Facile synthesis of 6-aryl-3-cyanopyridine-2-(1H)-thiones from aryl ketones

Article abstract of DOI:10.1080/00397911.2010.541964

An improved synthesis of 6-aryl-3-cyanopyridine-2-(1H)-thiones utilizing enaminones as starting materials catalyzed by 1,4-diazabicyclo[2.2.2]octane (DABCO) was described. Moreover, a convenient one-pot conversion of aryl ketones to 6-aryl-3-cyanopyridine-2-(1H)-thiones was also developed in moderate to good yields (up to 80%). Copyright Taylor & Francis Group, LLC.

Full text of DOI:10.1080/00397911.2010.541964

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Facile Synthesis of 6-Aryl-3-
cyanopyridine-2-(1H)-thiones from Aryl
Ketones
Ren-Lin Zheng a , Xiu-Xiu Zeng a b , Hai-Yun He a , Jun He b , Sheng-
Yong Yang a , Luo-Ting Yu a & Li Yang a
a State Key Laboratory of Biotherapy and Cancer Center, West China
Hospital, West China Medical School, Sichuan University, Chengdu,
China
b Department of Pharmaceutical and Bioengineering, School of
Chemical Engineering, Sichuan University, Chengdu, China
Accepted author version posted online: 21 Oct 2011.Version of
record first published: 25 Jan 2012.
To cite this article: Ren-Lin Zheng, Xiu-Xiu Zeng, Hai-Yun He, Jun He, Sheng-Yong Yang, Luo-Ting Yu &
Li Yang (2012): Facile Synthesis of 6-Aryl-3-cyanopyridine-2-(1H)-thiones from Aryl Ketones, Synthetic
Communications: An International Journal for Rapid Communication of Synthetic Organic Chemistry,
42:10, 1521-1531
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Synthetic Communications1, 42: 1521–1531, 2012
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397911.2010.541964
FACILE SYNTHESIS OF 6-ARYL-3-CYANOPYRIDINE-
2-(1H)-THIONES FROM ARYL KETONES
Ren-Lin Zheng,1 Xiu-Xiu Zeng,1,2 Hai-Yun He,1 Jun He,2
Sheng-Yong Yang,1 Luo-Ting Yu,1 and Li Yang1
1State Key Laboratory of Biotherapy and Cancer Center, West China
Hospital, West China Medical School, Sichuan University, Chengdu, China
2Department of Pharmaceutical and Bioengineering, School of Chemical
Engineering, Sichuan University, Chengdu, China
GRAPHICAL ABSTRACT
Abstract An improved synthesis of 6-aryl-3-cyanopyridine-2-(1H)-thiones utilizing enami-
nones as starting materials catalyzed by 1,4-diazabicyclo[2.2.2]octane (DABCO) was
described. Moreover, a convenient one-pot conversion of aryl ketones to 6-aryl-3-cyanopyr-
idine-2-(1H)-thiones was also developed in moderate to good yields (up to 80%).
Keywords 6-Aryl-3-cyanopyridine-2-(1H)-thiones; DABCO; enaminones; one-pot
synthesis
INTRODUCTION
3-Cyanopyridine-2-(1H)-thiones are valuable compounds in organic synthesis
not only because of their broad biological activities[1] but also because they serve as use-
ful synthetic intermediates in the preparations of dyes, pesticides, and cannabinoid-1
receptor inverse agonists.[2] For example, in our recent search for Aurora-A kinase
inhibitors,[3] compound 1 was prepared from 3-cyanopyridine-2-(1H)-thione 2 via
Thorpe–Ziegler cyclization[4] (Scheme 1).
Although a few procedures for accessing 6-aryl-3-cyanopyridine-2-(1H)-
thiones 6 (Scheme 2) have been reported employing enaminones (4 and 8) or sodium
Received December 7, 2009.
Address correspondence to Li Yang, State Key Laboratory of Biotherapy and Cancer Center, West
China Hospital, West China Medical School, Sichuan University, Chengdu, China. E-mail: yangli@
scu.edu.cn
1521

1522
R.-L. ZHENG ET AL.
Scheme 1. Synthesis of compound 1.
enolate (5),[5] these processes still have several limitations including the tedious
synthesis of 4 in pathway A and the moisture-sensitive intermediate 5 in pathway
B. Given the stability of 8 and the operational convenience of pathway C, we choose
pathway C to prepare structurally diverse 6-aryl-3-cyanopyridine-2-(1H)-thiones 6.
Herein, we describe an improved synthesis of 6-aryl-3-cyanopyridine-2-(1H)-thiones
6 from enaminones 8 (pathway C) using 1,4-diazabicyclo[2.2.2]octane (DABCO) as
the base as well as a convenient experimental protocol from aryl ketones 7 to 6
directly in one flask.
RESULTS AND DISCUSSION
A series of enaminone 8 were readily prepared in 75–95% yield by the treatment
of 7 with N,N-dimethylformamide dimethyl acetal (DMF-DMA) according to litera-
ture procedure[6] With enaminones 8 in hand, we set out to investigate the conden-
sation conditions of 8a with cyanothioacetamide under different basic conditions,
and the results are shown in Table 1. Generally, inorganic basic conditions such as
KOH=H2O,[7] EtONa=EtOH,[8f] and t-BuOK=DMF[2b] (entries 1–3) gave only poor
to moderate yields, while the Et3N=EtOH system (entry 4) provided a much better
result. Based on this observation, after screening of a range of organic bases (entries
4–9)[8a–c,8e,9] we were delighted to find that the yield could be improved to 79% using
DABCO as base (entry 9). Finally, increasing the amount of cyanothioacetamide
from 1.1 to 1.5 equiv. gave the best yield, 88%, as shown in entry 10.
To demonstrate the generality of this method, we next investigated the conden-
sation of a variety of enaminones 8 with cyanothioacetamide under the optimized
Scheme 2. Reported and proposed routes toward 6.

6-ARYL-3-CYANOPYRIDINE-2-(1H)-THIONES
1523
Table 1. Optimization of the cyclization of enaminone 8a with cyanothioacetamide
Entry
Solvent
Base
Temp. (ꢀC)
Time (h)
Yield (%)
1
2
H2O
10% KOH (aq.)
t-BuOK
EtONa
40 (0.5 h), 60 (4 h)
55
Reflux
4.5
9.5
8
17
38
6
DMF
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
3
4
Et3N
Piperidine
DBU
Reflux
Reflux
4
60
48
47
53
68
79
88
5
7
6
Reflux
Reflux
2
7
Diisopropylamine
DIPEA
2.5
4
8
Reflux
Reflux
Reflux
9
10a
DABCO
DABCO
4
4
aThe cyanothioacetamide amount used was 1.5 equiv.; the others were 1.1 equiv.
conditions (1.0 equiv. enaminone, 1.5 equiv. cyanothioacetamide, and 0.5 equiv.
DABCO were refluxed in ethanol for 4 h).
As shown in Table 2, reactions of substrates containing electron-donating
groups (entries 1–3) or electron-withdrawing groups (entries 5–8 and 10) on the phe-
nyl ring gave comparably excellent yields with those of unsubstituted acetophenone
(entry 4). Moreover, heteroaromatic ketones (entries 11, 12, and 13) could also
undergo smooth condensation to generate 6-heterocyclic-3-cyanopyridine-2-(1H)-
thiones 6k, 6l, and 6m in moderate yields. However, substrate with strong electron-
withdrawing ditrifluoromethyl substitute (Table 2, entry 9) gave only 40% yield.
To improve operational efficiency and yields, we speculated that the synthesis of
6-aryl-3-cyanopyridine-2-(1H)-thiones 6 might be achieved in one flask without
isolation and purification of enaminones 8 by a simple evaporation of excess
DMF-DMA in vacuo before condensation with cyanothioacetamide. This one-flask
procedure proceeded successfully, and a variety of 6-aryl-3-cyanopyridine-2-(1H)-
thiones were prepared from 7 directly in markedly greater overall yields (50–80%)
than that of stepwise synthesis (Table 3, entries 1, 3, 4, and 6). It is noteworthy
that the removal of excess DMF-DMA before the addition of cyanothioacetamide
is essential.
In conclusion, an improved and efficient method for the synthesis of 6-aryl-
3-cyanopyridine-2-(1H)-thiones has been developed. The approach features these
advantages: (1) using DABCO as base improved the yields remarkably. (2) The
convenient process allowed the two-step reaction to be done in a single reaction
vessel without isolation and purification of the enaminones and only a simple evap-
oration in vacuo. The synthesis of antiproliferative thieno[2,3-b]pyridine derivatives
employing these 6-aryl-3-cyanopyridine-2-(1H)-thiones is currently under investi-
gation in our laboratory and will be reported in due course.

1524
R.-L. ZHENG ET AL.
Table 2. Synthesis of compound 6
Entry
Starting materials
Product
Yield (%)
1
90
2
3
88
81
4
5
6
7
93
88
77
79
8
97
(Continued )

6-ARYL-3-CYANOPYRIDINE-2-(1H)-THIONES
Table 2. Continued
1525
Entry
Starting materials
Product
Yield (%)
9
40
10
95
11
12
13
40
68
62
aThe product was a new compound.
EXPERIMENTAL
All melting points were determined on an electric melting-point apparatus and
1
were uncorrected. H NMR spectra were carried out on a Bruker Avance (Varian
Unity Inova) 400-MHz spectrometer using tetramethylsilane (TMS) as internal
reference chemical shift in d (ppm). Low-resolution mass spectra (LRMS) were car-
ried out on a Waters Quattro Premier XE triple quadrupole mass spectrometer.
High-resolution mass spectra (HRMS) were recorded on a Waters Q-TOF Premier
mass spectrometer.
General Procedure for the Preparation of Enaminones 8
Method A (stepwise procedure). Aryl ketones (20 mmol) and N,N-
dimethylformamide dimethyl acetal (DMF-DMA) (40 mmol) were refluxed until
the starting materials were consumed, as determined by thin-layer chromatography

1526
R.-L. ZHENG ET AL.
Table 3. One-pot synthesis of compound 6 from aromatic ketone 7
Entry
Starting material
Product
Yield (%)
1
80=64b
2
c
75=ꢁ
3
65=52b
4
50=15
5
6
50=—c
65=58b
aThe coressponding enaminones was oil.
bThe overall yield from 7.
cThe experiment was not conducted.
(TLC), and then cooled to rt. The precipitate was filtered off and washed with cold
petroleum followed by cold ethanol. The product was pure enough for the next step.
Compounds 8b, 8d–8i, and 8k–8m were prepared with stepwise procedures.

6-ARYL-3-CYANOPYRIDINE-2-(1H)-THIONES
1527
3-(Dimethylamino)-1-(3-methoxyphenyl) prop-2-en-1-one (8a). Yield
1
75%, yellow solid, mp 43–44 ꢀC. H NMR (400 MHz, CDCl3): d2.92 (s, 3H), 3.14
(s, 3H), 3.86 (s, 3H), 5.70 (d, J ¼ 12.4 Hz, 1H), 6.99–7.02 (m, 1H), 7.29–7.33 (m,
1H), 7.45–7.47 (m, 2H), 7.80 (d, J ¼ 12.4 Hz, 1H).
Method B (one-pot procedure). Aryl ketones (20 mmol) and DMF-DMA
(40 mmol) were stirred under reflux until the starting materials was consumed as
determined by TLC. Then the mixture was cooled to room temperature, the excess
DMF-DMA was removed by evaporation in vacuum, and the residue was used directly
for the second step. Compounds 8c and 8j were prepared with one-pot procedures.
General Procedure for the Preparation of 6-Aryl-3-cyanopyridine-2-
(1H)-thiones (6a–6o)
Cyanothioacetamide (15 mmol) was added to a stirred suspension of the enam-
inone (8a–m) (10 mmol, prepared according to the procedure described previously) in
ethanol (20 mL) in the presence of DABCO (5 mmol) at room temperature. The
reaction mixture was stirred under reflux until complete conversion of the starting
materials (2–4 h, monitored by TLC). The mixture was then cooled to room tempera-
ture and neutralized with diluted HCl solution to precipitate the crude products,
which were washed with cold EtOH to give the products 6a–6o. It is noteworthy that
it is necessary to adjust the pH value of the reaction mixture to 7 with diluted HCl
solution, especially for 6g, 6h, and 6l. Other pH values of the reaction mixture might
1
result in an upfield chemical shift of the NH of the 2-position pyridine in H NMR
spectrum, together with a lowered yield.
6-(3-Methoxyphenyl)-3-cyanopyridine-2-(1H)-thiones (6a). Yield 90%,
1
yellow solid, mp 204–206ꢀC. H NMR (400 MHz, DMSO-d6): d 3.85 (s, 3H), 7.13–
7.16 (m, 2H), 7.33–7.37 (m, 2H), 7.45 (t, J ¼ 8.0 Hz, 1H), 8.15 (d, J ¼ 8.0 Hz, 1H),
14.22 (br, 1H). HRMS (ESI): calcd. for C13H11N2OS [M þ H]þ: 243.0587, found:
243.0589.
6-(4-Methoxyphenyl)-3-cyanopyridine-2-(1H)-thiones (6b). Yield 88%,
yellow solid, mp 205–207ꢀC (224–225ꢀC).[5a] 1H NMR (400 MHz, DMSO-d6):
d3.85 (s, 3H), 7.09 (dt, J ¼ 8.8, 2.6 Hz, 3H), 7.77–7.81 (m, 2H), 8.09 (d, J ¼ 8.0 Hz,
1H), 14.06 (br, 1H). HRMS (ESI): calcd. for C13H11N2OS [M þ H]þ: 243.0587,
found: 243.0591.
6-(3,4-Dimethoxyphenyl)-3-cyanopyridine-2-(1H)-thiones
(6c). Yield
81%, yellow solid, mp > 230ꢀC. 1H NMR (400 MHz, DMSO-d6): d3.81 (t, J ¼ 8.4 Hz,
3H), 3.88 (s, 3H), 7.11 (dd, J ¼ 8.4, 3.6 Hz, 1H), 7.17 (d, J ¼ 8.4 Hz, 1H), 7.40–7.44 (m,
2H), 8.10 (d, J ¼ 8.0 Hz, 1H), 14.04 (br, 1H). 13C NMR (100 MHz, DMSO-d6): d
179.67, 156.85, 148.38, 147.49, 140.72, 133.43, 122.86, 120.97, 117.09, 110.37,
108.58, 102.32, 56.11 (2C). HRMS (ESI): calcd. for C14H11N2O2S [M - H]ꢁ:
271.0547, found: 271.0545.
6-Phenyl-3-cyanopyridine-2-(1H)-thiones (6d). Yield 93%, yellow solid,
1
mp 222–224ꢀC (254–255ꢀC,[5a] 245–247[7d]). H NMR (400 MHz, DMSO-d6): d 7.10
(d, J ¼ 8.0 Hz, 1H), 7.52–7.61 (m, 3H), 7.76–7.78 (m, 2H), 8.15 (d, J ¼ 8.0 Hz, 1H),

1528
R.-L. ZHENG ET AL.
14.25 (br, 1H). HRMS (ESI): calcd. for C12H9N2S [M þ H]þ: 213.0481, found:
213.0485.
6-(3-Fluorophenyl)-3-cyanopyridine-2-(1H)-thiones (6e). Yield 88%, dark
1
brown solid, mp 198–200ꢀC. H NMR (400 MHz, DMSO-d6): d 7.14 (d, J ¼ 7.6 Hz,
1H), 7.45 (t, J ¼ 7.8 Hz, 1H), 7.56–7.63(m, 2H), 7.70 (d, J ¼ 10.0 Hz, 1H), 8.18 (d,
J ¼ 7.6 Hz, 1H), 14.31 (br, 1H).13C NMR (100 MHz, DMSO-d6): d 112.26, 115.59,
115.82, 117.23, 118.42, 118.63, 124.85, 131.05, 131.13, 144.96, 152.26, 179.02. HRMS
(ESI): calcd. for C12H7FN2NaS [M þ Na]þ: 253.0206, found: 253.0211.
6-(3-Chlorophenyl)-3-cyanopyridine-2-(1H)-thiones
(6f). Yield 77%,
1
yellow solid, mp 168–170ꢀC. H NMR (400 MHz, DMSO-d6): d 7.14 (d, J ¼ 7.6 Hz,
1H), 7.56 (t, J ¼ 7.6 Hz, 1H), 7.65 (d, J ¼ 7.6 Hz, 1H), 7.72 (d, J ¼ 7.2 Hz, 1H), 7.88
(s, 1H), 8.17 (d, J ¼ 7.6 Hz, 1H), 14.33 (br, 1H). 13C NMR (100 MHz, DMSO-d6):
d 106.09, 117.99, 125.63, 127.55, 128.73, 131.09, 131.28, 133.87, 137.92, 142.94,
157.44, 179.03. HRMS (ESI): calcd. for C12H8N2S [M þ H]þ: 247.0091, found:
247.0090.
6-(3-Bromophenyl)-3-cyanopyridine-2-(1H)-thiones (6g). Yield 79%,
yellow solid, mp 164–166 ꢀC. 1H NMR (400 MHz, DMSO-d6): d 7.10 (d, J ¼ 8.0 Hz,
1H), 7.42 (t, J ¼ 7.8 Hz, 1H), 7.54 (d, J ¼ 8.0 Hz, 1H), 7.61 (dd, J ¼ 8.0, 1.2 Hz, 1H),
7.96 (d, J ¼ 8.0 Hz, 1H), 8.21 (t, J ¼ 1.8 Hz, 1H), 13.85 (br, 1H). 13C NMR (100 MHz,
DMSO-d6): d 108.98, 110.33, 120.69, 122.05, 125.69, 129.40, 130.68, 131.72, 140.18,
141.13, 154.81, 182.32. HRMS (ESI): calcd. for C12H7BrN2NaS [M þ Na]þ:
312.9406, found: 312.9412.
6-(3,4-Dichlorophenyl)-3-cyanopyridine-2-(1H)-thiones (6h). Yield 97%,
yellow solid, mp 178–180ꢀC (220–221).[5a] 1H NMR (400 MHz, DMSO-d6): d7.14
(d, J ¼ 8.0 Hz, 1H), 7.53 (d, J ¼ 7.6 Hz, 1H), 7.71 (d, J ¼ 8.8 Hz, 1H), 7.98 (dd,
J ¼ 8.4, 2.0 Hz, 1H), 8.25 (d, J ¼ 2.0 Hz, 1H), 14.05 (br, 1H). HRMS (ESI): calcd.
for C12H6Cl2N2NaS [M þ Na]þ: 302.9521, found: 302.9529.
6-(3,5-Ditrifluoromethylphenyl)-3-cyanopyridine-2-(1H)-thiones (6i).
1
Yield 40%, yellow solid, mp 190–192 ꢀC. H NMR (400 MHz, DMSO-d6): d 7.34
(d, J ¼ 7.6 Hz, 1H), 8.24 (d, J ¼ 8.0 Hz, 1H), 8.34 (s, 1H), 8.50 (s, 2H), 14.61 (br,
1H). 13C NMR (100 MHz, DMSO-d6): d 179.32, 158.86, 141.75, 136.81, 131.87
(2C), 129.98 (2C), 124.71 (2C), 122.83, 121.75, 117.05, 101.78. HRMS (ESI): calcd.
for C14H7F6N2S [M þ H]þ: 349.0229, found: 349.0236.
6-(Biphenyl-4-yl)-3-cyanopyridine-2-(1H)-thiones (6j). Yield 95%, yellow
1
solid, mp>230ꢀC. H NMR (400 MHz, DMSO-d6): d 7.18 (d, J ¼ 7.6 Hz, 1H), 7.44
(t, J ¼ 7.8 Hz, 1H), 7.52 (t, J ¼ 7.6 Hz, 2H), 7.77 (d, J ¼ 7.2 Hz, 2H), 7.88 (q,
J ¼ 19.2 Hz, 4H), 8.17 (d, J ¼ 8.0 Hz, 1H), 14.28 (br, 1H). 13C NMR (100 MHz,
DMSO-d6): d 178.98, 158.96, 141.78, 140.85, 139.47, 137.91, 129.2 (2C), 128.38
(4C), 127.81 (2C), 127.28 (2C), 122.81, 117.09. HRMS (ESI): calcd. for C18H13N2S
[M þ H]þ: 289.0794, found: 289.0798.
6-(Pyridine-2-yl)-3-cyanopyridine-2-(1H)-thiones (6k). Yield 40%, dark
1
brown solid, mp 200–203ꢀC (230–231.[5a]). H NMR (400 MHz, DMSO-d6): d 7.18
(d, J ¼ 7.6 Hz, 1H), 7.58 (q, J ¼ 4.3 Hz, 1H), 8.17–8.22 (m, 2H), 8.75 (dd, J ¼ 4.8,

6-ARYL-3-CYANOPYRIDINE-2-(1H)-THIONES
1529
1.6 Hz, 1H), 8.93 (d, J ¼ 2.8 Hz,1H), 14.44 (br, 1H). HRMS (ESI): calcd. for
C11H8N3S [M þ H]þ: 214.0433, found: 214.0430.
6-(Thiazol-2-yl)-3-cyanopyridine-2-(1H)-thiones (6 l). Yield 68%, dark red
1
solid, mp:221–222 ꢀC. H NMR (400 MHz, DMSO-d6): d 7.48 (s, 1H), 8.13 (s, 2H),
14.02 (s, 1H). 13C NMR (100 MHz, DMSO-d6): d 180.01, 162.53, 161.79, 141.71,
123.92, 122.78, 117.21, 115.65, 101.85. HRMS(ESI): calcd. for C9H4N3S2
[M ꢁ H]ꢁ:217.9852, found: 217.9855.
6-(Furan-2-yl)-3-cyanopyridine-2-(1H)-thiones (6 m). Yield 62%, dark
brown solid, mp 201 ꢀC (221–222.[7f]). 1H NMR (400 MHz, DMSO-d6): d 6.81
(q, J ¼ 2.0 Hz, 1H), 7.13 (d, J ¼ 8.0 Hz, 1H), 7.89 (d, J ¼ 3.6 Hz, 1H), 8.05–8.09
(m, 2H), 14.15 (br, 1H). HRMS (ESI): calcd. for C10H7N2OS [M þ H]þ: 203.0274,
found: 203.0278.
6-(2-Methoxyphenyl)-3-cyanopyridine-2-(1H)-thiones (6n). Yield 75% for
1
two steps, yellow solid, mp 196–198 ꢀC. H NMR (400 MHz, DMSO-d6): d 3.83
(s, 3H), 6.92 (d, J ¼ 8.0 Hz, 1H), 7.05–7.11 (m, 1H), 7.17–7.20 (m, 1H), 7.43–7.48
(m, 1H), 7.52–7.56 (m, 1H), 8.13 (d, J ¼ 7.6 Hz, 1H), 14.06 (br, 1H). 13C NMR
(100 MHz, DMSO-d6): d56.10, 112.10, 113.67, 115.05, 117.37, 120.84, 130.68,
133.10, 145.08, 151.88, 157.00, 157.13, 177.84. HRMS (ESI): calcd. for C13H11N2OS
[M þ H]þ: 243.0587, found: 243.0588.
6-(2, 4-Dichlorophenyl) -3-cyanopyridine-2-(1H)-thiones (6o). Yield 50%
1
for two steps, yellow solid, mp 208–211 ꢀC. H NMR (400 MHz, DMSO-d6): d 6.92
(d, J ¼ 7.2 Hz, 1H), 7.61 (d, J ¼ 1.6 Hz, 2H), 7.84–7.86 (m, 1H), 8.21 (d, J ¼ 8.0 Hz,
1H), 14.51 (br, 1H). 13C NMR (100 MHz, DMSO-d6): d 114.08, 116.64, 117.00,
127.84, 129.46, 130.72, 132.84, 133.21, 136.37, 145.17, 150.42, 178.41. HRMS
(ESI): calcd. for C12H6Cl2N2NaS [M þ Na]þ: 302.9521, found: 302.9527.
One-Pot Synthesis of 6-Aryl-3-cyanopyridine-2-(1H)-thiones (6a)
3-Methoxyacetophenone (30 g, 200 mmol) and DMF-DMA (56 mL, 404 mmol)
were stirred under reflux for 24 h. Then the reaction mixture was cooled to room
temperature, and the excess DMF-DMA was removed by evaporation in vacuum.
The resulting residue in ethanol (400 mL) was added to cyanothioacetamide
(30 g, 300 mmol) in the presence of DABCO (20 g, 100 mmol) at room temperature,
and then the reaction mixture was stirred under reflux for 3 h. After it cooled to
room temperature, the reaction mixture was neutralized with diluted HCl to precipi-
tate the crude product, which was washed with cold EtOH to give a yellow product
(38.7 g, 80% for two steps), mp 234–236 ꢀC.
ACKNOWLEDGMENTS
This work was supported by the National Natural Science Foundation of
China (NSFC-81000982). We thank the Analytical and Testing Center of Sichuan
University for NMR spectral measurements. Valuable suggestions from Lin He
and Zhen-Lei Song are also gratefully acknowledged.

1530
R.-L. ZHENG ET AL.
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