TMSCl Promoted Direct sp3 C-H Alkenylation to Construct (E)-2-Styryl-tetrahydrobenzo[d]thiazoles

Article abstract of DOI:10.1002/cjoc.201500341

A high-efficient and stereo-specific approach for the preparation of biologically important (E)-2-styryl-tetrahydrobenzo[d]thiazoles has been developed via TMSCl promoted direct sp³ C-H alkenylation of 2-methyl-5,6-dihydrobenzo[d]thiazol-7(4H)-

Full text of DOI:10.1002/cjoc.201500341

FULL PAPER
DOI: 10.1002/cjoc.201500341
TMSCl Promoted Direct sp3 C-H Alkenylation to Construct
(E)-2-Styryl-tetrahydrobenzo[d]thiazoles
Chengqiao Cao, Wenbin Wang, Fan Zhang, Nianyu Huang,* Kun Zou
Hubei Key Laboratory of Natural Products Research and Development, College of Biological and Pharmaceutical
Sciences, China Three Gorges University, Yichang, Hubei 443002, China
A high-efficient and stereo-specific approach for the preparation of biologically important (E)-2-styryl-tetra-
hydrobenzo[d]thiazoles has been developed via TMSCl promoted direct sp3 C-H alkenylation of 2-methyl-5,6-di-
hydrobenzo[d]thiazol-7(4H)-one under metal-free conditions. Seventeen target compounds were synthesized in ex-
cellent yields of 82%－98% under the optimal conditions of 300 mol% TMSCl at 110 ℃ for 2 h, and their chemi-
cal structures were elucidated by IR, NMR, ESI-MS, elemental analyses and X-ray crystallography analysis. A
plausible mechanism was also proposed, and this method provided a good functional group conversion for the sp3
C-H substrates.
Keywords (E)-2-styryl-tetrahydrobenzo[d]thiazole, sp3 C-H alkenylation, TMSCl, synthesis
Introduction
described by an efficient and direct sp3 C-H alkenyla-
tion of 2-methyl-5,6-dihydrobenzo[d]thiazol-7(4H)-one
to construct 2-styryl-tetrahydrobenzo[d]thiazole under
metal-free conditions in this work.
Benzo[d]thiazole, especially tetrahydrobenzo[d]thia-
zole, constitutes one of the key core units in various
natural products, potent pharmaceutical compounds and
functional materials, which could be used as neuropro-
tective,[1,2] antimicrobial,[3,4] antileukemic,[5,6] antioxi-
dant and antitumor[7,8] agents. As a versatile synthetic
protocol, the styryl group allows a broad range of trans-
formations including addition, oxidation, reduction, cy-
clization and metathesis.[9-11] Therefore, the introduction
of the styryl group to the tetrahydrobenzo[d]thiazole
skeleton gains more and more attention due to their
recognized importance in biology, pharmacology, and
organic synthesis.
Experimental
Reagents and instruments
All chemical reagents and materials were purchased
from commercial suppliers and used without further
purification. The solvents of dichloromethane, ethyl
acetate (EtOAc) and n-hexane were dried by CaCl2 and
distilled immediately before use. N,N'-Dimethylforma-
mide (DMF) and trimethylsilyl chloride (TMSCl) were
dried over calcium hydride (CaH2) and distilled under
dry nitrogen atmosphere, respectively. Flash column
chromatography for purification was performed in a
glass column by using 200－300 mesh silica gel. Ana-
lytical thin layer chromatography (TLC) was conducted
using Kieselgel-G (Merck Si 245 F) layers (0.25 mm
thick) visualized in UV-cabinet (λmax＝254 and 365 nm).
Solvents were evaporated under reduced pressure at
50 ℃ in EYELA Rotavapor. Melting points were de-
termined with an uncorrected X-4 digital melting point
apparatus. Infrared radiation spectra (IR) were recorded
on a PE-983 infrared spectrometer as KBr pellets with
absorption in cm1. Nuclear magnetic resonance spectra
(NMR) were recorded in deuterated chloroform (CDCl3)
as solvent employing tetramethylsilane (TMS) as inter-
nal standard on Bruker AVANCE III 400 MHz Plus
The sp3 C－H bond is usually regarded as the low-
reactive functional group with high thermodynamic sta-
bilities, and directly constructing C－C bonds form C－
H bonds is highly desirable due to the streamline syn-
thetic scheme, high efficiency and atom economy.[12,13]
In recent years, the direct sp3 C－H bond functionaliza-
tion of methylhetarenes has attracted tremendous atten-
tions employing a variety of unique transition metal
catalysts, such as Au,[14,15] Pd,[16,17] Ir,[18] Rh,[19] Ni,[20,21]
Cu[22,23] or hypervalent iodine agent.[24] However, the
complex precursors, sensitive catalysts, tedious multi-
step synthesis and purification usually limited the fur-
ther application of direct functionalization of sp3 C－H
bond. Due to the importance of 2-styryl substituted het-
erocycles as pharmaceutical agents and building blocks
in organic synthesis, a new methodology was therefore
*
E-mail: hny115@126.com; Tel.: 0086-0717-6397980; Fax: 0086-0717-6397980
Received April 30, 2015; accepted May 30, 2015; published online July 22, 2015.
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/cjoc.201500341 or from the author.
Chin. J. Chem. 2015, 33, 1077—1083
© 2015 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
1077

Cao et al.
FULL PAPER
689; MS (ESI) m/z: 533.05 [2M＋Na]. Anal. calcd for
C15H13NOS: C 70.56, H 5.13, N 5.49; found C 70.48, H
5.07, N 5.39.
NMR spectrometer. Mass spectrometry (MS) data were
measured on API 4000 LC-MS/MS system. Elemental
analyses were carried out with a Vario EL III elementary
analysis instrument. The single-crystal X-ray diffraction
analysis was performed on a Rigaku Mecury CCD dif-
fractometer.
(E)-2-(2-Fluorostyryl)-5,6-dihydrobenzo[d]thiazol-
7(4H)-one (3b) Yellow solids, yield 84%, m.p. 111－
1
112 ℃. H NMR (400 MHz, CDCl3) δ: 7.73 (d, J＝
16.0 Hz, 1H), 7.61－7.56 (m, 1H), 7.38－7.31 (m, 2H),
7.18 (t, J＝7.2 Hz, 1H), 7.14－7.09 (m, 1H), 3.07 (t,
J＝6.0 Hz, 2H), 2.65 (t, J＝6.4 Hz, 2H), 2.27－2.21 (m,
2H); 13C NMR (100 MHz, CDCl3) δ: 192.2, 172.3,
167.6, 161.1 (d, J＝51.8 Hz), 131.1 (d, J＝8.7 Hz),
130.3 (d, J＝2.3 Hz), 128.5 (d, J＝2.7 Hz), 124.5 (d,
J＝3.6 Hz), 123.2 (d, J＝7.2 Hz), 123.1, 116.2 (d, J＝
21.8 Hz), 37.9, 27.3, 23.0; IR (KBr) ν: 1940, 1664, 1366,
960, 756; MS (ESI) m/z: 274.02 [M＋H]. Anal. calcd
for C15H12FNOS: C 65.91, H 4.43, N 5.12; found C
65.80, H 4.36, N 5.02.
(E)-2-(2-Chlorostyryl)-5,6-dihydrobenzo[d]thiazol-
7(4H)-one (3c) Yellow solids, yield 91%, m.p. 124－
126 ℃. 1H NMR (400 MHz, CDCl3) δ: 8.01 (d, J＝16.0
Hz, 1H), 7.69 (t, J＝9.2 Hz, 1H), 7.43 (t, J＝9.2 Hz,
1H), 7.31－7.23 (m, 3H), 3.07 (t, J＝6.0 Hz, 2H), 2.65
(t, J＝6.4 Hz, 2H), 2.24 (t, J＝6.4 Hz, 2H); 13C NMR
(100 MHz, CDCl3) δ: 192.3, 172.0, 167.7, 134.5, 133.4,
133.2, 130.5, 130.3, 130.2, 127.1, 127.0, 123.1, 37.9,
27.2, 23.0; IR (KBr) ν: 2947, 1659, 1364, 1324, 1305,
957, 757; MS (ESI) m/z: 290.27 [M＋H]. Anal. calcd
for C15H12ClNOS: C 62.17, H 4.17, N 4.83; found C
62.02, H 4.12, N 4.77.
(E)-2-(2-Bromostyryl)-5,6-dihydrobenzo[d]thiazol-
7(4H)-one (3d) Yellow solids, yield 92%, m.p. 128－
129 ℃. 1H NMR (400 MHz, CDCl3) δ: 7.97 (d, J＝16.0
Hz, 1H), 7.67 (dd, J＝8.0, 1.6 Hz, 1H), 7.62 (dd, J＝8.0,
0.8 Hz, 1H), 7.37－7.33 (m, 1H), 7.24－7.19 (m, 2H),
3.08 (t, J＝6.4 Hz, 2H), 2.65 (t, J＝6.4 Hz, 2H), 2.25 (q,
J＝6.4 Hz, 2H); 13C NMR (100 MHz, CDCl3) δ: 192.2,
172.0, 167.7, 136.1, 135.0, 133.5, 130.7, 130.4, 127.8,
127.2, 125.0, 123.4, 38.0, 27.3, 23.0; IR (KBr) ν: 2946,
1660, 1364, 956, 755; MS (ESI) m/z: 355.71 [M＋Na].
Anal. calcd for C15H12BrNOS: C 53.90, H 3.62, N 4.19;
found C 53.80, H 3.56, N 4.11.
(E)-2-(2-Methoxystyryl)-5,6-dihydrobenzo[d]thia-
zol-7(4H)-one (3e) Yellow solids, yield 87%, m.p.
171－173 ℃. 1H NMR (400 MHz, CDCl3) δ: 7.89 (d,
J＝16.4 Hz, 1H), 7.55 (dd, J＝7.6, 1.6 Hz, 1H), 7.38 (d,
J＝16.0 Hz, 1H), 7.36－7.32 (m, 1H), 7.00－6.92 (m,
1H); 13C NMR (100 MHz, CDCl3) δ: 192.3, 173.8,
167.6, 158.0, 133.5, 130.9, 129.6, 128.4, 123.9, 121.6,
120.8, 111.1, 55.4, 37.9, 27.3, 23.0; IR (KBr) ν: 2944,
1657, 1364, 1242, 1114, 967, 759; MS (ESI) m/z:
593.48 [2M＋Na]. Anal. calcd for C16H15NO2S: C 67.34,
H 5.30, N 4.91; found C 67.26, H 5.24, N 4.85. Anal.
calcd for C16H15NO2S: C 67.34, H 5.30, N 4.91; found
C 67.26, H 5.24, N 4.85.
General procedure for the synthesis of 2-methyl-5,6-
dihydrobenzo[d]thiazol-7(4H)-one (2)
In a round-bottomed flask (250 mL) equipped with a
stir bar, the mixture of 2-bromocyclohexan-1,3-dione
(19.1 g, 100 mmol) and thioacetamide (7.51 g, 100
mmol) were dissolved in anhydrous pyridine (120 mL)
and stirred at 115 ℃ for 8 h under the protection of
nitrogen atmosphere. The progress of the reaction was
monitored by TLC (eluent: n-hexane/EtOAc＝3∶1,
V/V). After disappearance of starting materials, the solu-
tion was cooled to room temperature, and 10% NaCl
solution (200 mL) was added, then the product was ex-
tracted with dichloromethane (80 mL×3). The organic
phase was separated, washed with saturated NaCl solu-
tion (100 mL×2) and dried over anhydrous sodium
sulphate. Removal of the solvent on a rotary evaporator
under high vacuum gave a viscous dark-red oil, which
was purified by flash column chromatography on silica
gel (eluent: n-hexane/EtOAc＝5∶1, V/V) to yield the
title compound as yellow oil[25] in 66% yield (11.15 g).
1H NMR (400 MHz, CDCl3) δ: 3.02 (t, J＝6.0 Hz, 2H),
2.75 (s, 3H), 2.61 (t, J＝6.8 Hz, 2H), 2.42－2.17 (m,
2H); 13C NMR (100 MHz, CDCl3) δ: 192.3, 173.3,
166.8, 130.9, 37.8, 27.1, 23.0, 20.0.
General procedure for the synthesis of 2-styryl-tetra-
hydrobenzo[d]thiazoles (3a–3q)
To the cold solution of aromatic aldehyde (1.0 mmol)
and
2-methyl-5,6-dihydrobenzo[d]thiazol-7(4H)-one
(1.0 mmol) in anhydrous DMF (10 mL) was added
TMSCl (3.0 mmol) successively. The mixture was al-
lowed to heat to 110 ℃ for 2 h under a glass Serpen-
tine condenser until reached completion (monitored by
TLC, eluent: n-hexane/EtOAc＝1∶1, V/V). After cool-
ing to room temperature, the mixture was diluted in wa-
ter (50 mL), and the product was extracted with di-
chloromethane (30 mL×3). The organic phase was
separated, washed with saturated NaCl solution (50 mL
×2), dried over anhydrous sodium sulphate and evapo-
rated. The crude product was purified by flash column
chromatography on silica gel (eluent: n-hexane/EtOAc
＝2∶1, V/V) to give the target compound.
(E)-2-Styryl-5,6-dihydrobenzo[d]thiazol-7(4H)-
one (3a) Yellow solids, yield 97%, m.p. 101 －
102 ℃.[26] 1H NMR (400 MHz, CDCl3) δ: 7.61 (d, J＝
16.0 Hz, 1H), 7.58－7.55 (m, 2H), 7.43－7.35 (m, 3H),
7.26 (d, J＝16.0 Hz, 1H), 3.07 (t, J＝6.4 Hz, 2H), 2.64
(t,
J＝6.8 Hz, 2H), 2.27－2.20 (m, 2H); 13C NMR
(E)-2-(3-Chlorostyryl)-5,6-dihydrobenzo[d]thia-
zol-7(4H)-one (3f) Yellow solids, yield 88%, m.p. 130
－131 ℃. 1H NMR (400 MHz, CDCl3) δ: 7.54 (t, J＝
8.0 Hz, 2H), 7.44－7.42 (m, 1H), 7.35－7.33 (m, 2H),
(100 MHz, CDCl3) δ: 192.3, 172.5, 167.6, 137.7, 134.9,
129.9, 129.8, 128.9, 127.6, 120.7, 37.9, 27.2, 23.0; IR
(KBr) ν: 3039, 2939, 1661, 1514, 1361, 1307, 951, 760,
1078
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Chin. J. Chem. 2015, 33, 1077—1083

TMSCl Promoted Direct sp3 C-H Alkenylation to Construct (E)-2-Styryl-tetrahydrobenzo[d]thiazoles
7.24 (d, J＝16.4 Hz, 1H), 3.07 (t, J＝6.4 Hz, 2H), 2.65
(t, J＝6.4 Hz, 2H), 2.27－2.21 (m, 2H); 13C NMR (100
MHz, CDCl3) δ: 192.2, 171.7, 167.7, 136.8, 135.8,
135.0, 130.3, 130.1, 129.5, 127.3, 125.7, 121.9, 37.9,
27.2, 22.9; IR (KBr) ν: 2943, 1655, 1364, 1324, 966,
788, 684; MS (ESI) m/z: 290.27 [M＋H]. Anal. calcd
for C15H12ClNOS: C 62.17, H 4.17, N 4.83; found C
62.06, H 4.13, N 4.78.
(E)-2-(3-Bromostyryl)-5,6-dihydrobenzo[d]thiazol-
7(4H)-one (3g) Yellow solids, yield 95%, m.p. 125－
126 ℃. 1H NMR (400 MHz, CDCl3) δ: 7.71 (s, 1H),
7.53 (d, J＝16.0 Hz, 1H), 7.50－7.46 (m, 2H), 2.28 (d,
J＝8.0 Hz, 1H), 2.23 (d, J＝16.4 Hz, 1H), 3.07 (t, J＝
6.4 Hz, 2H), 2.65 (t, J＝6.4 Hz, 2H), 2.27－2.21 (m,
2H); 13C NMR (100 MHz, CDCl3) δ: 192.2, 171.7,
167.7, 137.1, 135.7, 132.5, 130.4, 130.3, 130.2, 126.1,
123.1, 121.9, 37.9, 27.2, 23.0; IR (KBr) ν: 2941, 1655,
1509, 1365, 966, 786, 682; MS (ESI) m/z: 355.68 [M＋
Na]. Anal. calcd for C15H12BrNOS: C 53.90, H 3.62, N
4.19; found C 53.79, H 3.58, N 4.12.
171 ℃. 1H NMR (400 MHz, CDCl3) δ: 7.54 (t, J＝8.0
Hz, 3H), 7.42 (d, J＝8.4 Hz, 2H), 7.23 (d, J＝16.0 Hz,
1H), 3.06 (t, J＝6.4 Hz, 2H), 2.64 (t, J＝6.4 Hz, 2H),
2.27－2.19 (m, 2H); 13C NMR (100 MHz, CDCl3) δ:
192.2, 172.0, 167.7, 136.2, 133.9, 132.2, 131.7, 131.2,
130.2, 128.9, 123.9, 121.2, 37.9, 27.2, 23.0; IR (KBr) ν:
2942, 1664, 1488, 1362, 1325, 1068, 815; MS (ESI) m/z:
355.71 [M＋Na]. Anal. calcd for C15H12BrNOS: C
53.90, H 3.62, N 4.19; found C 53.79, H 3.57, N 4.15.
(E)-2-(4-Methylstyryl)-5,6-dihydrobenzo[d]thia-
zol-7(4H)-one (3l) Yellow solids, yield 85%, m.p. 161
1
－162 ℃. H NMR (400 MHz, CDCl3) δ: 7.58 (d, J＝
16.0 Hz, 1H), 7.46 (dd, J＝8.0, 3.6 Hz, 2H), 7.21 (dd,
J＝8.4, 4.0 Hz, 3H), 3.06 (t, J＝6.4 Hz, 2H), 2.64 (t,
J＝6.8 Hz, 2H), 2.38 (s, 3H), 2.26－2.20 (m, 2H); 13C
NMR (100 MHz, CDCl3) δ: 192.2, 172.9, 167.6, 140.2,
137.8, 132.3, 129.7, 128.2, 127.5, 119.8, 37.9, 27.3,
23.0, 21.4; IR (KBr) ν: 2942, 1658, 1511, 1363, 1181,
805; MS (ESI) m/z: 270.79 [M＋H]. Anal. calcd for
C16H15NOS: C 71.34, H 5.61, N 5.20; found C 71.28, H
5.57, N 5.15.
(E)-2-(3-Hydroxystyryl)-5,6-dihydrobenzo[d]thia-
zol-7(4H)-one (3h) Yellow solids, yield 90%, m.p.
118－119 ℃. 1H NMR (400 MHz, CDCl3) δ: 7.54 (d,
J＝16.0 Hz, 1H), 7.28－7.20 (m, 2H), 7.09 (t, J＝8.4
Hz, 2H), 6.88 (dd, J＝8.0, 0.8 Hz, 1H), 6.36 (brs, 1H),
3.06 (t, J＝6.0 Hz, 2H), 2.66 (t, J＝6.4 Hz, 2H), 2.27－
2.20 (m, 2H); 13C NMR (100 MHz, CDCl3) δ: 192.6,
172.8, 167.8, 156.4, 137.8, 136.4, 130.2, 129.8, 120.7,
120.4, 117.3, 113.9, 37.9, 27.2, 22.9; IR (KBr) ν: 3349,
2935, 1644, 1592, 1451, 1366, 957, 781, 686; MS (ESI)
m/z: 269.79 [MH]. Anal. calcd for C15H13NO2S: C
66.40, H 4.83, N 5.16; found C 66.31, H 4.79, N 5.09.
(E)-2-(4-Fluorostyryl)-5,6-dihydrobenzo[d]thiazol-
7(4H)-one (3i) Yellow solids, yield 89%, m.p. 144－
145 ℃. 1H NMR (400 MHz, CDCl3) δ: 7.57－7.53 (m,
3H), 7.17 (d, J＝16.0 Hz, 1H), 7.10 (t, J＝8.4 Hz, 2H),
3.07 (t, J＝6.4 Hz, 2H), 2.67－2.63 (m, 2H), 2.28－
2.20 (m, 2H); 13C NMR (100 MHz, CDCl3) δ: 192.3,
172.3, 167.6, 163.5 (d, J＝249.6 Hz), 136.3, 131.3 (d,
J＝3.4 Hz), 129.8, 129.3 (d, J＝8.2 Hz), 120.4 (d, J＝
2.5 Hz), 116.2 (d, J＝21.8 Hz), 37.9, 27.3, 23.0; IR
(KBr) ν: 2962, 1655, 1509, 1363, 1224, 1165, 976, 830;
MS (ESI) m/z: 274.02 [M ＋ H]. Anal. calcd for
C15H12FNOS: C 65.91, H 4.43, N 5.12; found C 65.80,
H 4.38, N 5.05.
(E)-2-(4-Chlorostyryl)-5,6-dihydrobenzo[d]thiazol-
7(4H)-one (3j) Yellow solids, yield 98%, m.p. 176－
177 ℃. 1H NMR (400 MHz, CDCl3) δ: 7.56 (d, J＝16.0
Hz, 1H), 7.49 (d, J＝8.4 Hz, 2H), 7.37 (d, J＝8.4 Hz,
2H), 7.21 (d, J＝16.0 Hz, 1H), 3.06 (t, J＝6.0 Hz, 2H),
2.64 (t, J＝6.4 Hz, 2H), 2.25 (q, J＝6.4 Hz, 2H); 13C
NMR (100 MHz, CDCl3) δ: 192.2, 172.0, 167.7, 136.1,
135.6, 133.5, 130.2, 129.2, 128.7, 121.2, 37.9, 27.2,
23.0; IR (KBr) ν: MS (ESI) m/z: 290.27 [M＋H]. Anal.
calcd for C15H12ClNOS: C 62.17, H 4.17, N 4.83; found
C 62.06, H 4.13, N 4.77.
(E)-2-[4-(Trifluoromethyl)styryl]-5,6-dihydroben-
zo[d]thiazol-7(4H)-one (3m) Yellow solids, yield
88%, m.p. 203－204 ℃. 1H NMR (400 MHz, CDCl3)
δ: 7.67－7.61 (m, 5H), 7.32 (d, J＝16.0 Hz, 1H), 3.08 (t,
J＝5.6 Hz, 2H), 2.66 (t, J＝6.0 Hz, 2H), 2.25 (t, J＝5.6
Hz, 2H); 13C NMR (100 MHz, CDCl3) δ: 192.3, 171.4,
167.7, 138.4, 135.6, 130.6, 127.6, 125.9 (d, J＝3.7 Hz),
122.9, 122.5, 37.9, 27.2, 22.9; IR (KBr) ν: 2951, 1665,
1363, 1323, 1162, 1120, 1066, 829; MS (ESI) m/z:
669.13 [2M＋Na]. Anal. calcd for C16H12F3NOS: C
59.43, H 3.74, N 4.33; found C 59.37, H 3.70, N 4.28.
(E)-2-[2-(Thiophen-2-yl)vinyl]-5,6-dihydrobenzo-
[d]thiazol-7(4H)-one (3n) Yellow solids, yield 82%,
m.p. 94－96 ℃. 1H NMR (400 MHz, CDCl3) δ: 7.74 (d,
J＝15.6 Hz, 1H), 7.37 (d, J＝4.8 Hz, 1H), 7.26 (s, 1H),
7.07－7.02 (m, 2H), 3.05 (t, J＝6.4 Hz, 2H), 2.64 (t,
J＝6.4 Hz, 2H), 2.26－2.20 (m, 2H); 13C NMR (100
MHz, CDCl3) δ: 192.2, 172.0, 167.7, 140.4, 130.3,
129.9, 129.8, 128.2, 127.8, 119.7, 37.9, 27.2, 23.0; IR
(KBr) ν: 2934, 1658, 1610, 1360, 938, 715; MS (ESI)
m/z: 545.00 [2M＋Na]. Anal. calcd for C13H11NOS2: C
59.74, H 4.24, N 5.36; found C 59.68, H 4.20, N 5.29.
(E)-2-[2-(Pyridin-2-yl)vinyl]-5,6-dihydrobenzo[d]-
thiazol-7(4H)-one (3o) Yellow solids, yield 85%, m.p.
123－125 ℃. 1H NMR (400 MHz, CDCl3) δ: 8.65 (d,
J＝4.0 Hz, 1H), 7.79 (d, J＝15.6 Hz, 1H), 7.74－7.69
(m, 1H), 7.65 (d, J＝15.6 Hz, 1H), 7.43 (d, J＝7.6 Hz,
1H), 7.27－7.23 (m, 1H), 3.08 (t, J＝6.4 Hz, 2H), 2.65
(t, J＝6.4 Hz, 2H), 2.27－2.21 (m, 2H); 13C NMR (100
MHz, CDCl3) δ: 192.3, 171.6, 167.7, 153.3, 150.1,
136.8, 135.9, 130.8, 124.2, 124.0, 123.6, 37.9, 27.3,
23.0; IR (KBr) ν: 2943, 1660, 1363, 990, 769; MS (ESI)
m/z: 256.8 [M＋H]. Anal. calcd for C14H12N2OS: C
65.60, H 4.72, N 10.93; found C 65.51, H 4.69, N 10.87.
(E)-2-[2-(Pyridin-3-yl)vinyl]-5,6-dihydrobenzo[d]-
thiazol-7(4H)-one (3p) Yellow solids, yield 89%, m.p.
115－116 ℃. 1H NMR (400 MHz, CDCl3) δ: 8.79 (s,
(E)-2-(4-Bromostyryl)-5,6-dihydrobenzo[d]thiazol-
7(4H)-one (3k) Yellow solids, yield 97%, m.p. 170－
Chin. J. Chem. 2015, 33, 1077—1083
© 2015 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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Cao et al.
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1H), 8.60 (s, 1H), 7.88 (d, J＝8.0 Hz, 1H), 7.60 (d, J＝
16.0 Hz, 1H), 7.37－7.33 (m, 1H), 7.28 (d, J＝8.0 Hz,
1H), 3.08 (t, J＝6.0 Hz, 2H), 2.66 (t, J＝6.4 Hz, 2H),
2.28－2.22 (m, 2H); 13C NMR (100 MHz, CDCl3) δ:
192.2, 171.3, 167.7, 150.3, 149.3, 133.6, 133.5, 130.9,
130.5, 123.8, 122.5, 37.9, 27.2, 22.9; IR (KBr) ν: 2943,
1664, 1511, 1362, 1326, 973, 803, 704; MS (ESI) m/z:
535.00 [2M＋Na]. Anal. calcd for C14H12N2OS: C 65.60,
H 4.72, N 10.93; found C 65.49, H 4.66, N 10.87.
(E)-2-[2-(Naphthalen-1-yl)vinyl]-5,6-dihydroben-
zo[d]thiazol-7(4H)-one (3q) Yellow solids, yield 88%,
m.p. 52－54 ℃. 1H NMR (400 MHz, CDCl3) δ: 8.46
(d, J＝16.0 Hz, 1H), 8.23 (d, J＝8.0 Hz, 1H), 7.89 (d,
J＝8.4 Hz, 2H), 7.83 (d, J＝7.2 Hz, 1H), 7.60－7.49 (m,
3H), 7.34 (d, J＝15.6 Hz, 1H), 3.10 (t, J＝6.4 Hz, 2H),
2.66 (t, J＝6.4 Hz, 2H), 2.26 (t, J＝6.4 Hz, 2H); 13C
NMR (100 MHz, CDCl3) δ: 192.3, 172.5, 167.7, 134.5,
133.7, 132.3, 131.3, 130.1, 128.8, 126.8, 126.2, 125.5,
124.5, 123.3, 123.1, 38.0, 27.3, 23.0; IR (KBr) ν: 2944,
1659, 1363, 1303, 793, 771; MS (ESI) m/z: 632.98 [2M
＋Na]. Anal. calcd for C19H15NOS: C 74.72, H 4.95, N
4.59; found C 74.65, H 4.90, N 4.52.
Results and Discussion
Optimization of conditions for the model reaction
Firstly, 2-methyl-5,6-dihydrobenzo[d]thiazol-7(4H)-
one (2)[25] was prepared according to the known
Hantzsch thiazole synthesis from the starting materials
of 2-bromocyclohexan-1,3-dione (1)[29] and thio-
acetamide in refluxing pyridine. In the preliminary ex-
periments, the sp3 C－H alkenylation reaction of
2-methyl-5,6-dihydrobenzo[d]thiazol-7(4H)-one (2)
with aromatic aldehydes was conducted in N,N'-dimeth-
ylformamide (DMF) at 80 ℃ for 12 h under the 20
mol% of transition metal halide catalyst, for example,
PdCl2, TiCl4, SrCl2, FeCl3, CoCl2 and ZnCl2. However,
the McMurry olefination product of trans-stilbene was
isolated when TiCl4 and zinc power were used[30] (Table
1, Entry 2), and the others showed no catalytic effect
except FeCl3 with 31% isolated yield (Entry 6). Subse-
quently, several representative protic acids, such as sul-
furic acid and hydrochloric acid were screened as addi-
tives, but no superior results were obtained (Entries 7－
8). Interestingly, when FeCl3 and p-toluenesulfonic acid
(p-TsOH) were added together, the promising
2-styryl-tetrahydrobenzo[d]thiazole (3) was obtained
with yield of 55% with two diastereomeric isomers
mixture (Entry 9). Although the dark-colored reaction
Crystal structure determination by X-ray diffraction
crystallography
Single crystals of compound 3e (C16H15NO2S, Mr＝
285.35) were obtained by slow evaporation from a 50∶
50 mixture of ethyl acetate and n-hexane at 4 ℃. A
colorless prism crystal with dimensions of 0.21 mm×
0.19 mm×0.18 mm was selected for measurement.
Diffraction data of the single crystal were collected at
296 K on a Rigaku Mecury CCD diffractometer
equipped with a graphite-monochromatic Mo Kα radia-
tion (λ＝0.71073 Å) by Crystal clear software. In an
asymmetric unit the molecule crystallized in monoclinic
space group P21/c with a＝13.366(15) Å, b＝7.161(7)
Table 1 Optimization of the reaction conditions
Entry Catalyst (equiv.)
Solvent Conditiona
Yieldb/%
1
2
3
4
5
6
PdCl2 (20 mol%)
TiCl4 (20 mol%)
SrCl2 (20 mol%)
CoCl2 (20 mol%)
ZnCl2 (20 mol%)
DMF
DMF
DMF
DMF
DMF
DMF
80 ℃, 12 h
80 ℃, 12 h
80 ℃, 12 h
80 ℃, 12 h
80 ℃ 12 h
80 ℃, 12 h
0
0
0
0
0
Å, c＝18.195(14) Å, Z＝4, V＝1417(2) Å3, Dcalc
＝
FeCl3 (20 mol%)
31
1.337 gm/cm3, F(000)＝600. A total of 14079 reflec-
tions were collected in the range of 1.87°≤θ≤27.44°
by using an ω-scan mode, of which 3222 were unique
with Rint＝0.1556 and 2577 were observed with I＞
2σ(I). Empirical absorption corrections were applied.
The structure was solved by direct methods using
SHELXS-97 programs.[27] All of the non-hydrogen at-
oms were located from difference Fourier maps, and
then refined anisotropically with SHELXL-97 via a full-
matrix least-squares procedure.[28] The hydrogen atoms
were added according to the theoretical model. The final
R＝0.0664, wR＝0.1805, (Δ/σ)max＝0.000, S＝1.057,
(Δρ)max＝0.644 and (Δρ)min＝0.415 e/Å3. Crystallo-
graphic data (excluding structure factors) have been
deposited with the Cambridge Crystallographic Data
Centre as supplementary publication number CCDC
1051976. Copies of the data can be obtained, free of
charge, on application to CCDC, 12 Union Road, Cam-
bridge CB2 1EZ, UK, (Fax:＋44-(0)1223-336033 or
e-mail: deposit@ccdc.cam.ac.uk).
FeCl3 (20 mol%)
＋H2SO4 (20 mol%)
FeCl3 (20 mol%)
＋HCl (20 mol%)
FeCl3 (20 mol%)
＋p-TsOH (20 mol%)
FeCl3 (20 mol%)
7
DMF
DMF
DMF
DMF
80 ℃, 12 h
80 ℃, 12 h
80 ℃, 12 h
80 ℃, 12 h
28
20
55
73
8
9
10
＋TMSCl (20 mol%)
TMSCl (100 mol%)
11
12
13
14
15
16
DMF
THF
80 ℃, 12 h
80 ℃, 12 h
85
0
TMSCl (100 mol%)
TMSCl (100 mol%)
TMSCl (100 mol%)
TMSCl (100 mol%)
TMSCl (100 mol%)
CHCl3 80 ℃, 12 h
CH3CN 80 ℃, 12 h
DMSO 80 ℃, 12 h
EtOH 80 ℃, 12 h
Toluene 80 ℃, 12 h
0
0
0
23
20
17 TMSCl (100 mol%)
a
Unless otherwise noted, all reactions were performed with 2
(0.1 mmol), benzaldehyde (0.1 mmol) in solvent (1.0 mL). b The
yield of the product 3 was monitored by H NMR (400 MHz,
CDCl3, 298 K) after the model reaction finished.
1
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Chin. J. Chem. 2015, 33, 1077—1083

TMSCl Promoted Direct sp3 C-H Alkenylation to Construct (E)-2-Styryl-tetrahydrobenzo[d]thiazoles
mixture was difficult to separate, the result did encour-
age us for seeking more efficient catalyst (Scheme 1).
Table 2 Optimization of the reaction conditions
Factor
level
Catalyst dosage
Temperature
Time Yield/%
Scheme 1 Model reaction for the sp3 C-H alkenylation reaction
1
2
3
4
5
6
7
8
9
1 (100 mol%)
1 (100 mol%)
1 (100 mol%)
2 (200 mol%)
2 (200 mol%)
2 (200 mol%)
3 (300 mol%)
3 (300 mol%)
3 (300 mol%)
88.0
1 (90 ℃)
2 (100 ℃)
3 (110 ℃)
1 (90 ℃)
2 (100 ℃)
3 (110 ℃)
1 (90 ℃)
2 (100 ℃)
3 (110 ℃)
89.0
1 (2 h)
2 (3 h)
3 (4 h)
2 (3 h)
3 (4 h)
1 (2 h)
3 (4 h)
1 (2 h)
2 (3 h)
92.7
85
89
90
88
93
95
94
98
99
－
－
－
－
O
O
Catalyst
S
N
S
N
Solvent
2
3
As a mild useful and inexpensive Lewis acid catalyst,
trimethylsilyl chloride (TMSCl) has been widespread
used in many organic transformations because of the
near neutral conditions, more reactivity and commercial
viability,[31-34] and many biologically important com-
pounds were successfully prepared by the promotion of
TMSCl in recent literatures.[35-38] Thus, TMSCl was
chosen as the co-catalyst with FeCl3 for constructing the
(E)-2-styryl-tetrahydrobenzo[d]thiazole (3), and 73%
yield of the target product was obtained (Table 1, Entry
10). Considering the dark color and separating difficul-
ties caused by the FeCl3 catalyst, searching for ideal
conditions included shortening the reaction time, con-
venient isolation and high yields was the goal of opti-
mizing the model reaction. Fortunately, we found 80%
yield of 3 could also be obtained by increasing the load
of TMSCl to three equivalents without the presence of
FeCl3 (Entry 11), which indicated TMSCl might be an
efficient catalyst in this transformation instead of FeCl3.
Furthermore, the best solvent was screened from
tetrahydrofuran (THF), chlrorform (CHCl3), acetonitrile
(CH3CN), dimethyl sulfoxide (DMSO), ethanol (EtOH)
and toluene. The reaction mixture became black viscous
mixture when DMSO was used, which might be relate
to the oxidation property of the solvent (Entry 15). Be-
sides the poor yield of ethanol and toluene, the other
solvent seemed to inhibit the catalytic activity of
TMSCl (Entries 12－14). Finally, DMF was proved to
be the most suitable solvent in the TMSCl-promoted sp3
C-H alkenylation.
a
k1
a
k2
92.0
93.3
92.0
a
k3
97.0
94.7
92.3
R
9.0
5.7
0.7
a
ki was the average scores of each factor at its different level (i
equals 1, 2, and 3, respectively).
The sp3 C-H alkenylation reaction and possible
mechanism
With the optimized conditions in hand, the scope of
sp3 C-H alkenylation reaction of 2-methyl-5,6-dihydro-
benzo[d]thiazol-7(4H)-one (2) was extended to various
aromatic or heteroaromatic aldehydes (Scheme 2). Fi-
nally, seventeen (E)-2-styryl-tetrahydrobenzo[d]thia-
zoles (3a－3q) were successfully prepared in the high
yields of 82%－98% (Table 3), and their chemical
structures were confirmed by IR, NMR, ESI-MS, ele-
mental analyses and X-ray crystallography analysis. The
reaction showed perfect stereo-selectivity of (E)-isomer
with the coupling constant of 15.6－16.4 Hz for the ole-
1
finic double bond in H NMR spectra. Application of
this method in the synthesis of bioactive antitumor
agents is currently in progress.
Scheme 2 Synthetic routes for the 2-styryl-tetrahydroben-
zo[d]thiazoles
To find the effects of the catalyst dosage on the
yields of the product, the reaction of 2-methyl-5,6-di-
hydrobenzo[d]thiazol-7(4H)-one (2) with benzaldehyde
was performed under the 100 mol% to 300 mol% of
TMSCl, and the reaction temperature was increased
from 90 to 110 ℃ with aim of shortening the reaction
time within 4 h. Therefore, a group of orthogonal ex-
periments[39,40] was designed and carried out in se-
quence to search the optimal conditions. The orthogonal
design table L9 (34) was obtained by SPSS software[41]
(Statistical Product and Service Solutions), and calcu-
lated results were given in Table 2. The results indicated
the main factor influencing the yields of sp3 C-H al-
kenylation was the catalyst dosage, and the order of sig-
nificance in decreasing order was: catalyst dosage＞
reaction temperature＞reaction time. Ultimately, the
most optimal conditions for the model reaction were
confirmed as 300 mol% TMSCl at 110 ℃ for 2 h.
According to some related literatures,[31,42,43] a pos-
sible mechanism of the TMSCl-promoted sp3 C-H al-
kenylation reaction for constructing 2-styryl-tetrahy-
drobenzo[d]thiazoles could be tentatively explained as
shown in Scheme 3, which might involve: (i) TMSCl
induced the 2-methyl-5,6-dihydrobenzo[d]thiazol-7(4H)-
Chin. J. Chem. 2015, 33, 1077—1083
© 2015 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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1081

Cao et al.
FULL PAPER
one (2) to give the thioenol tautomer (A), and also acti-
vated aldehyde by coordinating to the carbonyl group;
(ii) then a similar reaction of Adol-type condensation
occurred between the two intermediates, and resulted in
the corresponding addition product (B); (iii) finally ad-
duct (B) was aromatized to generate the product (3)
through the dehydration of TMSCl.
and benzene ring (C) of C(10)-C(11)-C(12)-C(13)-
C(14)-C(15). All ring atoms in the thiazole system (B)
were essentially coplanar with a maximum deviation of
0.0050(29) Å from the plane for C(7). The intermo-
lecular weak π-π stacking interactions between the ring
B and C helped to stabilize the 3D supramolecular ar-
chitecture of the crystal (Figure 2), and the centroid-to-
centroid distance of two rings was 3.9657(47) Å with
the interplanar angle of 6.921(80)° and perpendicular
distance of 3.467 Å.
Scheme 3 Proposed mechanism for the TMSCl-promoted sp3
C-H alkenylation reaction
H
Ar
Ar
O
TMSCl
S
CH2
HCl
+
N
H
TMSCl
O
-
TMSCl
TMS
O
H+
A
TMSCl
S
N
HO
O
CH3
CH Ar
H
S
N
HC
HCl
2
TMS
B
(TMS)2O + HCl
O
Figure 2 Packing diagram of 3e.
S
N
Ar
Table 3 Synthesis of the 2-styryl-tetrahydrobenzo[d]thiazole 3
3
No. Substituent (Ar)
3a Ph
State
Yielda/% Melting point/℃
Spectroscopy and X-ray crystal structural analysis
Yellow solids
Yellow solids
Yellow solids
Yellow solids
Yellow solids
Yellow solids
Yellow solids
Yellow solids
Yellow solids
Yellow solids
Yellow solids
Yellow solids
Yellow solids
Yellow solids
Yellow solids
Yellow solids
97
84
91
92
87
88
95
90
89
98
97
85
88
82
85
89
88
101－102
111－112
124－125
128－129
171－172
130－131
125－126
118－119
144－145
176－177
170－171
161－162
203－204
94－95
3b 2-FPh
The structure of compound 3e was confirmed by the
X-ray crystallographic analysis, and its ORTEP drawing
with common atom numbering scheme was shown in
Figure 1. The crystallographic data, selected bond
lengths, bond angles and torsion angles were listed in
the supporting materials. The 6-membered ring (A) of
C(1)-C(2)-C(3)-C(4)-C(5)-C(6) in Figure 1 shows a
distorted chair conformation [Φ＝302.1382(7145)°, θ＝
123.90(61)°, puckering amplitude (Q)＝0.3480(44)°].
The olefinic double bond C(8)＝C(9) is in a (Z)-con-
formation with the bond length of 1.335(3) Å (see Table
3), which formed a long-ranged conjugated system with
the thiazole system (B) of S(1)-C(6)-C(5)-N(1)-C(7)
3c 2-ClPh
3d 2-BrPh
3e 2-CH3OPh
3f 3-ClPh
3g 3-B-Ph
3h 3-HOPh
3i 4-FPh
3j 4-ClPh
3k 4-BrPh
3l 4-CH3Ph
3m 4-CF3Ph
3n Thiophen-2-yl
3o Pyridin-2-yl
3p Pyridin-3-yl
123－124
115－116
52－53
3q Naphthalen-1-yl Yellow solids
a Isolated yields.
Conclusions
In summary, an efficient strategy of TMSCl-pro-
moted sp3 C-H alkenylation reaction for the stereo-spe-
cific synthesis of (E)-2-styryl-tetrahydrobenzo[d]thia-
Figure 1 The ORTEP drawing of 3e with numbered atoms.
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Chin. J. Chem. 2015, 33, 1077—1083

TMSCl Promoted Direct sp3 C-H Alkenylation to Construct (E)-2-Styryl-tetrahydrobenzo[d]thiazoles
[17] Chan, K. S.; Wasa, M.; Chu, L.; Laforteza, B. N.; Miura, M.; Yu, J.
zoles has been developed in this work. This facial and
straightforward process has attractive features of high
selectivity, easy work-up and excellent conversion of
substrates. The proposed mechanism of this reaction
suggested that the alkenylation of other sp3 C-H sub-
strates will be further investigated in our laboratory.
Q. Nat. Chem. 2014, 6, 146.
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The authors thank the finance supported by the Na-
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Chin. J. Chem. 2015, 33, 1077—1083
© 2015 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.cjc.wiley-vch.de
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