Camphorquinone: A new and efficient oxidant for the preparation of 2-thio-substituted benzothiazoles from alcohols by oxidation-reduction condensation

Article abstract of DOI:10.1080/17415993.2014.907408

A convenient one-pot procedure for the preparation of various 2-thio-substituted benzothiazoles from alcohols and benzothiazole-2-thiol utilizing camphorquinone-mediated oxidation-reduction condensation is disclosed. The condensation between benzothiazole-2-thiol and alkyl diphenylphosphinites, generated in situ from alcohols and chlorodiphenylphosphine, proceeded smoothly in the presence of camphorquinone to furnish the corresponding benzothiazoles in good to moderate yields.

Full text of DOI:10.1080/17415993.2014.907408

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Camphorquinone: a new and efficient
oxidant for the preparation of 2-
thio-substituted benzothiazoles
from alcohols by oxidation-reduction
condensation
Wanchai Pluempanupatab, Parinthorn Temyarasilpac, Michael
Widhalmc & Warinthorn Chavasirid
a Department of Chemistry and Center of Excellence for Innovation
in Chemistry, Faculty of Science, Kasetsart University, Bangkok
10900, Thailand
b Special Research Unit in Advanced Magnetic Resonance,
Kasetsart University, Bangkok 10900, Thailand
c Institute of Organic Chemistry, Faculty of Chemistry, University
of Vienna, Währinger Straße 38, A-1090 Wien, Austria
d Natural Products Research Unit, Department of Chemistry,
Faculty of Science and Center for Petroleum, Petrochemicals,
and Advance Materials, Chulalongkorn University, Bangkok 10330,
Thailand
Published online: 15 Apr 2014.
To cite this article: Wanchai Pluempanupat, Parinthorn Temyarasilp, Michael Widhalm & Warinthorn
Chavasiri (2014) Camphorquinone: a new and efficient oxidant for the preparation of 2-thio-
substituted benzothiazoles from alcohols by oxidation-reduction condensation, Journal of Sulfur
Chemistry, 35:4, 418-430, DOI: 10.1080/17415993.2014.907408
To link to this article: http://dx.doi.org/10.1080/17415993.2014.907408
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Journal of Sulfur Chemistry, 2014
Vol. 35, No. 4, 418–430, http://dx.doi.org/10.1080/17415993.2014.907408
Camphorquinone: a new and efficient oxidant for the
preparation of 2-thio-substituted benzothiazoles from alcohols
by oxidation-reduction condensation
Wanchai Pluempanupata,b∗, Parinthorn Temyarasilpa,c, Michael Widhalmc and Warinthorn
Chavasirid
aDepartment of Chemistry and Center of Excellence for Innovation in Chemistry, Faculty of Science, Kaset-
sart University, Bangkok 10900, Thailand; bSpecial Research Unit in Advanced Magnetic Resonance,
Kasetsart University, Bangkok 10900, Thailand; cInstitute of Organic Chemistry, Faculty of Chemistry,
University of Vienna, Währinger Straße 38, A-1090 Wien, Austria; dNatural Products Research Unit,
Department of Chemistry, Faculty of Science and Center for Petroleum, Petrochemicals, and Advance
Materials, Chulalongkorn University, Bangkok 10330, Thailand
(Received 1 March 2014; accepted 19 March 2014)
A convenient one-pot procedure for the preparation of various 2-thio-substituted benzothiazoles from
alcohols and benzothiazole-2-thiol utilizing camphorquinone-mediated oxidation-reduction condensation
is disclosed. The condensation between benzothiazole-2-thiol and alkyl diphenylphosphinites, generated
insitu fromalcoholsandchlorodiphenylphosphine, proceededsmoothlyinthepresenceofcamphorquinone
to furnish the corresponding benzothiazoles in good to moderate yields.
Keywords: 2-thio-substitutedbenzothiazoles;alcohols;benzothiazole-2-thiol;camphorquinone;oxidation-
reduction condensation
1. Introduction
The 2-thio-substituted benzothiazoles are of widespread academic and commercial interest
since these compounds exhibit a range of desirable biological properties.[1–7] Although
they can be produced from a variety of starting materials, the simplest protocols gener-
ally involve the use of benzothiazole-2-thiol and alcohols, which are commercially available
at low cost.[8–10] The conversion of alcohols into 2-thio-substituted benzothiazoles tradi-
tionally requires oxidation-reduction condensation in conjunction with a reductant and an
∗Corresponding author. Email: fsciwcp@ku.ac.th
© 2014 Taylor & Francis

Journal of Sulfur Chemistry 419
oxidant. Reagents, including PPh3/diethyl azodicarboxylate, PPh3/diisopropyl azodicarboxylate
or PPh3/di-p-nitrobenzyl azodicarboxylate, have been reported as efficient combinations for the
thioetherification of alcohols.[11–15] Indeed, these reagents are particularly attractive since syn-
thesis can be performed under mild conditions with good yields. However, it has been observed
that sterically hindered secondary and tertiary alcohols do not always afford the corresponding
sulfides. Instead, olefinic products or unreacted alcohols are found.[16–19]
Mukaiyama and co-workers reported a new type of oxidation-reduction condensation of alkyl
diphenylphosphinites with benzothiazole-2-thiol (HSBtz, 3) in the presence of 1,4-benzoquinone
derivatives or azido compounds such as 2,6-di-tert-butyl-1,4-benzoquinone (DBBQ),[20,21] 2,6-
dimethyl-1,4-benzoquinone (DMBQ),[20–22] 2,6-dimethoxy-1,4-benzoquinone (DMOBQ) [23]
or ethyl azidoacetate [24,25]. Under optimized condensation conditions, alkyl diphenylphos-
phinites could be converted into the 2-thio-substituted benzothiazoles in high to excellent yields
with almost nearly complete inversion of configuration. In this work, we extend our investiga-
tion to search for a new and alternative oxidant because 1,4-benzoquinones derivatives such as
DBBQ and DMBQ are rather expensive. The 1,2-dicarbonyl derivatives were chosen to assess the
efficiency of our protocols. Although 1,2-dicarbonyl compounds are used to oxidize phosphine
compounds,[26–28] the compounds have never been reported as the oxidant for oxidation-
reduction condensation. The results were found that only camphorquinone was superior to the
previously applied 1,4-benzoquinones. Herein, we prepared 2-thio-substituted benzothiazoles
from alcohols and HSBtz in the presence of camphorquinone.
2. Results and discussion
While alkyl diphenylphosphinites are not commercially available, they can be easily prepared
from the corresponding alcohol by reacting with ClPPh2 in the presence of Et3N and DMAP
followed by purification using filtration through a pad of alumina-celite. However, when alkyl
diphenylphosphinites are exposed to air or humidity, the alkyl diphenylphosphine oxides are
formed.[20] This synthetic protocol requires strictly anhydrous conditions, which are not con-
venient in laboratories situated in tropical regions. Therefore, it would be highly desirable if
the protocol could be modified such that it is possible to avoid the isolation of the phosphinite
intermediates.
First, optimum conditions for the preparation of alkyl diphenylphosphinite from alcohol
utilizing a base and ClPPh2 were examined. Various parameters, including the type of base,
stoichiometric ratio of a base and ClPPh2, and the amount of solvent were examined using 4-
phenyl-2-butanol (1a) as a model substrate (Table 1). A typical procedure involved the reaction
of 1a (0.25 mmol), base, and ClPPh2 in CDCl3 at room temperature (30◦C) for 2 h. The degree
of conversion of 1a to 2a [29] was determined directly from the crude product 2a by 1H NMR.
The reaction did not occur in the absence of base (Entry 1) whereas the conversion to phosphinite
2a was significantly affected by the nature of the base. The most effective result was achieved when
Et3N was used (Entry 6). Nonetheless, the reaction did not proceed completely as evidenced by the
detectionofalcohol 1a.ThequantitiesofEt3NandClPPh2 werealsovariedinordertofindthemost
suitable stoichiometric ratio to provide the maximum possible yield of 2a. Increasing the amounts
of Et3N and ClPPh2 from 1 to 1.2 equivalents afforded the highest yield of the target product (Entry
7). On the other hand, the yield decreased slightly when both reagents were used in greater excess
(1.3 and 1.4 equivalents, Entries 8 and 9). In addition, the variation of reaction concentration and
temperature did not significantly affect the yield of the reaction (Entries 10 and 11).
Screening of various 1,2-dicarbonyl compounds as oxidants was performed using crude
2a, formed in situ from 1a, under optimized conditions. The HSBtz was used at the optimal

420 W. Pluempanupat et al.
Table 1. Effect of base in the preparation of alkyl diphenylphosphinite.
Base
ClPPh2
(equiv.)
Conc.
(M)
Yielda,b
(%)
Entry
Type
None
Eq
1
1.0
1.0
1.0
1.0
1.0
1.0
1.2
1.3
1.4
1.2
1.2
1.2
1.0
1.0
1.0
1.0
1.0
1.0
1.2
1.3
1.4
1.2
1.2
1.2
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
1.0
1.0
0
2
3
4
5
6
7
8
9
DMAP
Pyridine
4-Picoline
Piperidine
Et3N
Et3N
Et3N
Et3N
Et3N
54
28
44
26
80
85
80
74
86c
85
73d
10
11
12
Et3N
Et3N
aThe conversion was determined based on 1H NMR of crude reaction mixture.
bAlkyl chloride was obtained as an undesired product.
cThe reaction temperature was reflux.
d0.1 eq of DMAP was added.
Table 2. Effect of 1,2-dicarbonyl compounds as an oxidant.
Entry
Oxidant
Yielda (%)
1
2
3
4
5
6
7
8
9
10
None
0
Trace
Trace
Trace
0
2,3-Butanedione
3,4-Hexanedione
Benzil
1,2-Cyclohexanedione
3-Methyl-1,2-cyclopentanedione
Acenaphthenequinone
Camphorquinone
DBBQ
0
Trace
93, 13b, 67c
69
DMOBQ
75
aIsolated yield, corresponding to limiting amount of nucleophile.
bThe reaction concentration was 0.5 M in CHCl3 (instead of 1 M).
cHSBtz and camphorquinone were promptly added after the addition ClPPh2.
stoichiometric ratio of substrate and reagent previously reported in the literature.[20,21] These
results are listed in Table 2.
In the absence of an oxidant, the desired product (3a) was not obtained indicating that the
oxidant is crucial for this reaction (Entry 1). In the presence of 2,3-butanedione, 3,4-hexanedione,
benzil, and acenaphthenequinone, the desired product was obtained only in trace amounts (Entries

Journal of Sulfur Chemistry 421
2–4 and 7) whereas the use of 1,2-cyclohexanedione and 3-methyl-1,2-cyclopentanedione did not
yield 3a at all (Entries 5 and 6). We found that 3a was obtained in 93% yield in the presence of
camphorquinone (Entry 8). However, applying the reagent in more diluted form (0.5 M instead
of 1.0 M) resulted in a dramatically decreased yield (Entry 8). Next, the effect of the oxidants
was examined. Under our newly developed conditions, it was found that camphorquinone could
afford 3a in higher yield compared with DBBQ and DMOBQ (Entries 9 and 10).
According to previous studies, CHCl3 was the preferred medium for this reaction due to the
ability to solubilize both the substrate and reagent.[20,21] Therefore, we further examined the
effect of replacing CHCl3 with alternate solvents. It was found that the reaction performed in
CH2Cl2 led to a similar yield in comparison to CHCl3 (94%). In contrast, the yields of isolated
3a dropped to 59%, 28%, 17%, and 74% when ClCH2CH2Cl, toluene, THF, and CH3CN were
used, respectively.
The one pot protocol reported here does make the execution of oxidation-reduction conden-
sation reaction simpler and more convenient. Only one solvent is used throughout our two-step
(preparation of alkyl diphenylphosphinites and condensation) whereas one pot protocol where pre-
viouslyreportedprotocolrequirestheremovalofthefirstsolventpriortothesecond(condensation)
step.[30–33] We then performed camphorquinone-mediated oxidation-reduction condensation on
various alcohols with HSBtz under the optimized conditions (Table 3).
All of the primary alkyl alcohols studied here were smoothly transformed into alkyl
diphenylphosphinites. These intermediates then reacted with camphorquinone and HSBtz to give
the corresponding products 3b–3i in good yields (Entries 1–8). Similarly, products 3j–3k formed
from secondary alkyl alcohols could also be obtained in high yields (Entries 9–11). In contrast,
the cyclic compounds 1l and 1m were converted into 2-cycloalkylthiobenzothiazoles in moderate
yields (Entries 12 and 13). Even tertiary alcohols were converted to the corresponding products
3n and 3o (Entries 14 and 15), albeit at lower yields. Based on our results, the reactivity is not
heavily influenced by the presence of electron donating or withdrawing substituents. Addition-
ally, moderate steric interaction (primary versus secondary alcohols) was not found to hinder the
attack of the S-nucleophile whereas tertiary alcohols simply showed reduced reactivity. A closer
examination of the reaction mechanism was performed using an enantiomerically pure substrate,
(R)-1a. Applying standard conditions the non-racemic alcohol (R)-1a, 99% ee, was converted
25
into (S)-3a in 78% yield (Entry 16). The isolated sulfide displayed only 78% ee ([α]D − 30.7,
ca. 0.95, CHCl3). The incomplete inversion of chirality is indicative that a minor fraction of the
phosphonium salt intermediate is not transformed via the expected SN2 attack of the nucleophile.
The developed reactions were then utilized to study the scope of thioetherification using benzyl
alcohol derivatives with other sulfur nucleophiles (Table 4).
The reaction of benzyl diphenylphosphinites, prepared in situ from alcohols (1c–1f) with 1-
phenyl-1H-tetrazole-5-thiol (4) in the presence of camphorquinone afforded the corresponding
products 4c–4f in moderate to high yields (Entries 1–4). The desired products were obtained
in poor yields when the condensation was performed with O,O-diethyl phosphorothioic acid 5
(Entries 6–8). One exception was the use of alcohol 1c which provided the desired product 5c with
moderate yield (Entry 5). According to the previously reported method,[33] the use of disulfide
6 as a sulfur nucleophile was also examined. The reaction provided the corresponding sulfides
6c–6f in good yields without any assistance of camphorquinone (Entries 9–12).
3. Conclusions
We have developed a facile one-pot procedure for the transformation of alcohols into 2-thio-
substituted benzothiazoles or sulfur containing compounds using a modified oxidation-reduction

422 W. Pluempanupat et al.
Table 3. Scope of thioetherification of alcohols with 1,3-benzothiazole-2-thiol.
Entry
1
ROH
RSBtz
Yielda (%)
90
1b
3b
ꢀ
=
2
3
4
5
1c; Rꢀ
H
=
3c
3d
3e
3f
89
77
88
50
1d; R 2-NO2
ꢀ
=
1e; Rꢀ 4-Br
=
1f; R 3,4-OMe
6
1g
1h
3g
74
7
3h
87
8
9
1i
1j
3i
3j
77
72
10
11
1k
1l
3k
3l
73
74
12
13
14
1m
1n
1o
3m
3n
3o
47
58
64
15
16
1p
3p
50
78
(R)-1a
(S)-3a
aIsolated yield, corresponding to limiting amount of nucleophile.

Journal of Sulfur Chemistry 423
Table 4. Thioetherification of benzyl alcohols with selected S-nucleophiles.
Entry
S-nucleophile
Product
Yielda (%)
ꢀ
=
1
2
3
4
4c; Rꢀ
H
=
73
56
65
49
4d; R 2-NO2
ꢀ
=
4e; Rꢀ 4-Br
=
4f; R 3,4-OMe
ꢀ
=
5
6
7
8
5c; Rꢀ
H
=
58
13
15
11
5d; R 2-NO2
ꢀ
=
5e; R 4-Br
ꢀ
=
5f; R 3,4-OMe
ꢀ
85b,c
64b,c
83b,c
49b,c
=
9
PhSSPh 6
6c; Rꢀ
H
=
10
11
12
6d; R 2-NO2
ꢀ
=
6e; Rꢀ 4-Br
=
6f; R 3,4-OMe
aIsolated yield.
bThe reaction was performed in the absence of camphorquinone.
cThe reaction time was 12 h.
protocol with camphorquinone as a new and inexpensive oxidant. Products have been obtained in
moderate to good yields. Under the conditions employed the thioetherification proceeds mainly
via a SN 2 mechanism.
4. Experimental
4.1. General
All reagent-grade chemicals and solvents were purchased from commercial suppliers (Fluka,
Aldrich, Arcos and TCI). 1H and 13C NMR spectra were recorded on aVarian Inova 400 operating
at 400 MHz (1H), 100 MHz (13C) and 162 MHz (31P). The chemical shifts (δ) are reported in ppm
relative to tetramethylsilane. Splitting patterns were designated as s, singlet; d, doublet; t, triplet;
q, quartet; qui, quintet; sex, sextet; m, multiplet; br, broad. High-resolution mass spectra (HRMS)
were recorded on a MAXIS (Bruker). High-performance liquid chromatography (HPLC) was
carried out using a Shimadzu LC-20A.
4.2. General procedure for the preparation of 2-thio-substituted benzothiazoles
To a stirred solution of alcohol (1 mmol), Et3N (1.2 equiv.) in dry CH2Cl2 (1 mL) was successively
added chlorodiphenylphosphine (1.2 equiv.) at RT under N2 atmosphere.After 2 h, benzothiazole-
2-thiol (0.5 equiv.) and camphorquinone (1 equiv.) were added to the mixture, respectively. After
the mixture was stirred for 12 h, it was extracted with CH2Cl2/H2O. The combined organic layers
were washed with brine, dried over Na2SO4 and concentrated under reduced pressure. The residue
waspurifiedbypreparativeTLConsilicagel(hexane/EtOAc = 10/1)toaffordthedesiredproduct.

424 W. Pluempanupat et al.
4.2.1. 2-((4-Phenylbutan-2-yl)thio)benzo[d]thiazole (3a) [24]
Colorless oil. 1H NMR (400 MHz, CDCl3) δ 7.86 (d, J = 8.1 Hz, 1H), 7.72 (d, J = 7.7 Hz, 1H),
7.41 (d, J = 7.6 Hz, 1H), 7.31–7.18 (m, 6H), 3.99 (sex, J = 6.8 Hz, 1H), 2.82 (t, J = 7.6 Hz, 2H)
2.19–1.97 (m, 2H), 1.55 (d, J = 6.8 Hz, 3H). 13C NMR (100 MHz, CDCl3) δ 166.25, 153.26,
141.19, 135.24, 128.39, 125.96, 124.20, 121.55, 120.85, 43.91, 38.40, 33.18, 21.48.
4.2.2. (E)-2-(Hex-2-en-1-ylthio)benzo[d]thiazole (3b)
Colorless oil. 1H NMR (400 MHz, CDCl3) δ 7.87 (d, J = 8.0 Hz, 1H), 7.75 (d, J = 8.0 Hz, 1H),
7.41 (t, J = 7.8 Hz, 1H), 7.29 (t, J = 7.5 Hz, 1H), 5.83–5.76 (m, 1H), 5.67–5.59 (m, 1H), 3.96 (d,
J = 7.5 Hz, 2H), 2.01 (q, J = 7.0 Hz, 2H), 1.42–1.33 (m, 2H), 0.87 (d, J = 7.0 Hz, 3H). 13C NMR
(100 MHz, CDCl3) δ 166.88, 153.52, 136.23, 135.46, 126.14, 124.32, 123.84, 121.72, 121.22,
36.25, 34.53, 22.44, 13.81. HRMS (ESI) Calcd for C13H15NNaS2 272.0544 ([M + Na]+), Found
272.0539 ([M + Na]+).
4.2.3. 2-(Benzylthio)benzo[d]thiazole (3c) [24]
Colorless oil. 1H NMR (400 MHz, CDCl3) δ 7.84 (d, J = 8.0 Hz, 1H), 7.66 (d, J = 7.6 Hz, 1H),
7.39–7.12 (m, 7H), 4.53 (s, 2H). 13C NMR (100 MHz, CDCl3) δ 166.33, 152.96, 136.01, 135.16,
129.01, 128.58, 127.64, 125.95, 124.17, 121.40, 120.89, 37.58.
4.2.4. 2-((2-Nitrobenzyl)thio)benzo[d]thiazole (3d) [7]
Colorless oil. 1H NMR (400 MHz, CDCl3) δ 8.05 (d, J = 7.8 Hz, 1H), 7.90 (d, J = 7.8 Hz, 1H),
7.82 (d, J = 7.8 Hz, 1H), 7.72 (d, J = 7.8 Hz, 1H), 7.54 (t, J = 7.4, 1H), 7.44–7.40 (m, 2H), 7.29
(t, J = 7.2 Hz, 1H), 4.96 (s, 2H). 13C NMR (100 MHz, CDCl3) δ 165.80, 153.06, 148.52, 135.72,
133.66, 133.50, 132.88, 128.85, 126.20, 125.38, 124.52, 121.73, 121.19, 34.33.
4.2.5. 2-((4-Bromobenzyl)thio)benzo[d]thiazole (3e) [7]
Colorless oil. 1H NMR (400 MHz, CDCl3) δ 7.90 (d, J = 7.8 Hz, 1H), 7.74 (d, J = 8.2 Hz, 1H),
7.45–7.40 (m, 3H), 7.40–7.28 (m, 3H), 4.55 (s, 2H). 13C NMR (100 MHz, CDCl3) δ 165.86,
153.21, 135.69, 135.53, 131.93, 130.94, 126.25, 124.55, 121.83, 121.74, 121.18, 37.07.
4.2.6. 2-((3,4-Dimethoxybenzyl)thio)benzo[d]thiazole (3f) [10]
Colorless oil. 1H NMR (400 MHz, CDCl3) δ 7.82 (d, J = 8.0 Hz, 1H), 7.67 (d, J = 8.0 Hz, 1H),
7.37–7.32 (m, 1H), 7.26–7.16 (m, 1H), 6.92 (d, J = 8.0 Hz, 2H), 6.73 (d, J = 8.0 Hz, 1H), 4.48
(s, 2H), 3.78 (s, 3H), 3.77 (s, 3H). 13C NMR (100 MHz, CDCl3) δ 166.64, 153.32, 149.20, 148.86,
135.51, 128.66, 126.21, 124.70, 121.62, 121.53, 121.15, 112.55, 111.49, 56.05, 56.00, 38.09.
4.2.7. 2-(Phenethylthio)benzo[d]thiazole (3g) [6]
Colorless oil. 1H NMR (400 MHz, CDCl3) δ 7.91 (d, J = 8.4 Hz, 1H), 7.77 (d, J = 7.2 Hz, 1H),
7.44 (t, J = 7.6 Hz, 1H), 7.37–7.25 (m, 6H), 3.62 (t, J = 7.6 Hz, 2H), 3.16 (t, J = 7.6 Hz, 2H).
13C NMR (100 MHz, CDCl3) δ 166.19, 153.47, 142.12, 135.77, 128.82, 127.90, 127.53, 126.13,
124.46, 121.86, 121.09, 47.73, 22.79.

Journal of Sulfur Chemistry 425
4.2.8. 2-((2-Methoxyphenethyl)thio)benzo[d]thiazole (3h)
Colorless oil. 1H NMR (400 MHz, CDCl3) δ 7.89 (d, J = 7.9 Hz, 1H), 7.76 (d, J = 7.7 Hz, 1H),
7.42 (t, J = 7.0 Hz, 1H), 7.29 (t, J = 7.5 Hz, 1H), 7.22 (t, J = 5.8 Hz, 2H), 6.94–6.86 (m, 2H),
3.85 (s, 3H), 3.59 (t, J = 7.4 Hz, 2H), 3.14 (t, J = 7.8 Hz, 2H). 13C NMR (100 MHz, CDCl3) δ
164.41, 157.69, 153.57, 135.39, 130.62, 128.20, 127.95, 126.09, 124.21, 121.63, 121.03, 120.61,
110.47, 55.37, 33.56, 30.72. HRMS (ESI) Calcd for C16H15NNaOS2 324.0493 ([M + Na]+),
Found 324.0491 ([M + Na]+).
4.2.9. 2-((3-Phenylpropyl)thio)benzo[d]thiazole (3i) [34]
Colorless oil. 1H NMR (400 MHz, CDCl3) δ 7.86 (d, J = 8.0 Hz, 1H), 7.75 (d, J = 7.6 Hz, 1H),
7.41 (t, J = 7.6 Hz, 1H), 7.31–7.18 (m, 6H), 3.35 (t, J = 7.2 Hz, 2H), 2.82 (t, J = 7.2 Hz, 2H),
2.17 (qui, J = 7.2 Hz, 2H). 13C NMR (100 MHz, CDCl3) δ 166.89, 153.17, 140.75, 135.05,
128.39, 128.36, 126.00, 125.91, 124.05, 121.35, 120.82, 34.53, 32.75, 30.64.
4.2.10. Ethyl 3-(benzo[d]thiazol-2-ylthio)butanoate (3j)
Colorless oil. 1H NMR (400 MHz, CDCl3) δ 7.88 (d, J = 8.0 Hz, 1H), 7.74 (d, J = 8.0 Hz, 1H),
7.40 (t, J = 7.2 Hz, 1H), 7.29 (t, J = 7.6 Hz, 1H), 4.40–4.31 (m, 1H), 4.16 (q, J = 7.2 Hz, 2H),
2.98 (dd, J = 16.0, 5.6 Hz, 1H), 2.71 (dd, J = 16.0, 8.0 Hz, 1H), 1.57 (d, J = 6.8 Hz, 3H), 1.26
(t, J = 7.2 Hz, 3H). 13C NMR (100 MHz, CDCl3) δ 170.76, 165.22, 153.25, 135.31, 125.98,
124.36, 121.74, 120.91, 60.72, 41.46, 39.89, 20.81, 14.16. HRMS (ESI) Calcd for C13H16NO2S2
282.0622 ([M + H]+), Found 282.0609 ([M + H]+).
4.2.11. Ethyl 2-(benzo[d]thiazol-2-ylthio)-2-phenylacetate (3k)
Colorless oil. 1H NMR (400 MHz, CDCl3) δ 7.89 (d, J = 8.4 Hz, 1H), 7.74 (d, J = 7.9 Hz, 1H),
7.55 (d, J = 8.0 Hz, 2H), 7.44–7.28 (m, 5H), 5.79 (s, 1H), 4.34–4.26 (m, 1H), 4.21–4.14 (m, 1H),
1.26 (t, J = 7.4 Hz, 3H). 13C NMR (100 MHz, CDCl3) δ 169.65, 164.51, 153.04, 135.63, 134.43,
129.08, 128.91, 128.65, 126.13, 124.59, 121.83, 121.17, 62.31, 54.78, 14.20. HRMS (ESI) Calcd
for C17H15NNaO2S2 352.0442 ([M + Na]+), Found 352.0440 ([M + Na]+).
4.2.12. 2-((1-(Benzyloxy)propan-2-yl)thio)benzo[d]thiazole (3l)
Colorless oil. 1H NMR (400 MHz, CDCl3) δ 7.87 (d, J = 8.1 Hz, 1H), 7.75 (d, J = 7.4 Hz, 1H),
7.41 (d, J = 7.3 Hz, 1H), 7.34–7.27 (m, 6H), 4.61 (s, 2H), 4.31–4.22 (m, 1H), 3.83–3.79 (m, 1H),
3.70–3.67 (m, 1H), 1.56 (d, J = 7.0 Hz, 3H). 13C NMR (100 MHz, CDCl3) δ 166.13, 153.52,
138.28, 135.55, 128.57, 127.74, 126.12, 124.44, 121.82, 121.10, 73.77, 73.33, 43.58, 18.38.
HRMS (ESI) Calcd for C17H17NNaOS2 338.0649 ([M + Na]+), Found 338.0637 ([M + Na]+).
4.2.13. 2-((1,2,2a,3,4,8b-hexahydrocyclobuta[a]naphthalen-2-yl)thio)benzo[d]thiazole (3m)
Colorless oil. 1H NMR (400 MHz, CDCl3) δ 7.78 (d, J = 8.0 Hz, 1H), 7.67 d, J = 8.0 Hz, 1H),
7.32 (t, J = 8.0 Hz, 1H), 7.20 (t, J = 8.0 Hz, 1H), 7.11–7.09 (m, 3H), 6.99 (d, J = 8.0 Hz, 1H),
4.15 (q, J = 6.4 Hz, 1H), 3.71–3.65 (m, 1H), 2.98–2.90 (m, 2H), 2.75–2.60 (m, 2H), 2.50–2.43
(m, 1H), 2.00–1.94 (m, 1H), 1.78–1.72 (m, 1H). 13C NMR (100 MHz, CDCl3): δ 166.87, 153.70,
139.50, 137.35, 135.54, 128.98, 128.98, 126.70, 126.18, 126.03, 124.31, 121.81, 121.05, 42.20,

426 W. Pluempanupat et al.
41.61, 37.42, 33.37, 27.17, 25.10. HRMS (ESI) Calcd for C19H17NNaS2 346.0700 ([M + Na]+),
Found 346.0686 ([M + Na]+).
4.2.14. 2-(Adamantan-2-ylthio)benzo[d]thiazole (3n)
Colorless oil. 1H NMR (400 MHz, CDCl3) δ 7.86 (d, J = 8.0 Hz, 1H), 7.73 (d, J = 8.0 Hz, 1H),
7.39 (t, J = 7.6 Hz, 1H), 7.27 (t, J = 7.6 Hz, 1H), 4.36 (br s, 1H), 2.26 (br s, 2H), 2.14–2.10
(m, 2H), 1.96–1.91 (m, 6H), 1.79 (br s, 2H), 1.69–1.66 (m 2H). 13C NMR (100 MHz, CDCl3) δ
167.73, 152.63, 134.70, 126.12, 124.27, 121.32, 120.86, 56.36, 38.43, 37.39, 33.35, 32.60, 27.45,
27.06. HRMS (ESI) Calcd for C17H20NS2 302.1037 ([M + H]+), Found 302.1025 ([M + H]+).
4.2.15. 2-(Benzo[d]thiazol-2-ylthio)-2-methyl-1-phenylpropan-1-one (3o) [20]
Colorless oil. 1H NMR (400 MHz, CDCl3) δ 8.10 (d, J = 7.2 Hz, 2H), 7.89 (d, J = 8.4 Hz, 1H),
7.70 (d, J = 7.6 Hz, 1H), 7.48–7.26 (m, 5H), 1.87 (s, 6H). 13C NMR (100 MHz, CDCl3) δ 200.55,
161.34, 153.03, 136.65, 136.25, 131.70, 129.01, 127.89, 126.06, 124.93, 122.42, 120.92, 58.01,
27.31.
4.2.16. Methyl 2-(benzo[d]thiazol-2-ylthio)-2-methylpropanoate (3p) [20]
Colorless oil. 1H NMR (400 MHz, CDCl3) δ 7.92 (d, J = 8.4 Hz, 1H), 7.77 (d, J = 7.2 Hz, 1H),
7.42 (t, J = 7.2 Hz, 1H), 7.32 (t, J = 7.6 Hz, 1H), 3.74 (s, 3H), 1.74 (s, 6H). 13C NMR (100 MHz,
CDCl3) δ 173.78, 161.94, 153.24, 136.38, 126.10, 125.01, 122.54, 120.99, 53.93, 52.90, 26.35.
4.2.17. (S)-2-((4-phenylbutan-2-yl)thio)benzo[d]thiazole ((S)-3a) [24]
Colorless oil. 1H NMR (400 MHz, CDCl3) δ 7.87 (d, J = 8.4 Hz, 1H), 7.75 (d, J = 8.0 Hz, 1H),
7.41 (t, J = 7.6 Hz, 1H) 7.31–7.19 (m, 6H), 4.00 (sex, J = 6.8 Hz, 1H), 2.83 (t, J = 7.6 Hz,
2H), 2.19–1.98 (m, 2H), 1.56 (d, J = 6.8 Hz, 3H). The ee value was determined by chi-
ral HPLC analysis (DAICEL CHIRALCEL OD-H column, hexane/isopropanol = 250/1, flow
rate = 1.0 mL min−1); tR = 20.2 min (S), 33.3 min (R).
4.3. General procedure for the preparation of sulfides
To a stirred solution of alcohol (0.25 mmol), Et3N (1.2 equiv.) in dry CH2Cl2 (1 mL) was succes-
sively added chlorodiphenylphosphine (1.2 equiv.) at RT under N2 atmosphere. After 2 h, sulfur
nucleophile (1 equiv.) and camphorquinone (1 equiv.) were added to the mixture, respectively.
After the mixture was stirred for 12–20 h, it was extracted with CH2Cl2/H2O. The combined
organic layers were washed with brine, dried over Na2SO4 and concentrated under reduced pres-
sure. The residue was purified by preparative TLC on silica gel (hexane/EtOAc = 10/1) to afford
the corresponding sulfide.
4.3.1. 5-(Benzylthio)-1-phenyl-1H-tetrazole (4c) [9]
Colorless oil. 1H NMR (400 MHz, CDCl3) δ 7.54–7.50 (m, 5H), 7.43–7.41 (m, 2H), 7.35–7.29 (m,
3 H), 4.63 (s, 2H). 13C NMR (100 MHz, CDCl3) δ 153.93, 135.25, 133.67, 130.10, 129.76, 129.25,
128.85, 128.21, 123.82, 37.69. HRMS (ESI) Calcd for C14H12N4NaS 291.0680 ([M + Na]+),
Found 291.0673 ([M + Na]+).

Journal of Sulfur Chemistry 427
4.3.2. 5-((2-Nitrobenzyl)thio)-1-phenyl-1H-tetrazole (4d)
Colorless oil. 1H NMR (400 MHz, CDCl3) δ 8.14–8.11 (m, 1H), 7.97–7.64 (m, 1H), 7.64–7.47,
7H), 4.93 (s, 2H). 13C NMR (100 MHz, CDCl3) δ 134.24, 133.57, 133.49, 132.79, 130.71, 130.34,
130.11, 129.98, 129.55, 125.73, 124.14, 123.87, 35.28. HRMS (ESI) Calcd for C14H11N5NaO2S
336.0531 ([M + Na]+), Found 336.0531 ([M + Na]+).
4.3.3. 5-((4-Bromobenzyl)thio)-1-phenyl-1H-tetrazole (4e)
Colorless oil. 1H NMR (400 MHz, CDCl3) δ 7.55–7.48 (m, 5H), 7.45–7.41 (m, 2H), 7.32–7.29
(m, 2H), 4.55 (s, 2H). 13C NMR (100 MHz, CDCl3) δ 134.67, 133.63, 132.05, 131.05, 130.32,
129.92, 123.90, 122.35, 37.06. HRMS (ESI) Calcd for C14H11BrN4NaS 368.9785 ([M + Na]+),
Found 368.9777 ([M + Na]+).
4.3.4. 5-((3,4-Dimethoxybenzyl)thio)-1-phenyl-1H-tetrazole (4f)
Colorless oil. 1H NMR (400 MHz, CDCl3) δ 7.56–7.50 (m, 6H), 6.97–6.95 (m, 2H), 6.80 (d, J =
8.0 Hz, 1H), 4.59 (s, 2H), 3.86 (s, 3H), 3.85 (s, 3H). 13C NMR (100 MHz, CDCl3) δ 154.06, 149.30,
149.22, 133.82, 130.61, 130.21, 129.86, 123.96, 123.63, 121.84, 112.42, 111.38, 56.08, 38.00.
HRMS (ESI) Calcd for C16H16N4NaO2S 351.0892 ([M + Na]+), Found 351.0892 ([M + Na]+).
4.3.5. S-benzyl O,O-diethyl phosphorothioate (5c) [9]
Colorless oil. 1H NMR (400 MHz, CDCl3) δ 7.37–7.24 (m, 5H), 4.17–3.97 (m, 6H), 1.30–1.27 (m,
6H). 13C NMR (100 MHz, CDCl3) δ 137.54 (d, JPC = 6.2 Hz), 128.90, 128.65, 127.60, 63.50 (d,
JPC = 5.7 Hz), 34.98 (d, JPC = 3.0 Hz), 15.95 (d, JPC = 7.3 Hz). 31P NMR (162 MHz, CDCl3)
δ 26.67. HRMS (ESI) Calcd C11H17NaO3PS 283.0534 ([M + Na]+), Found 283.0524 ([M +
Na]+).
4.3.6. O,O-diethyl S-2-nitrobenzyl phosphorothioate (5e)
Colorless oil. 1H NMR (400 MHz, CDCl3) δ 8.06 (d, J = 8.4 Hz, 1H), 7.66–7.58 (m, 2H), 7.49–
7.45 (m, 1H), 4.39 (d, J = 15.6 Hz, 2H), 4.13–3.95 (m, 4H), 1.26 (t, J = 8.0 Hz, 6H). 13C NMR
(100 MHz, CDCl3) δ 133.86, 133.08, 129.16, 125.62, 63.98 (d, JPC = 6.2 Hz), 32.72 (d, JPC
=
4.0 Hz), 16.16 (d, JPC = 7.2 Hz). 31P NMR (162 MHz, CDCl3) δ 26.30. HRMS (ESI) Calcd for
C11H16NNaO5PS 328.0384 ([M + Na]+), Found 328.0376 ([M + Na]+).
4.3.7. S-4-Bromobenzyl O,O-diethyl phosphorothioate (5d)
1
Colorless oil. H NMR (400 MHz, CDCl3) δ 7.45 (d, J = 8.8 Hz, 2H), 7.24 (d, J = 7.2 Hz,
2H), 4.16–3.96 (m, 6H), 1.29 (t, J = 8.0 Hz, 6H). 13C NMR (100 MHz, CDCl3) δ 136.77 (d,
JPC = 4.9), 131.75, 130.61, 121.57, 63.64 (d, JPC = 6.1 Hz), 34.33 (d, JPC = 3.9 Hz), 15.95 (d,
JPC = 7.1 Hz). 31P NMR (162 MHz, CDCl3) δ 24.25. HRMS (ESI) Calcd for C11H16BrNaO3PS
360.9639 ([M + Na]+), Found 360.9641 ([M + Na]+).
4.3.8. S-3,4-Dimethoxybenzyl O,O-diethyl phosphorothioate (5f)
Colorless oil. 1H NMR (400 MHz, CDCl3) δ 6.90 (d, J = 7.2 Hz, 2H), 6.80 (d, J = 8.8 Hz, 1H),
4.18–4.00 (m, 6H), 3.88 (d, J = 8.0 Hz, 6H), 1.30 (t, J = 7.2 Hz, 6H). 13C NMR (100 MHz,

428 W. Pluempanupat et al.
CDCl3) δ 149.39, 145.33, 130.19, 121.35, 112.21, 111.30, 63.69 (d, JPC = 6.0), 56.10 (d, JPC
=
3.5 Hz), 35.21 (d, JPC = 4.2 Hz), 16.16 (d, JPC = 7.2 Hz). 31P NMR (162 MHz, CDCl3) δ 26.89.
HRMS (ESI) Calcd for C13H21NaO5PS 343.0745 ([M + Na]+), Found 343.0736 ([M + Na]+).
4.3.9. Benzyl(phenyl)sulfane (6c) [35]
1
Colorless oil. H NMR (400 MHz, CDCl3) δ 7.37–7.20 (m, 10H), 4.16 (s, 2H). 13C NMR
(100 MHz, CDCl3) δ 137.62, 136.52, 130.00, 129.46, 129.95, 128.61, 127.30, 126.48, 39.22.
4.3.10. (2-Nitrobenzyl)(phenyl)sulfane (6d) [36]
Colorless oil. 1H NMR (400 MHz, CDCl3) δ 7.93 (d, J = 8.0, 1H), 7.42–7.38 (m, 1H), 7.36–7.31
(m, 1H), 7.27–7.16 (m, 6H), 4.39 (s, 2H). 13C NMR (100 MHz, CDCl3) δ 134.84, 133.62, 133.08,
132.02, 131.90, 129.12, 128.33, 127.54, 125.36, 37.34.
4.3.11. (4-Bromobenzyl)(phenyl)sulfane (6e) [37]
Colorless oil. 1H NMR (400 MHz, CDCl3) δ 7.41–7.38 (m, 2H), 7.31–7.18 (m, 5H), 7.16–7.13
(m, 2H), 4.05 (s, 2H). 13C NMR (100 MHz, CDCl3) δ 136.85, 135.80, 131.70, 130.61, 130.45,
129.07, 126.85, 121.18, 38.82.
4.3.12. (3,4-Dimethoxybenzyl)(phenyl)sulfane (6f) [38]
Colorless oil. 1H NMR (400 MHz, CDCl3) δ 7.33–7.30 (m, 2H), 7.28–7.23 (m, 2H), 7.21–7.17
(m, 1H), 6.83–6.76 (m, 3H), 3.86 (s, 3H), 3.82 (s, 3H). 13C NMR (100 MHz, CDCl3) δ 149.04,
148.37, 136.52, 130.29, 130.09, 128.96, 126.55, 121.12, 112.09, 111.21, 56.04, 55.94, 39.25.
Acknowledgements
We thank Dr Pitak Chuawong and Dr Matthew Paul Gleeson, Kasetsart University for critical reading of the manuscript.
Funding
This work was supported by the Thailand Research Fund [MRG5280046]; the Center of Excellence for Innovation in
Chemistry (PERCH-CIC), Office of the Higher Education Commission, Ministry of Education; the Kasetsart University
Research and Development Institute (KURDI); the Faculty of Science, Kasetsart University [BRC and ScRF]; andASEA-
UNINET scholarship from the University of Vienna.
Supplemental data
Supplemental data for this article can be accessed 10.1080/17415993.2014.907408.
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