of diphenylsulfide 1j (37 mg, 0.20 mmol)
according to the general procedure afforded 40 mg (56%) of product 3j, isolated as a white solid:
mp 108–109 ◦C (lit. [29]; mp 109.0–109.5 ◦C); 1H NMR (500 MHz, CDCl3):
δ 7.74 (d, J = 9.0 Hz, 2H),
7.64–7.59 (m, 4H), 7.52–7.41 (m, 6H), 7.14 (d, J = 8.5 Hz, 2H), 2.33 (s, 3H).
S-Phenyl-S-benzyl-N-p-tosyl-sulfilimine (3k) [29]. Reaction of benzyl(phenyl)sulfide 1k (20 mg,
0.1 mmol) according to the general procedure afforded 24 mg (65%) of product 3k, isolated as a white
solid: mp 149–150 ◦C (lit. [29]; mp 147–148 ◦C); 1H NMR (500 MHz, CDCl3):
δ 7.62 (d, J = 8.0 Hz, 2H),
7.55–7.48 (m, 3H), 7.45–7.38 (m, 2H), 7.31–7.25 (m, 1H), 7.18 (t, J = 7.5 Hz, 2H), 7.07 (d, J = 8.0 Hz, 2H),
6.98 (d, J = 7.5 Hz, 2H), 4.34 (d, J = 12.8 Hz, 1H), 4.13 (d, J = 12.8 Hz, 1H), 2.32 (s, 3H).
S,S-Dibenzyl-N-p-tosyl-sulfilimine (3l) [51]. Reaction of dibenzylsulfide 1l (43 mg, 0.20 mmol)
according to the general procedure afforded 51 mg (66%) of product 3l, isolated as a white solid: mp
187–189 ◦C (lit. [51]; mp 191–193 ◦C); 1H NMR (500 MHz, CDCl3):
δ 7.43 (d, J = 8.0 Hz, 2H), 7.36–7.26
(m, 6H), 7.22 (d, J = 7.5 Hz, 4H), 6.97 (d, J = 8.0 Hz, 2H), 4.14 (d, J = 13.0 Hz, 2H), 4.06 (d, J = 13.0 Hz,
1H), 2.32 (s, 3H).
S,S-Dibutyl-N-p-tosyl-sulfilimine (3m) [49]. Reaction of dibutylsulfide 1m (29 mg, 0.20 mmol)
according to the general procedure afforded 52 mg (79%) of product 3m, isolated as a white solid: mp
64–65 ◦C (lit. [49]; mp 77.5–78.5 ◦C); 1H NMR (500 MHz, CDCl3):
δ 7.77 (d, J = 7.5 Hz, 2H), 7.23 (d,
J = 7.5 Hz, 2H), 2.88-2.78 (m, 2H), 2.77–2.68 (m, 2H), 2.38 (s, 3H), 1.59–1.46 (m, 4H), 1.36–1.22 (m, 4H),
0.82 (t, J = 7.0 Hz, 6H).
S,S-Dioctyl-N-p-tosyl-sulfilimine (3n). Reaction of dioctylsulfide 1n (52 mg, 0.20 mmol) according
to the general procedure afforded 77 mg (90%) of product 3n, isolated as a white solid: mp 82 ◦C; IR
(neat) cm−1: 2918, 2858, 1384, 1139, 716; 1H NMR (500 MHz, CDCl3):
δ
7.79 (d, J = 8.3 Hz, 2H), 7.22 (d,
J = 8.3 Hz, 2H), 2.89–2.80 (m, 2H), 2.73–2.64 (m, 2H), 2.39 (s, 3H), 1.64–1.58 (m, 4H), 1.34–1.12 (m, 20H),
0.88 (t, J = 7.3 Hz, 6H); 13C NMR (75 MHz, CDCl3):
δ 141.6, 141.5, 129.1, 126.3, 49.0, 31.7, 28.9, 28.9,
28.3, 22.8, 22.6, 14.1; HRMS (ESI-TOF-positive mode): calcd for C23H42NO2S2 ([M + H])+: 428.2657,
found: 428.2665.
S-(p-Tosylimino)thietane (3o) [52]. Reaction of thietane 1o (15 mg, 0.20 mmol) according to t◦he
general procedure afforded 47 mg (97%) of product 3o, isolated as a white solid: mp 103–104 C
(lit. [52]; mp 98 ◦C); 1H NMR (500 MHz, CDCl3):
δ
7.76 (d, J = 8.1 Hz, 2H), 7.25 (d, J = 8.1 Hz, 2H),
4.26–4.08 (m, 2H), 3.70–3.57 (m, 2H), 2.62–2.16 (m, 5H).
S-(N-p-Tosylimino)thiolane (3p) [53]. Reaction of tetrahydrothiophene 1p (18 mg, 0.20 mmol)
according to the general procedure afforded 45 mg (76%) of product 3p, isolated as a white solid: mp

Molecules 2019, 24, 979
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131–133 ◦C (lit. [53]; mp 132–134 ◦C); 1H NMR (300 MHz, CDCl3):
δ
7.79 (d, J = 8.1 Hz, 2H), 7.25 (d,
J = 8.1 Hz, 2H), 3.19–3.00 (m, 4H), 2.58–2.42 (m, 2H), 2.40 (s, 3H), 2.11–1.93 (m, 2H); 13C NMR (75 MHz,
CDCl3): δ 143.6, 139.1, 129.5, 126.5, 54.5, 25.6, 21.5.
S,S-Di-tert-butyl-N-p-tosyl-sulfilimine (3q) [54]. Reaction of di-tert-butylsulfide 1q (29 mg,
0.20 mmol) according to the general procedure afforded 5 mg (8%) of product 3q, isolated as a colorless
oil; 1H NMR (500 MHz, CDCl3):
δ 7.86 (d, J = 8.8 Hz, 2H), 7.33 (d, J = 8.8 Hz, 2H), 2.46 (s, 3H), 1.43 (s,
18H); 13C NMR (75 MHz, CDCl3): δ 144.5, 129.8, 129.5, 128.8, 49.6, 30.6, 21.7.
S-Methyl-S-phenyl-N-p-nosyl-sulfilimine (3r) [55]. Reaction of thioanisole 1a (25 mg, 0.20 mmol)
with imino-
of product 3r, isolated as a white solid: mp 167 C (lit. [55]; mp 164–165 C); H NMR (300 MHz,
λ
3-iodane 2b (97 mg, 0.24 mmol) according to the general procedure afforded 61 mg (92%)
◦
◦
1
CDCl3):
δ 8.20 (d, J = 8.7 Hz, 2H), 8.00 (d, J = 8.7 Hz, 2H), 7.70 (d, J = 8.1 Hz, 2H), 7.62-7.46 (m, 3H),
2.93 (s, 3H); 13C NMR (75 MHz, CDCl3): δ 149.8, 149.2, 135.1, 133.1, 130.3, 127.4, 125.9, 124.0, 39.2.
S-Methyl-S-phenyl-N-o-nosyl-sulfilimine (3s). Reaction of thioanisole 1a (25 mg, 0.20 mmol) with
imino-
product 3s, isolated as a colorless oil; IR (neat) cm−1: 3096, 3065, 3023, 2926, 1540, 1370, 1305, 1149,
1124, 852, 766; 1H NMR (300 MHz, CDCl3):
8.16 (d, J = 6.0 Hz, 1H), 7.79 (d, J = 8.1 Hz, 2H), 7.66–7.49
(m, 6H), 2.95 (s, 3H); 13C NMR (75 MHz, CDCl3):
147.5, 137.1, 136.2, 132.6, 132.2, 131.8, 130.3, 130.1,
λ
3-iodane 2c (97mg, 0.24 mmol) according to the general procedure afforded 33 mg (51%) of
δ
δ
125.8, 123.7, 39.1; HRMS (ESI-TOF-positive mode): calcd for C13H13N2O4S2 ([M + H])+: 325.0317,
found: 325.0319.
S-Methyl-S-phenyl-N-phenylsulfonyl-sulfilimine (3t) [56]. Reaction of thioanisole 1a (25 mg,
0.20 mmol) with imino-λ
3-iodane 2d (86 mg, 0.24 mmol) according to the general procedure afforded
38 mg (67%) of product 3t, isolated as a white solid: mp 89–90 ◦C; 1H NMR (300 MHz, CDCl3):
(d, J = 7.8 Hz, 2H), 7.68 (d, J = 8.1 Hz, 2H), 7.57-7.32 (m, 6H), 2.85 (s, 3H).
δ 7.85
4.3. Large Scale Reaction of 1a
Imino-λ
3-iodane 2a (448 mg, 1.20 mmol) was added at room temperature to a stirred mixture of
thioanisole 1a (124 mg, 1.00 mmol) and I2 (5 mg, 0.02 mmol) in dichloromethane (10.0 mL). The reaction
was stirred at room temperature for 24 h. After reaction, 5% aqueous Na2S2O3 (25 mL) was added
to the mixture and the solution was extracted with ethyl acetate. The organic layer was dried over
anhydrous Na2SO4 and concentrated under reduced pressure. The residue was separated by column
chromatography using the Hexane-EtOAc (1:1) to afford the pure product 3a in 76% (223 mg).
4.4. Reaction of Triphenylphosphine 4
Imino-
triphenylphosphine
λ
3-iodane 2a (90 mg, 0.24 mmol) was added at room temperature to a stirred mixture of
(52 mg, 0.20 mmol) and I2 (1 mg, 0.004 mmol) in dichloromethane (2.0 mL).
4
The reaction was stirred at room temperature for 24 h. After reaction, 5% aqueous Na2S2O3 (2.5 mL)
was added to the mixture and the solution was extracted with ethyl acetate. The organic layer was
dried over anhydrous Na2SO4 and concentrated under reduced pressure. The residue was separated
by preparative TLC using the Hexane-EtOAc (1:1) to afford the pure product 5 in 98% (84 mg).
◦
N-(p-Tosyl)◦iminotriphenylphosphorane (
5
) [39]. Isolated as a white solid: mp 190 C (lit. [39];
mp 185.5–186.2 C); 1H NMR (500 MHz, CDCl3):
δ 7.44 (dd, J = 12.3 Hz, 7.8 Hz, 2H), 7.57 (t, J = 7.8 Hz,
3H), 7.50 (d, J = 7.8 Hz, 2H), 7.46 (dt, J = 7.8 Hz, 3.0 Hz, 6H), 7.00 (d, J = 7.8 Hz, 2H), 2.23 (s, 3H).
Single crystals of product suitable for X-ray crystallographic analysis were obtained by slow
5
crystallization from dichloromethane solution. X-ray diffraction data for
previously reported compound [37].
5 was identical to the
5. Conclusions
In conclusion, we have developed the metal-free methodology of the sulfonyl group transfer
reaction of sulfides or triphenylphosphine using imino- in the presence of
3-iodanes
a catalytic amount of I2. The novel procedure gives the corresponding (N-sulfonyl)-sulfilimines
1
4
λ
2

Molecules 2019, 24, 979
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3
or (N-tosylimino)-triphenylphosphorane
5
in moderate to good yields. According to the blank
experiment study, the reaction mechanism most likely involved the amidyl radical species, which are
generated from imino-λ3-iodanes 2 and I2.
Supplementary Materials: The following are available online. The 1H and 13C NMR spectra of 3a–t
structure data of 5 can be found in the SI.
, 5, and X-ray
Author Contributions: Conceptualization, A.Y.; Methodology, A.Y. and C.L.M.; Investigation, C.L.M.; Resources,
C.L.M., P.S.P. and M.S.Y.; Data Analysis, C.L.M., M.E.J., M.T.S. and P.S.P.; Data Discussion, A.Y., C.L.M., G.T.R. and
A.S.; X-Ray Analysis, G.T.R.; Writing—Original Draft Preparation, A.Y.; Writing—Review and Editing, A.Y., C.L.M.,
G.T.R., A.S. and V.V.Z.; Supervision, A.Y.; Project administration, A.Y.; Funding acquisition, A.Y., M.S.Y. and A.S.
Funding: This work was supported by a research grant from the Russian Science Foundation (RSF-16-13-10081
and RSF-19-13-00011) and the Tomsk Polytechnic University Competitiveness Enhancement Program. A.S. is also
thankful to JSPS Fund for the Promotion of Joint International Research (Grant No 16KK0199).
Conflicts of Interest: The authors declare no conflict of interest.
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Sample Availability: Samples of the compounds 2a and 3a are available from the authors.
©
2019 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access
article distributed under the terms and conditions of the Creative Commons Attribution
(CC BY) license (http://creativecommons.org/licenses/by/4.0/).