Selective and mild sulfoxidation of 2-sulfylbenzothiazole using hydroperoxides derived from cyclohexanone in the absence of catalyst

Article abstract of DOI:10.1016/j.tet.2021.132203

Alkyl hydroperoxides derived from cyclohexanone are attractive oxidants because they are easily available, more reactive than TBHP but much less acidic than m-CPBA. Wherein 1,1′-peroxybis(1-hydroperoxycyclohexane) (C) can be generated by the current simply method and displays the excellent reactivity and selectivity based on oxidative reactions of various benzothiazolyl sulfides substituted by different function groups. The research found that the reactions can be performed in the absence of catalyst and under very mild conditions optimized. Yields of sulfoxides is higher than 90%, no or a little reaction happened at the proximal double bond、 N and S atoms in the benzothiazolyl moiety. Phenyl sulfide as the substrates was also examined for the reaction scope test. The results show that they were uniquely and completely oxidized to sulfoxides in 1 h. A mild, environmentally friendly, catalyst-free aryl sulfide sulfoxidation method has been developed.

Full text of DOI:10.1016/j.tet.2021.132203

Tetrahedron xxx (xxxx) xxx
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Selective and mild sulfoxidation of 2-sulfylbenzothiazole using
hydroperoxides derived from cyclohexanone in the absence of catalyst
Shihao Zhu, Chunmian Yu, Wenjun Shi, Xinrui Zhou*
State Key Laboratory of Fine Chemicals, Dalian University of Technology, Dalian, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Alkyl hydroperoxides derived from cyclohexanone are attractive oxidants because they are easily
available, more reactive than TBHP but much less acidic than m-CPBA. Wherein 1,10-peroxybis(1-
hydroperoxycyclohexane) (C) can be generated by the current simply method and displays the excel-
lent reactivity and selectivity based on oxidative reactions of various benzothiazolyl sulfides substituted
by different function groups. The research found that the reactions can be performed in the absence of
catalyst and under very mild conditions optimized. Yields of sulfoxides is higher than 90%, no or a little
reaction happened at the proximal double bond、 N and S atoms in the benzothiazolyl moiety. Phenyl
sulfide as the substrates was also examined for the reaction scope test. The results show that they were
uniquely and completely oxidized to sulfoxides in 1 h. A mild, environmentally friendly, catalyst-free aryl
sulfide sulfoxidation method has been developed.
Received 1 March 2021
Received in revised form
23 April 2021
Accepted 29 April 2021
Available online xxx
Keywords:
Cyclohexanone hydroperoxide
2-Sulfylbenzothiazole
Sulfoxide
© 2021 Elsevier Ltd. All rights reserved.
Selective oxidation
1. Introduction
ether with anhydrous H2O2. By elemental analysis, Milas identified
cyclohexanone peroxide as compound D. Later, this method was
Organic peroxide plays an important role in various types of
oxidative reactions especially in non-aqueous systems. Among
them one mostly used is alkyl hydroperoxide like TBHP [1]. How-
ever, alkyl hydroperoxide normally is too mild to react with the
substrates, the catalysts like mineral acid or metal oxides are
needed. Another one is peroxy acid such as peroxyacetic acid, m-
CPBA [2], etc., which are both oxidant and acidic catalyst. They are
very active, unfortunately, they can be unexpectedly too active to
keep the selectivity and from severe corrosion on surface of the
metallic equipment.
Alkyl peroxides derived from cyclohexanone [3] (CPO, Fig. 1) are
neutral and some are more reactive than tert-butyl hydroperoxide
and tert-amyl hydroperoxide hydroperoxide [4] as reported in our
previous research. They can be prepared respectively from cyclo-
hexanone using aqueous H2O2 or cyclohexanol using O2 as oxidant.
They have highly steric hindrance, which might provide the pos-
sibility for selective oxidation of certain compounds through spatial
adaptation. Peroxides derived from cyclohexanone have been long
historically applied. In 1942, Milas et al. [5] synthesized a substance
commonly known as cyclohexanone peroxide using a solution of
scaled up to produce a product known as commercial cyclohexa-
none peroxide. Cooper [6] studied the characteristic absorption
peak strength changes and the reaction kinetics of the reversible
decomposition of commercial cyclohexanone peroxide during the
reversible decomposition. Cooper's experiments demonstrated that
commercial cyclohexanone peroxide is a B compound. Kharasch [7]
then gave the first infrared spectra of B. However, these evidences
are still insufficient to prove the molecular structure of B. At pre-
sent, no NMR and molecular mass spectra of B have been reported
in the literature. In 1949, Criegee [8] synthesized C compound for
the first time, and determined the structure of C by elemental
analysis. However, his synthesis method used H2O2 solution of
ether as an oxidant, and the reaction conditions required heating,
thus this method has a highly safe risk. In addition, the reaction
yield of this method was only 21%. To make the reaction safer,
Busch [9] modified the preparation method, using acetonitrile as
the solvent, using 2 equiv of 90% H2O2 in water and controlling the
reaction temperature at room temperature, the reaction proceeded
smoothly and the final yield reached 94%. However, 90% H2O2 is still
too explosive to safely handle. Alexander [10] adopted a safer
condition based on the Busch method. 30% H2O2 solution was used
as the oxidant, and the reaction temperature was controlled at
10 ꢀC. Although the product yield was only 64%, the safety risk in
the preparation process was effectively reduced. At the same time,
* Corresponding author.
E-mail address: xinrui@dlut.edu.cn (X. Zhou).
https://doi.org/10.1016/j.tet.2021.132203
0040-4020/© 2021 Elsevier Ltd. All rights reserved.
Please cite this article as: S. Zhu, C. Yu, W. Shi et al., Selective and mild sulfoxidation of 2-sulfylbenzothiazole using hydroperoxides derived from
cyclohexanone in the absence of catalyst, Tetrahedron, https://doi.org/10.1016/j.tet.2021.132203

S. Zhu, C. Yu, W. Shi et al.
Tetrahedron xxx (xxxx) xxx
silica TLC displayed some important information that there were
three spots using KMnO4 as the chromogenic agent (SI Fig. S2), and
only two of them reacted to KI-starch agent with blue spots, which
indicated that there are at least three components, two of them
might be the hydroperoxide compounds. These three spots hadn't
always appeared together and their density changed with time.
Spot a appeared first and then b; while c appeared at last during the
time when a gradually was fading away. These three products are
proposed (Fig. 2, A, B and C), i. e. l,l'-dihydroxydicyclohexyl
peroxide A, 1-hydroxy-l'-hydroperoxy-dicyclohexyl peroxide B and
1,l'-dihydroperoxydicyclohexyl peroxide C, according to above in-
formation. Increasing the molar ratio of H2O2/cyclohexanone and
delaying reaction time allowed us to obtain the pure one of the
three products. Each molecular structure was further confirmed by
the necessary spectra.
Fig. 1. Structures of the CPO's components.
Although the compound in the form of B was numerously re-
ported, there are no NMR spectra reported for all we know. Ac-
cording to their method [14], we obtained the pure compound
supposed as B, which was coincident with our proposed B on TLC,
and then achieved its 1H NMR and 13C NMR (Figs. 3 and 4). 8 types
of hydrogen and 8 types carbon in unsymmetrical B have been
ascertained respectively by the peaks. To make the difference from
C, it is easy to see that compound B has more type of Hydrogens and
Carbons than symmetrical C. It is also easy to distinguish from A,
which does not react to KI-starch agent with blue-purple spot. Pure
A is synthesized by the method reported, and then serviced as the
standard substance. TLC results confirmed the first generated
product was compound A, and then B. Pure C was prepared with 2
equiv H2O2 to cyclohexanone was used (see 5.3). Its 13C NMR and 1H
NMR (Figs. 5 and 6) spectra agree well with ones reported in the
literature [10]. MS spectrum of C was first announced here (SI,
Fig. S3) that further confirmed C structure by the molecular weight
([M þ Na]þ ¼ 284.87, M ¼ 261.88 measured, M ¼ 262.14 calculated).
One more analusis, deuterium isotope experiment, was performed
Alexander also gave 1H NMR and 13C NMR data of C compound.
However, due to the inaccurate integral value of active hydrogen in
1H NMR and owning the same number type of carbon, NMR spectra
data couldn't assurance to C or D without standard data or further
information.
In our previous experiments, cyclohexanone peroxide was
prepared according to Kharasch's method for oxidative reaction of
dibenzothiophene. During the preparation, we observed two other
spots by thin-layer chromatography (TLC) besides B in the product.
In this work, we try to answer what they are, which compound is
more reactive and if it was more easily available under a definite
condition; and further confirm if it or other components have
special selectivity to a definite functional group and complete their
structure identification by the necessary spectrographic proof. Re-
sults reveal that there are A, B and C components in the CPO ob-
tained by the general method, while changing the conditions like
time or molar ratio bring out only one of them. Based on a series of
multi-functional 2-sulfylbenzothiazole compounds reactions re-
sults, we found that dihydroxydicyclohexyl peroxide C is much
more reactive than B, while A has no reaction with the substrates.
Although C is very active, but still has enough selectivity on aryl
sulfides to form aryl sulfoxide rather than sulfone, meanwhile no
reaction at the proximal double bond and on the N and S atoms of
the benzothiazolyl moiety were detected. Oxidation can be per-
formed in a suitable solvent, at near room temperature and in the
absence of catalyst. The selective product, aryl sulfoxide, is favorite
sulfur-containing intermediate in the organic synthesis [11], and in
the petroleum industry like the process of oxidative desulfurization
of fuels, because aryl sulfoxide is more easily separated from the
fuels than sulfones due to their high polarity [12]. We hope that this
simple method would contribute a mild and economic way toward
the related goals.
for confirming the active hydrogen existence. The peak (
d
¼ 9.54)
on the NMR spectrum asserted to (eOO)H declined remarkably
after a drop of D2O was added into C sample (Fig. 7), since hydro-
peroxide is weakly acidic so that partially ionizes to generate Hþ
exchanged by Dþ.
2.2. Selective synthesis of benzothiazolyl sulfoxide using B or C
Benzothiazolyl sulfoxide is a kind of favorite intermediate
applied in sulfoxide-modified Julia olefination. The simplest
method to prepare them is direct oxidation of benzothiazolyl sul-
fides, although the reaction selectivity normally is low. It is limited
to control the reaction to stop at the sulfoxidation stage, because
further sulfonation, epoxidation, hydroxylation or decomposition
etc., often happen, especially for benzothiazolyl sulfides containing
allylic, benzylic, alkynyl groups as substrates. In this work, various
benzothiazolyl sulfides substituted by different function groups
were selectively oxidized to the corresponding sulfoxides using 1 or
2. Results and discussion
2.1. Identify the composition of CPO and complete their
spectrographic proofs
Here CPO was prepared according to the modified milas method
[13] (see 5.3). The first spectrographic information of the product
was obtained with IR (SI, Fig. S1), which showed that the carbonyl
absorption peak (1707.19 cmꢁ1) disappeared instead by a group of
new peaks (944.33 cmꢁ1, 932.20 cmꢁ1 and 915.3 cmꢁ1) in the range
of the OeO stretching vibration frequency band. CPO was exam-
ined by Gas Chromatography (GC), but it failed to give any useful
information. The spectra displayed many small peaks in the range
of low boiling points, which means that the thermal decomposition
of CPO might occurred in the chromatographic column. However,
Fig. 2. Three products proposed.
2

S. Zhu, C. Yu, W. Shi et al.
Tetrahedron xxx (xxxx) xxx
Fig. 7. 1H NMR Spectrum of C in CDCl3 added a drop of D2O.
Fig. 3. 1H NMR spectrum of B.
reaction temperature can increase the reaction rate, but will in-
crease the by-products (Entry 1, 3). Minor sulfone was obtained in
the products of 2-(Methylthio)benzothiazole (a1) oxidation besides
of sulfoxide 2-(methylsulfinyl)benzo[d]thiazole (c1), probably
because the methyl group is less hindering group than others, the
sulfur atom connected to it is easier to be approached. c1 structure
was confirmed by 1H and 13C NMR (see 5.5.2) and HRMS (ESI, [M þ
H]þ ¼ 198.0041, [M þ Na]þ ¼ 219.9859) (SI, Fig. S6). NMR spectra of
a1 is also available in the 5.4.4. Oxidant C is much more reactive
than B (Table 1, entry 1 line 14, 15 and entry 3 line 10, 11), but still
keeps a good selectivity. One exception of this reaction success is
sulfoxidation of benzothiazolyl sulfide substituted by propargyl
group, only trace product was detected. Phenyl sulfide as the sub-
strates of the present method were also examined for the reaction
scope test and comparison with the methods widely investigated,
which adopted other oxidants and various metal or no metal cat-
alysts [15] like La2O3, Pt(II) coordination complexes, AgNO3 etc. The
results as shown in Table 1 (entry 7 and 8) that they were uniquely
and completely oxidized to sulfoxides with the present method in
1 h.
Fig. 4. 13C NMR spectrum of B.
3. Conclusion
In conclusion, this research completed the necessary spectro-
graphic identification for the composition and component struc-
ture of CPO generated by the current method. The results show that
there are three kinds of products, A, B and C. Depending on the time
and molar ratio, one of them or combination of them can be ob-
tained. Results reveal that there are A, B and C components in the
CPO obtained by the general method, while changing the condi-
tions like time or molar ratio bring out only one of them. Based on a
series of multi-functional 2-sulfylbenzothiazole compounds re-
actions results, we found that dihydroxydicyclohexyl peroxide C is
much more reactive than B, while A has no reaction with the
Fig. 5. 13C NMR spectrum of C.
Fig. 6. 1H NMR spectrum of C.
5 equiv of C or B as oxidant under very mild conditions in the
absence of catalyst (Fig. 8). The reaction solutions were examined
by the HPLC, the products were isolated and confirmed by NMR and
MS spectra. As shown in Table 1, most of the selectivity and yields
are higher than 90% at the optimized conditions (oxidant C, 45 ꢀC
and dependent time), benzothiazolyl sulfides had no or a little re-
action at the proximal double bond, N and S atoms of the benzo-
thiazolyl moiety are inert under the conditions. Reaction
temperature is important factor affecting selectivity and yield. High
Fig. 8. Sulfoxide reaction of aryl sulfides.
3

S. Zhu, C. Yu, W. Shi et al.
Tetrahedron xxx (xxxx) xxx
substrates. Although C is very active, but still has enough selectivity
on aryl sulfides to form aryl sulfoxide rather than sulfone, mean-
while no reaction at the proximal double bond and on the N and S
atoms of the benzothiazolyl moiety were detected. Oxidation can
be performed in a suitable solvent, at near room temperature and in
the absence of catalyst. Phenyl sulfide as the substrates of the
present method were also examined for the reaction scope test and
comparison with the methods widely investigated, which adopted
other oxidants and various metal or no metal catalysts. The results
showed that they were uniquely and completely oxidized to sulf-
oxides with the present method in 1 h. The advantage of the pre-
sent method is clear that the conditions are simple (no catalyst, no
high boiling and/or toxic agents) and mild (near room temperature
and in the atmospheric pressure).
2-Mercaptobenzothiazol (0.01 mol) was first added into a 50 mL
flask in the ultrasound water bath tank, following with acetone
(35 mL), triethylamine (0.01 mol) after 2-mercaptobenzothiazol
completely was solved, and then alkyl bromide (0.01 mol)
commercially obtained or self-made under the magnetic stirring.
Started 40 kHz ultrasound equipment to work. Kept the reaction at
RT under the ultrasound vibration for reaction time ranged from
10 min to 150 min.
5.4.1. 2-(Allylthio)benzothiazole (a3)
4. Acknowledgement
The corresponding alkyl bromide, allyl bromide was bought
commercially. a3 was prepared as general procedure. The reaction
stopped 10 min later. A lot of white precipitate can be seen. 100 mL
Deionized water was added to the mixture. Yellow oil droplets
generated. That was extracted with CH2Cl2, washed with HCl
(1 mol/L) to neutral. The organic phase was dried with MgSO4,
filtered and evaporated. a3 was got with a yield of 87%. 1H NMR
This research was supported by Zhejiang Jianye Chemical Co.,
Ltd.
5. Experimental section
5.1. Materials
(400 MHz, CDCl3)
d
7.86 (d, J ¼ 7.8 Hz, 1H), 7.69 (d, J ¼ 8.0 Hz, 1H),
2-Mercaptobenzothiazol, hydrogen bromide, H2O2 (30 wt%) and
tert-butyl hydroperoxide (TBHP) were Analytical Reagent (AR) and
purchased from Sinopharm Chemical Reagent Co. Ltd.1-Iodobutane
was chemically pure (CP) purchased from Shanghai Kefeng Reagent
Co. Ltd. Allyl bromide (CP) was purchased from Changzhou Xinhua
Active Material Institute. 1,4-pentadien-3-ol (AR) was provided by
Beijing Zhongsheng Huateng Technology Co. Ltd. Iodomethane (AR)
and 2,4-hexadien-1-ol (AR) were purchased from Energy Chemical
Co. Ltd.
7.37 (t, J ¼ 7.7 Hz, 1H), 7.24 (t, J ¼ 7.6 Hz, 1H), 5.99 (dd, J ¼ 15.4,
8.5 Hz, 1H), 5.34 (d, J ¼ 20.6 Hz, 1H), 5.16 (d, J ¼ 11.0 Hz, 1H), 3.96 (d,
J ¼ 8.9 Hz, 2H).
5.4.2. 2-(Penta-2,4-dien-1-ylthio)benzothiazole (a4)
The corresponding alkyl bromide was made by adding 0.01 mol
1,4-pentadien-3-ol to 0.01 mol aqueous HBr (40%) in a 25 mL re-
action bulb, the mixture was stirred under ice-bath lasting for a
night. When the solution was stratified, extract it with CH2Cl2. The
organic phase was dried with MgSO4, filtered, and evaporated. a4
was prepared as general procedure. This reaction stopped 2.5 h
later. The aftertreatment was the same as a3 except for washing it
with HCl. a4 was pale yellow liquid with a yield of 78%. 1H NMR
5.2. Analysis instruments
High Performance Liquid Chromatography-Tandem Mass Spec-
trometry (HPLC-MS, TSQ Quantum Ultra) was made by Thermo
Scientific, America. Hybrid FT MS Combines a Linear Ion Trap MS
and the Orbitrap Mass Analyzer (HRMS, LTQ Orbitrap XL TM) was
made by Thermo Scientific, America. High Performance Liquid
Chromatography (HPLC, Agilent1100) was made by Agilent, Amer-
ica. Nuclear Magnetic Resonance spectrometer (NMR, Avance II
400,400 MHz) was made by Bruker, Switzerland. Fourier Transform
Infrared Spectrometer (FT-IR, Nicolet 6700 Flex) was made by
Thermo Fisher Scientific, America.
(400 MHz, CDCl3)
d
7.87 (d, J ¼ 8.1 Hz, 1H), 7.73 (d, J ¼ 8.0 Hz, 1H),
7.40 (t, J ¼ 7.7 Hz, 1H), 7.27 (t, J ¼ 7.6 Hz, 1H), 6.33 (d, J ¼ 14.8 Hz,
2H), 5.87 (s, 1H), 5.32e5.16 (m, 1H), 5.09 (d, J ¼ 9.1 Hz, 1H), 4.03 (d,
J ¼ 7.4 Hz, 2H).
HPLC was performed under this condition: Column temperature
was set at a constant 30 ꢀC, detector light wavelength was chosen at
256 nm. The eluent composition was gradually changed from 30%
CH3OH in water during the beginning time of 25 min to 100%
CH3OH with the 1 mL/min of flow rate.
5.4.3. 2-(((2E,4E)-hexa-2,4-dien-1-yl)thio)benzothiazole (a5)
5.3. Syntheses of CPO
The synthesis of the corresponding alkyl bromide was the same
as a4 except for mixing 0.01 mol trans-2,4-hexadien-1-ol and
0.01 mol aqueous HBr (40%), stirring at room temperature and
lasting for 10 min. The product was advised to be washed with
saturated NaHCO3 solution to neutral after extracted with CH2Cl2.
a5 was prepared as general procedure and stopped 2.5 h later. The
Syntheses of CPO is referred to Ref. [3]. The detailed steps are in
Supporting Information.
5.4. General procedure [16] for synthesis of benzothiazolyl sulfide
aftertreatment was the same as a3. 1H NMR (400 MHz, CDCl3)
d 7.87
(d, J ¼ 8.2 Hz, 1H), 7.75 (d, J ¼ 7.9 Hz, 1H), 7.41 (t, J ¼ 7.1 Hz, 1H), 7.28
(dd, J ¼ 14.2, 5.9 Hz, 1H), 6.31 (dd, J ¼ 15.0, 10.4 Hz, 1H), 6.12e5.96
(m, 1H), 5.86e5.76 (m, 1H), 5.72 (dt, J ¼ 12.5, 6.3 Hz, 1H), 4.03 (d,
J ¼ 7.4 Hz, 2H), 1.74 (d, J ¼ 6.5 Hz, 3H).
4

S. Zhu, C. Yu, W. Shi et al.
Tetrahedron xxx (xxxx) xxx
Table 1
5.4.5. 2-(Butylthio)benzothiazole (a2)
Conditional experiments and substrate scope testd.
Entry
Substrate
Product
Time (h)
Temp.
ꢀC
Yield
%
Sel.
%
1
c1
5
25
35
45
55
65
75
25
35
45
55
25
35
45
45
45
45
21.2
35.3
53.3
79.8
38.2
11.0
25.1
42.5
69.7
98.1
35.9
60.2
95.1
96.4a
18.2b
96.8a
99.9
99.9
99.9
99.0
38.2
11.0
99.9
99.8
99.0
98.1
99.6
99.3
98.0
97.4
99.9
98.5
The corresponding alkyl bromide, 1-bromobutane was bought
commercially. The procedure was as general procedure and
stopped 10 min later. A lot of white precipitate can be seen. After-
treatment was as a2 and got a yield of 95%. 1H NMR (400 MHz,
CDCl3)
d
7.89 (d, J ¼ 8.6 Hz, 1H), 7.77 (d, J ¼ 8.0 Hz, 1H), 7.43 (t,
10
20
J ¼ 7.7 Hz, 1H), 7.35e7.23 (m, 1H), 3.50e3.21 (m, 2H), 1.84 (dd,
J ¼ 14.8, 7.4 Hz, 2H), 1.53 (dd, J ¼ 15.0, 7.4 Hz, 2H), 0.99 (t, J ¼ 7.4 Hz,
3H).
5.5. General procedure for benzothiazolyl sulfide oxidation with
CPO
21
36
2
3
c2
c3
Put 0.1 g of benzothiazolyl sulfide into 1 mL of MeOH in a flask.
Dissolve 5 equiv of CPO into 2.5 mL of methanol (CPO must be
completely dissolved). CPO solution was divided into five aliquots,
add one per hour into reaction flask and keep stirring sufficiently.
The reaction temperature is set to 45 ꢀC. Reaction is maintained for
a definited time according to the substrate. TLC examines the
product developed under ultraviolet light. After the reaction,
0.1 mol/L Na2SO3 solution is used to quench the remaining oxidant.
The product is extracted with CH2Cl2 (15 mL ꢂ 3), washed with
deionized water (15 mL ꢂ 3) for three times, and further purified by
silica column (petroleum ether: ethyl acetate ¼ 10:1).
5
25
35
45
55
25
35
45
25
35
45
55
45
45
8.6
99.9
99.9
98.8
35.0
99.7
99.0
98.2
99.0
97.7
95.5
97.4
93.9
92.0
15.1
30.2
34.8
9.7
19.8
53.3
20.1
43.3
78.9
7.4b
92.0a
91.0a
10
20
The original spectra of 1H NMR, 13C NMR, HRMS for unknown
products (c2, c3, c4, and c5) and MS for known products (c1, d1, and
d2) are available in SI.
48
48
4
5
c4
c5
5.5.1. (E)-2-(penta-2,4-dien-1-ylsulfinyl)benzo[d]thiazole (c4)
1H NMR (400 MHz, CDCl3)
d
8.08 (d, J ¼ 8.1 Hz, 1H), 8.00 (d,
36
45
92.8a
94.7
J ¼ 8.0 Hz, 1H), 7.57 (t, J ¼ 7.7 Hz, 1H), 7.50 (t, J ¼ 5.5 Hz, 1H), 6.29
(dd, J ¼ 19.5, 11.2 Hz, 2H), 5.65 (dd, J ¼ 22.2, 7.9 Hz, 1H), 5.16 (dd,
J ¼ 23.5,12.5 Hz, 2H), 4.05 (dd, J ¼ 13.1, 7.4 Hz,1H), 3.89 (dd, J ¼ 13.1,
7.7 Hz, 1H). HRMS m/z 250.0357 [M þ H]þ (calcd for C12H12NOS2,
250.0355).
6
7
c6
48
1
45
45
tracec
98.8a,c
-
5.5.2. 2-(methylsulfinyl)benzo[d]thiazole (c1)
1H NMR (400 MHz, CDCl3)
d
8.08 (d, J ¼ 8.3 Hz, 1H), 8.02 (d,
d1
99.9
J ¼ 8.1 Hz, 1H), 7.58 (t, J ¼ 7.7 Hz, 1H), 7.54e7.47 (m, 1H), 3.10 (s, 3H).
13C NMR (400 MHz, CDCl3)
d 178.44, 153.80, 136.03, 127.02, 126.30,
124.00, 122.36, 43.21. HRMS m/z 198.0041 [M þ H]þ (calcd for
8
d2
1
45
97.7a,c
99.9
C8H8NOS2, 198.0042).
5.5.3. 2-(((2E,4E)-hexa-2,4-dien-1-yl)sulfinyl)benzo[d]thiazole (c5)
1H NMR (400 MHz, CDCl3)
d
8.08 (d, J ¼ 8.2 Hz, 1H), 8.00 (d,
a
Isolated yield, the others are HPLC yields.
The oxidant was B, and the others were C.
1 equiv of oxidant was used.
Reaction conditions follow the general procedure (see 5.5).
J ¼ 8.0 Hz, 1H), 7.58 (d, J ¼ 8.2 Hz, 1H), 7.48 (d, J ¼ 7.1 Hz, 1H),
6.30e6.18 (m, 1H), 6.11e5.94 (m, 1H), 5.79e5.65 (m, 1H), 5.57e5.41
(m, 1H), 4.05e3.95 (m, 1H), 3.89 (d, J ¼ 7.8 Hz, 1H), 1.74 (s, 2H).
HRMS m/z 264.0511 [M þ H]þ (calcd for C13H14NOS2, 264.0511).
b
c
d
5.4.4. 2-(Methylthio)benzothiazole (a1)
5.5.4. 2-(allylsulfinyl)benzo[d]thiazole (c3)
1H NMR (400 MHz, CDCl3)
d
8.08 (d, J ¼ 8.2 Hz, 1H), 8.01 (d,
J ¼ 8.0 Hz,1H), 7.58 (t, J ¼ 7.7 Hz,1H), 7.50 (t, J ¼ 7.1 Hz,1H), 5.82 (dd,
J ¼ 18.4, 8.7 Hz, 1H), 5.39 (dd, J ¼ 25.4, 14.1 Hz, 2H), 4.06e3.95 (m,
1H), 3.88 (dd, J ¼ 13.2, 7.6 Hz, 1H). HRMS m/z 224.0201 [M þ H]þ
(calcd for C10H10NOS2, 224.0198).
Iodomethane was bought commercially. The procedure was as
general procedure. Pure a1 was obtained after final treatment
without separation, and with a yield of 89%. 1H NMR (400 MHz,
5.5.5. 2-(butylsulfinyl)benzo[d]thiazole (c2)
1H NMR (400 MHz, CDCl3)
d
8.06 (d, J ¼ 8.1 Hz, 1H), 8.00 (d,
CDCl3)
d
7.84 (d, J ¼ 8.2 Hz, 1H), 7.66 (dd, J ¼ 8.0, 0.4 Hz, 1H), 7.34 (t,
J ¼ 8.1 Hz, 1H), 7.56 (t, J ¼ 7.7 Hz, 1H), 7.48 (t, J ¼ 7.7 Hz, 1H),
J ¼ 8.3 Hz, 1H), 7.20 (t, J ¼ 7.6 Hz, 1H), 2.69 (s, 3H).
3.45e2.98 (m, 2H), 2.08e1.82 (m, 2H), 1.76e1.62 (m, 2H), 1.60e1.38
5

S. Zhu, C. Yu, W. Shi et al.
Tetrahedron xxx (xxxx) xxx
(m, 2H), 0.94 (t, J ¼ 7.3 Hz, 3H). HRMS m/z 240.0514 [M þ H]þ (calcd
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Declaration of competing interest
The authors declare that they have no known competing
financial interests or personal relationships that could have
appeared to influence the work reported in this paper.
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Appendix A. Supplementary data
Supplementary data to this article can be found online at
https://doi.org/10.1016/j.tet.2021.132203.
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